Re: [time-nuts] GPS active antenna delay ?
On 18 Feb 2015 04:20, Tom McDermott tom.n...@gmail.com wrote: Hi Dave - agree that VNA is one good way to measure the delay. If required accuracy is less than about 0.5 nsec, then Tx antenna to Rx antenna mutual impedance starts to become an issue. I don't see why. The two antennas can (and should) be a reasonable distance apart. There will be no significant interaction between them. The biggest problem might be reflections from the ground. Above about 1 nsec error probably most of these can be ignored. No access to a vector VNA that works at 1.5 GHz. unfortunately. If it was a 10-15 minute job I would not mind doing it for you as I have several VNAs that cover 1.5 GHz. But it would take quite a bit of time to build the appropriate antenna then mount the two in such a way that reflections were not an issue. It means errecting two masts on non conductive poles. It is basically a days work. If you have a spectrum analyzer, you could probably see the bandwidth of the filters from looking at the noise spectrum. From what someone wrote earlier, with typical delays vs bandwidth, you could perhaps get a rough estimate of the delay. I just wonder if there's some other way, especially if one has multiple GPS receivers, a fast scope but I can't think of anything. A VNA is the obvious tool to me, but I would not be surprised if there was some trick that could be used without a VNA. Thanks for the pointer to the Keysight VNA discussion list. No problem. For answers to VNA related questions, the Keysight forums are the place to go. Neither Anrisu or RS have anything like this. -- Tom, N5EG Dave. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On Wed, 18 Feb 2015 07:24:32 -0800 Jim Lux jim...@earthlink.net wrote: [1] http://miniradiosolutions.com/minivna-tiny And tough to find any substantive information on the hardware design. I poked around for a few minutes, but all I was able to find was software user manuals, but no hardware description. I assume that it's the usual 2 port, 1 direction thing.. A DDS for the RF source, and some sort of dual channel detector with directional couplers or a bridge on the output port When i had one on my desk, i opened it up, but apparently i forgot to take pictures. From what i remember, i think it works either similar to the VNWA design done by DG8SAQ[1,2] or by N2PK[3]. The tinyVNA can only do S11 and S12, lacking the additional source at the second port. Attila Kinali [1] http://sdr-kits.net/DG8SAQ/VNWA/baier_VNWA10_QEX.pdf [2] http://sdr-kits.net/DG8SAQ/VNWA/QEX-Letters.pdf [3] http://n2pk.com/VNA/n2pk_vna_pt_1_ver_c.pdf -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On Thu, 19 Feb 2015 10:51:04 +0100 Attila Kinali att...@kinali.ch wrote: When i had one on my desk, i opened it up, but apparently i forgot to take pictures. From what i remember, i think it works either similar to the VNWA design done by DG8SAQ[1,2] or by N2PK[3]. The tinyVNA can only do S11 and S12, lacking the additional source at the second port. Correction, a little bit of googling brought up [1] (sorry, mostly german). The discussion contains top[2], bottom[3] pictures and the block diagram[4] Attila Kinali [1] http://www.mikrocontroller.net/topic/351273 [2] http://www.mikrocontroller.net/attachment/238726/image.jpg [3] http://www.mikrocontroller.net/attachment/238727/image.jpg [4] http://www.mikrocontroller.net/attachment/243812/vna_scm_col_v3.jpg -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On 2/19/15 1:59 AM, Attila Kinali wrote: On Thu, 19 Feb 2015 10:51:04 +0100 Attila Kinali att...@kinali.ch wrote: When i had one on my desk, i opened it up, but apparently i forgot to take pictures. From what i remember, i think it works either similar to the VNWA design done by DG8SAQ[1,2] or by N2PK[3]. The tinyVNA can only do S11 and S12, lacking the additional source at the second port. Correction, a little bit of googling brought up [1] (sorry, mostly german). The discussion contains top[2], bottom[3] pictures and the block diagram[4] Thanks.. I can read the German, so that's ok. I just have to look up some of the part numbers. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On 2/18/15 1:49 AM, Attila Kinali wrote: You could try tinyVNA[1]. I have used it once, it has some quirks (it's half hobby, half commercial project and that shows) but works otherwise. I have no idea how accurate it is. Attila Kinali [1] http://miniradiosolutions.com/minivna-tiny And tough to find any substantive information on the hardware design. I poked around for a few minutes, but all I was able to find was software user manuals, but no hardware description. I assume that it's the usual 2 port, 1 direction thing.. A DDS for the RF source, and some sort of dual channel detector with directional couplers or a bridge on the output port. What would be interesting is to know what detection method they're using.. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On Tue, 17 Feb 2015 18:33:24 -0800 Tom McDermott tom.n...@gmail.com wrote: Hi Dave - agree that VNA is one good way to measure the delay. If required accuracy is less than about 0.5 nsec, then Tx antenna to Rx antenna mutual impedance starts to become an issue. Above about 1 nsec error probably most of these can be ignored. No access to a vector VNA that works at 1.5 GHz. unfortunately. You could try tinyVNA[1]. I have used it once, it has some quirks (it's half hobby, half commercial project and that shows) but works otherwise. I have no idea how accurate it is. Attila Kinali [1] http://miniradiosolutions.com/minivna-tiny -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
