Re: [time-nuts] Do ordinary clouds adversely affect GPS reception?
uBlox M8T & antenna behind two panes of glass skyview is a 170 degree sweep centred 30 degrees east of south I regularly see attenuation with overcast clouds, but only with some overcast clouds. It's not consistent enough to be able to say which types. The attenuation can be as much as 10 dBc, sometimes more. If all the sats suddenly show as way down, that's a sign to go outside and look as it's usually tornado-friendly conditions. And if the wind hasn't picked up yet, it soon will. Often, the attenuation from overcast clouds is relieved once the rain starts. But rain can also make it worse. Droplet size or rainfall density? No consistency with snow either, except for the really thick snowfall, which is usually, but not always, a wet snow. Few trees in my view to show differences when they're wet vs. dry. If the rain is being blown against the sides of the brick buildings low to the horizon across from me, once they're soaked, I get multi-path: - from the sats on the other side of my building, which are a little off from 180 degrees opposite my view, from a range roughly 30 degrees wide and between five to 35 degrees elevation; and, - also from a few weak sats signals from just around the corners of my building and just beyond the roof edge, usually within ten degrees beyond the edges of my building. The ground is almost always wet before the sides of those buildings are soaked, but the hit of multi-path comes with those building sides getting soaked. Long & tall hedge across in front of most of those buildings. I've always assumed it was reflecting off the buildings. Michael ___ 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] Do ordinary clouds adversely affect GPS reception?
As far as I know, my friend's GPS dropout problems have been associated with simple clouds with no rain (at least no rain reaching the surface). Dana On Wed, Oct 23, 2019 at 2:00 PM Tim Shoppa wrote: > I don't think clouds is the direct cause, but of course clouds in the sky > can be correlated with wet foliage. > > Especially if the GPS Field Of View has a lot of angle taken up by tree > canopy, wet foliage can substantially degrade not just GPS reception but > other VHF and UHF signals. > > I notice this the most in the fall when the leaves are large and mature and > are start losing their waxy coat, but have not yet fallen. > > Even after all the leaves have fallen, wet branches have attenuation > ability as well. > > Some research papers have connected windy conditions with UHF attenuation > especially deep fading as well ( > https://ieeexplore.ieee.org/document/1337081 > ). > > Tim N3QE > > On Tue, Oct 22, 2019 at 2:01 AM Dana Whitlow > wrote: > > > A friend of mine living in SE lower Michigan recently bought > > a Geppetto GPS clock, and swears that it tends to lose > > satellite lock on cloudy days but does OK on sunny days. > > > > He is admittedly using a very poorly-sited antenna, > > placed in a window because his house has aluminum > > siding. He reports that his Garmin handheld GPS > > has much less trouble acquiring and maintaining lock > > on cloudy days than does the Geppetto, but still tends > > to show higher levels of probable position error on > > cloudy days. I don't yet know if he takes the Garmin > > outside for these comparisons. > > > > Is this a real phenomenon, or is my friend just imagining > > things? > > > > Meanwhile I think I have finally persuaded him to install > > the antenna outside on the roof. > > > > Dana(K8YUM) > > ___ > > 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. > ___ 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] Do ordinary clouds adversely affect GPS reception?
I don't think clouds is the direct cause, but of course clouds in the sky can be correlated with wet foliage. Especially if the GPS Field Of View has a lot of angle taken up by tree canopy, wet foliage can substantially degrade not just GPS reception but other VHF and UHF signals. I notice this the most in the fall when the leaves are large and mature and are start losing their waxy coat, but have not yet fallen. Even after all the leaves have fallen, wet branches have attenuation ability as well. Some research papers have connected windy conditions with UHF attenuation especially deep fading as well (https://ieeexplore.ieee.org/document/1337081 ). Tim N3QE On Tue, Oct 22, 2019 at 2:01 AM Dana Whitlow wrote: > A friend of mine living in SE lower Michigan recently bought > a Geppetto GPS clock, and swears that it tends to lose > satellite lock on cloudy days but does OK on sunny days. > > He is admittedly using a very poorly-sited antenna, > placed in a window because his house has aluminum > siding. He reports that his Garmin handheld GPS > has much less trouble acquiring and maintaining lock > on cloudy days than does the Geppetto, but still tends > to show higher levels of probable position error on > cloudy days. I don't yet know if he takes the Garmin > outside for these comparisons. > > Is this a real phenomenon, or is my friend just imagining > things? > > Meanwhile I think I have finally persuaded him to install > the antenna outside on the roof. > > Dana(K8YUM) > ___ > 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] Do ordinary clouds adversely affect GPS reception?
