Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Jim wrote: That's why the FCC granted a conditional waiver of the rules. It was politically expedient, and I would imagine that the engineers at the FCC thought there's no way they'll be able to demonstrate no interference The conditional waiver of the rules was not so that the spectrum could be used for terrestrial service -- that was already the rule (ancillary terrestrial component). The conditional waiver was so LS could sell terrestrial-only service (it was a conditional waiver of the integrated service rule that would otherwise have required the terrestrial service to be available only to customers of the satellite service). The Commission not only thought LS would demonstrate non-interference, it put its thumb on the scale until the public outcry became too loud to ignore (the GPS interests took forever to wake up -- that didn't happen until all of the comment periods were long closed). It just didn't matter what the staff engineers thought -- which is business as usual at the FCC. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Hello Everyone, Thanks for the feedback - I certainly have a lot to think about. Seems eBay could be a preferred vendor for antennas. I don't need anything too fancy - but I would like something that does OK in wind and rain, I don't have to worry too much about snow at my current location - and I do have a mount point that will keep my cable length short - under 20 feet if I do it properly. Sounds like the '26dB' model will be fine. Is there a preferred vendor anyone wants to recommend? A reseller on eBay may not fit that category. Please e-mail me directly if you don't feel comfortable providing what could be construed as an opinion to a wide audience. Please, continue this discussion. It is quite interesting and I will try not to interfere too much. To say that I am a newbie or novice in the area of GPS is an understatement. I am finding what GPS satellites transmit quite fascinating. Thanks! John Westmoreland AJ6BC On Sun, Sep 15, 2013 at 10:24 PM, David J Taylor david-tay...@blueyonder.co.uk wrote: From: Bob Camp Hi All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape. No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus…. Bob ==**= .. and would the true time-nut add the delay through the filter to the delay in the feeder co-ax? I suppose that means you could only buy an antenna with a stated, calibrated delay? Limits the choice, a little! Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Hi Once the sat's all arrive at the antenna, a fixed delay (in general) does not impact things a lot. The gotcha with the filter is that it's delay is unequal across the GPS band. Doppler puts the sat's all over the place. That gives some more delay than others. Having unequal delay on sats is indeed an issue. As the filter changes delay with temperature things will move a bit more. Since it's a frequency high on approach / low on departure sort of thing it will average out on each pass. The main impact would be an increase in wander. Bob On Sep 16, 2013, at 1:24 AM, David J Taylor david-tay...@blueyonder.co.uk wrote: From: Bob Camp Hi All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape. No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus…. Bob === .. and would the true time-nut add the delay through the filter to the delay in the feeder co-ax? I suppose that means you could only buy an antenna with a stated, calibrated delay? Limits the choice, a little! Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
From: Bob Camp Hi Once the sat's all arrive at the antenna, a fixed delay (in general) does not impact things a lot. The gotcha with the filter is that it's delay is unequal across the GPS band. Doppler puts the sat's all over the place. That gives some more delay than others. Having unequal delay on sats is indeed an issue. As the filter changes delay with temperature things will move a bit more. Since it's a frequency high on approach / low on departure sort of thing it will average out on each pass. The main impact would be an increase in wander. Bob Bob, I am thinking about exact time measurement - getting your PPS edge exactly on the nanosecond. People can add in the length of the cable as an offset, so they must also need to enter any delay through any filters, mustn't they? Agreed that for position alone it doesn't matter as much. It's the antenna's approximate position which will be measured. Your points about dispersion in the filter, and temperature coefficient of delay are good ones. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