HI Tom... Good to see you getting into Time-Nuttery! How accurately do you need to know the delay? For absolute time, it is important, but it doesn’t really help much with position since the calculation doesn't know which direction your receiver is located from the antenna. For a time-base it probably doesn’t matter much either; the PPS will simply be out of sync with 'real' seconds. The above comments will likely get me chewed up by the gnat's-eyelash crowd but that's how we mere mortals learn. My first guess on the prop delay of the antenna would be the reciprocal of the bandwidth, but that is just a shot at getting into the ballpark. No doubt it varies over the BW and the amplifier adds a bit. Which leads back to how accurately do you need to know. I have some ideas for helping you out with the measurements if you want to contact me off list. My TAPR email will work just fine. Tom Holmes, N8ZM -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Tom McDermott Sent: Tuesday, February 17, 2015 9:33 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] GPS active antenna delay ? Hi Dave - agree that VNA is one good way to measure the delay. If required accuracy is less than about 0.5 nsec, then Tx antenna to Rx antenna mutual impedance starts to become an issue. Above about 1 nsec error probably most of these can be ignored. No access to a vector VNA that works at 1.5 GHz. unfortunately. Normally I would use a difference measurement (substitute known reference Rx antenna for Rx under test, and difference the two), but am afraid that the (reference Rx-to-Tx) and the (Rx under test-to-Tx) might have different mutual Z. Thanks for the pointer to the Keysight VNA discussion list. -- Tom, N5EG On Mon, Feb 16, 2015 at 6:12 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 7 Feb 2015 19:18, Tom McDermott tom.n...@gmail.com wrote: Has anyone on the list measured or otherwise estimated the active antenna delay including the amp and filters? -- Tom, N5EG I have never done this, but suspect that using a VNA is the best way to go. With a simple passive dipole on one port, and the active antenna and cable on the second port, a transmission measurement (S21) is probably the way to go. But I was unsure of exactly how to do it. Your question prompted me to ask on the Keysight VNA forum. There's a reply by Dr. Joel Dunsmore - one of the worlds leading authorities on VNAs. http://www.keysight.com/owc_discussions/thread.jspa?threadID=39151tstart=0 He asks what accuracy is needed. Being time-nuts, I think the answer is as high as possible. He writes With this method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we will have to be much more careful. You might want to contribute to that forum post. Dave. ___ 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] GPS active antenna delay ?
Hi: One of the chirp receivers I worked with was connected to the audio output of a shortwave receiver. Since chirp transmitters sweep frequency (typically 2 to 30 MHz) you don't tune in the frequency domain but rather in the time domain and compare to a GPS based 1 PPS. This time difference can be easily converted to the distance between the chirp transmitter and your antenna. So the delay inside the shortwave receiver needs to be known in order to get accurate timing, in a similar manner to the subject active GPS antenna. http://www.prc68.com/I/RCS-5A.shtml - general chirp stuff The solution for the chirp receiver was to use a modulated RF signal into the shortwave receiver and compare the output and input signals. http://www.prc68.com/I/Chirp.shtml This could be done for an active GPS antenna by square wave modulating a carrier at the L1 frequency and feeding the antenna output to a detector. The input signal level to the antenna will need to be as high as possible without damaging it, and maybe without saturating the internal amplifier. If the output signal is still too small for the detector to have a useable output and additional RF amplifier could be inserted after the active antenna bias-T and it's propagation delay subtracted for the measured value. PS This is a good application for a Tunnel (back) diode detector because they have very wide video bandwidth (fast rise times). http://www.prc68.com/I/Aertech.shtml#TDD Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
Hi By far the simplest way to do this is to use a broadband passive antenna with a short cable. They are a $10 item on the auction sites. Compare whatever comes out of the GPS running off the cheap antenna to your “full system” pps offset. What you are doing with this comparison is no different than the VNA approach. You are just using real GPS signals in your real environment to run the test. If the only delta is the delay in the cable / antenna amp / filter / distribution amplifier (antenna locations are the same) then it all should work out. Simply put: 1) Attach gps to simple broadband antenna with short cable. You may have to play some tricks to get the antenna current detect to stop complaining. A Tee connector and a resistor are generally all that takes. 2) Measure pps offset to a local standard (possibly a GPSDO on another antenna) 3) Attach gps to real antenna and what ever cable, (at the same location as the simple antenna) 4) Measure pps offset to the same standard 5) Repeat the process until you are convinced the results make sense. I’d do at least 5 loops to be reasonably sure. If you have enough gear, you can compare multiple receivers and antennas all at one time. Swap around the antennas and “stuff”. Ultimately you will come up with relative numbers for each item. This all assumes you are running timing grade receivers with sawtooth data. It also assumes you have a counter that’s good enough to collect the data. Since all that it way cheaper than a fully calibrated microwave VNA, I don’t think that is a terribly crazy assumption. Does this matter for a “frequency nut” - nope. Will it make your GPSDO work better -nope. Could it get you slightly closer to UTC - yup. 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.
