Re: [time-nuts] Antique pendulum clocks
Thanks for these links. The Harrison clocks are amazing -- I saw them at Greenwich some years ago. The Trinity reference also amuses me as that was my college (quite a long time ago). Back in the 60s, my father and his cousin were competing to produce accurate pendulum clocks with accuracies of the order of a fraction of a second per day. Invar pendulums, temperature and pressure compensation and temperature controlled environments. Electromagnetic pulse drive. All built with transistors... I wish that I could talk to them now Philip On Fri, Nov 22, 2019 at 9:30 AM Tony Finch wrote: > Philip Gladstone wrote: > > > > The data that I get is surprising in that the pendulum swing varies > > according to the position of the hands on the clock. > > Clocks with large outdoor faces have extra problems along those lines... > > http://trin-hosts.trin.cam.ac.uk/clock/main.php?menu_option=pigeons > > Tony. > -- > f.anthony.n.finchhttp://dotat.at/ > Sole, Lundy, Fastnet: Variable 4 or less, becoming north or northwest 4 to > 6, > occasionally 7 in Sole. Slight or moderate, occasionally rough in Sole. > Rain > or showers. Good, occasionally poor. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Antique pendulum clocks
I have two pendulum clocks, one a 1930s-era torsional pendulum clock from Bavaria and the other a swinging pendulum clock built around 1990. I will follow this thread closely. Tom, you mentioned that there are lots of resources out there - can you elucidate? Thanks. DaveD Sent from a small flat thingy > On Nov 20, 2019, at 21:18, Adrian Godwin wrote: > >> On Thu, Nov 21, 2019 at 2:01 AM Bill Beam wrote: >> >> Most people interested in this problem have been dead for about 200 years. >> >> I knew there was a reason why I didn't feel so well lately .. > > > I have an electric pendulum clock by Bulle. A coil swings in a short arc, > following a curved magnetic polepiece. At some point, contacts close and > provide a timed sustaining impulse to the coil. > > Out of sheer pigheadedness, I am attempting to monitor the movement with > antique (perhaps not quite so antique) timing equipment. I have an HP456A > current probe to capture the impulse instance, an HP 5275A counter to > measure the period and an HP101A oscillator to provide a reference. ADEV > calculations might be done by an HP9815 calculator or perhaps an HP41 if I > can't find the 9815's parallel interface. Non-HP equipment is permitted but > nothing suitable has come up so far. > > A difficulty at the moment is that the contacts bounce somewhat, making > the impulse timing poorly defined. I haven't yet got as far as seeing any > mechanically caused pattern to the errors. > > Thanks to Tom for giving me more distractions to read :) > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
On 11/22/19 2:29 PM, Hal Murray wrote: j...@febo.com said: I like the idea of inserting attenuation until the SNR or Cn values start to go down. That may be the most practical solution. Inserting attenuation is a good trick for the tool box. It is also used to measure error rates on fiber links. With a reasonable fiber setup, the error rate is so low that it is hard to measure. I don't know that this is the case all the time. On radio links, the kind of coding affects the BER vs Eb/No curve - and there's a variety of impairments that have the top part of the curve looking ok, and the low BER part looking funny. Figure 6 in this report (figure attached) shows this problem - "BER Flaring" https://ntrs.nasa.gov/search.jsp?R=20140008859 Granted, that example is because there was a bug in the implementation of the receiver software, however it can happen on other systems, due to various non-ideal implementation aspects. At low error rates, there is a simple relation between signal/noise and error rate. So insert enough attenuation until you can easily measure the error rate, then compute what it would be without the attenuation. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
Hi If NIST puts their real time data on any of the networks, you may be able to shortcut the process. Goddard puts up data so indeed NIST may also do so. The trick is to stream the data real time into the F9P or into a PC. You effectively solve for the distance and bearing to the “reference” station. This is what a typical survey crew does on a daily basis. Not much use for continental drift, may be a way to see if the house is sliding off into the gulch …. Bob > On Nov 22, 2019, at 1:17 PM, Eric Scace wrote: > > Thank you, everyone, for your enthusiastic guidance and observations to my > quirky question. > > Quite a few mentioned the difficulties in measuring rotation over a short > baseline. In response to the question of “is there another measurement point > 10 miles away”, the quick answer is yes: NIST is on the opposite side of > Boulder City from me. > > The question of a sturdy — i.e., dimensionally stable — antenna mount > brought to mind something I learned during my home inspection. My house is > built at the foothills of the Front Range in North Boulder. Soils there > include a kind of clay that swells significantly when exposed to water. As a > result, house foundations are build on a system of screw pilings that go down > to bedroom. The house’s cellar floor is a concrete slab poured on corrugated > steel plates supported by cross-web girders that sit on these pilings. The > cellar walls (to which the higher-precision pendulum clocks are mounted) are > poured concrete that also rests on these pilings. It seems the house > foundation is probably a better reference point for antennas than something > sitting on the ground at the corner of my (tiny) lot. > > Of course, my house and the neighbors’ houses are obstructions to signals > for an antenna attached directly to the foundation walls. > > The plan was to install two antennas (for two GPSDOs) mounted on short > roof-penetrating metal tubes secured to the roof framing, just high enough to > clear the neighborhood’s rooflines. This will give full sky access (except > for the portion obscured by the foothills of the Front Range, a problem that > plagues NIST as well). For time purposes, my understanding is that this > should be fine. > > For millimeter-scale position determination, this sounds like a more > difficult situation. The house is generally wood framing with some structural > steel elements (not in useful locations). Position measurements would contain > noise from the diurnal/seasonal changes of the house framing. Maybe that > could be averaged out? > > — Eric > >> On 2019 Nov 22, at 00:36 , Hal Murray wrote: >> >> Measuring rotation will be tough if your 2 stations are only 100 ft apart. >> Do >> you have a friend 1, 10, or 100 miles away? >> >> PS: Make sure that your antenna mounts are sturdy. You don't want them >> drifting as the house ages or you bump into them. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
Am 22.11.19 um 23:29 schrieb Hal Murray: j...@febo.com said: I like the idea of inserting attenuation until the SNR or Cn values start to go down. That may be the most practical solution. Inserting attenuation is a good trick for the tool box. It is also used to measure error rates on fiber links. With a reasonable fiber setup, the error rate is so low that it is hard to measure. At low error rates, there is a simple relation between signal/noise and error rate. So insert enough attenuation until you can easily measure the error rate, then compute what it would be without the attenuation. Unfortunately, in real life it's not so simple. There are more contributors than just SNR. In fact, when we were building 10 GBPS XFP fiber optic tranceivers, we got no bit errors at all. Just in one test, there was 1 failing bit per day or so. It turned out that the polynomial used to generate the data for that test had unusual long and unluckily grouped runlengths of the same polarity. Someone had decided that 10 nF coupling capacitors on the differential CML lines were large enough for 10 GBPS and they did fit better onto the microstrips than the usual 100nF ones. That did cost us a lot of time and money. regards, Gerhard ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] tracking position & orientation
NRCAN / csrs-ppp will do L1 only data. Typical results have errror ellipses in the 300-500 mm range. It also seems to be the only free site that handles RINEX V3.xx data. They only use GPS and GLONASS measurements, -- >I do not know of any free sites that will post process “L1 only” data. Without post processing, you will not get mm level results. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
