Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers
On 10/10/2012 06:30 AM, Hal Murray wrote: albertson.ch...@gmail.com said: The satellites are in 12 hour orbits. Everything repeats every 12 hours. But the sun is on a 24 hr. period and if you did two 12 hour tests you don't want to do one at night and one in day. So start each test at the same time of day let it run for 12+ hours. Thanks. After poking around a bit... That's 12 Sidereal hours rather than 12 UTC hours. Rarther, it's 11 hours and 58 minutes UTC. It revolves about 2x366.35 times the globe over a year. I don't remember why they choose such an orbit, but it has its uses. 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] To use or not to use transmission line splitters for GPS receivers
Hi! I forgot to mention, but the peak group delay of a pole pair is d_peak = 2*Q/w0 = Q / (pi * f0) Hence, the group delay increases linearly with increasing Q values. Shift the Q, and your delay vary, shift the center-frequency, and you dip off the peak. Cheers, Magnus On 10/09/2012 10:55 PM, Magnus Danielson wrote: On 10/09/2012 09:27 PM, John Ackermann N8UR wrote: Here's a link to a USNO paper that measured the tempco of three GPS amplifiers: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA490830 They found that amplifier filtering was the prime cause of tempco, and the narrowest bandpass amplifier they looked at had a group delay range of 4 nanoseconds over the range of -15 to +45 degrees C. This is a good paper. I've read it before. It presents three strategies for GPS amplifiers: 1) Wide-band amplifier, represented by the AOA Wideband amplifier 2) Narrow-band amplifier with peaks, represented by the AOA narrow band amplifier 3) Narrow-band amplifier with no peaks, represented by the KW microwave phase-stable narrow band amplifier. The wide-band amplifier has around 4 ns group delay, and it is fairly flat and stable. Since there isn't much delay to start with, it doesn't change a whole lot either. Since the amplifier isn't very flat, it also has some variations in group delay. It's fairly natural. The downside is that it has no suppression of interference, so we should do some damping. The second case tries to achieve just that, but in order to create steep slopes around the pass-band, they have used two resonances, one on each side of the pass-band. You see the peaking effect on the gain curve of figure 1, but oh... they show up clearly in the group delay measurement of figure 2 too. This is expected from the theory, as these two pole-pairs has fairly high Q, their group delay will show this property in the direct vicinity of their respective resonances, just as their contribution to gain will do. So, nice steep slopes and good suppression, but lots of group delay, and by that higher sensitivity to environmental effects, i.e. temperature. The third example shows wider but much flatter amplitude response, and essentially flat group delay. This is what you expect from maximum flat group delay filters such as Bessel/Thompson. No wonders those are specified as measuring filters for digital transmission. Lesser delay, and lesser sensitivity. The downside is that the cost of steep slopes comes from a higher number of needed poles/zeros. Just as I expect from traditional signal theory. Again, you get what you pay for. Now you know why I want a network analyzer reaching this area at home. 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. ___ 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] To use or not to use transmission line splitters for GPS receivers
Hi …. and if we have to go to something more exotic than simple two pole filters the group delay (and it's variation) has got to go up. At least some of the HP splitters have RF filters in them. The same is true of GPS receivers. A receiver or splitter in the attic will have many of the same group delay issues as an antenna. I know, who would put one in the attic. Just how warm does that rack get as the air-conditioning cycles and the vents clog up? Bob On Oct 10, 2012, at 4:11 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi! I forgot to mention, but the peak group delay of a pole pair is d_peak = 2*Q/w0 = Q / (pi * f0) Hence, the group delay increases linearly with increasing Q values. Shift the Q, and your delay vary, shift the center-frequency, and you dip off the peak. Cheers, Magnus On 10/09/2012 10:55 PM, Magnus Danielson wrote: On 10/09/2012 09:27 PM, John Ackermann N8UR wrote: Here's a link to a USNO paper that measured the tempco of three GPS amplifiers: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA490830 They found that amplifier filtering was the prime cause of tempco, and the narrowest bandpass amplifier they looked at had a group delay range of 4 nanoseconds over the range of -15 to +45 degrees C. This is a good paper. I've read it before. It presents three strategies for GPS amplifiers: 1) Wide-band amplifier, represented by the AOA Wideband amplifier 2) Narrow-band amplifier with peaks, represented by the AOA narrow band amplifier 3) Narrow-band amplifier with no peaks, represented by the KW microwave phase-stable narrow band amplifier. The wide-band amplifier has around 4 ns group delay, and it is fairly flat and stable. Since there isn't much delay to start with, it doesn't change a whole lot either. Since the amplifier isn't very flat, it also has some variations in group delay. It's fairly natural. The downside is that it has no suppression of interference, so we