On 9/15/13 10:24 PM, David J Taylor wrote: From: Bob Camp Hi All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape. No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus…. Bob === .. and would the true time-nut add the delay through the filter to the delay in the feeder co-ax? I suppose that means you could only buy an antenna with a stated, calibrated delay? Limits the choice, a little! Of course they would factor all this in. That's why the UNAVCO site has all the phase center locations and delay behavior for the various antennas. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
On 9/16/13 6:03 AM, David J Taylor wrote: I am thinking about exact time measurement - getting your PPS edge exactly on the nanosecond. People can add in the length of the cable as an offset, so they must also need to enter any delay through any filters, mustn't they? Agreed that for position alone it doesn't matter as much. It's the antenna's approximate position which will be measured. Your points about dispersion in the filter, and temperature coefficient of delay are good ones. It's trying to get nice flat group delay in the filter that causes all the issues with Light Squared. *small*, *inexpensive* brickwall bandpass filters tend not to have nice delay properties, or at least ones that are temperature stable. Spectrum regulators know this, of course, and assign adjacent services accordingly. If you're only worrying at the few nanosecond level, you probably don't have to take into account continental drift (periodic resurveys of location to account for several cm/year?) and solid earth tides (on the order of 30-50 cm). And, really, for a lot of applications, you're interested in relative timing, so the solid earth tide shift of 1-2 ns every day isn't a big deal. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
From: Jim Lux Of course they would factor all this in. That's why the UNAVCO site has all the phase center locations and delay behavior for the various antennas. === Didn't know about: http://www.ngs.noaa.gov/ANTCAL/ Jim, so thanks for that. David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Jim wrote: Spectrum regulators know this, of course, and assign adjacent services accordingly. They do? Remember, it was the FCC that came up with the idea of using the Mobile Satellite Service L-band downlink spectrum for terrestrial broadband service in the first place (setting the stage for the LightSquared debacle). IMO, the Communications Act should be amended to require at least one FCC Commissioner to be an engineer, so that there would be at least the theoretical possibility of technical sanity checks at the Commission level. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Hi Bob, Doppler shift is +-3.5kHz. Bandwidth for the CA signal is ca 2MHz, narrow correlator receivers takes in 10MHz to mitigate multipath errors. So doppler spread is about 1/1000 of the spread spectrum signal. Does the filter delay really change that much with 7kHz total doppler variation? For Glonass receivers this is more of a problem, since Glonass is a FDMA system. -- Björn Hi Once the sat's all arrive at the antenna, a fixed delay (in general) does not impact things a lot. The gotcha with the filter is that it's delay is unequal across the GPS band. Doppler puts the sat's all over the place. That gives some more delay than others. Having unequal delay on sats is indeed an issue. As the filter changes delay with temperature things will move a bit more. Since it's a frequency high on approach / low on departure sort of thing it will average out on each pass. The main impact would be an increase in wander. Bob On Sep 16, 2013, at 1:24 AM, David J Taylor david-tay...@blueyonder.co.uk wrote: From: Bob Camp Hi All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape. No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus . Bob === .. and would the true time-nut add the delay through the filter to the delay in the feeder co-ax? I suppose that means you could only buy an antenna with a stated, calibrated delay? Limits the choice, a little! Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Hi On Sep 16, 2013, at 9:48 AM, Jim Lux jim...@earthlink.net wrote: On 9/16/13 6:03 AM, David J Taylor wrote: I am thinking about exact time measurement - getting your PPS edge exactly on the nanosecond. People can add in the length of the cable as an offset, so they must also need to enter any delay through any filters, mustn't they? Agreed that for position alone it doesn't matter as much. It's the antenna's approximate position which will be measured. Your points about dispersion in the filter, and temperature coefficient of delay are good ones. It's trying to get nice flat group delay in the filter that causes all the issues with Light Squared. *small*, *inexpensive* brickwall bandpass filters tend not to have nice delay properties, or at least ones that are temperature stable. Spectrum regulators know this, of course, and assign adjacent services accordingly. If you're only worrying at the few nanosecond level, you probably don't have to take into account continental drift (periodic resurveys of location to account for several cm/year?) and solid earth tides (on the order of 30-50 cm). And, really, for a lot of applications, you're interested in relative timing, so the solid earth tide shift of 1-2 ns every day isn't a big deal. Well maybe it is…. If 1) Your antenna is ~ 2 ns out of position 2) you have a small number of sats 3) Everything else is doing very well Then as you take sat's in and out of the mix, you will could get 2 ns more pop than you would have otherwise. