Re: [time-nuts] web presentation of data
On 8/6/12 10:43 AM, Chris Albertson wrote: On Mon, Aug 6, 2012 at 8:34 AM, Jim Lux jim...@earthlink.net wrote: what would be useful is to have some sort of plotting engine that is a canned webpage (or stored locally on the user/client computer) that can ingest fairly raw data from a URL.. something, conceptually, like this: BODY *invocation of plotting engine* data value 1 data value 2 data value 3 /BODY What you are saying is that the data needs to be rendered to a graphic locally. I think the simplest way is to create vector based plots on the server (I've used GNU Plot inside a CGI script) but there is a system to pretty much what you are asking for. http://code.google.com/p/flot/ Somehow, I don't think running Gnuplot on a Arduino is feasible. ABout all it can do is respond to the HTTP Get with the right page. That's why I want to push the hard work of doing the rendering onto the client (i.e. the browser). The comm link is fast, and an SD card on the Arduino can hold tons of stuff, so serving a page containing 100kbytes of Java or similar isn't a problem. But doing any computation is probably not in the picture. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] What size graphs do people like? (How big is your screen?)
On 8/5/12 10:35 PM, Hal Murray wrote: david-tay...@blueyonder.co.uk said: I load screen shots into Corel Photo Paint 8 and resample the image to a good size for a web page somewhere between 600 and 800 pixels horizontally. Where did 600 or 800 come from? 800 is historical, as is 640 (resolution of VGA adapter) I use 800x600 (or thereabouts) a lot when converting a photograph to something reasonable to paste into a document. finer than 72 pixels/inch (which I'm sure comes from printer's points, and was tied to the resolution of dot matrix printers). You want something where the pixel size is small enough that when someone is reading the doc, it doesn't look too bad, but also isn't huge. Obviously a scalable vector form would be better, but not every program generates them. Overall, I have the best luck (ultimately generating docs in MS Word or Powerpoint) with having tools like matlab squirt them out as enhanced meta files. But once into the MS environment, you pretty much have to stay there. It doesn't work well going back and forth between, say, Open Office and MS Office. This kind of thing is where the inconsistencies between OO and MSO show up. I suppose .ps and LaTeX would work, but those have their issues as well (when distributing or rendering... there's a lot of ugly font substitutions out there.) WHile I like nice typography and layout as much as the next person, I also think we spend too much time on it. I'm all for double spaced Courier, numbered sections, and being done with it. I don't care what the answer is. I'm just curious and/or want to make graphs that most people can easily use. Here are 3 samples: http://www.megapathdsl.net/~hmurray/time-nuts/coax/Front-5ns-1200x800.png http://www.megapathdsl.net/~hmurray/time-nuts/coax/Front-5ns-800x600.png http://www.megapathdsl.net/~hmurray/time-nuts/coax/Front-5ns-640x480.png ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] web presentation of data
what would be useful is to have some sort of plotting engine that is a canned webpage (or stored locally on the user/client computer) that can ingest fairly raw data from a URL.. something, conceptually, like this: BODY *invocation of plotting engine* data value 1 data value 2 data value 3 /BODY that way, a relatively dumb controller (think arduino-ish) could talk to the instrument and build a web page on the fly without having to do much formatting. The java/javascript/whathaveyou would do all the plotting work on the client side (where, presumably, they have a display and some computational horsepower to drive it) A low end microcontroller has no problem serving readonly pages from flash/SD, it just has a tough time doing graphics. And, if you wanted the raw data, you serve up a page called raw.html or something that just has the raw data. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] web presentation of data
On 8/6/12 9:16 AM, Hal Murray wrote: jim...@earthlink.net said: what would be useful is to have some sort of plotting engine that is a canned webpage (or stored locally on the user/client computer) that can ingest fairly raw data from a URL.. ... A low end microcontroller has no problem serving readonly pages from flash/ SD, it just has a tough time doing graphics. I'd do something like that in two separate steps: The microcontroller would collect the data. A separate job on a real computer would occasionally grab the data. I'm assuming we are discussing some sort of long running project. The real computer has a bigger disk and some sort of backup/archiving setup so I'd want to get the data there anyway. Once it's there graphics isn't a problem. More like a field data collection system where you want to get at it via WiFi and a laptop. I don't want a PC turned on all the time logging the data. The arduino is perfectly suited to grabbing data periodically and writing it into a SD card, from which the webserver code can grab it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GLONASS receiver
On 8/5/12 5:24 PM, Hal Murray wrote: li...@rtty.us said: The next most likely would be a trucker trying to jam the location stuff on his truck. I'm betting that they will be buying multi mode jammers soon… What is the frequency used by Glonass or Galileo? (I think they are close to and/or overlapping GPS.) What's the bandwidth of the typical ebay jammer used by truckers? My guess is they are wide band to cover manufacturing tolerances and will wipe out all 3 sources of time/location. http://www.positim.com/gnss_signals.html has some nice charts as does wikipedia L1 and E2 are collocated. E5 (Galileo) and L5 (GPS) are on top of each other. They're both safety of life frequencies, unlike L2 Glonass's two signals are higher than both L1 and L2 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] HP 58503A
On 8/2/12 6:24 PM, Doug Reed wrote: I ran into a wiki description of GPS using WGS84 a couple days ago. It included a mention of ESEC and it was something like: Earth Static, Earth Centric. I think I was following a link about the Z3801A. It referred to the fact that lat-lon is referenced to a static grid on the Earth and doesn't change as the Earth rotates on its axis or around the sun. Earth static and Earth centric. Earth Centered Inertial - ECI centered on the earth, doesn't rotate with earth - very popular with earth orbiting satellites, because their center of rotation is at the center of the earth but their orbital plane is fixed in celestial terms. like RA/Decl Earth Centered Earth Fixed - ECEF (or ECF) centered on earth, rotates with earth. More like conventional lat/lon. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightsquared questionfor SFO area....
On 7/28/12 1:32 AM, Said Jackson wrote: We have about 25 different GPSDOs running from four cheap antennae on the roof in Los Gatos right next to Hwy 17, and have not noted any unusual outages at all, even during the recent solar flare. I guess any truckers with jammers on hwy 17 pass by so fast we don't notice anything. I think the notable problems at Newark airport were because the jammer containing vehicles were sitting around in one place. http://www.gpsworld.com/government/personal-privacy-jammers-12837 is one among many articles about it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightsquared questionfor SFO area....
On 7/27/12 6:42 PM, Brian, WA1ZMS wrote: Does anyone know if there is ANY recent active Lightsquared testing taking place in the SFO area of the US? Very unlikely.. they've lost their experimental license. I'm dealing with a day-job issue with GPS clocks in the Bay Area showing GPS unlocked errors from 3rd party equipment. there are myriad sources of interference out there. Jammers are a BIG problem in urban areas (truckers and cab drivers use them to defeat their GPS based tracking systems and time clocks). there's a great set of articles over the past few months in GPS World about it. -Brian, WA1ZMS ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Looking for info on an old WWVB receiver
On 7/24/12 8:48 PM, ed breya wrote: I recently picked up an interesting early 1970s vintage WWVB receiver, Model 630, made by Specific Products of Monrovia, CA - that's what the adhesive sticker on the front says, and the name 1 MHz Time Base Calibrator (Utilizes WWVB accuracy of 2 parts in 10^11). There's also a pair of banana jacks labeled 1 MHz Input, a row of incandescent lamps for a signal strength indicator, and a power switch. The back says Model LF 60S, and has six RCA jacks for 100 kHz Output, 60 kHz Output, Recorder Output, Antenna Input, (divide sign) 10 Output, and Time Code Output. There's also the line cord and a +12VDC output RCA jack. I'm wondering if anyone knows anything or sources of info about this thing. With all the recent talk of WWVB changing to spread-spectrum, it may be useless anyway, except for some parts, but I'm curious about whether it's worth saving. Well, a bit of casual googling shows that Specfic Products made lots of this kind of thing, and they are shown as being in, variously, Los Angeles, Woodland Hills, and Monrovia. Technically Woodland Hills is in the city of LA, but in any case, they seem to have moved a bit. I found a reference in a USGS report Specific Products, 1965, NBS time code decoder chart: Bulletin Number 226, 21051 Costanso St., Woodland Hills, Calif. Now, as it happens, that's the address (today) of someone's garage. They seem to have been a popular item for generating timecode in various recorders for USGS (turned up several mentions in papers from the 60s and 70s recording things like volcanic eruptions and the like) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Shorthand
On 7/23/12 3:23 PM, Tom Van Baak wrote: Hi Pete, Yes, there are several ways to represent frequencies: 1) Absolute units of Hz. For example 60 Hz, or 32.768 kHz, or 3.579545 MHz, or 9.192631770 GHz. Note some modern texts use s⁻¹ (1/s or s-1) instead of Hz or Hertz. Or, you can always show your age and use cps (cycles per second). or, as the directional couplers I've been working with the last few weeks say, 2-4 KMC We have boxes of these Narda 10,20 and 30 dB couplers with N connectors, all bought for Ranger and Mariner. I joke that they are older than most of the engineers using them. The cal tags on some probably qualify as historical documents. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
On 7/19/12 4:09 PM, Magnus Danielson wrote: On 07/20/2012 12:33 AM, li...@lazygranch.com wrote: Are you speaking of slew rate limiting in the strict sense of the word, that is a current starved input stage due to the presence of a compensation cap? Or are you using the term slew more vaguely. I am speaking neither. If you have a sine of a particular frequency and amplitude, then you have a known slew-rate, it peaks at 2*pi*f*A, where A is the amplitude of the sine. As you amplify this signal, the slew-rate will grow proportionally. Recall that the jitter of a trigger point is noise divided by slew-rate. This is why we want to increase the slew-rate to a maximum while adding minimal noise. snip nice simple explanation... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] WWVB and Free Democracies Survival
On 7/15/12 12:38 PM, Mark Spencer wrote: Some form of backup to gps would be nice for timing purposes. I wonder if a secondary sattelite based system for timing use only over the continental US might be the way to go. (Ie. a transmitter on a geo stationary sattelite that could emulate enough of the gps signals to allow statioanry timing receivers to function.) You mean like WAAS? It's a GPS like signal broadcast from GEO. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] WWVB and Free Democracies Survival
On 7/15/12 1:32 PM, Mark Spencer wrote: In my view a backup solution that allows the existing gps based timing receivers to be used makes a reasonable ammount of sense. Another approach could involve ground based transmitters on high buildings or mountain tops. Retuned Lightsquared sites? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] WWVB and Free Democracies Survival
On 7/15/12 6:25 PM, Chris Albertson wrote: On Sun, Jul 15, 2012 at 5:24 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: The benefit of WAAS and EGNOS is that they have a fixed location in the sky. so you could use a highly directional antenna, like a parabolic antenna, which would provide suppression of most jamming signal unless they are overhead. I've seen a military GPS antenna that was a large phased array. I guess the idea was to use the almanac to track the moving GPS sats. The goal was to reject jammers by using a dozen or so synthesized pencil beams. (like a radar in a fighter jet) You could not put this in a hand held device as it was as BIG.That is the main problem with directional antenna they need to be large with respect to the wavelength. I don't know if this ever was used in a real deployed system. Doesn't need to be all that big... lambda at 1.5 GHz is 20cm.. an array that's, say, 50x50 cm would have significant interference rejection capability (i.e. you don't have to synthesize a pencil beam, you just need to put a null on the interference.. and you can null N-1 sources when you have N elements, so a 9 element (3x3) array would do nicely.. (and give you your attitude as a side effect) I think this antenna type was also the design proposed for a distributed low orbit comms system too. The current geo-sync comm-sats make for simple antenna but all of the proposed tactical launch on an hour notice comm-sats would be in LEO (low earth orbit) and launched with something like Pegasus or a re-purposed ICBM. The problem is that having a few dozen low power sats in LEO seriously complicates the portable ground stations, hence experiments with flat-plate phased array. Not really.. it depends on the frequency and the number of sources you need to track. THis is a very active research area. The very last payload deployed by the Space Shuttle was pico-sat a 5x5x10 inch satellite. It was built at the place I worked at as a test of a new pico-sized bus. This example had some sensors but really the test was if the thing could be commanded from the ground and do anything usfull at all. Look at the photo in the link. The sat is the box inside the bigger box.One of the recent innovations was to cut out patterns in sheets metal and stack many sheets to create a 3D tank and plumbing system with integrated rocket nozzles. The goal was to reduce costs by having a design that can be manufactured by robots. http://www.space.com/12354-final-space-shuttle-satellite-deployment-picosat.html So YES everyone knows these big satellites are targets. In a major war with a sophisticated enemy they would be gone soon. So the plan is to design systems that can be built stored and launched on VERY short notice in very large numbers.This kind of research has maybe a 25 year horizon maybe longer as you need to build up a new eco system of space qualified parts and engineers familiar with them and do many launches and tests. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Solar flare alert
On 7/14/12 9:19 AM, Joseph Gray wrote: Perhaps some of the cellular bands aren't affected, perhaps some are. I don't know the specific cause of yesterday's loss.. GPS uses around 1200/1500 MHz. The phone in question uses 850/1900 Mhz bands, so I think we're in the neighborhood. GPS signals pass through the ionosphere which greatly affected by solar weather. Terrestrial cellphone signals do not pass through the ionosphere, so flares don't necessarily change things. There is anecdotal evidence, though, that solar activity can change the environmental RF background noise level, and that could have an effect on cellphone link margins. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt mounting
On 7/11/12 7:00 PM, Mike S wrote: On 7/11/2012 8:15 PM, Chris Wilson wrote: Does anyone know if there's a means to log max and min temps for these things? I was going to make a crude box for mine out of 2 inch cavity wall insulation hard foam, The TB reports it's own temperature. Lady Heather will track it. I'm surprised no one has mounted one to a Peltier cooler, and stabilized the temp with PID control, based on the self-reported temp. Why not run it cooler than ambient? I'd assume a simple microcontroller could handle the task, but don't have any deep PID control knowledge myself. PID controller code for Arduinos and the like is readily available.. However, as to why not run it cooler? The internal oven tries to keep the crystal at the temperature where the frequency vs temp curve has the lowest slope. If you cool the outside, then you just burn more power in the internal oven. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer
On 7/7/12 9:21 AM, Dr. David Kirkby wrote: I can confirm that I'm 100% sure that the polarization of the two antennas needs to be the same - i.e. both RHCP or both LHCP. I built two of them for RHCP, and got appreciate gain. Despite what other may say, there does seem to be a lot of confusion about this issue, but I've satisfied myself by building them and testing the gain using a VNA as the signal source and detector. Nothing like an actual test to clarify things, eh? wind one for LHCP and you can play with the reversal after a reflection.. In the latest Ant and Prop Magazine there's an article about a antenna lab with demos from Cal Poly SLO. Very cool.. all at 900 MHz, so things are small, but not so small that skin depth and precision measurements come into place. Lots of different kinds of antennas, and they built a nice little LED bargraph signal strength display. Reminiscent of a video taped lecture from Kraus that I saw. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer
Exactly. Reflections reverse the cp sense On Jul 7, 2012, at 11:40, Tom Knox act...@hotmail.com wrote: Thanks for clearing up any confusion Magnus, one more question, are the any conditions such as reflected signals that can reverse polarization? Thomas Knox ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] gps jamming source found
On 7/5/12 10:45 PM, Robert Atkinson wrote: Hi Ed, It's not just just cheap and nasy regens that cause this problem. Some aircraft navigation and communication receivers where found to have enough local oscillator harmonic leakage at 1575 MHz through the antenna port to jam GPS then tuned to specific frequences. The cure was a tuned stub filter on the Nav or Comm. see http://www.aircraftspruce.com/catalog/avpages/tednotch.php for an example. or choosing the UHF link frequency for Mars Reconnaissance Orbiter at 400 MHz, nicely the third harmonic of the 133 MHz flight computer clocks (or 6th harmonic of 66, etc.) Unlike GPS, though, the desired signal is narrowband (though the receiver isn't) so a DSP software fix in the FPGA could implement a new filter (and shift the desired signal to the other end of the IF passband. EMI/EMC problems, your name is legion. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Allan Deviation question
On 7/6/12 7:51 AM, Azelio Boriani wrote: Yes, I'm also interested in how-to. At the moment I think it is a hack: there is no sound card AFAIK that accepts a reference input. I have recently bought an Acqiris/Agilent DP105/U1067A 150MHz 500Ms/s digitizer PCI card that accepts an external 10MHz as a reference for the sampling process. while there are no sound cards (in the sense that they physically plug into the PC bus) with external clock inputs, there are quite a few sound interfaces that take a sample clock input (e.g. at 44.1, 48,96, 192) of some sort. A lot of them use 1394/Firewire (for historical reasons) what you're looking for is word clock in or similar things On Fri, Jul 6, 2012 at 4:43 PM, Stewart Bryant stew...@g3ysx.org.uk wrote: ... and running it to a sound card (oscillator gps disciplined) How did you achieve this? Thanks Stewart __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Allan Deviation question
On 7/6/12 7:51 AM, Azelio Boriani wrote: Yes, I'm also interested in how-to. At the moment I think it is a hack: there is no sound card AFAIK that accepts a reference input. I have recently bought an Acqiris/Agilent DP105/U1067A 150MHz 500Ms/s digitizer PCI card that accepts an external 10MHz as a reference for the sampling process. oops I was wrong.. there ARE people making PCI multichannel audio interfaces with external clock.. RME in Germany makes more than one. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] gps jamming source found
On 7/5/12 6:33 PM, gary wrote: I believe all electronics needs FCC approval for emissions. [Not my job, but I know engineers that complain about compliance testing.] 433MHz is a freeband (ISM). Still, you are supposed to be clean. 433 is NOT an ISM band in the US (or in region 2, for that matter), but it is in Region 1 (EU), so there's lots of parts available. It is also not an Part 15 band (distinguish from Part 18 ISM)... 27 MHz, 49 MHz, 900 MHz, 2.45 GHz, those are ISM and Part 15 bands... On 7/5/2012 4:41 PM, Michael Blazer wrote: A badly tuned/designed super-regenerative receiver can put out a lot of garbage. For commercial products, the receiver needs FCC approval to ensure this doesn't happen. Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is Timelab with a Prologix-Eth and a PM6680 - working ?