should do some damping. The second case tries to achieve just that, but in order to create steep slopes around the pass-band, they have used two resonances, one on each side of the pass-band. You see the peaking effect on the gain curve of figure 1, but oh... they show up clearly in the group delay measurement of figure 2 too. This is expected from the theory, as these two pole-pairs has fairly high Q, their group delay will show this property in the direct vicinity of their respective resonances, just as their contribution to gain will do. So, nice steep slopes and good suppression, but lots of group delay, and by that higher sensitivity to environmental effects, i.e. temperature. The third example shows wider but much flatter amplitude response, and essentially flat group delay. This is what you expect from maximum flat group delay filters such as Bessel/Thompson. No wonders those are specified as measuring filters for digital transmission. Lesser delay, and lesser sensitivity. The downside is that the cost of steep slopes comes from a higher number of needed poles/zeros. Just as I expect from traditional signal theory. Again, you get what you pay for. Now you know why I want a network analyzer reaching this area at home. 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. ___ 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] To use or not to use transmission line, splitters for GPS receivers
On 10/10/2012 8:00 AM, time-nuts-requ...@febo.com wrote: albertson.ch...@gmail.com said: The satellites are in 12 hour orbits. Everything repeats every 12 hours. But the sun is on a 24 hr. period and if you did two 12 hour tests you don't want to do one at night and one in day. So start each test at the same time of day let it run for 12+ hours. Thanks. After poking around a bit... That's 12 Sidereal hours rather than 12 UTC hours. Rarther, it's 11 hours and 58 minutes UTC. It revolves about 2x366.35 times the globe over a year. I don't remember why they choose such an orbit, but it has its uses. Cheers, Magnus Isn't that half of a sidereal day? A sidereal day being ~4 minutes shorter than UTC day... ___ 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] To use or not to use transmission line, splitters for GPS receivers
Hi: The reason for the GPS orbits is so that the ground track repeats. Have Fun, Brooke On 10/10/2012 8:00 AM, time-nuts-requ...@febo.com wrote: albertson.ch...@gmail.com said: The satellites are in 12 hour orbits. Everything repeats every 12 hours. But the sun is on a 24 hr. period and if you did two 12 hour tests you don't want to do one at night and one in day. So start each test at the same time of day let it run for 12+ hours. Thanks. After poking around a bit... That's 12 Sidereal hours rather than 12 UTC hours. Rarther, it's 11 hours and 58 minutes UTC. It revolves about 2x366.35 times the globe over a year. I don't remember why they choose such an orbit, but it has its uses. Cheers, Magnus Isn't that half of a sidereal day? A sidereal day being ~4 minutes shorter than UTC day... ___ 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] To use or not to use transmission line, splitters for GPS receivers
On 10/10/12 8:10 AM, bro...@pacific.net wrote: Hi: The reason for the GPS orbits is so that the ground track repeats. Have Fun, Brooke and that makes it easy to predict visibility. Tomorrow will be the same as today, shifted by 4 minutes. ___ 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] To use or not to use transmission line, splitters for GPS receivers
. Tomorrow will be the same as today, shifted by 4 minutes. Seems to work as a predictor for a lot of things :)... 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] To use or not to use transmission line splitters for GPS receivers
On 10/10/2012 01:09 PM, Bob Camp wrote: Hi …. and if we have to go to something more exotic than simple two pole filters the group delay (and it's variation) has got to go up. Yes and no. As you add pole-pairs, their group delay contributions adds up. However, as you add pole-pairs you also get a pair of zeros for the slopes (typically located in 0 and infinity for band-pass response) and you can back off considerably in Q values, and aim for maximum flat group delay in the pass-band. See the difference between the amplifiers in the article. At least some of the HP splitters have RF filters in them. The same is true of GPS receivers. A receiver or splitter in the attic will have many of the same group delay issues as an antenna. I know, who would put one in the attic. Just how warm does that rack get as the air-conditioning cycles and the vents clog up? The filters do add up, true. But then one should also recall the cable in the total, as covered by others. 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] To use or not to use transmission line splitters for GPS receivers