Re: [time-nuts] GPS active antenna delay ?
thol...@woh.rr.com said: How accurately do you need to know the delay? For absolute time, it is important, but it doesnât really help much with position since the calculation doesn't know which direction your receiver is located from the antenna. GPS tells you the location of the receiving antenna. Without correction, it also tells you the time the signal was received at the antenna. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
Hi Dave - agree that VNA is one good way to measure the delay. If required accuracy is less than about 0.5 nsec, then Tx antenna to Rx antenna mutual impedance starts to become an issue. Above about 1 nsec error probably most of these can be ignored. No access to a vector VNA that works at 1.5 GHz. unfortunately. Normally I would use a difference measurement (substitute known reference Rx antenna for Rx under test, and difference the two), but am afraid that the (reference Rx-to-Tx) and the (Rx under test-to-Tx) might have different mutual Z. Thanks for the pointer to the Keysight VNA discussion list. -- Tom, N5EG On Mon, Feb 16, 2015 at 6:12 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 7 Feb 2015 19:18, Tom McDermott tom.n...@gmail.com wrote: Has anyone on the list measured or otherwise estimated the active antenna delay including the amp and filters? -- Tom, N5EG I have never done this, but suspect that using a VNA is the best way to go. With a simple passive dipole on one port, and the active antenna and cable on the second port, a transmission measurement (S21) is probably the way to go. But I was unsure of exactly how to do it. Your question prompted me to ask on the Keysight VNA forum. There's a reply by Dr. Joel Dunsmore - one of the worlds leading authorities on VNAs. http://www.keysight.com/owc_discussions/thread.jspa?threadID=39151tstart=0 He asks what accuracy is needed. Being time-nuts, I think the answer is as high as possible. He writes With this method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we will have to be much more careful. You might want to contribute to that forum post. Dave. ___ 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] GPS active antenna delay ?
On 7 Feb 2015 19:18, Tom McDermott tom.n...@gmail.com wrote: Has anyone on the list measured or otherwise estimated the active antenna delay including the amp and filters? -- Tom, N5EG I have never done this, but suspect that using a VNA is the best way to go. With a simple passive dipole on one port, and the active antenna and cable on the second port, a transmission measurement (S21) is probably the way to go. But I was unsure of exactly how to do it. Your question prompted me to ask on the Keysight VNA forum. There's a reply by Dr. Joel Dunsmore - one of the worlds leading authorities on VNAs. http://www.keysight.com/owc_discussions/thread.jspa?threadID=39151tstart=0 He asks what accuracy is needed. Being time-nuts, I think the answer is as high as possible. He writes With this method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we will have to be much more careful. You might want to contribute to that forum post. Dave. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott tom.n...@gmail.com wrote: While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I would be very much interested in those papers. Could you list their titles and authors at least? I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
Attila, On 02/08/2015 11:11 AM, Attila Kinali wrote: On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott tom.n...@gmail.com wrote: While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. I've seen a few different approaches. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I would be very much interested in those papers. Could you list their titles and authors at least? Indeed. LC filters should avoid too high Q in pass-band, but should have a bunch of zeros a bit further out to punch out the stop-bands properly. SAW-filters should similarly avoid high Q notches, but there it is easy to achieve higher degree systems such that you achieve the filtering without going to high-Q systems. I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). Works great unless you have a radio amateur doing L-band (23 cm) transmissions. Here in Sweden you can transmit 1 kW in that band, just a handfull of MHz from L2. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
On 2/8/15 2:11 AM, Attila Kinali wrote: On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott tom.n...@gmail.com wrote: While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. One has to be very careful about reading group delay specs on wideband devices. Sometimes, the group delay (or its flatness/deviations from a straight line) is measured ONLY over the frequency band of interest, which might not be the filter passband. You could have wild fluctuations of phase vs frequency somewhere, but as long as dphase/dfreq is constant in the desired area, the filter/amplifier meets spec. I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). There might be a wideband (500MHz) filter in front of the LNA, and then separate narrow band filters for each of the three frequencies. The wideband filter could be LC or coupled microstripline equivalents. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