On 7/3/12 7:34 AM, cfo wrote: I just got a PM6680/016 - Std. Osc + GPIB + 1.3Ghz -Chan.C The best my budget could afford :-) I would like to try out John's Timelab. But only have a Prologix-Ethernet GPIB adapter , no USB version. I was wondering if anyone can confirm that Timelab would work on a PM6680 , using a Prologix-Eth ? Timelab certainly works with the Prologix GPIB.. I use it all the time (with a HP counter, not the PM6680). A few things to think about.. run the Prologix configurator first to make sure the darn thing is talking at the address you expect it to be at. I spent hours fooling with various things, carrying that darn Prologix up and down stairs between lab and office before I finally figured out it was my cheap $10 USB/Ethernet dongle that was screwing me up. (I wanted a private network at 192.168.1.x for this stuff) Once you have verified connectivity with the Prologix, then timelab works easily.. I'm still fooling with making it all work under Centos (not timelab.. python and sockets) and a 33120 ARB. (It works fine.. I'm just fooling with the python part) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] HP-5065a advise and purchase decision
On 7/1/12 2:43 PM, b...@lysator.liu.se wrote: Tom, Chris, The HP 5065A is one of the best Rb ever made. /tvb (iPhone4) Have you or any other list member had the opportunity to take measurements on the ElmerPerkin/EGG Space rubidiums (in a lab environment)? http://www.excelitas.com/Downloads/DTS_Frequency_Standards_RAFS.pdf -- are those the ones in GPS satellites? (for instance?) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Leap second? Yay or nay?
On 7/1/12 10:54 PM, Poul-Henning Kamp wrote: In message 4ff0f373.1020...@pacific.net, Brooke Clarke writes: Would you rather have these minor problems or have a much bigger one when they make a larger correction? But isn't that exactly why it is a problem ? News coverage of leapseconds are mostly along the lines of What can you do with an extra second ? as filler material on page 7 Whereas coverage of DST changes is REMEMBER TO SET YOUR CLOCKS! on the frontpage. which is an interesting thing.. if instead of DST (for which I think there's little practical reason to have in the first place).. say you just shifted the clock one minute earlier or later each day, gradually moving it to the new alignment relative to solar day. Most people wouldn't notice: they use their phone as a time standard, and the phone would display the current time. People with analog clocks would reset them. People with drifting digital clocks would reset them (just like I do with the one in the car every once in a while). Sure, there would be some whining from software developers at first, but once you've figured out to smoothly handle arbitrary drops and adds, it's done forever. Yes, we'd lose the annual cue to replace our smoke alarm batteries. Oh, and we'd lose the clever newspaper articles about more/less drinking time, due to bar closing on or after the transition time. An abrubt 1 hour change is much more disruptive for things like employee time cards than a gradual one minute change per day. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Leap second? Yay or nay?
On 7/2/12 6:19 AM, Poul-Henning Kamp wrote: In message 4ff19d3c.4050...@earthlink.net, Jim Lux writes: which is an interesting thing.. if instead of DST (for which I think there's little practical reason to have in the first place).. say you just shifted the clock one minute earlier or later each day, gradually moving it to the new alignment relative to solar day. Why bother ? Just make everybody use TAI and make T-O-D alignment a cultural thing rather than a numerological superstition ? I agree with you, P-H... but if we ARE going to establish artificial connections between wall clock time (work hours, store opening times, bar closing times, etc.) and the sun, why not do it gradually. People are used to accommodating small deltas in time (e.g. my wife, who sets the dash clock in her car 10-15 minutes fast) and periodically readjusting to personal preference. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Leap second? Yay or nay?
On 7/2/12 7:08 AM, Mike S wrote: On 7/2/2012 9:28 AM, Jim Lux wrote: but if we ARE going to establish artificial connections between wall clock time (work hours, store opening times, bar closing times, etc.) and the sun, why not do it gradually. Time and the sun are certainly a _natural_ connection, not an artificial one. Units of time start with the day. Subdivided, we get HMS, measured from the maximum height of the sun. Greater, years, which were measured in days. It's the artificial definition of the SI second which has caused all the problems. I was thinking of the artificial connection between wall clock and sun in the daylight saving time sense. We already deal with the variation between clock time and solar time during the year (equation of time, and all that) which is of a much larger magnitude than the leap second, and that probably antedates SI time (or mean time, in any case) since however long we've had clocks that are stable enough to measure it. If we are to retain the idea of the sun rising and setting later during the warmer months (relative to mean time or normal clock time), then I would suggest we do away with the large step change twice a year and replace it with a 1 minute/day shift during 2 months, and then repeat the process again later to bring it back into alignment. This will have the benefit of: 1) providing work for software developers, who otherwise be laid off for lack of work, and would no doubt do things bad for society: idle hands and all that are bad enough; intelligent idle hands are even more dangerous. 2) improving the overall time change robustness of the software which has an increasingly pervasive effect on our day to day life 3) provide work for many, many congressional aides and news media to come up with talking points, analysis, and so forth; avoiding laying them off as well; although I don't know that the danger of idle hands from ex congressional aides is more or less than unemployed software developers. 4) provide a political issue of little real consequence to occupy the time and minds of legislators: a displacement activity, much like cleaning out the garage when you should be doing your tax returns or paying the bills. 5) provide work and employment for petition signature gatherers who will no doubt appear in front of my local supermarket for initiatives to either support or suppress or some of both the new scheme. 6) provide income for media outlets to run the plethora of advertisements pro and con 7) provide something for the extraordinarily wealthy to spend their money on through nebulous organizations to pay for those ads that provides some degree of entertainment for time-nuts, without seriously affecting the overall health and well-being of the populace, no matter which way the decision goes. Finally, my modest hope is that this scheme will achieve for me the fame it achieved for Ben Franklin inventing daylight saving time. I look forward to my great-great-grandchildren (should I have any) learning about Lux time as being the revolution that fixed the problems with Franklin time. (Ol' Ben and I have many shared interests.. electricity, time, artificial tornadoes, lightning, etc., and I'm always pleased when I can carry his finely engraved picture in my wallet) I mean, who can name an arbitrary Nobel prize winner? But everyone knows who Ben is. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] [OT] Paywall Rant (was Re: Spoofing GPS)
On 6/28/12 5:22 AM, J. Forster wrote: FYI, MIT got anal about IP policy in the early 1970s, demanding a transfer of all IP rights to the Institute for everything everyone did. I quit and went into the Consulting business (and wound up getting paid a LOT more for the same work). There is a fundamental conflict between the IP rights of sponsors and the open flow of information... even more so if you include international IP theft. Essentially today, if you work for somebody, they own you. I think one of the big changes in the US was the Bayh-Dole act, at least with respect to government funded research at universities. Prior to that most university grants were structured so that if the taxpayer paid for it, it's available to anyone (barring the whole journal pubs/page charge issue.. but you see a lot of Government Work not protected by copyright on older IEEE papers, for instance. I think those are mostly work at Govt labs, though) After Bayh-Dole in 1980, which was intended to stimulate the nascent genetic and bioengineering fields, universities (like Caltech, for which I work, since they run JPL) can retain the rights to anything produced at the institution. The Government gets a fully paid, non-exclusive, royalty free government purpose rights license, but the institution owns it and can sell it for whatever the market will bear. This substantially changed the whole IP landscape. I think, before, universities by and large actually didn't pay much attention to it. Sure, there were professors spinning off a private operation, but the uni didn't get a slice of the pie, since the uni developed piece (which inevitably had public funds) was free to all. One commentator said The Bayh-Dole Act, which was enacted on December 12, 1980, was revolutionary in its outside-the-box thinking, creating an entirely new way to conceptualize the innovation to marketplace cycle. It has lead to the creation of 7,000 new businesses based on the research conducted at U.S. Universities. Prior to the enactment of Bayh-Dole there was virtually no federally funded University technology licensed to the private sector, no new businesses and virtually no revolutionary University innovations making it to the public I wouldn't agree with the last statement... what's more accurate, I think is that nobody was able to make substantial money with a university innovation by itself. Lots of revolutionary innovations made it into industry and to the public, unsung, unheralded, etc. How many people use a variant of BSD Unix? Spice? etc. There are tons of niche businesses (some in the time and frequency business, no less) that basically have a few products based on some research done at a University, and they have commercialized it in a useful and unexceptional way. When people started to see the potential for *billions* in revenue, and some actually made millions, the Uni-s started to get interested. (one of Caltech and JPL's poster children for this is the database product known as Vulcan at the lab, which became dBase which turned into Ashton-Tate) Now we are VERY sensitive to IP rights. (look at the big case about Stanford v. Roche and their patent agreement.. small changes in wording about agree to assign vs assign rights, and all) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] [OT] Paywall Rant (was Re: Spoofing GPS)
On 6/28/12 6:38 AM, Peter Gottlieb wrote: Very true, and in some cases (Texas case) a judge ruled that an employee that left a firm can never work in that same field again for the rest of their life due to both positive and negative knowledge. Not in California, where such agreements are specifically prohibited by law. And, for that matter, the later legal strategy calling out inevitable disclosure (that is, that if you work in the same field you will inevitably disclose something that is trade secret) has been held invalid in a variety of courts. This doesn't stop company A from threatening to sue Company B who wants to hire someone from Company A, but it turns the threat into nothing, if Company B's lawyer writes a nice letter citing the half dozen or so cases to Company A's lawyer. In effect telling A, pound sand with your stupid extortion It *is* still effective in the old boys network.. executive from company A mentions to executive from company B, you know, if you hire good ol' Bob, it could get sticky, legally. You sure you want to take that on. Of such are things like illegal anti-poaching agreements made and of such are consent decrees issued. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Injection locking interconnect
On 6/28/12 3:07 PM, Bill Dailey wrote: Guys, I am looking for info on injection locking. I have been searching around for info. I found an article that probably answers my question but I can't get to it. http://www.oldcitypublishing.com/FullText/JAPEDfulltext/JAPED2.1fulltext/11-24pp%20GC05-06%20%28Rajput%29.pdf Can anyone give me a reference regarding the required interconnection? I understand the ho and why... I just am wondering how you make sure locking occurs in the right direction. In other words the target oscillator gets locked to the injected signal and not the other way around. The application is a synthesized frequency source injection locking a tcxo to improve phase noise. What you might look for is literature on coupled oscillators, for which there is quite a lot. If you have something like an isolator or other non-reciprocal device, then you can make sure that power flows mostly from good to bad. I believe, also, that it has to do with the relative Q of the two oscillators. The higher Q (e.g. stiffer) will drive the lower (softer), for equal powers transferred in each direction and equal powers out of the oscillators. One way to look at it is that there is more stored energy in the resonator of the higher Q oscillator (Q = stored energy/output energy), so the contaminating energy has a smaller relative effect. One can also demonstrate this nicely with a pair of coupled pendulums with different weights on the bob. (strings on a broomstick work nicely) with equal weights, the power couples back and forth periodically. With one heavy and one light, the light one always follows the heavy. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Injection locking interconnect
On 6/28/12 3:22 PM, Magnus Danielson wrote: Bill, On 06/29/2012 12:07 AM, Bill Dailey wrote: Guys, I am looking for info on injection locking. I have been searching around for info. I found an article that probably answers my question but I can't get to it. http://www.oldcitypublishing.com/FullText/JAPEDfulltext/JAPED2.1fulltext/11-24pp%20GC05-06%20%28Rajput%29.pdf Can anyone give me a reference regarding the required interconnection? I understand the ho and why... I just am wondering how you make sure locking occurs in the right direction. In other words the target oscillator gets locked to the injected signal and not the other way around. If you have two oscillators of the same frequency, these may injection-lock to each other, in which case the injection locking causes mutual synchronisation, which is a little forgotten research field all on it's own. This is a great starting point on injection locking that fellow time-nut Bruce Griffith wrote and collected references for: http://www.ko4bb.com/~bruce/InjectionLocking.html I've always wondered about injection locking a 2.45 GHz oven magnetron, and whether you could use it to do something like FM. The magnetron is a pretty crummy source phase noise wise, but is that because of low Q (and the frequency is just unstable, which locking would help) or because the amplification mechanism is noisy (in which case locking doesn't help). That is, is injection locking more like a MOPA or a locked power oscillator. (we're talking oven magnetrons here, not radar magnetrons for doppler radar which are actually designed for injection locking, etc. ) There's an interesting paper out there using a bunch (half dozen?) magnetrons as a microwave weed killer, where they all locked to each other, so the power was appropriately combined with minimal loss. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] !0 MHz standard frequency intruder
On 6/28/12 6:48 PM, David McGaw wrote: You know, if one could get accurate delays from a number of locations, one could triangulate its location - just thinking. :-) This is timenuts... we should collect statistics on the signal and figure out what kind of oscillator they're using... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Spoofing GPS