j...@febo.com said: > I like the idea of inserting attenuation until the SNR or Cn values start to > go down. That may be the most practical solution. Inserting attenuation is a good trick for the tool box. It is also used to measure error rates on fiber links. With a reasonable fiber setup, the error rate is so low that it is hard to measure. At low error rates, there is a simple relation between signal/noise and error rate. So insert enough attenuation until you can easily measure the error rate, then compute what it would be without the attenuation. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
You can get the data from The manufacturer or from some calibration database like NOAA https://www.ngs.noaa.gov/ANTCAL/# Or geo++ Or the list of antennas built into the post processing software. /Björn Sent from my iPhone > On 22 Nov 2019, at 19:02, Bill Dailey, MD, MSEng, MSMI > wrote: > > Interesting. No, there was no data with __ > -- > Doc > > Bill Dailey > KXØO > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
I lived near Lyons, CO for about 20 years. ISTR that there is a fault line in CO, I think on the western slope. DaveD Sent from a small flat thingy > On Nov 22, 2019, at 02:36, Hal Murray wrote: > > > e...@scace.org said: >> I moved to Boulder CO a few months ago. The “curiosity” is to determine >> the position of two antennas at either end of my house and monitor it over >> time, with the idea that one could see plate movement in 3 dimensions plus >> rotation around the axes. > > How much does Boulder move? I'd guess not much so measuring motion will be > tough. You could try to get a lower limit on the speed. > > Looks like that part of the country is not interesting to the USGS: > https://earthquake.usgs.gov/monitoring/gps > > Ballpark numbers. > With a good setup, GPS gives location to about 1 mm. > I live a few miles from the San Andreas fault system. It is shifting about > as fast as your fingernails grow, roughly an inch per year. > > Measuring rotation will be tough if your 2 stations are only 100 ft apart. > Do > you have a friend 1, 10, or 100 miles away? > > PS: Make sure that your antenna mounts are sturdy. You don't want them > drifting as the house ages or you bump into them. > > -- > > There is a major USGS campus on the Boulder side of Denver. You might wander > down there and ask around to see if you can find anybody familiar with either > GPS or earthquakes. Or try their web pages. There is probably a public > information contact. > > -- > > From a USGS talk tonight on Sea Level Rise. > California is rising about 2 mm per year. Sea level is rising about 3 mm > per year. Net is 1. > East coast is sinking about 3 mm per year. > (Major risk is surge and waves from hurricanes.) > > > -- > These are my opinions. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
On 11/22/19 10:17 AM, Eric Scace wrote: Thank you, everyone, for your enthusiastic guidance and observations to my quirky question. Quite a few mentioned the difficulties in measuring rotation over a short baseline. In response to the question of “is there another measurement point 10 miles away”, the quick answer is yes: NIST is on the opposite side of Boulder City from me. The question of a sturdy — i.e., dimensionally stable — antenna mount brought to mind something I learned during my home inspection. My house is built at the foothills of the Front Range in North Boulder. Soils there include a kind of clay that swells significantly when exposed to water. As a result, house foundations are build on a system of screw pilings that go down to bedroom. The house’s cellar floor is a concrete slab poured on corrugated steel plates supported by cross-web girders that sit on these pilings. The cellar walls (to which the higher-precision pendulum clocks are mounted) are poured concrete that also rests on these pilings. It seems the house foundation is probably a better reference point for antennas than something sitting on the ground at the corner of my (tiny) lot. Of course, my house and the neighbors’ houses are obstructions to signals for an antenna attached directly to the foundation walls. Interesting problem.. You could put a steel (or Invar?) pipe down the side of the house to hit the foundation, but then as the house moves from side to side (wind, temperature, humidity) it would move the antenna. Some form of rigid spaceframe around the house would result in aesthetic problems. And drilling a hole all the way from the roof to the foundation is probably a non-starter (although, in my house, there is a sort of utility chase that does go from top of 2nd floor to 1st floor), but there's probably something in the way (HVAC vents, most likely). I'm not that much of a GPS nut (yet) (because you know, living in southern California, there's not much in the way of geodetic measurement infrastructure I can leverage - Self reliance - at the end of civilization as we know it, at least you'd be able to measure continental drift without depending on others...) For millimeter-scale position determination, this sounds like a more difficult situation. The house is generally wood framing with some structural steel elements (not in useful locations). Position measurements would contain noise from the diurnal/seasonal changes of the house framing. Maybe that could be averaged out? Maybe, but if the uncertainties are big enough over time, then no amount of averaging helps. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
>For millimeter-scale position determination, this sounds like a >more difficult situation. The house is generally wood framing with >some structural steel elements (not in useful locations). Position >measurements would contain noise from the diurnal/seasonal changes >of the house framing. Maybe that could be averaged out? This is partly[1] why I'm doing the same exercise[2]: I just built a new house and it seems that nobody in Denmark knows how much the wooden roof construction moves over a climatic year. Poul-Henning [1] The other part is that I cannot imagine a more relaxing hobby than "Watching continental drift in real time" :-) [2] But only one antenna because Scandinavia has no noticeable rotation. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
Thank you, everyone, for your enthusiastic guidance and observations to my quirky question. Quite a few mentioned the difficulties in measuring rotation over a short baseline. In response to the question of “is there another measurement point 10 miles away”, the quick answer is yes: NIST is on the opposite side of Boulder City from me. The question of a sturdy — i.e., dimensionally stable — antenna mount brought to mind something I learned during my home inspection. My house is built at the foothills of the Front Range in North Boulder. Soils there include a kind of clay that swells significantly when exposed to water. As a result, house foundations are build on a system of screw pilings that go down to bedroom. The house’s cellar floor is a concrete slab poured on corrugated steel plates supported by cross-web girders that sit on these pilings. The cellar walls (to which the higher-precision pendulum clocks are mounted) are poured concrete that also rests on these pilings. It seems the house foundation is probably a better reference point for antennas than something sitting on the ground at the corner of my (tiny) lot. Of course, my house and the neighbors’ houses are obstructions to signals for an antenna attached directly to the foundation walls. The plan was to install two antennas (for two GPSDOs) mounted on short roof-penetrating metal tubes secured to the roof framing, just high enough to clear the neighborhood’s rooflines. This will give full sky access (except for the portion obscured by the foothills of the Front Range, a problem that plagues NIST as well). For time purposes, my understanding is that this should be fine. For millimeter-scale position determination, this sounds like a more difficult situation. The house is generally wood framing with some structural steel elements (not in useful locations). Position measurements would contain noise from the diurnal/seasonal changes of the house framing. Maybe that could be averaged out? — Eric > On 2019 Nov 22, at 00:36 , Hal Murray wrote: > > Measuring rotation will be tough if your 2 stations are only 100 ft apart. > Do > you have a friend 1, 10, or 100 miles away? > > PS: Make sure that your antenna mounts are sturdy. You don't want them > drifting as the house ages or you bump into them. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