On Oct 10, 2012, at 5:05 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 10/10/2012 01:09 PM, Bob Camp wrote: Hi …. and if we have to go to something more exotic than simple two pole filters the group delay (and it's variation) has got to go up. Yes and no. As you add pole-pairs, their group delay contributions adds up. However, as you add pole-pairs you also get a pair of zeros for the slopes (typically located in 0 and infinity for band-pass response) and you can back off considerably in Q values, and aim for maximum flat group delay in the pass-band. See the difference between the amplifiers in the article. Unless you need to go to something with sharp skirts. Then you are likely to start from a fairly high Q lowpass prototype and add a delay equalizer. Starts to add up pretty fast... At least some of the HP splitters have RF filters in them. The same is true of GPS receivers. A receiver or splitter in the attic will have many of the same group delay issues as an antenna. I know, who would put one in the attic. Just how warm does that rack get as the air-conditioning cycles and the vents clog up? The filters do add up, true. But then one should also recall the cable in the total, as covered by others. indeed, but it's a bit tough to keep the cable all indoors. 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. ___ 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] To use or not to use transmission line splitters for GPS receivers
On 10/11/2012 12:03 AM, Bob Camp wrote: On Oct 10, 2012, at 5:05 PM, Magnus Danielsonmag...@rubidium.dyndns.org wrote: On 10/10/2012 01:09 PM, Bob Camp wrote: Hi …. and if we have to go to something more exotic than simple two pole filters the group delay (and it's variation) has got to go up. Yes and no. As you add pole-pairs, their group delay contributions adds up. However, as you add pole-pairs you also get a pair of zeros for the slopes (typically located in 0 and infinity for band-pass response) and you can back off considerably in Q values, and aim for maximum flat group delay in the pass-band. See the difference between the amplifiers in the article. Unless you need to go to something with sharp skirts. Then you are likely to start from a fairly high Q lowpass prototype and add a delay equalizer. Starts to add up pretty fast... True. But we are talking about wise design for GPS antenna use. At least some of the HP splitters have RF filters in them. The same is true of GPS receivers. A receiver or splitter in the attic will have many of the same group delay issues as an antenna. I know, who would put one in the attic. Just how warm does that rack get as the air-conditioning cycles and the vents clog up? The filters do add up, true. But then one should also recall the cable in the total, as covered by others. indeed, but it's a bit tough to keep the cable all indoors. Indeed it is, which is why it may contribute significantly unless done with care. I do know those that temperature stabilizes both the concrete pillar and cable conduct. 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] To use or not to use transmission line splitters for GPS receivers
On Oct 10, 2012, at 7:03 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 10/11/2012 12:03 AM, Bob Camp wrote: On Oct 10, 2012, at 5:05 PM, Magnus Danielsonmag...@rubidium.dyndns.org wrote: On 10/10/2012 01:09 PM, Bob Camp wrote: Hi …. and if we have to go to something more exotic than simple two pole filters the group delay (and it's variation) has got to go up. Yes and no. As you add pole-pairs, their group delay contributions adds up. However, as you add pole-pairs you also get a pair of zeros for the slopes (typically located in 0 and infinity for band-pass response) and you can back off considerably in Q values, and aim for maximum flat group delay in the pass-band. See the difference between the amplifiers in the article. Unless you need to go to something with sharp skirts. Then you are likely to start from a fairly high Q lowpass prototype and add a delay equalizer. Starts to add up pretty fast... True. But we are talking about wise design for GPS antenna use. …. unless we suddenly need much steeper skirts due to a change in band allocations. At least some of the HP splitters have RF filters in them. The same is true of GPS receivers. A receiver or splitter in the attic will have many of the same group delay issues as an antenna. I know, who would put one in the attic. Just how warm does that rack get as the air-conditioning cycles and the vents clog up? The filters do add up, true. But then one should also recall the cable in the total, as covered by others. indeed, but it's a bit tough to keep the cable all indoors. Indeed it is, which is why it may contribute significantly unless done with care. I do know those that temperature stabilizes both the concrete pillar and cable conduct. 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. ___ 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] To use or not to use transmission line splitters for GPS receivers
mag...@rubidium.dyndns.org said: I do know those that temperature stabilizes both the concrete pillar and cable conduct. I hadn't thought about the support pillar. CTE of concrete is 8-12 PPM/C, so a 10 C change would be 100 PPM. 10 meters would be 1000 micrometers or 1 mm. I think that's 3 picoseconds. I couldn't measure that, but I expect it's important for the big boys. I was thinking of 10 meters as being the height of a building. A stand alone pillar in the middle of a field wouldn't need to be that tall. The cable to the lab would be longer, but you could run two cables and measure the length of the other one with TDR. I was thinking of a pillar as primarily in the vertical direction so maybe it doesn't matter as much. But if it's on the corner of a building, maybe the whole building shrinks/grows in the horizontal dimensions too. Most buildings are more than 10 meters long, but the temperature on the inside is usually constant so maybe the building doesn't change size much in any dimension. What's the temperature time constant of a building or (unheated) antenna pillar? What's the skin depth at 24 hours or 1 year? (Steel is the same ballpark: 14 PPM/C) -- 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] To use or not to use transmission line splitters for GPS receivers