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Hello Everyone, While we're on the subject - not to get too far off on a tangent - I have been doing 'web-research' on this - but can someone recommend a great site or reference for the specifications of the GPS signaling sent down by a GPS satellite? For instance, I learned that PPS for a military satellite and a civilian satellite are not the same thing. PPS meaning Precise Positioning Service. Thanks and 73's, John AJ6BC (Ham call sign) On Mon, Sep 16, 2013 at 2:51 PM, Bob Camp li...@rtty.us wrote: Hi On Sep 16, 2013, at 9:48 AM, Jim Lux jim...@earthlink.net wrote: On 9/16/13 6:03 AM, David J Taylor wrote: I am thinking about exact time measurement - getting your PPS edge exactly on the nanosecond. People can add in the length of the cable as an offset, so they must also need to enter any delay through any filters, mustn't they? Agreed that for position alone it doesn't matter as much. It's the antenna's approximate position which will be measured. Your points about dispersion in the filter, and temperature coefficient of delay are good ones. It's trying to get nice flat group delay in the filter that causes all the issues with Light Squared. *small*, *inexpensive* brickwall bandpass filters tend not to have nice delay properties, or at least ones that are temperature stable. Spectrum regulators know this, of course, and assign adjacent services accordingly. If you're only worrying at the few nanosecond level, you probably don't have to take into account continental drift (periodic resurveys of location to account for several cm/year?) and solid earth tides (on the order of 30-50 cm). And, really, for a lot of applications, you're interested in relative timing, so the solid earth tide shift of 1-2 ns every day isn't a big deal. Well maybe it is…. If 1) Your antenna is ~ 2 ns out of position 2) you have a small number of sats 3) Everything else is doing very well Then as you take sat's in and out of the mix, you will could get 2 ns more pop than you would have otherwise. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
On 9/16/13 6:43 PM, John C. Westmoreland, P.E. wrote: Hello Everyone, While we're on the subject - not to get too far off on a tangent - I have been doing 'web-research' on this - but can someone recommend a great site or reference for the specifications of the GPS signaling sent down by a GPS satellite? For instance, I learned that PPS for a military satellite and a civilian satellite are not the same thing. PPS meaning Precise Positioning Service. It's all defined in IS-GPS-200G, IS-GPS-800C, IS-GPS-705C, and IS-GPS-060B http://www.navcen.uscg.gov/?pageName=gpsReferenceInfo Brought to you by your friends at Department of Homeland Security (see, not everything they do is horrible, TSA notwithstanding)... Semper Paratus... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
On 9/16/13 9:13 AM, David J Taylor wrote: From: Jim Lux Of course they would factor all this in. That's why the UNAVCO site has all the phase center locations and delay behavior for the various antennas. === Didn't know about: http://www.ngs.noaa.gov/ANTCAL/ For what it's worth, we've been using a lot of AR25s recently at JPL.. 3 band antenna, multiband choke ring, not too horribly expensive (for a brand new geodetic quality antenna/LNA) More than a Ford Fiesta, Less than a BMW. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
Thanks Jim. Best Regards, John W. On Mon, Sep 16, 2013 at 9:25 PM, Jim Lux jim...@earthlink.net wrote: On 9/16/13 6:43 PM, John C. Westmoreland, P.E. wrote: Hello Everyone, While we're on the subject - not to get too far off on a tangent - I have been doing 'web-research' on this - but can someone recommend a great site or reference for the specifications of the GPS signaling sent down by a GPS satellite? For instance, I learned that PPS for a military satellite and a civilian satellite are not the same thing. PPS meaning Precise Positioning Service. It's all defined in IS-GPS-200G, IS-GPS-800C, IS-GPS-705C, and IS-GPS-060B http://www.navcen.uscg.gov/?**pageName=gpsReferenceInfohttp://www.navcen.uscg.gov/?pageName=gpsReferenceInfo Brought to you by your friends at Department of Homeland Security (see, not everything they do is horrible, TSA notwithstanding)... Semper Paratus... __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