Interesting. No, there was no data with it. On Fri, Nov 22, 2019 at 12:00 PM Björn wrote: > The N for North is because the phase center offsets are not symmetrical. > With a convention to orient the antennas the same way the offset could be > corrected. > > /Björn > > Sent from my iPhone > > > On 22 Nov 2019, at 17:07, Bill Dailey wrote: > > > > I would like to tag on to this. I have a large Leica L1 choke ring > antenna. It has an indicator for “N”. Not sure why. I placed it on the > roof without respect to directionality. I will rotate it with “N” facing > north in a month or so to see if there is any effect. > > > > Bill Dailey > > > > Negativity always wins the short game. But positivity wins the long > game. - Gary Vaynerchuk > > > > Don’t be easy to understand, > > Be impossible to misunderstand > > - Steve Sims > > > >> On Nov 21, 2019, at 6:00 PM, Dana Whitlow > wrote: > >> > >> Most modern GPS receivers are very quiet even barefoot. So, one could > >> argue that one should > >> not have much more LNA gain in the antenna than required to make up for > >> feedline loss, which > >> should be easily calculable. While excess gain in the antenna can > improve > >> overall system noise > >> figure a small amount, it will degrade intermod performance, which is > >> likely to be a worse problem > >> than simple weak signals. It's likely that the cure is worse than the > >> disease, as my doctor likes to > >> say. > >> > >> Dana > >> > >> > >> > >>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < > >>> time-nuts@lists.febo.com> wrote: > >>> > >>> So concensus is, 50dB gain antenna is too much gain, unless feed > line > >>> is too long, reception is poor, or there are other circumstances extra > gain > >>> is desired? > >>> > >>> --- > >>> (Mr.) Taka Kamiya > >>> KB4EMF / ex JF2DKG > >>> > >>> > >>> On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < > >>> kb...@n1k.org> wrote: > >>> > >>> Hi > >>> > >>> That is indeed the gotcha. Once you get past a certain amount of gain > in > >>> the > >>> preamp, the C/N levels don’t change enough to notice. Looking today vs > >>> looking > >>> tomorrow is unlikely to be of any help if you are after a fraction of a > >>> db. > >>> > >>> About the only way to check would be to fast switch an attenuator in > and > >>> out of > >>> the signal path. Watch things for a minute at one setting and then do > the > >>> same at > >>> another setting. Run for a while and log all the deltas. If you see a > >>> degradation of > >>> more than a few tenths of a db, you are getting towards the minimum > gain > >>> point. > >>> > >>> Indeed there are some receivers that have an AGC built in. *IF* your > >>> receiver has one > >>> and *IF* you can get at it, that would be a great way to work this out. > >>> Indeed anybody > >>> who makes it past both of those constraints has a pretty unique device. > >>> > >>> > >>> > >>> Simple answer for a 50 db antenna is to put an attenuator in after the > DC > >>> has > >>> been eliminated from the circuit. It’s not idea, but it’s the best you > can > >>> do. Running > >>> a great big splitter is one great way to come up with attenuation ….. > >>> > >>> Bob > >>> > >>> > > On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR > wrote: > > Bob, this is a great summary, thanks! > > One related question, especially with mixed systems -- how do you tell > if you have optimum signal level at the receiver? > > Most show some sort of SNR or Cn value. What should we look for? > What > are the indication of *too much* signal? One issue in particular is > how > to handle a modern GPS that expects modest antenna gain when it's > plugged into a system with a 50dB gain antenna at the top. > > Thanks! > John > > > > On 11/21/19 8:00 AM, Bob kb8tq wrote: > > Hi > > > > Way back in time, the first gear out there to use what we now look at > >>> as “normal” antennas > > was survey gear. For various reasons they decided on a 12V power > supply > >>> and 40 to 50 db > > of gain in the preamp mounted in the antenna. They also got into L1 / > >>> L2 pretty quickly. > > > > A bit later the cell phone (and later broadcast) guys got into this. > In > >>> a location with a lot of > > RF (like a cell site) having a lot of gain at the antenna didn’t work > >>> all that well. IMD issues > > got into the act pretty quickly. In addition, front end filtering was > >>> required to reduce overload > > issues. The focus was on L1 only so filtering was relatively easy. > > > > There is a whole separate set of antennas that put a big chunk of the > >>> RF portion of the radio > > in the antenna. Those still survive here and there. I have one of > them > >>> and probably a couple > > of dozen of the more “normal” antennas. > > > > As time marched on, supply
Re: [time-nuts] tracking position & orientation
On 11/22/19 12:21 PM, Tim Lister wrote: > You probably don't need to wait that many days for the Final GPS > satellite orbits; the IGS products page > (https://www.igs.org/products)shows that even the real-time > ultra-rapid products are a factor of 20x better in the orbit (but > interestingly not the satellite clocks) than the broadcast ephemeris. > But if you are trying to find small drifts over a year, rather than > say doing real-time RTK corrections, you have the luxury of time to > wait for the absolute best orbits before doing the processing. My (limited) experience with sending L1/L2 data to both NRCan and OPUS is that there is a noticeable improvement from the "ultra-rapid" to the "rapid" results a day or so later. The difference from "rapid" to "final" is barely noticeable (but is real). ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
Thanks to Bob, Achim, Greg and others for their input on this. It seems the real challenge is that the outputs available from most GPS don't provide the kind of info that would let you know if IMD or overload are occurring. In most cases we can only infer from positioning performance, which is hard to quantify or correlate. I like the idea of inserting attenuation until the SNR or Cn values start to go down. That may be the most practical solution. John On 11/21/19 4:05 PM, Greg Troxel wrote: > John Ackermann N8UR writes: > >> One related question, especially with mixed systems -- how do you tell >> if you have optimum signal level at the receiver? >> >> Most show some sort of SNR or Cn value. What should we look for? What >> are the indication of *too much* signal? One issue in particular is how >> to handle a modern GPS that expects modest antenna gain when it's >> plugged into a system with a 50dB gain antenna at the top. > > Too much gain can manifest in at least two different ways: > > 1) intermodulation distortion in the preamp > > 2) distortion/overload in the GPS receiver > > Adding an attenuator or cable as someone suggested can help you > determine if the preamp gain is excessive *given your cabling and GPSr > frontend*. If you add 10 dB of loss, and the C/N0 doesn't change, > arguably you have gain you didn't need, and which therefore has elevated > risk of IMD. If it goes up, you (mostly) know you are overdriving your > receiver (which would be surprising to me). If it drops, then you > probably need most of the gain. > > This is tricky, because a system with too much preamp gain will be prone > to IMD if other signals appear but may operate just fine when they > don't. > > That said, I am unclear on: > > typical filtering before the antenna preamp (very little in a > dual-frequency antenna?) > > 3rd-order IMD dynamic range in these preamps > > strength of non-GNSS signals that appear in the filter passband > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