On 6/25/12 7:11 PM, Chris Albertson wrote: On Mon, Jun 25, 2012 at 6:43 PM,li...@lazygranch.com wrote: Yeah, I read it. Typical Fox. The headline isn't accurate since they spoofed the civilian GPS system, not the military GPS. I think it is. Currently the military uses GPS guided drones put the article says they will see more and more used, even by companies like Fed Ex. I don't think I deliver this will happen soon but it might. The article says that these new drones will be susceptible to GPS spoofing. But there is a simple fix that to me seem obvious. When you design a nab system for a drone they should use inertial nav. You can't spoof an IMU. But the cheap IMUs drift and need GPS updates. So each time you update the INU to do a sanity check on the GPS and see if it is within the drift range of the IMU. If not you assume the GPS is being spoofed and continue using the INU data. And of course, this *is* the way almost every autopilot/nav system out there works.. You use IMU+GPS... GPS is long term, but crummy in the short term; IMU is good short term (e.g. to stabilize flight path), but crummy long term. Not to mention that spoofing GPS is actually fairly hard to do, reliably.. you have to have an internally consistent set of signals and observables that seamlessly connects to the original natural set and then walks off. jamming is easy, spoofing is hard. I would also expect that these things will very quickly go to L1/L5 for safety of life applications, and spoofing 2 frequencies is just that much harder. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Spoofing GPS
On 6/26/12 3:38 PM, J. Forster wrote: Whether it's spoofing or jamming, domestic drones are becoming ubiquitous, because they are just so tempting, and sooner or later one is gonna crash onto a populated area, either by accident or deliberate mischief. A piloted aircraft may be able to avoid hitting a school; a drone may not. That *is* the significant problem with non-government UAVs. All fine to run them over the desert on the southern border or out over the Mojave. By and large, UAV failures, as you note, don't have the option of doing a Great Santini. The (catastrophic) failure rate of UAVs is something like 100 or 1000 times higher than for military piloted craft, which in turn is something like 100 or 1000 times that for civilian craft. I did some calculations last year, and if Los Angeles decided to put up a UAV 24/7 to replace things like helicopters, we could expect a crash into the city about once a week. The MQ-9 Reaper and RQ-1 Predator have a reported Class A mishap rate of about 10 per 1000 flight hours... Class A = $1M in damage or death.. bear in mind that if a $500k drone augers in out in the desert, that's not a Class A mishap. So, 1 year is about 8760 hours, so we could expect 87.6 Class A mishaps/year if the LAPD decided to fly the current flavor of UAV. Yes, that would create some interesting news stories. How long til we see a tailfin with LAPD sticking out of an elementary school a'la Cerritos. For comparison, in around 2000-2005, the commercial accident rate was about 0.01 per 100k hours. The Air Force reported about 1 per 100k hours. General aviation is 10/100k hours. (these are non-specific accidents, so they aren't directly comparable to Class A mishaps) There's a great report from MIT on this.. google for Weibel ICAT report UAV safety ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Widdershins
On 6/26/12 11:05 AM, Bill Hawkins wrote: Around 1530, it was considered very bad luck to walk around a church widdershins (see the Wikipedia article). I think it goes back earlier than that, to a time well before clocks. If widdershins means counter-clockwise, how did they know which way clocks ran? Widdershins (or it's opposite, deosil) doesn't really refer to clockwise or counterclockwise, it refers to turning left or turning right. Turning left (sinister, gauche) is clearly a bad plan. Aleister Crowley (noted Himalayan mountaineer and the wickedest man alive) has a whole pile of explanation of this in Magick I don't think this is necessarily sundial related, but if you stand in the doorway looking generally south, the sun appears to move from left to right (in the northern hemisphere, which is all the civilized world had when these words were invented).. widdershins derives from Middle low german weddersines from Middle High German widersinnes, wider=back + sinnes=in the direction of deosil is apparently from Scottish roots in turn from Latin dexter. (I found out all about this back when reading the Nine Tailors, but then, Sayers did have a classical education, and the term dates back quite far. OED has it in 1513) The answer lies in northern hemisphere sundials. When clocks with faces were invented, they ran in the same direction as the shadow of the gnomon on a sundial. Widdershins also means anti-sunwise, which would be blasphemous to people that used to believe that the sun was a powerful god. There's lots of angles to this time stuff. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Spoofing GPS
On 6/26/12 4:42 PM, J. Forster wrote: IMO, your failure rate estimate does not include the probability that some people might not like being spied on by UAVs. I can easily see a market for ground based GPS jammers, especially, in the more rugged, fertile, and inaccessible areas of California. The GPS antennas on the UAVs face up, and have a (not very deep) null facing down, so those rustic farmers are going to need a fair amount of power facing up... (and besides, why do it outside, when you can inexpensively rent large industrial concrete tilt-up buildings with water, heavy power, and a loading dock..) And, as far as remote sensing goes.. commercial overhead imagery from aerial photo and satellites (SPOTimage, etc) is sufficiently good to detect this kind of thing (as well as things like unpermitted swimming pools on which property tax is not being paid). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Spoofing GPS
On 6/26/12 5:51 PM, Chris Albertson wrote: On Tue, Jun 26, 2012 at 3:59 PM, Jim Luxjim...@earthlink.net wrote: I did some calculations last year, and if Los Angeles decided to put up a UAV 24/7 to replace things like helicopters, we could expect a crash into the city about once a week. But they could be made very safe for only a little bit of money. Say you add a rocket deployed parachute triggered by ground proximity. These kind of chutes are made large enough for light aircraft. Lots of other things to do for safety like a video camera that is monitored and then you'd know in a minute if the aircraft was going the right way. No, that doesn't make it safe.. it still fails (engine failure is most common) it just potentially allows you to crash somewhere less obnoxious. I suspect that the overall system reliability of a UAV is *substantially* lower than a military jet. They're not doing things like multiple redundant communication links on different bands, or redundant control systems or redundant anything (all of which commercial aircraft have).. Dropping a UAV by parachute onto a school is not quite as bad as augering into a pre-school, but not by much. Or in the middle of the freeway during non-rush hour. When I was getting my pilots license, I used to have bad dreams about having an engine failure flying along PCH in Malibu at 1500-2000 ft, and trying to decide whether to land on PCH (tons of wires) or the beach (tons of people). We used to have discussions about whether it's better to land on the freeway going with traffic (lower closing velocity but you're coming up on people from behind) or going against traffic (people will see you coming and hopefully dive for the shoulder). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
On 6/15/12 9:49 PM, Mark Sims wrote: Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. you can do what I do to drive mars time clocks. Hydrogen maser derived 10 MHz into a HP 3325B set for the right rate for the clock (i.e. slightly less than 32kHz). I wouldn't be true sidereal time (because the rate is uniform), but it's an easy and straightforward approach. (and no, the Maser derived 10 MHz isn't needed, but I happen to have it handy, so why not) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Paper about DCF77 performance
On 6/13/12 1:38 PM, Bob Camp wrote: Hi Do they grant the right, or do people just get away with it? it is formally granted.. the IEEE instructions for authors or something like that talks about it. You can put your own papers up on your own website, and you make sure you have appropriate attribution, etc. I'll look for the reference. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt cabling questions
On 6/11/12 10:31 PM, Hal Murray wrote: albertson.ch...@gmail.com said: But you know what? If you simply place an automotive puck type GPS antenna on your roof you have to do the same thing. It must be grounded the same way, same lightening protection and so on. So in the end you may as well put up a professional looking and permanent steel mast. It is not that much more work. What about putting a skylight high on the roof and putting the antenna up in it? What's magic about inside vs outside the roof/skylight envelope? --- I have a large pine tree out front. It's roughly 3x the height of my (one story) house. What are the chances of any lightning hitting my house rather than the tree? What if I put an antenna on the top of my house so the tree is only 2x the height of my antenna? Of course, that depends on how far the tree is from my house. Not far. Call it 45 degrees from the back of my house to the top of the tree. An antenna on the top of my house would probably be below that sight line. Is there a good book or URL on lightning vs antennas? Again, I'm interested in both the technical issues as well as the local zoning/legal issues. http://www.amazon.com/The-Art-Science-Lightning-Protection/dp/052187811X Martin Uman and his collaborator Rakov have probably forgotten more about lightning than everyone on this list collectively knows about it. This one is a bit pricey still, but is the definitive tome. A Dover Press version of Uman's The Lightning Discharge is $20, and well worth the investment if you're interested in lightning. Ronald Standler's book Protection of Electronic Circuits from Overvoltages is a great source on overvoltage protection in general. $20 in paperback. Lots of useful information on how to design/purchase transient suppression for all kinds of signals. And surprising information on how certain kinds of techniques can actually make things worse. One wants to be careful about texts published by manufacturers of protection equipment. Yes, they typically have valid information, but it *is* coming from a source which wants you to buy more stuff, so they tend to be a bit more conservative (more protection = better, even if the physics doesn't support it). That said, much of the high quality peer reviewed research on things like lightning rods (aka air terminals) does come from companies making such things. Also, there are several pubs out there widely distributed aimed at applications like FAA Control Towers or high reliability 24/7 land mobile radio. The recommendations in those books may prove to be somewhat of overkill for a couple reasons: most amateurs don't need that level of protection; the suggestions aren't always supported by the physics, but are there because they don't hurt, triggering the nobody got fired for buying IBM mainframes phenomenon... if it's small differential cost, why not do it, because if we don't do it, and something goes wrong, we'll be blamed. Legality wise Nat Elec Code (aka NFPA70) has bonding and grounding requirements. Art 250 on grounding, Arts in the 800s on antennas. Expensive ($80-100) if you buy it, but since it forms the basis for California's Title 24 (State Electrical Code), a scanned version is online at https://public.resource.org/. The antenna grounding stuff doesn't change very much, so an older code found at a used book store might also work. NFPA780 is the lightning protection code. IEEE 1100 - The Emerald Book - is very useful on grounding, transient protection, etc. issues in general. Pretty expensive.. find it in a library. http://standards.ieee.org/findstds/standard/1100-2005.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Quadrifilar Helix Antenna
On 6/9/12 6:50 PM, David Kirkby wrote: On 10 June 2012 01:39, Jim Luxjim...@earthlink.net wrote: NEC can do a pretty good job on a helix, and it's free. I like 4nec2 as a front end. I've never tried NEC on them. I quite like MMANA-GAL myself. But it only supports NEC2. 4nec2 does both NEC2 and NEC4 NEC will also do a patch: Model it as a grid of wires using the guideline of surface area of wire is spacing between wires.. that is, if you have wires on a 1cm grid, then the wire diameter should be 1/pi cm. Even if you thin the wires out (so you can get them closer to the ground plane), it still works pretty well. I found a paper about that rule with NEC, and it basically showed it was not a good of thumb. I just can't think where it is (what computer, what directory). funny.. the rule of thumb comes from Jerry Burke (one of the NEC authors) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt cabling questions
On 6/10/12 4:24 PM, Chris Albertson wrote: On Sun, Jun 10, 2012 at 2:50 PM,b...@lysator.liu.se wrote: ... 3m of antenna cable is no problem. Antenna position is more important than the exact type of antenna. I'd rather have a decent antenna at a very good site, than a very good antenna at a slightly worse antenna site 3M is trivial. 30M will work fine too. I agree about the location really mattering more than anything else. What I did was drill a 2 hole through the roof up from the attic and push a 10 foot gallanvised iron plumbing pipe up. you would probably want appropriate flashing around that to prevent water (and vermin) ingress. The antenna sits on thop ithe pipe and is higher then the roof top ridge and then the cable go down the center of the pipe. I pipe flange on top of the pipe makes a perfect mounting platform. I used a timing antenna comes inside a white pointed plastic radome. These sell for just under $30 on eBay. Maybe it is coincidence or not but the four holes pin the standard pipe flange match up with the four holes in the bottom of my antenna and there is enough room inside the hole in the center for an N connector. It is worth getting the antenna done right because it is the most important part of the entire system. Those dome type antenna are worth it. the shape is designed to shed both bird poop, and snow. Birds can be an issue with a flat top antenna, no snow here. You probably get snow every few decades (it snowed in Malibu a couple years ago, for instance), but I wouldn't worry about snow loads, even so. grin HOWEVER, your scheme is going to be tricky to pass muster with the National Electrical Code. Two aspects need attention: You need to have a ground wire from the mast to the ground point and You need to have some form of ground of the coax shield at the point where the coax enters the building. (a listed antenna discharge unit is the usual way). While Southern California isn't exactly the lightning capital of the world, we do get some. A bigger concern (and the primary reason for the code requirement) is that above ground power lines can come down and touch your antenna. And someone living in a more lightning prone area is going to want to take those precautions. The installations I've seen typically use the same general pipe scheme (using rigid conduit, which looks a lot like pipe, but has a smooth inside with no burrs) to a box on the roof, and then regular conduit running down the outside of the building. Then at the point of entrance, the ground bonding conductor goes from the conduit to ground, and there's a coax grounding block in a box at the place where the hole in the wall is. Granted, if lightning does hit, everything connected to the antenna is going to fry, unless you have some sort of reradiation scheme to provide an air gap. That's what we do when we test GPS receivers destined for space, where you don't want to take the risk of killing the expensive flight hardware. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt cabling questions
Totally agree On Jun 10, 2012, at 19:34, Chris Albertson albertson.ch...@gmail.com wrote: On Sun, Jun 10, 2012 at 4:43 PM, Jim Lux jim...@earthlink.net wrote: HOWEVER, your scheme is going to be tricky to pass muster with the National Electrical Code. Two aspects need attention: You need to have a ground wire from the mast to the ground point and You need to have some form of ground of the coax shield at the point where the coax enters the building. (a listed antenna discharge unit is the usual way). Yes, all true. I didn't really want to right a book about it. Yes there is flashing around the pipe. It is handled the same is for other pipes that come up through the rook to vent plumping. And yes you ground the pipe just like you ground an old off-the-air TV antenna mast and so on. My VHF (two and four meter) antenna and by HF wire antenna all have lightening arasters and big ground rod systems, and the ground rods are tried together an. But you know what? If you simply place an automotive puck type GPS antenna on your roof you have to do the same thing. It must be grounded the same way, same lightening protection and so on. So in the end you may as well put up a professional looking and permanent steel mast. It is not that much more work. Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Procom GPS4 quadrifilar antenna...