Andy, Isn't DirecTV downlinking around 12 GHz? Yet GPS L1 is at only ~1575 MHz. That's a huge difference with regard to scattering losses, and probably a fair amount of difference for water absorption losses as well. I've recommended that my old friend try putting his GPS antenna up in the attic as close to the peak of the roof as he can do. Thanks, Dana On Wed, Oct 23, 2019 at 12:01 PM Andy wrote: > Having had DirecTV on the roof for a few years, and having experienced > regular significant signal loss events during heavy rain and snow (loss of > reception was a rather good predictor that "the skies were about to open > up" with rain), I can confirm that signal strength deteriorates noticeably > during these events. They are in the same general frequency range. There > are distinct frequencies where the loss is even more significant. > > DirecTV probably tells you that this doesn't happen, but they are wrong; > but that's their salesmen speaking. Experience shows that it's real. When > it rains, I could watch the signal levels drop on their meters, then watch > the channel banks disappear. > > If someone had reasonably good GPS reception, then the signal loss might be > small enough to go unnoticed by the majority of users. If your friend's > reception was already near borderline, then it should be obvious that any > little bit can put it over the top. I think your friend did not imagine > it. I think the loss is more than a few dBs when it's raining, not > trivial. It's probably small when it is just cloudy, but like I say, under > the right conditions even a small change can put it over the top. > > Andy > ___ > 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] Do ordinary clouds adversely affect GPS reception?
Having had DirecTV on the roof for a few years, and having experienced regular significant signal loss events during heavy rain and snow (loss of reception was a rather good predictor that "the skies were about to open up" with rain), I can confirm that signal strength deteriorates noticeably during these events. They are in the same general frequency range. There are distinct frequencies where the loss is even more significant. DirecTV probably tells you that this doesn't happen, but they are wrong; but that's their salesmen speaking. Experience shows that it's real. When it rains, I could watch the signal levels drop on their meters, then watch the channel banks disappear. If someone had reasonably good GPS reception, then the signal loss might be small enough to go unnoticed by the majority of users. If your friend's reception was already near borderline, then it should be obvious that any little bit can put it over the top. I think your friend did not imagine it. I think the loss is more than a few dBs when it's raining, not trivial. It's probably small when it is just cloudy, but like I say, under the right conditions even a small change can put it over the top. Andy ___ 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] Do ordinary clouds adversely affect GPS reception?
Hi jimlux -- unfortunately my domain expertise is in the digital domain (computer science) and I'm having a hard time in following this paper. I do understand that "space weather", i.e. CMEs (coronal mass ejections) will significantly impact GPS/GLONASS operations when the charged particles reach earth. One question I would have for you is on the ionospheric delays due to weather conditions like moderate or heavy rain, thunderstorms and more severe weather fronts. My understanding of it is that when it comes to GPS usage for positioning purposes, the use of DGPS or some kind of augmentation system like WAAS provides "good enough" corrections to compensate for ionospheric perturbations. Whereas for timing applications, using stationary mode (i.e. either manually programming station coordinates into the GPS receiver or having the GPS receiver compute them over several hours by averaging out positioning data) is enough for "good" enough timing measurements. How much is "good enough" is not quite clear to me. What would be the magnitude of timing errors with GPS in stationary mode, assuming my understanding of stationary mode is correct? My current Oscilloquartz DGPS, BG7TBL DGPS and GPS + Symmetricom BCP 635 timing board setups gives me an estimated best time accuracy in the order of 5 to 50 microseconds (my own estimate -- unfortunately I don't have access to a lab with calibrated reference cesium oscillators), which is enough for my "time-nuts" hobby. I wonder if I would be able to measure ionospheric delays -- perhaps I could measure them by comparing the difference of my "well known" GPS coordinates once Oscilloquartz DGPS locks in stationary mode versus the GPS coordinates I receive with a UBLOX-7 vanilla receiver? Apologies for the many questions. -- Fio Cattaneo Universal AC, can Entropy be reversed? -- "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER." On Tue, Oct 22, 2019 at 6:06 AM jimlux wrote: > > On 10/22/19 1:13 AM, Poul-Henning Kamp wrote: > > > > In message > > , > > Fiorenzo Cattaneo writes: > > > >> Any kind of atmospheric disturbance has a measurable effect on GPS > >> space and time precision, [...] > > > > Actually, it's even simpler than that: > > > > Any electrical charge in the freshnell-zone between the two antennas > > delays the signal. > > > > In practice that means "any ion ..." > > > > Rain clouds harbour significant ionization, long before they become > > thunderstorms. > > > That's still a pretty small effect for RF propagation at L-band > > and here's a paper discussing just such effects > https://iopscience.iop.org/article/10.1088/1742-6596/1112/1/012021/pdf > > what happens here is that charge in a large thunderstorm affects the ion > density in the ionosphere. > > However, I don't think that's "cloudy day vs sunny day" > > > > > > > > Apart from that, the lower atmosphere is pretty predictable with > > respect to ionization. > > > > > ___ > 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] Do ordinary clouds adversely affect GPS reception?
