Re: [time-nuts] OT: Audiophoolery
It's the $250 HDMI cable (http://www.audioconnect.com/html/hdmi-3_hdmi_cable.html) that takes the prize IMHO - analog is voodoo to most people and they can be bamboozled by talk of SWR's etc- but digital is just digital - it works or it doesn't. I'd be willing to bet that this $250 cable is no better than the $19.95 one hooked to my Apple TV (neat toy BTW). Then again most people are happy with a cheap timex and a clock radio - I have three independent GPS clocks and two WWV clocks so maybe I shouldn't be too quick to comment. John (who still wears a mechanical watch) Daun Yeagley wrote: I had passed a couple of these posts on to one of my buddies at Motorola, since we and a few others have by chance been having a parallel discussion of such topics. Check out his message. OK, This is as crazy as it gets. I have seen the high end power cables before and consider this the ultimate in audiophoolishness ... I'm not sure this is the most expensive example, but it surely establishes that there is no connection between reality and audiophoolery. Check it out: http://www.audioconnect.com/html/pk10_palladian.html SWR enhanced God, it's so simple, why didn't I think of it? Jim This one just fit so nicely into our discussions! Daun -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Pettitt Sent: Friday, April 20, 2007 1:03 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] OT: Audiophoolery Dr. David Kirkby wrote: On Fri, 2007-04-20 at 02:21, Bruce Lane wrote: Discussions involving audiphoolery, particularly where silly things like $500 knobs and atomic references for CD writing are involved, never fail to amuse me. With that in mind, and given the current thread about Antelope Audio, I feel compelled to point out a link which, I think, illustrates one of the peaks to which audiophools will go to satisfy their obsessions. http://www.monstercable.com/productDisplay.asp?pin=195 I invite all to have a good chuckle over this one. ;-) Keep the peace(es). Take a look at this Aromatherapy and Audiophools which appeared in Electronics World and Wireless World, October 1999. I thought it was so funny I scanned it and stuck it on my web site. http://www.g8wrb.org/useful-stuff/audiophools.pdf I still remember the mercury filled speaker wires post - see also http://www.geocities.com/CapeCanaveral/hall/8701/Audio_BS.htm and in case anybody still needs convincing http://www.avreview.co.uk/news/article/mps/UAN/632/v/3/sp/332683698431330268420 *Harmonic Technology Fantasy *In our test system Fantasy proved to be an extremely charming cable, it is extremely fine and smooth while being able to resolve detail with ease. Acoustic space is well defined and instrument tone is pretty good too. Excuse me while I gag. $900 for a par of 3m wires! John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] OT: Audiophoolery
Dr. David Kirkby wrote: On Fri, 2007-04-20 at 02:21, Bruce Lane wrote: Discussions involving audiphoolery, particularly where silly things like $500 knobs and atomic references for CD writing are involved, never fail to amuse me. With that in mind, and given the current thread about Antelope Audio, I feel compelled to point out a link which, I think, illustrates one of the peaks to which audiophools will go to satisfy their obsessions. http://www.monstercable.com/productDisplay.asp?pin=195 I invite all to have a good chuckle over this one. ;-) Keep the peace(es). Take a look at this Aromatherapy and Audiophools which appeared in Electronics World and Wireless World, October 1999. I thought it was so funny I scanned it and stuck it on my web site. http://www.g8wrb.org/useful-stuff/audiophools.pdf I still remember the mercury filled speaker wires post - see also http://www.geocities.com/CapeCanaveral/hall/8701/Audio_BS.htm and in case anybody still needs convincing http://www.avreview.co.uk/news/article/mps/UAN/632/v/3/sp/332683698431330268420 *Harmonic Technology Fantasy *In our test system Fantasy proved to be an extremely charming cable, it is extremely fine and smooth while being able to resolve detail with ease. Acoustic space is well defined and instrument tone is pretty good too. Excuse me while I gag. $900 for a par of 3m wires! John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Droitwich
Neville Michie wrote: Hello all, I have a HP 5090A fixed frequency receiver which I believe was made to recover precision frequency signals from Droitwich radio station. I can not find any technical information on this receiver, can anyone tell me is Droitwich still active as a stable frequency reference, and where can I find a manual for the receiver? cheers, Neville Michie ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts See http://tx.mb21.co.uk/gallery/droitwich/droitwich-lf-data.asp - half a megawatt now on 198kHz John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Latitude and longitude question