On 6/8/12 5:20 AM, Michael Baker wrote: Time-nutters-- The Procom website lists the noise-figure of their quadrifilar LNA as: GAIN 30 dB NOISE FIGURE 3 dB (incl. input filter). Typ. approx. 3 dB I am a little surprised at this relatively high NF for a product in this price category. Even most low-end mass-produced consumer grade GPS antennas are spec'd at 1.5 to 2.0 dB NF. One thing to check on NF specs is the temperature range over which they are valid. A consumer spec might be at room temperature only, a more rigorous spec might be at -20 to +50C. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Procom GPS4 quadrifilar antenna...
On 6/8/12 9:21 AM, steve heidmann wrote: Is it worth driving from Thousand Oaks to Altadena for Snowcones (qty 5) tomorrow ? --- On Fri, 6/8/12, Jim Luxjim...@earthlink.net wrote: http://www.jpl.nasa.gov/events/open-house.cfm Well.. they've got all the stuff setup for JPL open house.. Is it worth an hour's drive? The weather is nice. There's lots of MSL related stuff out. If you have little kids, there's the usual drive a rover over a row of children thing. I don't know if the totally cool Athlete rovers will be out. Hopefully yes. The Mars Yard is always fun, and they'll have something out crawling around. http://www.jpl.nasa.gov/video/index.cfm?id=922 Will there be tours of the frequency and timing lab? (which would be of particular interest to time-nuts).. nope.. But, if you're in the area some other time, send me a note, and I'll see what I can do. Down in my lab, we don't have anything nearly as good as what they've got up there. (but they send me their maser derived reference on a fiber optic pipe...) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] zero crossing of venus
On 6/5/12 5:20 PM, Tom Van Baak wrote: Attached are two snapshots of a NASA live feed -- an interesting reminder about the difficulty measuring timing signals with great precision. When you look closely, the leading edge of the sun is rather ill-defined, not unlike many 1PPS pulses. I suppose with enough photos, modeling, and image processing one could pinpoint when the transit (zero crossing) really occurs to great precision. Does anyone know more details how this is done? Is the state-of-the-art at the millisecond level? microsecond? nanosecond? Thanks, /tvb Speaking of this.. does anyone have a reference to the math and process used to measure distance from earth to sun using transit of venus? I assume it makes use of some astronomical time measure to determine when Venus enters and leaves from different viewing places. but that would require a clock that can time from night (when you get an astronomical measurement) to day reasonably accurately. Or, do you measure the position of the sun in the sky (something that's fairly easy to do) But maybe not.. maybe it's more about where it enters and leaves the solar disk (in an angular sense, i.e. what's the length of the chord) positionally, in which case the time is less important. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] zero crossing of venus
On 6/6/12 7:02 AM, Mike S wrote: On 6/6/2012 9:09 AM, Jim Lux wrote: does anyone have a reference to the math and process used to measure distance from earth to sun using transit of venus? http://transitofvenus.nl/wp/getting-involved/measure-the-suns-distance/ Of course, back in the 1700s, they didn't have nice iPhone apps to give good time hacks.. I see that Halley's scheme relied on measuring the length of the chord of the transit, which could be done geometrically (at least from the drawing, it looks that way), without needing time involved. http://www.transitofvenus.nl/halleysmethod.pdf seems to say that a precision of around 1 second for the duration between contacts would do. (of course, here in southern California, we couldn't do it, because the sun set before 3rd contact) Delisle's technique seems to require synchronized clocks. How well synchronized? A good math treatment of the technique would be nice to find, then one could take known clock and measurement accuracy and figure this kind of thing out. I think this has more of the info http://www.venus2012.de/venusprojects/contacttimes/basicidea/basicideatimes.php but I'm still looking through it. I'm also interested in how did they get their absolute time hack for the Delisle technique. It's an astronomical measurement, so maybe the lunar distances or Jovian moons approaches would work, but then you have to have a stable enough clock to last from night until day. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS through windows
On 6/4/12 10:24 PM, Hal Murray wrote: Does window glass have significant attenuation at GPS L1? What if it's a big window on a modern green office building and has some sort of coating/content to reduce IR transmission? Google found an (expensive) paper from IEEE where the abstract said: At average, about 30 dB attenuation is observed from 800 MHz to 6 GHz so I assume the answer is mostly sure does. Does anybody have more info? Is there a rule of thumb? (maybe X dB, or X dB/inch) Does it vary wildly from brand to brand of glass? varies wildly.. I remember being at a conference in Santa Clara in 1993 with a Trimble Scout (one of the very first handheld GPS units that was practical.. the Sony one ate batteries). Inside the main indoor hall with all the skylights you couldn't get a fix at all. And the LA Convention Center had a similar problem in the mid 90s, when cellphones were really getting popular. You couldn't get a cell signal, and there were all these conspiracy theories that it was the convention center wanting people to pay for wireline phone at their booth. by the way... There was a fantastic project by a young woman from Ilmenau Germany at the International Science and Engineering Fair this year. She modified thermal insulating windows (with the metallic coating) by designing a pattern of slots in the coating which passed cell phone and WiFi frequencies, without markedly affecting the thermal properties. You can't arrange the slots any old way, or you get grating lobes (Young two slit experiment with a vengeance). -- Context is that I took some low cost consumer GPS toys when I visited a friend who had recently moved into a new office building. He's on the 4th floor, well above anything else on that side, so we had a clear view for half of the sky looking West or slightly North of West. We tried a SiRF III and a Sure demo board. I had forgotten to update the Sure clock the night before so it was having a hard time getting off the ground. We took everything outside where they locked up within a few minutes. Back inside with the antennas on a window sill, both just barely worked some of the time. The glass below the sill was a different color, slightly less yellow. We tried the lower (floor level) sill but didn't notice any difference. That wasn't a serious test with numbers and error bars, but we probably would have noticed if it had suddenly started working much better. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nutcan answer
On 6/4/12 10:44 PM, Chris Albertson wrote: On Mon, Jun 4, 2012 at 10:18 PM, Hal Murrayhmur...@megapathdsl.net wrote: What is the significance of the pointy tops of the long skinny antennas? Guessing. Terminates the end of the conductor to prevent a discontinuity and reflection more likely it's for structural reasons. A lot of helical antennas are a wire or tape on a cruciform cross section core (rather than on a tube). You don't want that corner sticking out. On the tube, it's easier to make a cone end, then a flat pillbox, and you don't have the diaphragm vibration mode on the flat end. How about the collars at the base of them? Another guess: They kill multi path reflections from supporting structure or provide a better match. Or both.. An awful lot of antenna designs out there work about the same, particularly for endfire helicals, so if you have a design that works in one application and you want to change it, you might just scale for size, rather than trying to come up with a completely new design. it's like the HeliBowl antennas.. Turns out they're totally non critical and they all work just about the same. Plastic party cup and cheap mixing bowl, and you're in business. Broadside short helices, particularly quad helices are a bit trickier, especially if you're using the one pair a bit long and the other pair a bit short to get the 90 degree phasing. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS through windows
On 6/5/12 9:14 AM, Chris Albertson wrote: On Mon, Jun 4, 2012 at 11:26 PM,li...@lazygranch.com wrote: The low-E coatings are known to attenuate WIFI. WIFI is probably a worse case than GPS, but the availability of the gear makes experimenting easy. I think they are sputtered metal either on the glass or on a thin film applied to the glass. Southwall Technology in Palo Alto pioneered or at least commercialized the technology. They are interference filters. Layered coating 1/4 wavelength thick that send some waves back in phase and other out of phase, they reflect heat and UV be let light go through. I think it is a tin oxide coating of some kind. or Indium Tin Oxide (ITO) which is transparent and conductive. Sometime they use silver but only on the inside of a double pane window with the inside filled with inert gas, otherwise the silver tarnishes. OK, I think they can also over coat the silver with an oxide to keep the air away from it yes.. the german young lady was working with triple pane windows filled with Argon I think my windows at home have both. I can see the 1/4 wave coating change color with the angle I look at the glass, the silver simply darkens the glass. The argon gas between the panes is for insulation. I assume it is the metallic silver coat the messes with RF signals. I think the silver is very common in large buildings. But with a large building they make the glass custom to the architect's specifications so no one can know what is in your building. Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] zero crossing of venus
On 6/5/12 5:20 PM, Tom Van Baak wrote: Attached are two snapshots of a NASA live feed -- an interesting reminder about the difficulty measuring timing signals with great precision. When you look closely, the leading edge of the sun is rather ill-defined, not unlike many 1PPS pulses. I suppose with enough photos, modeling, and image processing one could pinpoint when the transit (zero crossing) really occurs to great precision. Does anyone know more details how this is done? Is the state-of-the-art at the millisecond level? microsecond? nanosecond? Thanks, /tvb or do something like compare the centroid of venus to centroid + radius of sun (or segment thereof.. ) it's pretty easy to get 0.1 pixel centroid precision, from what the star tracker, tiny moon finder folks tell me. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS and Rubidium frequency standards and noise question (newbie).
On 6/2/12 2:57 PM, Chris Wilson wrote: I am looking to get a frequency standard for my amateur radio shack, initially for verifying test gear readings, but later as a standard to lock receiver and transmitter oscillators to. I was going to buy a GPS frequency standard but a friend warned me these may have noise issues when I come to use it with an oscillator in RX / TX applications. It's not something I had considered, so what's the score here please? Should I not buy a GPS standard? Thanks. Any links to known safe suitable purchase sources from personal experience welcome, either here or by PM or e-mail. I am in the UK. What's your need, frequency accuracy wise? What's your phase noise requirement? The first thing to look at would be an ovenized quartz oscillator. They're stable (aging rate is around 1E-10/day.. ) and pretty quiet (-165 dBc at 10kHz out). They run $50-100 on eBay or similar, and are pretty easy.. you hook up a 12 or 15V DC power supply and they put out 10 MHz.. Like an old HP 10811 or a Wenzel Streamline would do you nicely. (BTW, a lot of test equipment has a decent oscillator inside.. so you if you got a suitable counter or signal generator, surplus, that has a good oscillator, then you just use the reference output from the instrument. Ask on this list about candidate instruments) if 1E-10/day isn't good enough... (maybe you're doing microwave hilltopping every 6 months.. 1E-10/day would be 0.01 ppm, so your 10GHz signal would be off by 100 Hz every time you went out) Then, a GPS disciplined quartz oscillator (any of several kinds are available surplus or cobble one together yourself) is probably your best bet. Even without the GPS signal, it will typically be pretty quiet and stable (because basically it's an ovenized XO). HP Z3801As used to be common, Trimble Thunderbolts are more recent, etc. A Rb source (bunches of these on the surplus market recently) is another choice. Just like the GPS, they usually are disciplining a quartz oscillator, so the output spectral purity is really that of the quartz oscillator. Advantage of a Rb is that it works indoors or underground where there is no GPS. And, it's accurate sooner after applying power in most cases. But they DO age, and you need to adjust them (still, pretty good.. aging might be 1E-8 over 20 years. ) The lamp wears out too, so a 25 year old surplus Rb might be near end of life (or might not). google the FS725 for an example of what a current inexpensive Rb reference looks like. Surplus, the internal source can be in the $100 range, but you'll have to cobble up a power supply, and probably modify some connectors. This list has lots of people who can give you advice on this, though. But it gets back to.. how good do you need? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] is there a cheap and simple way to measure OCXOs?
On 5/30/12 6:11 AM, Attila Kinali wrote: Hi, I recently bought some Oscilloquartz 8663 from ebay and am now wondering how to check whether they are working correctly or whether they are out of specs. Unfortunately, although i have a reasonable park of measurement instruments, none of them are in the precision range that i'd need to characterize the 8663's. I have three oscilloscopes (analog 20MHz, digital 200MHz and 1GHz), a cheap handheld frequency counter and a couple of multimeters of various quality. I also have a FE-5680A at hand as frequency reference. Got a mixer around, so you can beat them against each other (or against your 5680)? Any ideas what i could do to measure phase noise and frequency without buying a lot of stuff? Soldering is not a problem though. Attila Kinali ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Water Proof Vent
On 5/15/12 9:05 AM, Brooke Clarke wrote: Hi: You might consider using a piece Tyvek material. You can get it free from the USPS in the form of a priority mailing envelope or at a construction site where it's used to warp the outside of houses. Passes water vapor and air but not water. I don't know that all things labeled as Tyvek have that semi-porous property.There are hazmat suits made of Tyvek, and I doubt they're porous. According to Dupont, Tyvek (r) is a whole family of spun bonded olefin stuff (polyethylene fibers that are matted and melted). It can be made in a variety of forms, some porous, some not. http://www2.dupont.com/Tyvek/en_US/products/structure_types.html type 16 is used in disposable garments and is perforated with tiny holes (much like GoreTex is). 130-510 microns, which is pretty big, compared to GoreTex (around 1 micron holes) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Trimble Resolution SMT - good/bad/indifferent?