I believe that's to avoid errors from phase center offset -- when the antenna calibrations are done, the measurements are taken with the antenna aligned that way so aiming it in the fields ensures releatability. On Nov 22, 2019, 12:01 PM, at 12:01 PM, Bill Dailey wrote: >I would like to tag on to this. I have a large Leica L1 choke ring >antenna. It has an indicator for “N”. Not sure why. I placed it on >the roof without respect to directionality. I will rotate it with “N” >facing north in a month or so to see if there is any effect. > >Bill Dailey > >Negativity always wins the short game. But positivity wins the long >game. - Gary Vaynerchuk > >Don’t be easy to understand, >Be impossible to misunderstand >- Steve Sims > >> On Nov 21, 2019, at 6:00 PM, Dana Whitlow >wrote: >> >> Most modern GPS receivers are very quiet even barefoot. So, one >could >> argue that one should >> not have much more LNA gain in the antenna than required to make up >for >> feedline loss, which >> should be easily calculable. While excess gain in the antenna can >improve >> overall system noise >> figure a small amount, it will degrade intermod performance, which is >> likely to be a worse problem >> than simple weak signals. It's likely that the cure is worse than >the >> disease, as my doctor likes to >> say. >> >> Dana >> >> >> >>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>> So concensus is, 50dB gain antenna is too much gain, unless feed >line >>> is too long, reception is poor, or there are other circumstances >extra gain >>> is desired? >>> >>> --- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> >>> >>>On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < >>> kb...@n1k.org> wrote: >>> >>> Hi >>> >>> That is indeed the gotcha. Once you get past a certain amount of >gain in >>> the >>> preamp, the C/N levels don’t change enough to notice. Looking today >vs >>> looking >>> tomorrow is unlikely to be of any help if you are after a fraction >of a >>> db. >>> >>> About the only way to check would be to fast switch an attenuator in >and >>> out of >>> the signal path. Watch things for a minute at one setting and then >do the >>> same at >>> another setting. Run for a while and log all the deltas. If you see >a >>> degradation of >>> more than a few tenths of a db, you are getting towards the minimum >gain >>> point. >>> >>> Indeed there are some receivers that have an AGC built in. *IF* your >>> receiver has one >>> and *IF* you can get at it, that would be a great way to work this >out. >>> Indeed anybody >>> who makes it past both of those constraints has a pretty unique >device. >>> >>> >>> >>> Simple answer for a 50 db antenna is to put an attenuator in after >the DC >>> has >>> been eliminated from the circuit. It’s not idea, but it’s the best >you can >>> do. Running >>> a great big splitter is one great way to come up with attenuation >….. >>> >>> Bob >>> >>> > On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR >wrote: Bob, this is a great summary, thanks! One related question, especially with mixed systems -- how do you >tell if you have optimum signal level at the receiver? Most show some sort of SNR or Cn value. What should we look for? >What are the indication of *too much* signal? One issue in particular >is how to handle a modern GPS that expects modest antenna gain when it's plugged into a system with a 50dB gain antenna at the top. Thanks! John On 11/21/19 8:00 AM, Bob kb8tq wrote: > Hi > > Way back in time, the first gear out there to use what we now look >at >>> as “normal” antennas > was survey gear. For various reasons they decided on a 12V power >supply >>> and 40 to 50 db > of gain in the preamp mounted in the antenna. They also got into >L1 / >>> L2 pretty quickly. > > A bit later the cell phone (and later broadcast) guys got into >this. In >>> a location with a lot of > RF (like a cell site) having a lot of gain at the antenna didn’t >work >>> all that well. IMD issues > got into the act pretty quickly. In addition, front end filtering >was >>> required to reduce overload > issues. The focus was on L1 only so filtering was relatively easy. > > There is a whole separate set of antennas that put a big chunk of >the >>> RF portion of the radio > in the antenna. Those still survive here and there. I have one of >them >>> and probably a couple > of dozen of the more “normal” antennas. > > As time marched on, supplying 12V to antennas became a bit less >>> popular. Most of the cell > guys went over to a 5V antenna supply. The net result was 12V 50 >db >>> survey antennas that did > L1/L2 and much smaller 5V 25 db antennas for “timing”. The timing >>> antennas didn’t do L1/L2 so > not going t
Re: [time-nuts] Difference in antennas
Hi If your antenna has test data associated with it (or even if it does not) there may / will be differences in the phase response for various angles both in the vertical and horizontal planes. Indeed some antennas have very minor changes vs angle and others move quite a bit. To keep this somewhat under control, survey antennas get a mark on them to tell you which direction to point north. The idea being that if orientation is known, post processing corrections to eliminate ( or at least reduce) the phase issues are possible. If you are not doing post processing, there really isn’t much value in the magic “this way north” marking. Bob > On Nov 22, 2019, at 11:07 AM, Bill Dailey wrote: > > I would like to tag on to this. I have a large Leica L1 choke ring antenna. > It has an indicator for “N”. Not sure why. I placed it on the roof without > respect to directionality. I will rotate it with “N” facing north in a month > or so to see if there is any effect. > > Bill Dailey > > Negativity always wins the short game. But positivity wins the long game. - > Gary Vaynerchuk > > Don’t be easy to understand, > Be impossible to misunderstand > - Steve Sims > >> On Nov 21, 2019, at 6:00 PM, Dana Whitlow wrote: >> >> Most modern GPS receivers are very quiet even barefoot. So, one could >> argue that one should >> not have much more LNA gain in the antenna than required to make up for >> feedline loss, which >> should be easily calculable. While excess gain in the antenna can improve >> overall system noise >> figure a small amount, it will degrade intermod performance, which is >> likely to be a worse problem >> than simple weak signals. It's likely that the cure is worse than the >> disease, as my doctor likes to >> say. >> >> Dana >> >> >> >>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>> So concensus is, 50dB gain antenna is too much gain, unless feed line >>> is too long, reception is poor, or there are other circumstances extra gain >>> is desired? >>> >>> --- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> >>> >>> On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < >>> kb...@n1k.org> wrote: >>> >>> Hi >>> >>> That is indeed the gotcha. Once you get past a certain amount of gain in >>> the >>> preamp, the C/N levels don’t change enough to notice. Looking today vs >>> looking >>> tomorrow is unlikely to be of any help if you are after a fraction of a >>> db. >>> >>> About the only way to check would be to fast switch an attenuator in and >>> out of >>> the signal path. Watch things for a minute at one setting and then do the >>> same at >>> another setting. Run for a while and log all the deltas. If you see a >>> degradation of >>> more than a few tenths of a db, you are getting towards the minimum gain >>> point. >>> >>> Indeed there are some receivers that have an AGC built in. *IF* your >>> receiver has one >>> and *IF* you can get at it, that would be a great way to work this out. >>> Indeed anybody >>> who makes it past both of those constraints has a pretty unique device. >>> >>> >>> >>> Simple answer for a 50 db antenna is to put an attenuator in after the DC >>> has >>> been eliminated from the circuit. It’s not idea, but it’s the best you can >>> do. Running >>> a great big splitter is one great way to come up with attenuation ….. >>> >>> Bob >>> >>> > On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR wrote: Bob, this is a great summary, thanks! One related question, especially with mixed systems -- how do you tell if you have optimum signal level at the receiver? Most show some sort of SNR or Cn value. What should we look for? What are the indication of *too much* signal? One issue in particular is how to handle a modern GPS that expects modest antenna gain when it's plugged into a system with a 50dB gain antenna at the top. Thanks! John On 11/21/19 8:00 AM, Bob kb8tq wrote: > Hi > > Way back in time, the first gear out there to use what we now look at >>> as “normal” antennas > was survey gear. For various reasons they decided on a 12V power supply >>> and 40 to 50 db > of gain in the preamp mounted in the antenna. They also got into L1 / >>> L2 pretty quickly. > > A bit later the cell phone (and later broadcast) guys got into this. In >>> a location with a lot of > RF (like a cell site) having a lot of gain at the antenna didn’t work >>> all that well. IMD issues > got into the act pretty quickly. In addition, front end filtering was >>> required to reduce overload > issues. The focus was on L1 only so filtering was relatively easy. > > There is a whole separate set of antennas that put a big chunk of the >>> RF portion of the radio > in the antenna. Those still survive here and there.