The 26 dB antenna I use has a 'vertical spiral' element under the 'egg shaped dome'. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Jim Lux Sent: Sunday, September 15, 2013 6:55 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation On 9/15/13 4:33 PM, Bob Camp wrote: Hi All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape. I don't know that the thermal expansion effects on the ceramic or the antenna elements would be all that huge (it's a wideband low-Q device, after all), compared, say, to the CTE effects on the coax, or the temperature effects on components inside the LNA. No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus.. I'd guess that the crossed drooped dipole or quad helix or quad spirals might have a more consistent phase center as a function of look angle. And a bigger radome is always good, because crud on the radome is farther away and will have less effect. Hi Bob, Many of the midrange antennas have one or more significant differences from the cheap pucks. Firstly they generally have better filtering, many pucks have none. This is important if you are co-located with transmitters. Yes. We have some timing type antennas at work which are effectively jammed by a cellphone near by. And, the geodetic GPS folks are not looking forward to wider deployment of LTE/4G, which uses bands closer to the GPS bands (presumably the 1700 MHz ones), although keeping the phones 10 meters or so away seems to be enough to fix that (barring Light Cubed rising from the dead carcass of Light Squared) Secondly many use quad-helix antenna elements rather than the off-set feed ceramic patches in the pucks. The heical elements have better control of the radiation pattern and along with a larger radome are less likely to be affected by external contamination. I also wonder how the tuning of a cheap ceramic patch holds up over the range of temperatures seen by a fixed antenna. Modern receivers compensate well for poor antennas, try using an early receiver on an internal patch and you won't get great results. You might be able to design a patch that self compensates.. the antenna gets bigger as temperature goes up, but also moves away from the ground plane AND the effective epsilon gets lower because the material is less dense. In any case, it's a small effect. ALumina has a CTE of 6-8 and Copper is about 17, so the thermal effect of an air dielectric copper antenna might be bigger than a plated onto alumina one. Robert G8RPI. From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, 15 September 2013, 22:19 Subject: Re: [time-nuts] Req: Decent GPS Antenna Active/Passive Recommendation Hi Worth noting: The mid class antennas are not a lot different electrically than the low end antennas. The main differences are mechanical: 1) You get a much more weather tight housing 2) You get a rational way to mount the antenna 3) There's a connector on it so you can put a good piece of coax on it 4) The housing *may* be more immune to snow / ice buildup and bird nests RDR Electronics on the usual auction site appears to be selling some nice ones at the moment. Bob On Sep 15, 2013, at 4:36 PM, Hal Murray hmur...@megapathdsl.net wrote: j...@westmorelandengineering.com said: Well, I need something that I can put outside, in the weather, with my verticals, and other antennas. I am a Ham radio enthusiast, and I want something I can properly mount and can be an all-weather device and can live happily 'in the farm' so to speak. I split GPS antennas into 3 clumps. At the low cost end are the small mouse or hockey-puck type units, usually with a magnetic mount. They typically come with 10 or 15 feet of thin (lossy) cable. Ballpark price is $10. In the middle are the typical cones that you see on cell phone stations. The Lucent 26 dB ones are common on eBay. Ballpark price is $50. The same or very similar thing is also available with different brand names. Some of them come with a pipe mounting setup such that the coax and connector is inside the pipe and out of the weather. http://www.megapathdsl.net/~hmurray/time-nuts/Lucent-Antenna.jpg At the top end are the choke ring antennas intended for surveying. They are mostly out of my price range so I haven't looked carefully. -- I haven't seen a GPS antenna without an amplifier, but I haven't been looking. They also include a filter. See the LightSquared flame-wars for a discussion of filters. I think the choke ring
Re: [time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation
From: Bob Camp Hi All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape. No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus…. Bob === .. and would the true time-nut add the delay through the filter to the delay in the feeder co-ax? I suppose that means you could only buy an antenna with a stated, calibrated delay? Limits the choice, a little! Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