On 5/11/12 4:34 AM, shali...@gmail.com wrote: Yes, I moved them yesterday Didier KO4BB --Original Message-- From: Mark Sims Sender: time-nuts-boun...@febo.com To: Time-Nuts ReplyTo: Time-Nuts Subject: [time-nuts] Trimble Resolution SMT - good/bad/indifferent? Sent: May 10, 2012 11:02 PM Why in the hell would anybody build a 50 channel receiver? At most you MIGHT see 12 usable GPS sats... I don't think that I've seen over 10. WAAS should be fairly useless for a timing receiver. Supposedly the Nortel NTGS50AA docs and support info (including GPSMONITOR were uploaded to the KO4BB site). ___ channel in GPS receiver speak is more than a single satellite.. L1 + L2 + L5 would be three channels. Sometimes the P/Y code is considered a separate channel. And when you start adding in other constellations and S/Vs (QZSS, Galileo, GLONASS), you add channels. ANd here's another reason to claim X channels where YX is the most you're likely to use. It gives an indication of processor/FPGA resources consumed, and can be used to estimate margin in a utilization review. For instance, if I've demonstrated acquiring and tracking 100 channels in the lab, and I know I'm never going to see more than, say, 12, in the field, then it is unlikely that there's some obscure timing/processor loading bug that's going to cause a problem. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocks for Audio gear
On 5/11/12 12:48 AM, MailLists wrote: Who would listen to pure sine tones? As a youth, I listened to WWV, which is a pure sine tone, in between the ticks. Drove my parents batty. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Trimble Resolution SMT - good/bad/indifferent?
On 5/11/12 2:38 AM, Hal Murray wrote: Why in the hell would anybody build a 50 channel receiver? At most you MIGHT see 12 usable GPS sats... I don't think that I've seen over 10. WAAS should be fairly useless for a timing receiver. I can think of a couple of reasons. I'm sure there are more. One would be marketing type bragging rights. I can scan more channels than you. Another area would be cold-start time. If you have to search N slots, more searchers runing in parallel is likely to speed things up. Searchers and trackers are often different logic, these days.. Searching is very efficiently done with a FFT correlator, because you can search all lags simultaneously with NlogN effort as opposed to O(N/2) effort with a sequential search. Same for Doppler. But once you've acquired, you track with a conventional Early/Prompt/Late scheme. When you get into full-up implementations, where there is coupling between the tracking loops (think of a 2 frequency receiver.. L1 and L5 will have related doppler), there are other economies of scale possible. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] question about Thunderbolt geo acuracy
On 5/11/12 5:23 AM, swingbyte wrote: s disappointing! I need to measure the height of my house floor to be above the flood plane contour. I might have a look at some dted from work. Might have to pay a real surveyor to measure the height datum. Thanks for all the info though guys for that, you need a real surveyor who can provide a legally accepted measurement. Someone who can a) know from the flood level definition what vertical datum they are using (probably NOT something normal in the geodesy world) b) knows the legalities of establishing the difference The mechanics of surveying (leveling in this case) are straightforward to learn. The legalities and local practices in documentation are not. This is what getting a Land Surveyor's license is all about. There's also a question of what the legal height of your house is, relative to the property (from a flood insurance standpoint). They might have some arbitrary offset in the rules. Sort of like how baseline electrical power consumption is actually about 2/3 of the expected minimum consumption in the area for a given size house and appliances (e.g. nobody is likely to consume less than baseline) There are some mortgage servicers, by the way, who take property addresses that have been geolocated and FEMA flood plain definition maps to determine whether you definitely don't, definitely do, or just might need flood insurance. The maps change (as does the geolocation). From what I understand, about 3-5% of the properties scanned require some sort of manual intervention (maybe the address doesn't geolocate, or it's right on the line, or) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] question about Thunderbolt geo acuracy
On 5/11/12 5:54 AM, Chuck Harris wrote: Go to your local building and planning commission, and get yourself a copy of the topographical map for your address. They are cheap, and are the standard by which everyone (insurance, zoning, ...) determines your flood plane exposure. I have been informed (in the last 5 minutes) that whether you are in a flood plain, these days, are determined almost entirely by the geographic position of your property on the FEMA flood plain map. (at least as far as lenders and HO insurance goes) FEMAs maps may or may not align with USGS maps. They almost certainly do NOT align with the county recorder's maps. If you're in an area where FEMA doesn't issue maps then it's something else, and USGS or local maps may determine. But I notice from the FEMA Flood Map server that they cover even things up in the mountains (e.g. Alpine county in California) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Calculating phase jitter from phase noise - appnote by silabs
On 5/11/12 1:51 AM, Attila Kinali wrote: Moin, I just stumbled over a nice little summary how to calculate the jitter of a signal from its phase noise plot by silicon labs: http://www.silabs.com/Support%20Documents/TechnicalDocs/AN256.pdf Attila Kinali and one from Wenzel http://www.wenzel.com/documents/spread1.htm ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] question about Thunderbolt geo acuracy
On 5/10/12 6:08 AM, Magnus Danielson wrote: On 05/10/2012 02:50 PM, swingbyte wrote: Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. There are many sides to this issue. You will most definitely be best served by a choke-ring or similar antenna that suppresses multi-path reflections. In addition to that, you would want Lady Heather to do a 24 hour position averaging. This should give you an OK solution, but really not the best achievable. Accurate height data is complex, since besides the receiver and antenna issues, height data has more uncertainty than longitude and latitude measures, and also since even if precise WGS84 height is achieved, you would need to correct it to your datum, your sea-level etc. You would also like to have better ionspheric correction than a plain GPS solution gives you, but the Thunderbolt does not give you direct support for such corrections. Exactly how much effort you need to do depends on how accurate you need it, +/- 10 m, 1 m, 1 dm, 1 cm or 1 mm. If you can get RINEX format files, you can post process them through GIPSY at JPL and get higher precision, using post determined ionospheric and other corrections. My friends in the GPS world say that getting to 1 meter absolute position is fairly straightforward but once you start getting finer than that, all the various factors start ganging up on you: ionosphere, solid earth tides, multipath, phase center shifts, etc.etc. Likewise, getting 1mm + 1 ppm of separation distance sorts of uncertainty in a differential measurement is fairly straightforward. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] question about Thunderbolt geo acuracy
On 5/10/12 6:42 AM, mike cook wrote: A man with only one GPS Surveys from different receivers I have. All taken at the same height from prolonged surveys. WGS84 datum. Oncore UT+ A 207,62m Oncore UT+ B 209,24m Z3801A 180,72m Oncore VP A 229,95m TBolt 207.00m That's a pretty big variation (10s of meters), a lot more than I'd expect (I'd expect variations more like the difference between the two UT+s and the Tbolt). I wonder what about the VP and Z3801 fixes pushes them so far away. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] question about Thunderbolt geo acuracy
On 5/10/12 7:40 AM, Arthur Dent wrote: I've found significant altitude errors using a GPS and the following quotes found on the internet will explain why. From my experience of hiking in the mountains of New Hampshire an aneroid altimeter will vary with atmospheric pressure about 200 feet for a change of 0.2 of mercury so you have to continually set it at known waypoints, just like setting a frequency standard against a known reference, and then it will be 'accurate' for some length of time, and then you set it again. GPS altitude will be off but it should be fairly consistent in spite of the changing atmospheric pressure. The earth neither spins at a constant rate nor is it a perfect sphere. Maybe we need to trade it in for a newer model. ;-) GPS altitude measures the users' distance from the center of the SVs orbits. Not precisely true. The SV orbits follow the usual Keplerian things so the focus of the ellipse is close to the barycenter of Earth, but of course, the moon and non uniform gravity of the Earth affect it too. GPS fixes are relative to WGS84 coordinate system (x,y,z) 0,0,0 in WGS84 is within a few cm of the center of mass of the Earth. WGS 84 also defines a datum for the surface (which is not, generally, the geoid) as an ellipsoid of revolution. (compare to the Clarke 1866 ellipsoid) These measurements are referenced to geodetic altitude or ellipsoidal altitude in some GPS equipment. This is a bit fuzzy... there are differences between geodetic and geocentric altitude for instance. And then there's the reference ellipsoid (e.g. Clarke 1866), or more generally the geoid Garmin and most equipment manufacturers utilize a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model. Mmm.. I don't know that it roughly approximates.. WGS84 is precisely defined (that's the coordinate system). The geoid (in terms of the sea surface is defined in terms of spherical harmonics and varies some 100m or thereabouts from the reference datum. WHether your GPS uses the WGS84 datum (simple ellipsoid) or the fancier geoid, is something you'd have to look up. As with any model, there will be errors as the earth is not a simple mathematical shape to represent. What this means is that if you are walking on the seashore, and see your altitude as -15 meters, you should not be concerned. First, the geodetic model of the earth can have much more than this amount of error at any specific point and second, you have the GPS error itself to add in. As a result of this combined error, I am not surprised to be at the seashore and see -40 meter errors in some spots. Actually, no.. the geodetic model (e.g. the EGM96) should be VERY close to the actual sea surface (barring tides and local geographic effects.. the Gulf Stream sits several meters higher because it's warmer and less dense) The ellipsoid could easily be off by tens of meters. We have to make some assumptions about the shape of the earth. WGS84 has defined that shape to be an ellipsoid, with a major and minor axis. The particular dimensions chosen are only an approximation to the real shape. Ideally, such an ellipsoid would correspond precisely to sealevel everywhere in the world. As it turns out, there are very few places where the WGS84 ellipsoid definition coincides with sealevel. On average, the discrepancy is zero, but that doesn't help much when you're standing at the water's edge of an ocean beach and your GPS is reading -100ft below sealevel. The deviation can be as large as 300ft in some isolated locations. When the National Marine Electronics Association came up with the NMEA standard, they decreed that altitudes reported via NMEA protocol, shall be relative to mean (average) sea level. This posed a problem for GPS manufacturers. How to report altitudes relative to mean sea level, when they were only calculating altitude relative to the WGS84 ellipsoid. Ignoring the discrepancy wasn't likely to make GPS users very happy. As it happens, there is actually a model of the difference between the WGS84 ellipsoid and mean sea level. This involves harmonic expansions at the 360th order. It's a very good model, but rather unusable in a handheld device. It was determined that this model could be made into a fairly simple lookup table included in the GPS receiver. The table is usually fairly coarse lat/lon wise, but the ellipsoid to mean sea level variation, known as geoidal separation, varies slowly as you move in lat/lon. And that is a more accurate description.. The question really is what does YOUR receiver report.. if it's MSL in NMEA strings then I would imagine all modern receivers use some form of geoid model with error probably 1 meter. If it's WGS84, then it ignores the geoid. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
Re: [time-nuts] question about Thunderbolt geo accuracy
On 5/10/12 9:18 AM, Chris Albertson wrote: On Thu, May 10, 2012 at 9:07 AM, Bob Campli...@rtty.us wrote: . Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. It will give pretty good height data. Within a few meters but you have to know how to translate between different definitions of sea level to make best use of the data. If you live in the USA you can now download for free the USGS topographic maps. I'm pretty sure thy have full coverage of all of the US. THese will have 20 foot contour intervals and you can interpolate to at least half that. So for most normal purposes you can find your elevation without a GPS. Just look on the topo map. Most of these maps where made with stereo camera pairs. They get relative elevation optically by matching the two images and then they sent survey teams to ground check some points. And updated the elevation data with radar measurements from SRTM, as well. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] question about Thunderbolt geo acuracy
On 5/10/12 10:46 AM, Chris Albertson wrote: mean sea level is not meaningful any more. What shape is the ocean and what if you live in Kanas? How to extrapolate the ocean level to Kanas? The answer is to use a model of some kind mean sea level, these days, is a name for a particular height that matches the long term average of the ocean, where there is ocean to be measured, and which smoothly varies in between those points. The trouble with a defining it is that it will not match what you measure with your stick in the sand.So there are any number of local definitions that are closer matches to measured heights WGS84 won't match the stick in the sand, but one of the modern reference geoids most certainly will match it, within a few cm. It's important these days, where there are property boundaries referenced to things like mean high tide line. Measuring sea height (the actual height) to an accuracy of cm over a global scale is pretty straightforward these days (that's what TOPEX/JASON is all about). After that, it's a matter of choosing an appropriate averaging technique to remove the effect of tides (which you need to do on solid land, as well) WGS84, is pretty much the simplest model, and is more about defining the directions of X,Y, and Z (or lat/lon) than where the surface of the earth is. The root of the problem is that the earch has a very complex shape. It is lumpy in random ways and you can't model this, you have to measure it and then look it up. You CAN model it.. and that's what the EGM model is.. using multihundred order spherical harmonics. The model isn't simple, but neither is it just a table lookup of measured data. And, as mentioned in an earlier set of posts.. since the bumps aren't huge, if you're only interested in meter scale uncertainties, a fairly small table will give you the local variation between WGS84 ellipsoid (no bumps at all) and EGM. Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocks for Audio gear
On 5/10/12 11:36 AM, Hal Murray wrote: albertson.ch...@gmail.com said: I've alway have thought that if nanosecond level jitter is bad then breathing while listening must be really bad. If you inhale the path length from your ear to the speaker changes at the microsecond level. You'd think the resulting doppler shift would drive these audiophiles nuts. All that pitch shifting. Perhaps the spectrum of the jitter matters. If the frequency is low enough, I call it wander rather than jitter. Audio doesn't need DC or low frequencies so wander is easy to filter out with a simple high-pass filter. Heartbeats may be more interesting than breathing. Does anybody know of spectrum domain data? It should be possible to collect position info while also monitoring heartbeat and chest diameter and then crunch some numbers do see how much of the position correlates with heartbeat vs breathing and then plot each part in the frequency domain. oddly, I happen to have just that data to hand, having been looking at ballistocardiography. If you put someone in a bed, suspended by 4 wires (one at each corner), your heart beat results in about 1mm displacement (head to foot). 1 degree phase shift at 1 kHz, or thereabouts. in terms of displacement in general, breathing is on the order of 1cm (at 0.1 Hz) and heartbeat is on the order of 0.1-1mm, depending on where you look. (look up microwave cardiography for instance) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocks for Audio gear
On 5/10/12 12:44 PM, Chris Albertson wrote: On Thu, May 10, 2012 at 10:25 AM, Heinzmann, Stefan (ALC NetworX GmbH)stefan.heinzm...@alcnetworx.de wrote: Benjamin and Gannon, the first reference in Ashihara's paper, come to lower figures for sinusoidal jitter with carefully selected frequencies relative to the main signal, which is also sinusoidal. Their results reach down to the single figure nanosecond range, and that can be regarded as the real limit of audibility. Are there any real audio systems with sinusoidal jitter. powerline ripple on a signal going into a threshold detector that drive the sample clock would be a nice way to generate sinusoidal jitter. I've got a nice example where 66MHz processor clock modulates a 49MHz sample clock (well, it's not perfectly sinusoidal, but if you digitize a clean sine wave, you get nice aliases of the modulation frequency). I'd goes that it would all be random. I can see where I could build a system with that defect if I wanted to but are there any systems on the market like this? Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why 9,192,631,770 ??