Re: [time-nuts] Difference in antennas
The "N" indeed points north. This is because these large reference-station choke-ring antennas are often calibrated for phase center with respect to north. Did you get the phase center calibration data with your antenna? Pointing the "N" towards north will not have much effect on timing accuracy, but mm-level accuracy for positioning requires this. A note on gain and noise figure: best fix (smallest positioning point cloud) obtained when full system noise figure is equivalent to the antenna LNA noise figure. If you are using an antenna with a very short (few cms) coax to the antenna, amplification in the antenna makes little sense, unless your GNSS receiver has a noisy front-end. When you have significant runs of coax between antenna and receiver (meters, 10s of meters), 10-15 dB of loss is not uncommon. If you have 15dB of loss in a cable run, your system noise figure will be worse than 15dB. If you have an antenna with 30 or 40dB of gain and a noise figure of say 1.5 to 2dB, the 15 dB loss in the cable will have a negligible effect on overall system noise figure and S/N ratio of the GNSS signals at the receiver will not be degraded by the coax losses. Too much gain in antenna LNA can render the GNSS receiver susceptible to interference or saturation of the receiver front-end by noise, depending on how AGC is implemented and how much gain and what filtering is present inside the GNSS receiver. Bill On 22/11/19 17:07, Bill Dailey wrote: > I would like to tag on to this. I have a large Leica L1 choke ring antenna. > It has an indicator for “N”. Not sure why. I placed it on the roof without > respect to directionality. I will rotate it with “N” facing north in a month > or so to see if there is any effect. > > Bill Dailey > > Negativity always wins the short game. But positivity wins the long game. - > Gary Vaynerchuk > > Don’t be easy to understand, > Be impossible to misunderstand > - Steve Sims > >> On Nov 21, 2019, at 6:00 PM, Dana Whitlow wrote: >> >> Most modern GPS receivers are very quiet even barefoot. So, one could >> argue that one should >> not have much more LNA gain in the antenna than required to make up for >> feedline loss, which >> should be easily calculable. While excess gain in the antenna can improve >> overall system noise >> figure a small amount, it will degrade intermod performance, which is >> likely to be a worse problem >> than simple weak signals. It's likely that the cure is worse than the >> disease, as my doctor likes to >> say. >> >> Dana >> >> >> >>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>> So concensus is, 50dB gain antenna is too much gain, unless feed line >>> is too long, reception is poor, or there are other circumstances extra gain >>> is desired? >>> >>> --- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> >>> >>> On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < >>> kb...@n1k.org> wrote: >>> >>> Hi >>> >>> That is indeed the gotcha. Once you get past a certain amount of gain in >>> the >>> preamp, the C/N levels don’t change enough to notice. Looking today vs >>> looking >>> tomorrow is unlikely to be of any help if you are after a fraction of a >>> db. >>> >>> About the only way to check would be to fast switch an attenuator in and >>> out of >>> the signal path. Watch things for a minute at one setting and then do the >>> same at >>> another setting. Run for a while and log all the deltas. If you see a >>> degradation of >>> more than a few tenths of a db, you are getting towards the minimum gain >>> point. >>> >>> Indeed there are some receivers that have an AGC built in. *IF* your >>> receiver has one >>> and *IF* you can get at it, that would be a great way to work this out. >>> Indeed anybody >>> who makes it past both of those constraints has a pretty unique device. >>> >>> >>> >>> Simple answer for a 50 db antenna is to put an attenuator in after the DC >>> has >>> been eliminated from the circuit. It’s not idea, but it’s the best you can >>> do. Running >>> a great big splitter is one great way to come up with attenuation ….. >>> >>> Bob >>> >>> > On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR wrote: Bob, this is a great summary, thanks! One related question, especially with mixed systems -- how do you tell if you have optimum signal level at the receiver? Most show some sort of SNR or Cn value. What should we look for? What are the indication of *too much* signal? One issue in particular is how to handle a modern GPS that expects modest antenna gain when it's plugged into a system with a 50dB gain antenna at the top. Thanks! John On 11/21/19 8:00 AM, Bob kb8tq wrote: > Hi > > Way back in time, the first gear out there to use what we now look at >>> as “normal” antennas > was survey gear.
Re: [time-nuts] Difference in antennas
The N for North is because the phase center offsets are not symmetrical. With a convention to orient the antennas the same way the offset could be corrected. /Björn Sent from my iPhone > On 22 Nov 2019, at 17:07, Bill Dailey wrote: > > I would like to tag on to this. I have a large Leica L1 choke ring antenna. > It has an indicator for “N”. Not sure why. I placed it on the roof without > respect to directionality. I will rotate it with “N” facing north in a month > or so to see if there is any effect. > > Bill Dailey > > Negativity always wins the short game. But positivity wins the long game. - > Gary Vaynerchuk > > Don’t be easy to understand, > Be impossible to misunderstand > - Steve Sims > >> On Nov 21, 2019, at 6:00 PM, Dana Whitlow wrote: >> >> Most modern GPS receivers are very quiet even barefoot. So, one could >> argue that one should >> not have much more LNA gain in the antenna than required to make up for >> feedline loss, which >> should be easily calculable. While excess gain in the antenna can improve >> overall system noise >> figure a small amount, it will degrade intermod performance, which is >> likely to be a worse problem >> than simple weak signals. It's likely that the cure is worse than the >> disease, as my doctor likes to >> say. >> >> Dana >> >> >> >>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>> So concensus is, 50dB gain antenna is too much gain, unless feed line >>> is too long, reception is poor, or there are other circumstances extra gain >>> is desired? >>> >>> --- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> >>> >>> On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < >>> kb...@n1k.org> wrote: >>> >>> Hi >>> >>> That is indeed the gotcha. Once you get past a certain amount of gain in >>> the >>> preamp, the C/N levels don’t change enough to notice. Looking today vs >>> looking >>> tomorrow is unlikely to be of any help if you are after a fraction of a >>> db. >>> >>> About the only way to check would be to fast switch an attenuator in and >>> out of >>> the signal path. Watch things for a minute at one setting and then do the >>> same at >>> another setting. Run for a while and log all the deltas. If you see a >>> degradation of >>> more than a few tenths of a db, you are getting towards the minimum gain >>> point. >>> >>> Indeed there are some receivers that have an AGC built in. *IF* your >>> receiver has one >>> and *IF* you can get at it, that would be a great way to work this out. >>> Indeed anybody >>> who makes it past both of those constraints has a pretty unique device. >>> >>> >>> >>> Simple answer for a 50 db antenna is to put an attenuator in after the DC >>> has >>> been eliminated from the circuit. It’s not idea, but it’s the best you can >>> do. Running >>> a great big splitter is one great way to come up with attenuation ….. >>> >>> Bob >>> >>> > On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR wrote: Bob, this is a great summary, thanks! One related question, especially with mixed systems -- how do you tell if you have optimum signal level at the receiver? Most show some sort of SNR or Cn value. What should we look for? What are the indication of *too much* signal? One issue in particular is how to handle a modern GPS that expects modest antenna gain when it's plugged into a system with a 50dB gain antenna at the top. Thanks! John > On 11/21/19 8:00 AM, Bob kb8tq wrote: > Hi > > Way back in time, the first gear out there to use what we now look at >>> as “normal” antennas > was survey gear. For various reasons they decided on a 12V power supply >>> and 40 to 50 db > of gain in the preamp mounted in the antenna. They also got into L1 / >>> L2 pretty quickly. > > A bit later the cell phone (and later broadcast) guys got into this. In >>> a location with a lot of > RF (like a cell site) having a lot of gain at the antenna didn’t work >>> all that well. IMD issues > got into the act pretty quickly. In addition, front end filtering was >>> required to reduce overload > issues. The focus was on L1 only so filtering was relatively easy. > > There is a whole separate set of antennas that put a big chunk of the >>> RF portion of the radio > in the antenna. Those still survive here and there. I have one of them >>> and probably a couple > of dozen of the more “normal” antennas. > > As time marched on, supplying 12V to antennas became a bit less >>> popular. Most of the cell > guys went over to a 5V antenna supply. The net result was 12V 50 db >>> survey antennas that did > L1/L2 and much smaller 5V 25 db antennas for “timing”. The timing >>> antennas didn’t do L1/L2 so > not going to work for survey. The survey antennas had way to