On 10/22/19 1:13 AM, Poul-Henning Kamp wrote: In message , Fiorenzo Cattaneo writes: Any kind of atmospheric disturbance has a measurable effect on GPS space and time precision, [...] Actually, it's even simpler than that: Any electrical charge in the freshnell-zone between the two antennas delays the signal. In practice that means "any ion ..." Rain clouds harbour significant ionization, long before they become thunderstorms. That's still a pretty small effect for RF propagation at L-band and here's a paper discussing just such effects https://iopscience.iop.org/article/10.1088/1742-6596/1112/1/012021/pdf what happens here is that charge in a large thunderstorm affects the ion density in the ionosphere. However, I don't think that's "cloudy day vs sunny day" Apart from that, the lower atmosphere is pretty predictable with respect to ionization. ___ 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] Do ordinary clouds adversely affect GPS reception?
On 10/22/19 2:23 AM, Jim Palfreyman wrote: I see no attenuation at 1376 MHz (close to GPS frequency) when observing pulsars with a radio telescope. Even the brightest pulsar (Vela) is so much fainter than a GPS signal which boom in when they happen to pass into the telescope's beam. It definitely happens at higher frequencies though. Up around 20 GHz it's a different story. On a sensitive receiver I operated at 13.402 GHz in New Mexico, I could easily tell when it was overcast or not by the noise temperature. There was some discussion about whether we were seeing the physical temperature of the clouds, or we were seeing a reflection of the earth off the water particles in the clouds. We didn't go any further, since our project was to measure a radar signal, but it was interesting. ___ 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] Do ordinary clouds adversely affect GPS reception?
On 10/21/19 10:06 PM, Dana Whitlow wrote: A friend of mine living in SE lower Michigan recently bought a Geppetto GPS clock, and swears that it tends to lose satellite lock on cloudy days but does OK on sunny days. He is admittedly using a very poorly-sited antenna, placed in a window because his house has aluminum siding. He reports that his Garmin handheld GPS has much less trouble acquiring and maintaining lock on cloudy days than does the Geppetto, but still tends to show higher levels of probable position error on cloudy days. I don't yet know if he takes the Garmin outside for these comparisons. Is this a real phenomenon, or is my friend just imagining things? Clpuds and even light rain won't change the received SNR very much at L band. I'm going to guess that there's something that is cloud correlated - open and closing ventilation shutters? Soil or ground cover moisture changes, which changes the strength of a multipath signal. Some sort of thermal expansion effects changing the spacing of siding panels when the sun shines on them vs no. Meanwhile I think I have finally persuaded him to install the antenna outside on the roof. Dana(K8YUM) ___ 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] Do ordinary clouds adversely affect GPS reception?
In message , Fiorenzo Cattaneo writes: >Any kind of atmospheric disturbance has a measurable effect on GPS >space and time precision, [...] Actually, it's even simpler than that: Any electrical charge in the freshnell-zone between the two antennas delays the signal. In practice that means "any ion ..." Rain clouds harbour significant ionization, long before they become thunderstorms. Apart from that, the lower atmosphere is pretty predictable with respect to ionization. -- 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] Do ordinary clouds adversely affect GPS reception?
I see no attenuation at 1376 MHz (close to GPS frequency) when observing pulsars with a radio telescope. Even the brightest pulsar (Vela) is so much fainter than a GPS signal which boom in when they happen to pass into the telescope's beam. It definitely happens at higher frequencies though. Up around 20 GHz it's a different story. On Tue, 22 Oct 2019 at 17:01, Dana Whitlow wrote: > A friend of mine living in SE lower Michigan recently bought > a Geppetto GPS clock, and swears that it tends to lose > satellite lock on cloudy days but does OK on sunny days. > > He is admittedly using a very poorly-sited antenna, > placed in a window because his house has aluminum > siding. He reports that his Garmin handheld GPS > has much less trouble acquiring and maintaining lock > on cloudy days than does the Geppetto, but still tends > to show higher levels of probable position error on > cloudy days. I don't yet know if he takes the Garmin > outside for these comparisons. > > Is this a real phenomenon, or is my friend just imagining > things? > > Meanwhile I think I have finally persuaded him to install > the antenna outside on the roof. > > Dana(K8YUM) > ___ > 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] Do ordinary clouds adversely affect GPS reception?