On 5/9/12 4:27 PM, Charles P. Steinmetz wrote: Don wrote: It's interesting to note (to ask?): When did someone get smart enough to start measuring 1/86 thousandth of a day That is generally considered to be the 10th/11th century Persian Muslim mathematician and astronomer, Abu al-Rayhan Muhammad ibn Ahmad al-Biruni (a.k.a. Alberonius and Al-Biruni). His eclipse data was accurate enough that it was used in the late 18th century to help quantify the acceleration of the moon, and is still used by astronomers today. as for why a second? That's because of the popularity of base 60. Dividing the day into 24 hours (twice 12) relates a day to a year to zodiac constellations. it's also got a lot of factors (2,3,4,6,etc) Then dividing hours into 60 minutes, and minutes into 60 seconds makes sort of sense. 1 second is also close to the human heartbeat period (as opposed to, say using 1/100 hour or something like that) The French Revolution did try to decimalize things, of course. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Faster than light of a different type
On 5/9/12 11:06 AM, Attila Kinali wrote: On Mon, 07 May 2012 15:16:51 -0700 jim sj...@jwsss.com wrote: Sadly the actual information is behind a paywall. BTW: Little known fact: most university libraries have site subscriptions for the most popular/relevant scientific journals. You usually can access these journals from the computers at the libary for free. (free as in paid by your tax money). I'm not so sure about that, in general. (the access to the public, not the tax funding).. A lot of universities have put badge readers on a lot of areas that one might think are totally public access. Now, they might be wide open during the middle of the day, but at some point, you have to badge in to get access (so that my daughter studying at 3AM doesn't meet up with weirdness, probably). There's also more and more badge access to computers (so that they know you have agreed to the acceptable use policy and/or can pay for your printer output). The need for you badge on campus is so pervasive there are big signs on my daughter's dorm doors did you remember your J-card? (if for no other reason than you can't get back into the building without it, unless you get security to let you in, and if it's sleeting that's miserable) I'll have to ask her about whether there are access controls on online databases. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Faster than light of a different type
On 5/9/12 10:04 PM, Attila Kinali wrote: On Wed, 09 May 2012 18:11:22 -0700 Jim Luxjim...@earthlink.net wrote: I'm not so sure about that, in general. (the access to the public, not the tax funding).. A lot of universities have put badge readers on a lot of areas that one might think are totally public access. Now, they might be wide open during the middle of the day, but at some point, you have to badge in to get access (so that my daughter studying at 3AM doesn't meet up with weirdness, probably). Ok.. The universtities i know here in Europe are pretty much open. During the day there are usually no entrance controls, only for special areas like the chemistry labs with the dangerous stuff (but not the chemistry building itself). Of course, they lock the doors in the evening and you need a badge or a key to get in afterwards. But it's obvious why you don't want to have random people being able to walk in during the night... Anyways.. it's getting OT again... I just wanted to say that it's possible to get access to a lot of scientific publications using the university library. Which, at least here in Europe, have usually also subscriptions for people who are not enroled (in Switerland, they are for free, but you have to get a card/badge). Because folks DO want to get those papers.. I talked to my daughter tonight.. At Johns Hopkins (probably typical of big uni in a urban area)... during the day, you have to show some sort of ID to get in (not college ID, just some sort of ID), at night, uni ID swiped in the badge reader. Some journals are unrestricted, others you need to have a JHU id to get access to. Depends on the journal. social science (unlikely to be of extreme interest to time-nuts, unless looking up behavior of mailing lists) are more likely to be in the must be staff/student bucket. hard science technical journals are more wide open. If you want to print, you need to have the special debit card (which anyone can buy and load with cash) In the U.S., local municipal/county libraries can usually request bound journals from other libraries for free (or nominal charge). That probably works pretty well for things in the greater than 10 but less than 30 years old. Newer stuff is online, and there aren't any bound copies. older stuff has been scrapped to save space. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] helibowl GPS antennas
So, I've looked at several dozen helibowls and talked to makers of said items.. There is no published design, per se. The instructions, as I was told, are go and buy a cheap mixing bowl The ones I saw used things like plastic cups as a form, on which a wire or piece of copper tape was spiraled. I suppose you'd use the usual non-critical guideline of circumference comparable to wavelength, so 20cm circumference is 6 cm diameter, etc. But I would say that the notorious red beer cup is too big. What you want is the smaller cups, but not the short fat ones. The stove burner liners have also been used (they're basically a bowl with a hole in the middle). The late (nov 2009) Don Spitzmesser, who is generally given credit for inventing it, apparently said, the bowl is a ground plane, who cares what shape it really is Cheng's MS thesis http://etd.ohiolink.edu/view.cgi/Cheng%20ChinYuan.pdf?ohiou1176838193 actually talks about modeling it and has, of all things, somewhat unreadable design drawings from a commercial manufacturer on page 53 of the pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Oh dear
On 5/7/12 7:39 AM, Burt I. Weiner wrote: A friend of mine signed me up for a catalog from the Audio Advisor. He said I deserved this - I was afraid to ask what he meant by that! Spend a few minutes looking over this site: http://www.audioadvisor.com/ Be sure to check out their Power cords at: http://home-audio.audioadvisor.com/search?w=Power+Cords Burt, K6OQK Well.. this is where folks on this list can do the world a service.. The whole thing about timing, stability, phase noise, Allan deviations, etc. *is* complex, and it's tricky to come up with easy to understand, short, descriptions of why using a Rb for your CD player is BS. We've all had to learn this stuff, and we do it in different ways, so maybe the collective hive-mind is a good way to come up with decent responses (after the initial wave of can you believe it) It's like explaining RF exposure limits. There's a certain amount of physics you have to know in order to understand how the limits work. Most people do understand what's BS and what's not, once they understand why. - the recent GPS filtering thing.. it took a YEAR for someone in the PNT community to finally come up with a good, simple explanation of why L^2 arguments were invalid. And it comes down to the fact that GPS isn't a communication link, so you can't use that conceptual model to analyze it. Once you get that, then people go oh! That's why we can't do that and have it still work And, on a more technically sophisticated level, there's lots of engineers who are still wrapping their heads around the duality of time domain (ADEV) and frequency domain (Phase noise) measurements, and when you might use one or the other. I've found a lot of good stuff on this list for explaining it (and improving my own understanding.. nothing like needing to explain it to someone else to test your own conceptual understanding) Interestingly, setting someone up with a counter, timelab, and a not so hot function generator and letting them record and play for a couple days (or over the weekend) is a great way. You see things like diurnal variation, the HVAC cycling on and off, the sun shining through the window. The spectrum analyzer does the phase noise thing fairly well (although not for close in), and concepts like reciprocal mixing from a noisy LO gunking up your narrow band signal are pretty obvious. After that it's practical applications.. Just how bad can the noise be for a particular application? Are you interested in integrated jitter? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] frequency (absolute) accuracy in sound recording/playback
One area where accuracy is important is not because of pitch (nobody can hear 1ppm differences), but because of the need to synchronize sound from different sources, particularly with video or motion picture frames. 1000 seconds (20 minutes, give or take) with the sampler off by 1ppm will be 1 millisecond out of sync, which is probably hearable, and is 1/30th of a frame time. A 2 hour movie (about 7000 seconds) would be 7 ms out of sync. Yes, we're not looking at needing Cs accuracy, but 10-20 ppm probably isn't good enough. So you're pretty much not going to be able to use the $10 oscillator in a can. So maybe a decent Rb, which is good to 1E-9 without doing anything special, wouldn't be a bad thing. And yes, there's a whole art to synchronizing stuff which was recorded or filmed with incorrect sample rates, or ones that are slightly off. It wasn't too long ago that quartz lock for a motion picture camera was something that was a special order from the camera rental house. I used to modify PC video cards for external clock input so I could adjust the refresh rate to match the camera speed (aka gen lock). There's a time nuts challenge... synchronizing something normally driven off a quartz oscillator (however crummy) to a mechanical device (the movie camera shutter). And given the creative hierarchy on a set, it's going to be you that adjusts to them, not vice versa. There are directors who (for whatever motivation) also don't want things like timebase correction used. Since I used to work for a physical effects company, I thought that these guys and gals who are hung up on the purity of the process were wonderful, since they typically wanted real special effects, not something composited in later by optical or computer techniques. There's a whole industry supplying 24/48 Hz refresh hardware, as well. Well.. there used to be.. I'm not in that business anymore, and I don't see credits for 24fps video as much, so they probably just paint the screen blue or green or put registration dots on it and comp in the images later. (Yes, I'm one of those people who watch all the obscure credits at the end for things like assistant hod carrier and such.) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] frequency (absolute) accuracy in sound recording/playback
On 5/7/12 6:13 PM, J. Forster wrote: A movie may be 7000 seconds, and you may need a fairly stable timebase, but every movie I've watched is made up of short (300 second) scenes that are placed sequentially on the framework. You are not meshing together a pair or multiplicity of 7000 second event sequences. E#very time you edit in another scene, you put the bricks end to end, so to speak. That's a good point.. In any case, though, I can see where someone might want a decent always good enough reference, as opposed to some lame non TC XO. It's sort of a quantum thing... rather than almost good enough just bite the bullet, buy the equivalent of a prs10 with the right interface and you never have to think about it again. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Faster than light of a different type
On 5/7/12 8:45 PM, Hal Murray wrote: One thing that might help is if everybody would get in the habit of scanning all their mail before responding to anything. The idea is that if a discussion explodes while you are sleeping (or away from your mail for whatever reason), you will learn that a topic has exploded before you contribute your wise-ass or me-too comment. Even if your answer is technical and valuable, you might notice that somebody has already said exactly what you were about to say. AN interesting comment.. I wonder if the nature of email and how it gets read has any effect on usenet lists. Think back to expensive dialup days.. you'd dial up, download the batch, and then hangup. So you'd go through all the mail (almost like a digest) before responding. Now zap forward and you're reading on an iPhone, which tends to promote a more interactive style of usage. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS, USGS Early Earthquake Warning
On 4/27/12 5:39 PM, Hal Murray wrote: Back to somewhat time-nutty stuff... Does anybody understand how they are using GPS and/or have performance numbers? They don't need the actual position (DC), just the changes in position. They need it now. They can't wait for post processing. I'm not sure how much accuracy they need. I'd guess in the cm range. (Maybe I can learn more at the open house.) I'm going to guess that GPS doesn't have much to do with the detection, per se, an accelerometer works quite nicely. What you want GPS for is precision timing, so you can figure out where the shock wave started and is going, but combining data from multiple stations. zipping along at a few thousand meters per second, timing to milliseconds is probably good enough, but pretty darn tough to do in a field site without something easy like GPS to give you a nice time hack. the physical displacement during an earthquake isn't all that much (a few mm or cm, unless you're right on the fault and/or it's a big one) here's a M4 a couple months ago http://earthquake.usgs.gov/earthquakes/eventpage/ci15141521#summary shows max accels of around 0.2 %g (I assume that means about 0.002g, or 0.02 m/s^2) that works out to a displacement on the order of mm, over a time of tens of milliseconds. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] PICTIC II ready-made?
On 4/28/12 12:10 PM, shali...@gmail.com wrote: I have not studied CPLDs but Actel has the only true Flash based FPGAs. The flash cells directly control the FPGA fabric. As such, they are mostly immune to Single Event Upset that plagues just about any other FPGA technology, and there is no configuration step at power up. .. the flash contents can still be lost(although Actel claims that their flash is pretty neutron and alpha particle immune.. but heavy ions?).. the Actel anti-fuse parts, like the AX and RTAX series, have logic that can't be changed. We use a lot of the Actel flash parts (ProASIC3) for prototyping, then burn it to an rtax for final. I think there's a similar path for the 54SX parts (i.e. a reprogrammable version and an antifuse OTP part) Here's what was in a Brookhaven report about using FPGAs in PHENIX The Actel FPGAs do not have SRAM configuration memory so they are immune to this form of upset. FLASH memories exhibit dissipation of the charge on the floating gate after 20kRad of integrated dose. The dissipation is not permanent damage and is remediated by reprogramming the device. Flash memories also displayed SEE problems during programming during radiation exposure that included gate punch-through, a destructive effect. These types of SEEs are avoided by not programming the FLASH under radiation exposure conditions, namely during machine operation. Practically speaking 20kRad is a fairly decent dose (it's a typical design requirement for a trip to Mars or for GEO).. you pick up about a kRad/year In LEO it's a lot lower (otherwise astronauts in ISS would die). Around Jupiter it's a lot higher (typical design requirements for Europa missions and such are 1 MRad) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS, USGS Early Earthquake Warning
On 4/28/12 3:32 PM, Tom Van Baak wrote: Related to that, are there any seismometer experts on the list? I've always wondered why they don't augment the extremely sensitive detectors with less sensitive detectors? Of course a really good detector will overload; so just co-locate cheap detectors that are 40 and 80 dB less sensitive. That way you get a clean signal no matter how close or far the epicenter is from the detector. here in southern California they have what they call strong motion stations which are exactly what you describe. (and probably other places, I just happen to know about the one that is co-located with a regular station near where I live, because you can see the data online). A lot of these are colocated with SCIGN stations (which have geodetic quality GPS stations). The sensors have maximums of several G as I recall. I think the peak accelerations in 94 were around 1 G or a bit over. That is, stuff, like houses, literally got launched into the air, as opposed to just shaken til collapse. And of course, structural resonance effects amplify it substantially. There was a bigger push to get them going after Loma Prieta and Jan 94 Northridge, as I recall, because structure and other damage had hot spots (due to various propagation effects across the santa monica mountains, for instance), and they wanted better knowledge in a (certain to occur) future event. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] PICTIC II ready-made?