Joseph Gray wrote: Let me first say that I don't know anything about surveying. I have a copy of the plat survey for my house. On the survey are four sets of coordinates that resemble lat/long numbers, but obviously aren't. What are these coordinates and is there any way to calculate a lat/long of a specific point on my property from these numbers? If so, how accurate could I expect the result to be? I assume that a professional survey should be highly accurate. Any pointers to information on doing this would be appreciated. Where are you? Some countries (for example the UK) have their own grid system. A survey should be accurate to around 20mm +/- 50ppm - see http://www.acsm.net/alta99.pdf John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Latitude and longitude question
Joseph Gray wrote: Where are you? Some countries (for example the UK) have their own grid system. A survey should be accurate to around 20mm +/- 50ppm I'm in NM, USA. I wanted to see if I couldn't come up with a more accurate lat/long than the Z3801 survey function provides. Dumb question time - have you tried asking the surveyor what the numbers are and how to convert? John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dual PPS ntpd
Glenn Powers wrote: The question of using Dual PPS inputs with ntpd/FreeBSD came up a long time ago on the ntp:questions list, but it doesn't look like it was ever resolved. Has anyone here used ntpd with two PPS inputs? What I want to do is to connect an Oncore GPS / 1 PPS to serial0 and connect an undisciplined Rb. Osc. 1 PPS to serial1. (Even better would be to use the RTS line on serial0 for the 2nd PPS, but that would require some driver work.) I'd like to use ntp to find the offset between the two PPS's and then apply that offset in ntpd to the second PPS. Then, if I lose GPS coverage, the second PPS should kick in with the offset applied. I know the accuracy won't be as good as a directly disciplined Osc., but I think it would good enough for ntp. I think this design would qualify for the Cheapest GPS Disciplined True Atomic Clock with NTP Server. thoughts? glenn If you want to use the Rb as a Backup PPS I'd suggest not using noselect but instead fudging it's stratum to 1 rather than 0 - you'll still need a prefer clock for it to diciplin (it seems you can have several prefer clocks) ntp.conf would look something like this: #GPS Clock - adjust mode to taste server 127.127.20.1 mode 2 version 4 prefer #atom driver for Rb PPS server 127.127.22.0 fudge 127.127.22.0 time1 whatever your offset is fudge 127.127.22.0 stratum 1 fudge 127.127.22.0 refid ATOM #other servers follow with at least one set prefer server x.x.x.x prefer what should happen is that if the GPS is valid the system will use it but if it's not the system will use the Rb - don't set flag3 to use the kernel PPS because it does not understand multiple PPS devices and more importantly does not understand that if the NMEA message say the invalid fix the GPS PPS is not to be trusted. If you use noselect the system will happily see and ignore the Rb PPS which works for finding the offset but doesn't help if you want it to work as a backup to the GPS. I've not actually tested this (however I'm going to go try it since I have three GPS/PPS sources here I can unplug the antenna on one and see if it actually fails over) John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Recommendations for NTP server
David Andersen wrote: You'll get more than you expect -- the offset you're observing on ADSL is very likely wrong, because the delays your packets experience on adsl aren't symmetric. NTP assumes symmetry. So I wouldn't actually believe that a 1ms offset is really 1ms off, depending on the RTT to your ISP. But there actually are ways to mitigate the offset spikes. You might be able, for instance, to configure your gateway to prioritize NTP packets over everything else, which will help with half of the problem. You won't be able to do the same at your ISP, of course, so it's not a perfect solution. Installing a local GPS-synched server is the right answer if you really care. And it's fun. :) The Soekris boxes rock. I assume you've already seen Poul-Henning Kamp's page about using his net4801 with FreeBSD to act as a high precision timeserver? If you want sub-microsecond, you'll probably have to replace the oscillator on the 4801. And - most OSes should do the trick. FreeBSD has a really nice precision timekeeping interface, though -- and it makes a marvelously solid time server. I'm running it on a few Net4801s and recommend it. You can very easily build an image for it using another bit of phk's magic called 'nanobsd' (it's in the source