Re: [time-nuts] tracking position & orientation
On Fri, Nov 22, 2019 at 9:01 AM Bob kb8tq wrote: > > Hi > > At least right now, it is the “king of the hill” in terms of low cost modules > that > will do L1 / L2. > > If the target application is precision survey work, you do want (at least) > dual > band reception. All of the post processing outfits are looking for that sort > of data. > > I do not know of any free sites that will post process “L1 only” data. Without > post processing, you will not get mm level results. The NRC Precise Point Positioning service (https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php?locale=en) will do L1 only but it seems to be the only one. Have used it successfully with ublox6 L1-only data and after waiting the 12-18 days for the Final GPS orbits to be available and resubmitting, it did improve the residuals considerably. It still won't be to the mm-level that you would get from dual frequency L1/L2 data of course. You probably don't need to wait that many days for the Final GPS satellite orbits; the IGS products page (https://www.igs.org/products)shows that even the real-time ultra-rapid products are a factor of 20x better in the orbit (but interestingly not the satellite clocks) than the broadcast ephemeris. But if you are trying to find small drifts over a year, rather than say doing real-time RTK corrections, you have the luxury of time to wait for the absolute best orbits before doing the processing. > > Indeed with any of these numbers you can wonder what the errors might really > be. If the claim is 5 mm, could it really be 8 mm? sure it could. If I > average L1 > data for a few days and think I’m at 500 mm could I really be over 800 mm off? > Yes, and I do have data on that. > > If you are after things like continental drift or wander of a post in the > ground, > you are after mm level numbers. > > Bob > Cheers, Tim ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Difference in antennas
I would like to tag on to this. I have a large Leica L1 choke ring antenna. It has an indicator for “N”. Not sure why. I placed it on the roof without respect to directionality. I will rotate it with “N” facing north in a month or so to see if there is any effect. Bill Dailey Negativity always wins the short game. But positivity wins the long game. - Gary Vaynerchuk Don’t be easy to understand, Be impossible to misunderstand - Steve Sims > On Nov 21, 2019, at 6:00 PM, Dana Whitlow wrote: > > Most modern GPS receivers are very quiet even barefoot. So, one could > argue that one should > not have much more LNA gain in the antenna than required to make up for > feedline loss, which > should be easily calculable. While excess gain in the antenna can improve > overall system noise > figure a small amount, it will degrade intermod performance, which is > likely to be a worse problem > than simple weak signals. It's likely that the cure is worse than the > disease, as my doctor likes to > say. > > Dana > > > >> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < >> time-nuts@lists.febo.com> wrote: >> >> So concensus is, 50dB gain antenna is too much gain, unless feed line >> is too long, reception is poor, or there are other circumstances extra gain >> is desired? >> >> --- >> (Mr.) Taka Kamiya >> KB4EMF / ex JF2DKG >> >> >>On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < >> kb...@n1k.org> wrote: >> >> Hi >> >> That is indeed the gotcha. Once you get past a certain amount of gain in >> the >> preamp, the C/N levels don’t change enough to notice. Looking today vs >> looking >> tomorrow is unlikely to be of any help if you are after a fraction of a >> db. >> >> About the only way to check would be to fast switch an attenuator in and >> out of >> the signal path. Watch things for a minute at one setting and then do the >> same at >> another setting. Run for a while and log all the deltas. If you see a >> degradation of >> more than a few tenths of a db, you are getting towards the minimum gain >> point. >> >> Indeed there are some receivers that have an AGC built in. *IF* your >> receiver has one >> and *IF* you can get at it, that would be a great way to work this out. >> Indeed anybody >> who makes it past both of those constraints has a pretty unique device. >> >> >> >> Simple answer for a 50 db antenna is to put an attenuator in after the DC >> has >> been eliminated from the circuit. It’s not idea, but it’s the best you can >> do. Running >> a great big splitter is one great way to come up with attenuation ….. >> >> Bob >> >> On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR wrote: >>> >>> Bob, this is a great summary, thanks! >>> >>> One related question, especially with mixed systems -- how do you tell >>> if you have optimum signal level at the receiver? >>> >>> Most show some sort of SNR or Cn value. What should we look for? What >>> are the indication of *too much* signal? One issue in particular is how >>> to handle a modern GPS that expects modest antenna gain when it's >>> plugged into a system with a 50dB gain antenna at the top. >>> >>> Thanks! >>> John >>> >>> >>> On 11/21/19 8:00 AM, Bob kb8tq wrote: Hi Way back in time, the first gear out there to use what we now look at >> as “normal” antennas was survey gear. For various reasons they decided on a 12V power supply >> and 40 to 50 db of gain in the preamp mounted in the antenna. They also got into L1 / >> L2 pretty quickly. A bit later the cell phone (and later broadcast) guys got into this. In >> a location with a lot of RF (like a cell site) having a lot of gain at the antenna didn’t work >> all that well. IMD issues got into the act pretty quickly. In addition, front end filtering was >> required to reduce overload issues. The focus was on L1 only so filtering was relatively easy. There is a whole separate set of antennas that put a big chunk of the >> RF portion of the radio in the antenna. Those still survive here and there. I have one of them >> and probably a couple of dozen of the more “normal” antennas. As time marched on, supplying 12V to antennas became a bit less >> popular. Most of the cell guys went over to a 5V antenna supply. The net result was 12V 50 db >> survey antennas that did L1/L2 and much smaller 5V 25 db antennas for “timing”. The timing >> antennas didn’t do L1/L2 so not going to work for survey. The survey antennas had way to much gain >> and no filtering so not going to work for a cell site. Indeed things did and do get crossed up in various pro and basement >> systems. With care and the right set of circumstances things may work. In other cases the >> result can be an ongoing set of systems issues over an entire network of stations. Prices for a good new survey a
Re: [time-nuts] tracking position & orientation
On 11/22/19 5:04 AM, Bob kb8tq wrote: Hi Indeed, I do a better job of detecting the impact of humidity ( = rainy season ) on my deck then I do detecting anything else on a fairly short baseline. I *do* get correct distances and angles between the antennas (as verified with a tape measure). One thing you can do (with some effort) is to collect a lot of data. There is nothing magic about a 24 hour run. A two week run is also do-able. Lots of data will *not* take care of all problems. It will get the portion related to SNR down to some very small numbers. For continental drift sort of things, find a solid chunk of rock. If it’s connected to something very deep, that’s best. Tie the antenna to it, possibly with a fairly short mast. Best to have a good view of the sky so a short mast may not be practical. In the various papers on the subject you see antennas on a 2’ mast mounted on tops of hills if it’s a “quick” setup. That may only be 2 feet sticking up above the surface. There could well be a 10 meter deep double pipe. I can't seem to find the website now, but for SCIGN they had instructions on drilling a hole down to rock, putting a large PVC casing in, then putting a second steel pipe inside the large casing that actually carried the antenna, to decouple the surface movement effects (soil moisture making the soil expand and contract, for instance). Try here: https://kb.unavco.org/kb/article/permanent-gnss-gps-station-planning-technology-equipment-costs-55.html and https://kb.unavco.org/kb/article.php?id=104 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