On 4/26/12 10:46 PM, cfo wrote: On Thu, 26 Apr 2012 14:58:26 -0700, Jim Lux wrote: On 4/26/12 1:24 PM, Hal Murray wrote: albertson.ch...@gmail.com said: 2) The IDE is written in Java and is portable. It is truly identical on all platforms. Yes it uses gcc but the end user never has to deal with gcc or even know what gcc is. Same with saving your code, hit just puts it some place and keeps track of it Do I have to use their particular style/GUI? Or can I drive it from make, mixing in pieces I like? How is the documentation on the tool chain and libraries? Are their good man pages? The Arduino IDE is NOT make compatible, as far as I know.. The Arduino IDE is basically an advanced JAVA Editor , that hides avr-gcc for you. The IDE part is that it knows how/where to include/look for the CPP libraries. It's not like a gcc toolchain where you have a separate compiler, linker, binhex, etc and utilities.. It uses a 100% standard avr-gcc toolchain as backend , and just creates the commandline call for using that. So avr-gcc , avr-as , avr-ar , avr-objcopy etc. are used behind the curtains. Fascinating.. Are avr-* also java? Or are there just binary versions that run on all platforms? The other advantage is that there are so many premade/downloadable libraries out there , that you can make : ie. a PID controller wo. knowing much about PID. And you can add a Temp sensor a LCD wo. ever having opened a datasheet. The disadvantage is that due to the hiding/hw-abstraction layer , the generated standard librarycode tends to be slow. But in many cases ie. a DS1820B temp sensor can only make a measurement every 700 ms. So who cares if the 16Mhz was able to query it 1000 times/ sec , in optimized C. But absolutely nothing prevents you to , combine your own Optimized C / asm code , with the arduino libraries. And get the best from both worlds. Very useful to know.. I must say that the IDE hides it very well.. (which I guess means they did a good job... Overall, I'm fairly pleased with the Arduino, although I would like a way to set breakpoints and look at variables for debugging... but hey, printf works) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] In the atomclock repairshop...
On 4/26/12 11:56 AM, Magnus Danielson wrote: Hi, On 26/04/12 10:53, Rob Kimberley wrote: Nice article. Good to see a fellow 'Nut enjoying his hobby. Oh yes, I do enjoy it. ...now to brush up on my Swedish And, since NASA pays my salary, at least indirectly, nice to see you wearing a shirt with a NASA logo on it... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] PICTIC II ready-made?
On 4/26/12 1:24 PM, Hal Murray wrote: albertson.ch...@gmail.com said: 2) The IDE is written in Java and is portable. It is truly identical on all platforms. Yes it uses gcc but the end user never has to deal with gcc or even know what gcc is. Same with saving your code, hit just puts it some place and keeps track of it Do I have to use their particular style/GUI? Or can I drive it from make, mixing in pieces I like? How is the documentation on the tool chain and libraries? Are their good man pages? The Arduino IDE is NOT make compatible, as far as I know.. The documentation is mostly wiki-like, as well as several books out there. Lots of online forums It's not like a gcc toolchain where you have a separate compiler, linker, binhex, etc and utilities.. It's an *integrated* development environment. If you want a free Java based cross platform IDE that is compatible with make and extensible, etc. look at Eclipse. It's what I use at work for (mostly) C development on Windows, Linux, and RTEMS targets (using cross compilers). It's VERY cool, there's tons of documentation, there's tons of useful plugins for lots of languages and capabilities (cvs, svn, git, etc.) What's nice is that the UI is really the same between my mac laptop, my windows desktop machine, and the linux boxes down in the lab (although, I confess that recently, I've been doing more ssh -X labmachine, because it's hooked up to the target). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 93, Issue 96
On 4/18/12 6:56 AM, Attila Kinali wrote: On Wed, 18 Apr 2012 09:28:17 -0400 Dan Kemppainend...@irtelemetrics.com wrote: Wouldn't get broken if you hand carried it. I've carried on similar equipment when flying across the US. I'm guessing you may not have to check it for an internationl flight... Thanks to Home Land Security, the rules on what you may carry on a plane got very much restricted, especially when flying from and to the US. Basically anything unusual is prohibited. Actually, it's not necessarily TSA/DHS that is the problem.. it's that other downstream consumers of the rules may have different interpretations. The guy standing at the gate or checkpoint gets to make an on the spot determination of what might be dangerous Example: The small roll of PVC electrical tape I had in my backpack being taken at secondary inspection (walking down the jetway) in Heathrow when getting on the plane home to Los Angeles. Am I going to argue with the guy from British Airways about specifically which rule he thinks my tape violates? When the plane is leaving 3 hours late already? Nope.. Example: the round pointed school scissors in my daughter's backpack getting on the plane in Rome? They were willing to let her take them, but we said, nope, just throw them away, because next stop is Zurich, and we KNOW that they won't make it past the inspection there. I got tagged in Zurich before for having my toothpaste tube in a gallon bag, instead of the required no more than 1 liter bag. So, carrying that oscilloscope on? If the inspector's fiance(e) just ran off with a EE/CS major the night before, you're doomed. However, in general, I've not had many problems with obvious commercially manufactured gear. And oddly, not much problem with random piles of protoboards and boxes with wires and cables stuffed into a backpack, as long as there were no large blobs in the X-ray that weren't obviously batteries on visual inspection. (Friends of mine say that trying to carry on a small lead acid battery that looks like a brick is often a challenge..especially if you've wrapped it in tape to hold it to the circuit board. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Chinese Scopes
On 4/17/12 6:56 AM, shali...@gmail.com wrote: I agree that memory depth is an under appreciated parameter, but even 2,500 points like what's available on the cheap Tek scopes is quite useful. On the other hand, I had a few LeCroy with 50k deep memories and there are cases where that is very useful too. I can't imagine real life use cases when I would need multiple MB. It would be nice to have but seldom used. oddly enough, I had a case where very deep memory was useful last fall. It was an issue with logic that was switching from one clock source to another where the clocks were orders of magnitude different frequency (10Hz and 300kHz or something like that), and it was the relative timing of the edges that was important, so you needed a bunch of cycles of the low frequency clock (i.e. record length of half a second or so), but enough samples to see the timing of the 300kHz at the same time. Another deep memory use was when I used a fast 20GHz sample rate Tek scope a few years back (2007) debugging a radar target simulator (for the landing radar that's going to be used to land on Mars in August) and deep buffers were nice there, because we essentially needed to capture multiple pulses that were 4 ns to several microseconds long. The requirement was that the delta phase (and time) of successive pulses be within a certain value (the radar used what's known as two pulse doppler) following a pre-programmed simulated descent profile. We also wanted the pulse timing after the trigger to be accurate to, as I recall, 0.5 or 1 ns. The PRF is pretty high, so you don't have time to unload the memory in between pulses. So we did something like 500 pulses, captured 16,384 samples at a time at 20GS/sec to make a dataset of 16 million samples. You learn a lot about what's hidden in the specs on inexpensive signal generators like the Agilent E4421B when you start comparing phase for 1600 pulses 1 microsecond apart. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Chinese Scopes
On 4/17/12 7:15 AM, Robert Darlington wrote: I need lots of memory on scopes. A buddy of mine I worked with in the ultrasound world actually yelled at the Tek product management and asked if they actually *use* oscilloscopes. The answer was a sheepish no, and yet they felt qualified to develop the products for the company. The cheap Aktakom scope I have has plenty. 10 million samples (you can select less if you want) and will write out to usb thumb drives. It's definitely a toy scope with lots of noise, but it's useful for some things. What we do is send out pulses or chirps and look at what returns. There are tens of millisecond delays between what we send out and what we receive and the echos.With traditional low memory scopes we simply can't get by. Thankfully Tek is learning that memory is cheap and 2500 samples was hardly sufficient in the 70s, let alone now! Yes, just like in the radar world (really, ultrasound and radar are really similar.. same kinds of pulse compression and signal processing) Back in 1998-1999, I was buying digitizer cards from Gage Applied Sciences (since acquired by Tek, as it happens), and one of their big markets was for ultrasound. Same for Signatec (another mfr of fast digitizer cards for PCs) Another case where deep memory is nice is when you don't know exactly when the signal is going to arrive, it's very low SNR, so you want to record a long time, and then go look for the signal later. But that's more a data capture problem than a bench oscilloscope problem. say you were recording off-the-air GPS signals. You want to record a couple milliseconds, at least (so you get at least 1 code epoch), and you need to record at least 10 MHz bandwidth. That's only, say, 64,000 samples, but you might want to record a whole 50 bps nav message bit, so then you need ot record 40-50 milliseconds, and the record length starts to grow. Again, that's more of a data recording problem than an oscilloscope problem. It's the wideband pulsed waveforms where you want to compare pulse to pulse is where deep memory in an oscilloscope is nice. The digitizer cards are ok, but real oscilloscopes tend to have better input amplifiers and such. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Chinese Scopes
On 4/17/12 7:55 AM, John Lofgren wrote: One feature of the Agilent and Rohde scopes (maybe Tek, too?) that can help in some situations is segmented memory. It allows you to capture periodic or random events with the full sample rate but to ignore all the dead time between events. For each trigger it stores one sweep with a time stamp. When you want to look at the record you can roll back through memory and look at each individual event with full resolution. This isn't a cure-all because the time stamps will have limited resolution and some amount of jitter, but it can be helpful in some applications. It also assumes that you know what you're looking for and can trigger on it :) Yes, this was a tek..it does the same thing (called fast frame in their manual) and the trigger time stamps were actually high resolution (higher than the sample rate). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Chinese Scopes
On 4/16/12 8:19 AM, Eric Garner wrote: I have the latest and greatest from both Tek and Agilent at work, designed and made right here in the states. They suffer from menu-itis just like the chinese stuff does. My Tek DSA 72004 at work is a complete PITA to use unless I have the mouse and keyboard attached. In my opinion, it's just how things are in the modern age. yes.. they save knobs by not having on a spectrum analyzer for instance, a separate knob for center frequency, span, and reference level. On the scopes, it's not so bad.. you have one knob for vertical and one for horizontal, and it seems to make sense. But the UI is what has always separated brands of test equipment. Those of us who grew up with Tek Scopes always found the HP scopes a bit weird to use. Likewise, you get used to the HP spectrum analyzer and signal generator, and going to something else is a bit weird. Power supplies are the worst. even within the same mfr, it seems every PS has different ways to do the current limit, the OVP, to switch the metering, etc. The new Agilent supplies (like the N6700 series), though, are very cool.. they have a built in ARB to do soft starts and transient testing, and a built in oscilloscope function to look at inrush. And they're available in two versions.. one with knobs on the front panel and binding posts for bench use, and a basically identical unit with a few buttons on the front panel, and connections on the back for use in a rack. These days, I look for the remote interface, and if I'm going to be typing on a keyboard, I'd rather do it on the host PC, not the instrument. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Looking for CA3130E IC...
On 4/15/12 3:46 AM, Attila Kinali wrote: On Sat, 14 Apr 2012 20:11:14 -0500 h...@hiwaay.net wrote: CA3130EZ is the lead-free version of the part. Looks like good stock (both Newark and Avnet have thousands on the shelf), and should be usable unless you're sending it into space or something. Why is the chip case being lead free a problem for space? I thought the major issue was that the solder is lead free and showes all kinds of nasty behaviour? Attila Kinali Tin whiskers Rather than tin-lead solder dip, it's typically pure tin on the leads, and that's evil. You can take the part and redip the leads, but that's a pain. Yeah, the solder requires better temperature control, but most stuff for space is done with automated processes and dialing in the temperature profiles for arbitrary solder isn't that hard. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Antenna restrictions [was Lucent 40 dB Antenna]
On 4/15/12 6:20 AM, gary wrote: The dummy pipe would be fine. In theory ABS makes a good radome, but in practice whatever you get at the hardware store effects antennas significantly. [ABS and PVC is the first thing that comes to mind when weather proofing home made antennas.] The AWACS uses S-2 glass for it's radome. The dielectric constant is worse than ABS, but perhaps when the dust settles, the S-2 glass can be thinner that ABS for the same strength. So perhaps in practice it is a better radome. black ABS Drain/Waste/Vent (DWV) pipe is typically actually foam with a skin on the inside and outside, so it's pretty transparent and low epsilon, EXCEPT.. they use carbon black as the pigment. PVC is something else to watch out for. The outside is white (or grey or purple) but the inside might not be. I was quite surprised when I was turning a piece of PVC pipe on a lathe and found the inside of the wall was a amazing variety of colors (hey, they recycle all manner of stuff, it's just ground up and extruded). the microwave oven test might be appropriate (2.45GHz vs 1.5GHz).. put a chunk in the oven and see if it gets hot. A cup of water somewhere if your oven needs a load. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] LORAN-C at MIT
On 4/15/12 3:09 PM, li...@lazygranch.com wrote: It is all over in the bay area. When manufacturing got outsourced, so did the surplus. A lot of my lab is made up of Foothill and Livermore flea market purchases. (The local Metro PCS tech had the surplus Symetricomm and similar gear.) Foothiil begat the Lockheed parking lot which begat DeAnza. It is mostly junk. Livermore did good until the community college decided not to allow it to be hosted there. It was moved to a park and ultimately shut down. The TRW swapmeet is on my bucket list. hmm.. it's not all that wonderful either.. Several problems 1) different processes at large companies that used to buy lots of equipment, and then keep it for a while.. now they contract it out to equipment rental places, so they don't have the gear on the books. To the ultimate customer, it makes no difference. 2) a much more diverse and rich environment for used gear to flow into. the internet has made it easier to put buyers and sellers together 3) different surplus equipment policies. along with #1, there's not as much company owned gear to be surplused, and the processes don't lend themselves to Bob loading up the truck and taking it down to the swapmeet Various and sundry ethics rules prevent surplus sales to employees (to prevent declaring that brand new VNA as surplus). These days, often they will contract with somone to haul away scrap and surplus, and that contractor counts on a good mix of valuable and not so valuable. (At JPL, dumpster diving is a definite no-no) 4) less user serviceable stuff in general. If it breaks, it's scrap, not repairable. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Antenna restrictions [was Lucent 40 dB Antenna]
On 4/15/12 2:09 PM, DaveH wrote: I am on the Tesla email list and people there have noted that some of the black plumbing pipe actually has carbon black added to it -- this renders the pipe conductive and not good for a Tesla secondary form. Would not be good for RF either. It varies.. I've had ABS that was fairly conductive (terrible for an electrostatic charging machine) and ABS that's pretty good. Electrical and RF properties just aren't something they care about, so a lot depends on the mix of the day ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Best location for a GPS antenna...?
On 4/12/12 2:09 AM, Rob Kimberley wrote: There are commercial re-radiators for GPS. I found these on Google: http://www.gps-repeating.com/?gclid=COTV88D6rq8CFcwTfAodhSKvmQ http://gpsnetworking.com/GPS-re-radiating-kits.asp One of my old suppliers in the UK was marketing a range of these, but I seem to remember some problem in getting approval in the UK, and they had to drop them. Things may have changed as this was a few years ago. Interestingly I've just been looking into this... Why would you need anything special to reradiate.. It's not like you need a particular antenna pattern or constant gain or something. What about something like a fat monopole against a ground plane, with a attenuator at the feed to provide a good terminating impedance for the LNA/Line driver. If it's L1 only, you don't even need particularly wide bandwidth (1%) Yes, I've seen setups at JPL where they reradiate with DM or Ashtech chokering antennas (or even helibowls), but that might be because we've got a bunch of them sitting around, so why not use it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thoughts on lightning protection measures....