I think that the surplus HP/Agilent GPS splitters may have an SAW filter. If so, measuring the delay of one of those could yield at least an approximation. I may have that data laying around; I'll do some digging. John On 02/08/2015 05:11 AM, Attila Kinali wrote: On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott tom.n...@gmail.com wrote: While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I would be very much interested in those papers. Could you list their titles and authors at least? I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). Attila Kinali ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
j...@febo.com said: OK, so I had an HP 58535A two-port GPS splitter handy and put it on the VNA. It clearly has a filter of some sort, as shown by the S21 frequency response. The delay at the center of the passband is about 21ns, and it increases to about 26ns at the edges. Thanks. It seems a bit strange that HP didn't mention the delay. That part seems likely to be used with their GPS gear that is setup to compensate for cable delays. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
OK, so I had an HP 58535A two-port GPS splitter handy and put it on the VNA. It clearly has a filter of some sort, as shown by the S21 frequency response. The delay at the center of the passband is about 21ns, and it increases to about 26ns at the edges. That delay consists of the physical length of the signal path in the splitter, plus the effects of a 6dB amplifier, SAW filter, and a hybrid 2-way splitter. The noise in the delay plot is because I had to avoid overdriving the splitter amp, so the input signal was 40dB lower than normal for the VNA. Thus the analyzer receivers had pretty weak signals to work with (and I didn't do anything heroic to compensate, other than use a large averaging factor plus smoothing). I don't know how applicable this would be to the circuit in an antenna. I suspect the biggest difference might be due to the higher gain amp in the antenna vs. 6dB in the splitter. On 02/08/2015 08:29 AM, John Ackermann N8UR wrote: I think that the surplus HP/Agilent GPS splitters may have an SAW filter. If so, measuring the delay of one of those could yield at least an approximation. I may have that data laying around; I'll do some digging. John On 02/08/2015 05:11 AM, Attila Kinali wrote: On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott tom.n...@gmail.com wrote: While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I would be very much interested in those papers. Could you list their titles and authors at least? I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). Attila Kinali ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS active antenna delay ?
Hi all. The papers are: 1) SAW Filter Modeling in MATLAB for GNSS Receivers, S.H. Abbas, et al., IJECE Oct 2013, ISSN: 2088-2078 The authors de-embed the group delay using FFT and MATLAB. Eyeball about 15-20 nsec. for a pretty wide filter. 2) The Effects of SAW Group Delay Ripple on GPS and Glonass Signals, Simon Adams, Novatel, Inc., Calgary AB The author computes a group delay ripple of 38 nsec for a specific SAW filter due to triple-transit reflections. 3) GPS + Modernized GPS + Gallileo Signal Timing Biases, Chris Hegerty, Ed Powers, Blair Fonville, all of USNO, GPS World, March 2006 pp 49-54. Figure 2 shows group delay minima of about 65 nsec. for the RF/IF filtering. 4) Arbiter Systems Datasheet for AS0087800 active timing antenna, the datasheet is numbered PD0050600A. Arbiter systems, Paso Robles, CA. They specify (or measured?) the antenna delay exclusive of any cable as 43 nsec. In reading through the various SAW filter specifications on the web, I've found a few that specify the group delay ripple, but none that specify the group delay itself. -- Tom, N5EG On Sun, Feb 8, 2015 at 2:11 AM, Attila Kinali att...@kinali.ch wrote: On Sat, 7 Feb 2015 10:07:44 -0800 Tom McDermott tom.n...@gmail.com wrote: While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. Not surprising. Group delay is not considered of any importance in most RF designs. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I would be very much interested in those papers. Could you list their titles and authors at least? I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. Unlikely. LC filters are not sharp enough and difficult to build reliably at those frequencies. I would rather assume that there are no filters at all (beside the antenna characteristics). Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] GPS active antenna delay ?
I have a white-hockey-puck style active GPS antenna, probably about 1998 vintage with no markings except 'Made in Mexico'. While compensating for cable delay is relatively straight forward by measuring the length and compensating for the velocity factor, a question is: how much amplifier / filter group delay is to be expected within the antenna itself? I'd assume that the amplifier in the antenna probably has pretty small group delay, but the RF filter may be significant. Looking through GPS SAW filter datasheets seems to show none with group delay specifications. googling leads to some research papers with delays of about: L1 - 20 MHz wide SAW filter has about 15 nsec of group delay L1 - 2 MHz wide SAW filter has about 65 nsec of group delay L1 - LC filter - can't find anything, but suspect it's probably just a few nanoseconds. I'm not sure a consumer grade antenna even has a SAW filter, it may simply be an LC filter. If it does include a SAW filter, then just using cable delay alone would seem to underestimate the actual antenna delay compensation needed for GPSDO, perhaps significantly. Has anyone on the list measured or otherwise estimated the active antenna delay including the amp and filters? -- Tom, N5EG ___ 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.