tree). -Dave I'll second the soekris box - my box time.no-such-agency.net is a 4801 running FreeBSD with a GPS18LVC.You can expect offsets in the +/- 5us range except when the box is stressed - the standard xtal in the box is not temperature compensated so offsets will spike to as much as 250us when the system does something compute intensive. If you don't need the HD consider the 4501 as it has the ability to timestamp a PPS using internal counters rather than the DCD kludge. - Again see phk's excellent work on the subject including the code in FreeBSD to support PPS on a 4501. Regarding DSL - I now have three stratum one servers here: a GPS18LVC, a TrueTime NTS100 and TrueTime GPS XL-DC (it is addictive isn't it) - my ISP just installed a GPS18LVC based server one hop (on gig-e) from my DSL concentrator so I can get a very clear picture of the error introduced by my DSL asymmetry. For my line (6000 down 608 up backhauled over ATM) it's 1.5ms. In a perfect world NTP would allow a fudge offset to be applied to subnets (in my case 1.5ms on the default and 0.0 on the local LAN) which would factor out the know DSL error - alas it doesn't do that right now. John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Recommendations for NTP server
Geoff Powell wrote: And - most OSes should do the trick. FreeBSD has a really nice precision timekeeping interface, though -- and it makes a marvelously solid time server. I'm running it on a few Net4801s and recommend it. You can very easily build an image for it using another bit of phk's magic called 'nanobsd' (it's in the source tree). As I just asked John A. - is it in the default kernel? It's a trivial recompile (kernel rebuilds are really easy on FreeBSD). John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Thought experiment on a low cost timing board
Paul Boven wrote: Hi everyone, Poul-Henning Kamp wrote: You don't even need 32bits for that: http://phk.freebsd.dk/pubs/timecounter.pdf And doing it in hardware would be more expensive than in software, hardware access is much slower than memory access. How about taking one of the bigger FPGA's, that can hold a complete stand-alone microcontoller, running a Unix-like OS? You could implement several fast, wide synchronous counter/latches in the same FPGA fabric, so there would be no need to bother with things like PCI busses. Does FreeBSD run on any of these chips? With a serial (for NMEA) and PPS input, and ethernet output, you'd have an NTP-server-on-a-chip. Add a D/A-converter to discipline a TCXO, and you're all set. An FPGA with relatively few pins, hence no BGA, would suffice. Building such a device would be within the capabilities of some of the more dedicated timenuts in here. Regards, Paul Boven - PE1NUT I seriously thought about that - if you go that route you rapidly end up with a Sokeris board with timing control added which is pretty much where I started. It would be fun to build a single chip ntp box but the development effort is substantial. I'm not married to the PCI approach but I do need to be able to read the counters in a predictable time and PCI (or some other bus) seems to be the only way to do that. There are some great FPGA demo boards with USB on them but USB is so unpredictable that it defeats the object. John - W6/G6KCQ ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Thought experiment on a low cost timing board
Hal Murray wrote: What prompted this in the first place was the horrible temperature sensitivity my soekris boxes exhibit - I can only keep them to within 10us of the gps 95% of the time and the occasional 100us excursion is not uncommon. I want to be stable to the limit of the gps I'm using - for no other reason than the belief that I can do it for way less than commercial devices using open source software and low cost hardware. In other works I'm hacking for the sake of it :-) Is there a temperature sensor on the Soekris box? Is it located anywhere near the crystal? Good read on that topic: http://www.ijs.si/time/temp-compensation/ It runs out there is a temp sensor on the board - it only reads in one degree C steps but if I take a 10 min rolling average of the temperature I can fit the temp curve almost exactly to the ntp frequency compensation (it's drifting by about 0.44 PPM per degree C). I'm going to hack some code into ntpd tomorrow and see if I can do the same compensation as in the example above. John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Thought experiment on a low cost timing board
Tom Van Baak wrote: I'm curious about the 10 kHz signal. Can you send me a pointer to it? Usually 1 Hz is good enough and in practice most GPSDO use an averaging algorithm that is more akin to 0.01 Hz to 0.001 Hz. /tvb See http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