On 4/12/12 6:22 AM, Michael Baker wrote: Time-nutters-- Around here (N. Central Flori-DUH) it is not uncommon for near-by lightning strikes to damage underground cables and wiring. This is why buried wiring to things like driveway gate-openers are often placed in conduit rather than done with direct-burial wiring so that if lightning damages the wiring a new cable can be pulled through the conduit without having to re-dig the burial trench. Some years ago I had occasion to hold some long discussions with Martin Uman, one of the worlds most distinguished and eminent lightning researchers. He commented that even with the most extraordinary and costly efforts to install protection measures, that-- sooner or later-- there was a good chance that lightning would find a way to damage things. Dr. Uman (and his colleague Dr. Rakov) probably know about lightning and effects than any other humans alive. He's making an excellent point: at some point, the cost to replace the gear (or the cost of being off the air) is smaller than the cost of the protection scheme. Sometimes, you're better off having a sacrificial element, and a spare in the closet for speedy repair. His lightning research laboratory was located here in N.Central Florida because it is in the heart of the most dense strike area in N. America. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Best location for a GPS antenna...?
On 4/12/12 12:50 PM, li...@lazygranch.com wrote: I'd suggest getting Dr. Uman's All About Lightning as a starter. You could read it in an afternoon, so to be correct, the book is all about lightning, but it doesn't contain all the world's knowledge. ;-). It isn't very technical, though he has written technical books as well. An excellent book, as is the Dover book Lightning. Regarding schemes to prevent lightning hits, they are all controversial. That is, scientists argue over the effectiveness. The one I see often in the high desert looks like a brush made out of metal fibers. Controversial is an understatement. When there was an IEEE journal paper (well reviewed) essentially saying that they don't work, one of the manufacturers of such devices sued the author and the IEEE (unsuccessfully). The same manufacturer proudly proclaims as used by NASA and the US Air Force when what really happened is that both bought them as test articles, for tests which failed. There's a great picture of a lightning bolt coming down from the sky, skipping the top of the tower and hitting the lightning eliminator square in the middle of the panel. I've got to see ground hits in the desert twice. Amazing. The spot hit glows yellow, which I presume is sodium ionization. Or, yellow heat as in blackbody radiation.. it gets hot enough to fuse sand into glass (fulgurites) and it takes a while to cool off. Some years back, I was trying to make artificial fulgurites in my back yard with large high voltage capacitor banks (hey, quarter shrinking gets boring after a while). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Best location for a GPS antenna...?
On 4/12/12 12:02 PM, David McGaw wrote: Best would be to have a lightning rod in the vicinity of and above the antenna. A sharp-pointed rod does not attract lightning, it REPELS it and has a cone of protection under it. While the effect is not understood, it apparently discharges the surrounding air through corona discharge - the sharper the better. Cone of protection it is, but it's because the lightning preferentially hits the rod, rather than something below it. There's no discharging the earth/cloud capacitance. That theory has been thoroughly debunked, both analytically and experimentally. There's some great papers by some scientists at Erico in Australia where they were looking for better designs for lightning rods, so they set up a test facility to replicate the charge distributions and fields in the prestrike time. This is very much trickier operation than testing for the discharge itself, or for EMP, where you just need a big Marx generator. It's essentially a high voltage arbitrary waveform generator into a carefully designed TEM test cell of sorts. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Opera coordinator has resigned
On 4/7/12 2:47 AM, Attila Kinali wrote: Moin, On Sun, 01 Apr 2012 16:54:09 -0700 Jim Luxjim...@earthlink.net wrote: Not a whole lot, but the whole paper goes into the various factors involved. Ultimately, it winds up that the mismatch from SMAs is a) a whole lot less than the usual worst case spec of 1.05:1 or 1.03:1 (which is basically a measurement limit) and b) doesn't change much with many mate/demate cycles He did look at things like coupling nut friction and what not. Do you have the name of the paper? It might be interesting to read. Attila Kinali I'll try to find it. I've got the pdf somewhere on my computer.. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz More or Less
On 4/7/12 3:17 AM, Attila Kinali wrote: On Mon, 02 Apr 2012 07:18:18 -0700 Jim Luxjim...@earthlink.net wrote: John Strong's book on making stuff (procedures in experimental physics) probably has a lot of the details (like how they put the reflective coating on the mirror). That book is a fascinating look at state of the art in the early part of the 20th century (you want to make your own Geiger-Muller tubes... it's in there). Every physics/lab tinkerer should have a copy (it's cheap in paperback from Lindsay books (http://www.lindsaybks.com/... don't know if they still have it), or probably Amazon, too)(just checked amazon.. $35 for used??? what are they thinking) Oh.. 35USD isnt that bad... Yeah, but this is a book that's out of copyright that Lindsay was selling for something like $6 paperback.. Lindsay Publications is an interesting company.. they do a lot of get old out of print book and reprint Very much oriented towards do-it-yourself things, industrial revolution and later. You want to make a locomotive, starting with iron ore, in your backyard? Lindsay has all the books on how to do it, from building a cupola furnace to make the iron and reduce it to steel, to building your own machine tools (sand casting is your friend), to laying out the plates for the boiler and so forth. I don't think there's a book on building your own rolling mill, but that's about it. So the Strong book fits right in. If you were working at Univ of Chicago with Fermi, this is the book you'd have handy. The mechanical fabrication info is great because, face it, not much has changed with metalworking hand and low end shop tools in more than 100 years. We might have nice numerical readouts on the mill (and maybe CNC) but as a rookie, you still need advice on what kind of cutter to use, how many flutes, what speed, etc. The book The Quantum Physics of Atomic Frequency Standards by Vanier and Audoin has been out of print for a while now. You're lucky to find any used book at all (and the price is usally in the hundreds of USD). But, you can buy the PDFs of the scanned book from the publisher... for just 750USD (i'm not joking!) And those PDFs are simple scans, no OCR and no correction of typos or anything. Fortunately, if you have access to an large university library, they might have an account with CRC Press and you can download the PDFs for free. Attila Kinali ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FPGA GPSDO (Was: Re: NTP jitter with Linux)
On 4/7/12 4:47 AM, Javier Herrero wrote: El 07/04/2012 13:19, Azelio Boriani escribió: The Xilinx and Altera have their embedded CPUs (Microblaze and Nios) IP. I'm not familiar with them and don't know how much they cost. Until now I have developed on Xilinx 50Kgates FPGA and 128 cells CPLD with the Xilinx's free tools. Mostly expensive for amateur use, although reduced free versions exists (for Nios-II it is Nios-II/e without MMU and no cache, I suppose that something similar for Microblaze). But both are closed-source. There are open-source soft processors like LatticeMico32 and LEON3. I'm moving to one of these for a next project (not yet decided which one, since in this case it will be a bare-metal application, with no operating system, but I would like to use a processor that is supported by Linux distribution for the future). Linux is ported to both, and for LM32 (not sure if for LEON3), RTEMS also (see www.milkymist.org , an open source hardware and software project with an LM32 implementation on a Spartan 6 FPGA using RTEMS. Also there is a plethora of soft implementation of several processors in OpenCores (ranging from 6502 to OpenRISC) and also somewhere I read about an implementation of a Cray-1 in a Spartan-3 :) I'm very familiar with the LEON and RTEMS, having managed a software development project with it for the last 3 or 4 years at work. http://www.gaisler.com/ for LEON http://www.rtems.org/ for RTEMS And yes, there is a port (maybe two) of Linux for the LEON as well (A few years ago, we loaded up the Snapgear port, but since we went RTEMS, I haven't fooled with it). You'd have to check the Gaisler.com website. You can drop a LEON core into a Virtex II in about a day, and judging from the traffic on the LEON yahoo list (where the Gaisler folks hang out), lots of people are doing things like multiple cores and things on all manner of Xilinx eval boards. Gaisler's GPL library of assorted cores (pretty much all using AMBA) make life pretty easy from a hardware interface standpoint. Their basi strategy is that source and documentation is free, but that if you want the fault tolerant versions, or the versions intended for spaceflight, or the testbenches for the cores, you have to go with a license ( a few thousand bucks per core, depending on what it is). Gaisler's basic business model (hopefully I'm summarizing correctly..) is that they do custom FPGA/ASIC designs for people, putting together pieces of their library, possibly adding new modules, targeted to platforms like the Actel AX2000 (or Xilinx, or FPGA-ASIC). SO you have products like the Atmel AT697 (A LEON-FT with memory controllers and peripherals) which we use in JPL's space radios) or the Aeroflex UT699 (another LEON core with various peripherals). RTEMS wise... It's pretty well supported by the community, it's open source, it does all the stuff you want a RTOS to do. it's NOT a multitasking, dynamic loading OS like Linux. That is it doesn't support an MMU and process space isolation (although that might be possible in newer versions.. there's a lot of configurability). It's basically a statically linked single task with threads. They've got RAM (and disk) file systems, IP stacks, a shell, YAFFS, etc. Like all open source, there's quite a lot of interesting stuff available (not from rtems.org, but others) that is 90% complete. Somebody at Google Summer of Code or for their Masters decides to implement something cool, and gets most of the way done, then wanders away (the summer ended, they got their degree, the usual story). But there's also a core of users who are serious and rigorous and contribute back, so the main stuff in the distribution from Joel Sherrill at OAR (who make RTEMS) is pretty rock solid. ESA has several rigorously verified flight qualified versions of RTEMS (in Portugal and Austria, as I recall) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FPGA GPSDO (Was: Re: NTP jitter with Linux)
On 4/7/12 10:08 AM, Javier Herrero wrote: El 07/04/2012 16:02, Jim Lux escribió: RTEMS wise... It's pretty well supported by the community, it's open source, it does all the stuff you want a RTOS to do. it's NOT a multitasking, dynamic loading OS like Linux. That is it doesn't support an MMU and process space isolation (although that might be possible in newer versions.. there's a lot of configurability). It's basically a statically linked single task with threads. They've got RAM (and disk) file systems, IP stacks, a shell, YAFFS, etc. But there's also a core of users who are serious and rigorous and contribute back, so the main stuff in the distribution from Joel Sherrill at OAR (who make RTEMS) is pretty rock solid. I will learn more about RTEMS. For the application I've (and this links directly to the message from Javier Serrano), the hardware platform is one of the CERN Open Hardware ones, the SPEC. For the purpose and interface needs, really an operating system is not required (no filesystem, no TCP/IP needed, no multitasking, no framebuffer...), and certainly a Linux would have a very large footprint without providing any real help. RTEMS might be just what you need. Kernel, basic OS calls for scheduling, queues, etc. It's nice when you decide you want threading to not have to graft it into a big loop no-OS style program. You can use native calls or POSIX style (I like POSIX, because I can develop on Linux and just recompile for the RTEMS target). There's all the usual GDB support as well. And about the processor selection, the trade-off that Javier exposes are the same I'm confronting. Both are open-sourced and well supported, and in one side the LM32 is smaller, in the other the LEON3 has more capabilities that can be implemented or not (like MMU or FPU, and better multi-core support, although not currently needed in my project). I probably will take the LEON3 road, but also because it is more popular in my current field, but for now I usually do not need the FT version since I'm more related with GSEs. And that's good because the FT version costs money, but the regular old LEON2 and LEON3 are free, and pretty bulletproof by now. ESA has several rigorously verified flight qualified versions of RTEMS (in Portugal and Austria, as I recall) Yes, this is one of the reasons to gain experience in that road :) I have some tendency to stay in Linux because I'm very familiarized with it in the non-MMU implementations (for Blackfin) and also with MMU - and I've found that for a small embedded system, to have the MMU is not so important, even sometimes it is a drawback. Device drivers are easy to write for RTEMS, and it has VERY fast ISRs. That's probably one of the big advantages.. It's a small footprint, stripped down RTOS, but because you can work with POSIX API calls, you can do most of your development in Linux (particuarly things like calibration interfaces and computational stuff) and then it ports very easily when you move it to RTEMS on the target. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FPGA GPSDO (Was: Re: NTP jitter with Linux)
On 4/7/12 8:57 AM, Chris Albertson wrote: If you are looking for free soft core CPUs for use in an FPGA then look here: http://opencores.org/projects Look under processors for many CPU cores. They also have some Eithernet controllers you'd need. Like all things opencores/sourceforge/etc you need to examine whats out there... We've used a SDRAM controller from opencores (and modified it for our puproses) and it works pretty well. Some other stuff, maybe not so finished and ready for use. It all depends on provenance To blow our horn a bit, we've got some useful building blocks available for free.. We are targeting Xilinx Virtex II, but they're designed to be pretty generic Verilog for any target. If you need a 64 bit timer core with a bunch of latches and a programmable pulse generator, let me know. We've got one at JPL we're happy to distribute (for free). Goddard Space FLight Center has a variety of SpaceWire cores (in VHDL), and we've got a Verilog wrapper for it at JPL. Simple cores to do things like record samples from an ADC into a giant SDRAM buffer or play back samples from SDRAM into a DAC, we've also got. You want that digital oscilloscope or ARB with a 10s of MegaSample buffer.. we've got it. Gaisler has a lot of useful, well debugged, cores for free.. Ethernet, RAM controlkers, various other peripherals. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Improving performance of a GPS antenna...?
On 4/4/12 6:56 AM, Robert Berg wrote: You can get inexpensive conductive foam from Amazon. Not all conductive foam works as a decent RF absorber. If the conductivity isn't well matched to 377 ohms, then the RF reflects right off of it. The black foam that ICs used to come in is a good example. The sheet RF absorber (as opposed to the pyramidal kind) typically has multiple layers of conductive sheet separated by a fairly lossless foam, with the conductivities and spacing of sheets chosen to optimize the absorption for a particular frequency range and angle of incidence. As with any RF load, the important thing is the match. Pyramidal absorbers (like you see in an anechoic chamber) make use of cones (so there's not a real sharp transition in impedance), and for higher frequencies, the reflections head down deeper into the valleys between the peaks. (at least for angles of incidence close to normal). All of the absorbers have very different properties at grazing angles than they do at normal incidence. And, what you might be seeing is actually a magnetic absorber to suppress creeping waves along the surface. It's a ferrite loaded elastomer. We use a lot of it at work, for instance, around the outside of a corrugated horn to suppress back/side lobes. There's a new choke ring style antenna (patented, of course, and they deserve it) which uses spikes instead of solid rings. And, they wrap the choke over a hemispherical surface as opposed to on a plane. Much tougher to design and fabricate (no buying sets of cake pans any more), but if you want to differentiate yourself from the horde of Ashtech/DM style chokes, you need something. At JPL, we also use what's called a helibowl for ground testing. It's a quad helix or other element inside a bowl. Doesn't have much pattern close to the horizon. I suspect you can google and find more details, or if people are interested, I can ask around about design information. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