Hi At least right now, it is the “king of the hill” in terms of low cost modules that will do L1 / L2. If the target application is precision survey work, you do want (at least) dual band reception. All of the post processing outfits are looking for that sort of data. I do not know of any free sites that will post process “L1 only” data. Without post processing, you will not get mm level results. Indeed with any of these numbers you can wonder what the errors might really be. If the claim is 5 mm, could it really be 8 mm? sure it could. If I average L1 data for a few days and think I’m at 500 mm could I really be over 800 mm off? Yes, and I do have data on that. If you are after things like continental drift or wander of a post in the ground, you are after mm level numbers. Bob > On Nov 22, 2019, at 7:28 AM, Hal Murray wrote: > >> The “cheap” approach these days is to use a uBlox ZED-F9P > > There are a zillion GPS modules available these days. Is there something > special about that one? How many others provide whatever is needed to make > RINEX files? > > -- > These are my opinions. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
Hi Indeed, I do a better job of detecting the impact of humidity ( = rainy season ) on my deck then I do detecting anything else on a fairly short baseline. I *do* get correct distances and angles between the antennas (as verified with a tape measure). One thing you can do (with some effort) is to collect a lot of data. There is nothing magic about a 24 hour run. A two week run is also do-able. Lots of data will *not* take care of all problems. It will get the portion related to SNR down to some very small numbers. For continental drift sort of things, find a solid chunk of rock. If it’s connected to something very deep, that’s best. Tie the antenna to it, possibly with a fairly short mast. Best to have a good view of the sky so a short mast may not be practical. In the various papers on the subject you see antennas on a 2’ mast mounted on tops of hills if it’s a “quick” setup. = If you are going to all the trouble of setting up three or more L1 / L2 systems with good antennas on them *and* monitoring that for months / years ….. I’d suggest that watching the PPS out of each of the receivers might be interesting as well …. :) The uBlox units mentioned earlier do have a PPS out that is pretty good. They have a cousin, the F9T that is slightly more timing oriented. The F9P board is a much better deal / easier to get. (though uBlox *is* very quick at shipping the F9T’s direct from Europe). Bob > On Nov 22, 2019, at 5:00 AM, Tom Van Baak wrote: > > Eric, > > Good idea to experiment with an antenna on each end of the house. You'll get > all sorts of data and your eyes will be eager to read house movement into the > plots. The problem is you won't know for sure if the results are real or not; > there are many factors, especially for a house made of wood. See plots for my > home/lab. [1] > > So a suggestion is to place at least one of the antenna on a waterproof > turntable and continuously rotate it, off center, very slowly, maybe one turn > a week, or month. Then look at your data and see how well you can detect that > *known* movement. > > By comparing actual GPS data with your calculated turntable antenna location > you can establish the position detection sensitivity of your setup. Which is > to say, if you can't detect a *known* antenna movement of a few inches around > a month there's little chance that you're going to confidently detect an > *unknown* seasonal or tectonic ground motion of a few mm a year. > > Alternatively, use a waterproof linear XY stage and each midnight shift the > antenna 1 to 12 inches north and 1 to 31 mm east based on the month and day > number. At the end of the year you will have created the coolest GPS plot > ever seen. It's kind of a slow motion version of "geowriting". [2] > > /tvb > > [1] http://leapsecond.com/pages/quake/ > > [2] http://leapsecond.com/pages/geowrite/ > > > On 11/21/2019 11:36 PM, Hal Murray wrote: >> e...@scace.org said: >>>I moved to Boulder CO a few months ago. The “curiosityâ€� is to >>> determine >>> the position of two antennas at either end of my house and monitor it over >>> time, with the idea that one could see plate movement in 3 dimensions plus >>> rotation around the axes. >> How much does Boulder move? I'd guess not much so measuring motion will be >> tough. You could try to get a lower limit on the speed. >> >> Looks like that part of the country is not interesting to the USGS: >> https://earthquake.usgs.gov/monitoring/gps >> >> Ballpark numbers. >> With a good setup, GPS gives location to about 1 mm. >> I live a few miles from the San Andreas fault system. It is shifting about >> as fast as your fingernails grow, roughly an inch per year. >> >> Measuring rotation will be tough if your 2 stations are only 100 ft apart. >> Do >> you have a friend 1, 10, or 100 miles away? >> >> PS: Make sure that your antenna mounts are sturdy. You don't want them >> drifting as the house ages or you bump into them. >> >> -- >> >> There is a major USGS campus on the Boulder side of Denver. You might wander >> down there and ask around to see if you can find anybody familiar with either >> GPS or earthquakes. Or try their web pages. There is probably a public >> information contact. >> >> -- >> >> >From a USGS talk tonight on Sea Level Rise. >> California is rising about 2 mm per year. Sea level is rising about 3 mm >> per year. Net is 1. >> East coast is sinking about 3 mm per year. >> (Major risk is surge and waves from hurricanes.) >> >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time
Re: [time-nuts] Antique pendulum clocks
You may be interested in a thread here earlier this year titled "Absolute time accuracy pre-Cesium?" starting March 25. Also, look for references to John Harrison in the archives. There's a video showing several of his clocks running with the grasshopper escapement, and one of his long clocks being taken apart. http://lists.febo.com/pipermail/time-nuts_lists.febo.com/ On Wed, Nov 20, 2019 at 8:00 PM Philip Gladstone wrote: > > I've started to monitor the individual ticks on a grandfather clock from > the 1790s. Essentially I timestamp whenever the pendulum breaks/restores a > light beam. > > The data that I get is surprising in that the pendulum swing varies > according to the position of the hands on the clock. It appears that the > amplitude of the swing depends on the driving force imparted by the > escapement. Since the second hand is not counterweighted, there is slightly > more energy available to drive the escapement during the first half of each > minute and slightly less in the second half. There is much bigger effect at > the end of each hour when the mechanism has to move a lever to trigger the > strike mechanism. This 'end of hour' effect changes the pendulum swing > enough so that the period is noticeably affected (maybe by 300ppm) > > Anyway, my google-fu did not reveal anybody else interested in this > stuff... Anybody here interested? > > Philip > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Antique pendulum clocks
Philip Gladstone wrote: > > The data that I get is surprising in that the pendulum swing varies > according to the position of the hands on the clock. Clocks with large outdoor faces have extra problems along those lines... http://trin-hosts.trin.cam.ac.uk/clock/main.php?menu_option=pigeons Tony. -- f.anthony.n.finchhttp://dotat.at/ Sole, Lundy, Fastnet: Variable 4 or less, becoming north or northwest 4 to 6, occasionally 7 in Sole. Slight or moderate, occasionally rough in Sole. Rain or showers. Good, occasionally poor. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
> The âcheapâ approach these days is to use a uBlox ZED-F9P There are a zillion GPS modules available these days. Is there something special about that one? How many others provide whatever is needed to make RINEX files? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