Any kind of atmospheric disturbance has a measurable effect on GPS space and time precision, the question is more about how much the impact is. Presuming that the GPS receiver is stationary, the antenna has a clear visibility of the sky, then "ordinary weather" like clouds, moderate rain or snow, should not have a large effect. The GPS signal will be attenuated by rain and snow, but precision should not be impacted provided that the GPS receiver is operating in stationary mode (I'm referring to stationary mode as I presume the goal here is to get precise GPS or UTC time, not position). The signal quality will definitely be very poor if keeping the antenna window mounted, especially if there are nearby metal surfaces. I see a significant difference in quality between an antenna by the window in my basement (up to and including complete periodic loss of GPS lock) versus keeping the antenna in the attic (composition roof in my case). In the basement there is only 1/4 sky direct view as opposed to the attic which has essentially unobstructed view. The antenna in the attic never gave me trouble. I have not compared the difference in signal quality between an attic mounted antenna versus an externally mounted antenna so I don't know about that. I haven't seen loss of GPS lock under light to moderate rain, let alone simple clouds. Heavy rain doesn't seem to be a big problem either. Your friend's experience of losing GPS lock on cloudy days seems very, very strange to me. Barring malfunctioning receiver or a defective antenna, I would first make sure to have the antenna externally mounted, or at least in the attic if the roof is composition or wood shingles. Your friend could collect NMEA data on PDOP, HDOP, satellites view with signal strengths and how many satellites are tracked and part of the GPS solution. I definitely see better signal quality with the BG7TBL GPSDO as opposed to a Garmin 18x with serial output and PPS. The Oscilloquartz Star IV GPSDO seems to give even better results than the BG7TBL, although having just recently bought them, I don't have enough statistical data. Another thing to try would be setting the minimum elevation threshold for a satellite to be included in the position and time solution to make sure to avoid surrounding hills or mountains, if any. Both the Oscilloquartz Star IV GPSDO as well as the plain old UBLOX-7 GPS receiver with PPS allow you to set the minimum elevation threshold. The BG7TBL GPSDO does not allow you to do that. You should look at the specifications of the two GPS receivers. At the very high end of measurements, there are observable effects during weather fronts -- which are of course much more severe than simply ordinary clouds or light rain. This article is rather dated but very interesting. With dual frequency receivers (L1 and L2 bands) they can observe precision errors down to the order of about 3 - 10 centimeters : http://geodesy.unr.edu/publications/gpsworld.may98.pdf -- Fio Cattaneo Universal AC, can Entropy be reversed? -- "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER." On Mon, Oct 21, 2019 at 11:01 PM Dana Whitlow wrote: > > A friend of mine living in SE lower Michigan recently bought > a Geppetto GPS clock, and swears that it tends to lose > satellite lock on cloudy days but does OK on sunny days. > > He is admittedly using a very poorly-sited antenna, > placed in a window because his house has aluminum > siding. He reports that his Garmin handheld GPS > has much less trouble acquiring and maintaining lock > on cloudy days than does the Geppetto, but still tends > to show higher levels of probable position error on > cloudy days. I don't yet know if he takes the Garmin > outside for these comparisons. > > Is this a real phenomenon, or is my friend just imagining > things? > > Meanwhile I think I have finally persuaded him to install > the antenna outside on the roof. > > Dana(K8YUM) > ___ > 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.
[time-nuts] Do ordinary clouds adversely affect GPS reception?
A friend of mine living in SE lower Michigan recently bought a Geppetto GPS clock, and swears that it tends to lose satellite lock on cloudy days but does OK on sunny days. He is admittedly using a very poorly-sited antenna, placed in a window because his house has aluminum siding. He reports that his Garmin handheld GPS has much less trouble acquiring and maintaining lock on cloudy days than does the Geppetto, but still tends to show higher levels of probable position error on cloudy days. I don't yet know if he takes the Garmin outside for these comparisons. Is this a real phenomenon, or is my friend just imagining things? Meanwhile I think I have finally persuaded him to install the antenna outside on the roof. Dana(K8YUM) ___ 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.