Eric, Good idea to experiment with an antenna on each end of the house. You'll get all sorts of data and your eyes will be eager to read house movement into the plots. The problem is you won't know for sure if the results are real or not; there are many factors, especially for a house made of wood. See plots for my home/lab. [1] So a suggestion is to place at least one of the antenna on a waterproof turntable and continuously rotate it, off center, very slowly, maybe one turn a week, or month. Then look at your data and see how well you can detect that *known* movement. By comparing actual GPS data with your calculated turntable antenna location you can establish the position detection sensitivity of your setup. Which is to say, if you can't detect a *known* antenna movement of a few inches around a month there's little chance that you're going to confidently detect an *unknown* seasonal or tectonic ground motion of a few mm a year. Alternatively, use a waterproof linear XY stage and each midnight shift the antenna 1 to 12 inches north and 1 to 31 mm east based on the month and day number. At the end of the year you will have created the coolest GPS plot ever seen. It's kind of a slow motion version of "geowriting". [2] /tvb [1] http://leapsecond.com/pages/quake/ [2] http://leapsecond.com/pages/geowrite/ On 11/21/2019 11:36 PM, Hal Murray wrote: e...@scace.org said: I moved to Boulder CO a few months ago. The “curiosity� is to determine the position of two antennas at either end of my house and monitor it over time, with the idea that one could see plate movement in 3 dimensions plus rotation around the axes. How much does Boulder move? I'd guess not much so measuring motion will be tough. You could try to get a lower limit on the speed. Looks like that part of the country is not interesting to the USGS: https://earthquake.usgs.gov/monitoring/gps Ballpark numbers. With a good setup, GPS gives location to about 1 mm. I live a few miles from the San Andreas fault system. It is shifting about as fast as your fingernails grow, roughly an inch per year. Measuring rotation will be tough if your 2 stations are only 100 ft apart. Do you have a friend 1, 10, or 100 miles away? PS: Make sure that your antenna mounts are sturdy. You don't want them drifting as the house ages or you bump into them. -- There is a major USGS campus on the Boulder side of Denver. You might wander down there and ask around to see if you can find anybody familiar with either GPS or earthquakes. Or try their web pages. There is probably a public information contact. -- >From a USGS talk tonight on Sea Level Rise. California is rising about 2 mm per year. Sea level is rising about 3 mm per year. Net is 1. East coast is sinking about 3 mm per year. (Major risk is surge and waves from hurricanes.) ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
> What hardware/software would be suitable for a TimeNuts (PositionNuts?) > project like this? You want 'gpsd' which can collect RINEX files for you, and then run them through https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php Where you remember to pick "ITRF" output. If you need to convert the result to any other coordinate-system or projection, 'proj4' is your software. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
Hi, You would probably want to have three antennas and receivers, and we talk about choke-ring antennas and two-frequency receivers. You should have your receivers hooked up to a common clock, such as a rubidium clock. The continental drift is measureable by GPS, and is in the range of mm/year. You would need quite a bit of data and post-process it with reference to other data to be able to draw good conclusions. You can however to some degree detect rotation, but you have to realize that the distance between the antennas becomes the limitation to it's ability to detect rotation and rotation speed. Realize that sagging of antenna mounts can introduce false sense of rotation. Rotation will probably not provide very useful info. Remember to do a baseline measurement down at Baseline Rd. :) Cheers, Magnus On 2019-11-21 21:13, Eric Scace wrote: > I need another project like a hole in the head — but curiosity > continues to nag me. > > I moved to Boulder CO a few months ago. The “curiosity” is to > determine the position of two antennas at either end of my house and > monitor it over time, with the idea that one could see plate movement > in 3 dimensions plus rotation around the axes. > > What hardware/software would be suitable for a TimeNuts > (PositionNuts?) project like this? > > — Eric K3NA > > >> On 11/21/19 8:00 AM, Bob kb8tq wrote: >> Hi >> >> Way back in time, the first gear out there to use what we now look at >> as “normal” antennas was survey gear. For various reasons they >> decided on a 12V power supply and 40 to 50 db >> of gain in the preamp mounted in the antenna. They also got into L1 / >> L2 pretty quickly. >> A bit later the cell phone (and later broadcast) guys got into this. >> In a location with a lot of RF (like a cell site) having a lot of >> gain at the antenna didn’t work all that well. IMD issues got into >> the act pretty quickly. In addition, front end filtering was required >> to reduce overload >> issues. The focus was on L1 only so filtering was relatively easy. >> >> There is a whole separate set of antennas that put a big chunk of the >> RF portion of the radio >> in the antenna. Those still survive here and there. I have one of >> them and probably a couple >> of dozen of the more “normal” antennas. >> As time marched on, supplying 12V to antennas became a bit less >> popular. Most of the cell guys went over to a 5V antenna supply. The >> net result was 12V 50 db survey antennas that did L1/L2 and much >> smaller 5V 25 db antennas for “timing”. The timing antennas didn’t do >> L1/L2 so >> not going to work for survey. The survey antennas had way to much >> gain and no filtering so not going to work for a cell site. >> Indeed things did and do get crossed up in various pro and basement >> systems. With care and >> the right set of circumstances things may work. In other cases the >> result can be an ongoing set >> of systems issues over an entire network of stations. >> Prices for a good new survey antenna are up in the many thousands of >> dollars range. They have >> very stable phase centers and (usually) test results to allow >> correction of any residual phase issues. This is part of what lets >> you get into the “couple of mm” range on a survey. >> For timing, you have to dig a bit and answer a few questions. Is your >> concern how close you >> are to BIH? If so you will need to know all the delays in your >> system. This includes the delays >> in the antenna filters and the preamp. Is your concern (or measure) >> the ADEV at 1 second? >> If so the delays are not a concern. Your antenna choice may be a bit >> different depending on >> this focus. >> >> Bob > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] tracking position & orientation
e...@scace.org said: >I moved to Boulder CO a few months ago. The âcuriosityâ is to determine > the position of two antennas at either end of my house and monitor it over > time, with the idea that one could see plate movement in 3 dimensions plus > rotation around the axes. How much does Boulder move? I'd guess not much so measuring motion will be tough. You could try to get a lower limit on the speed. Looks like that part of the country is not interesting to the USGS: https://earthquake.usgs.gov/monitoring/gps Ballpark numbers. With a good setup, GPS gives location to about 1 mm. I live a few miles from the San Andreas fault system. It is shifting about as fast as your fingernails grow, roughly an inch per year. Measuring rotation will be tough if your 2 stations are only 100 ft apart. Do you have a friend 1, 10, or 100 miles away? PS: Make sure that your antenna mounts are sturdy. You don't want them drifting as the house ages or you bump into them. -- There is a major USGS campus on the Boulder side of Denver. You might wander down there and ask around to see if you can find anybody familiar with either GPS or earthquakes. Or try their web pages. There is probably a public information contact. -- >From a USGS talk tonight on Sea Level Rise. California is rising about 2 mm per year. Sea level is rising about 3 mm per year. Net is 1. East coast is sinking about 3 mm per year. (Major risk is surge and waves from hurricanes.) -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