Crosstalk? With the same signal? On Tue, Oct 9, 2012 at 4:31 AM, Edgardo Molina xe1...@amsat.org wrote: Dear Group, Good evening. I just arrived home after the first day of conferences at the Electrical Metrology Forum 2012 at Mexico's metrology center CENAM. I attended several presentations of time and frequency, very interesting indeed. At last I understood some concepts hard to land in theory. I will be attending the whole week long and half of next week. I will have the pleasure and honour to meet Dr. Judah Levine from NIST, who has shown a very nice attitude towards me and accepted to talk a little bit around my thesis in network synchronization. Now to the point if you kindly allow. I got involved in a round table discussion around the use of GPS antennas for time and frequency GPS receivers. I tried to make some points from my personal perspective. I got resistance from the audience and the topic went hot very quickly and didn't set at the end. Honestly I would like to share my doubts and opinions with you in order to enhance my experience about the topic. In the end it could also be beneficial to close this debate tomorrow while attending to CENAM's time and frequency forum. Facts and thoughts: 1. The time and frequency attendees at CENAM`s time and frequency forum is reluctant to use GPS antenna splitters for a number of reasons I couldn't conceive. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical GPS receivers each one with it's own antenna, could eventually cause spatial diversity reception for a system of two receivers conceptually set as one for comparison purposes. Different satellites being tracked on each receiver if not connected to a common antenna. Even if antennas and transmission lines are identical. Question is: Am I wrong doing the above mentioned assumptions while considering the use of GPS transmission line splitters? I which scenarios are the splitters recommended? In which cases they are rather not to be considered? Better ask as to start buying more antennas or feel comfortable with my original RF distribution design using splitters. Your kind comments and expert advise is always welcome. Thank you! Best regards, Edgardo Molina Dirección IPTEL www.iptel.net.mx T : 55 55 55202444 M : 04455 20501854 Piensa en Bits SA de CV Información anexa: CONFIDENCIALIDAD DE INFORMACION Este mensaje tiene carácter confidencial. Si usted no es el destinarario de este mensaje, le suplicamos se lo notifique al remitente mediante un correo electrónico y que borre el presente mensaje y sus anexos de su computadora sin retener una copia de los mismos. Queda estrictamente prohibido copiar este mensaje o hacer usode el para cualquier propósito o divulgar su en forma parcial o total su contenido. Gracias. NON-DISCLOSURE OF INFORMATION This email is strictly confidential and may also be privileged. If you are not the intended recipient please immediately advise the sender by replying to this e-mail and then deleting the message and its attachments from your computer without keeping a copy. It is strictly forbidden to copy it or use it for any purpose or disclose its contents to any third party. Thank you. ___ 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] To use or not to use transmission line splitters for GPS receivers
I was wondering about that myself, but my guess is the crosstalk would be from whatever grunge was coming from the other GPS. Every amplifier has reverse parameters, so a small amount of the crud (circuitry noise) from one GPS will reach the other GPS. Not much, but some people are nuts about time. This is a bigger problem with radios, where the locals from one radio can reach the input to the other radio. I was also confused on the notion of a transmission line splitter. Is this a Wilkinson or something else? On 10/9/2012 12:40 AM, Azelio Boriani wrote: Crosstalk? With the same signal? ___ 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] To use or not to use transmission line splitters for GPS receivers
This article discusses timing errors due to mismatch and multiple reflections in transmissin lines: http://www.dtic.mil/dtic/tr/fulltext/u2/a508044.pdf Adrian Edgardo Molina schrieb: Dear Group, Good evening. I just arrived home after the first day of conferences at the Electrical Metrology Forum 2012 at Mexico's metrology center CENAM. I attended several presentations of time and frequency, very interesting indeed. At last I understood some concepts hard to land in theory. I will be attending the whole week long and half of next week. I will have the pleasure and honour to meet Dr. Judah Levine from NIST, who has shown a very nice attitude towards me and accepted to talk a little bit around my thesis in network synchronization. Now to the point if you kindly allow. I got involved in a round table discussion around the use of GPS antennas for time and frequency GPS receivers. I tried to make some points from my personal perspective. I got resistance from the audience and the topic went hot very quickly and didn't set at the end. Honestly I would like to share my doubts and opinions with you in order to enhance my experience about the topic. In the end it could also be beneficial to close this debate tomorrow while attending to CENAM's time and frequency forum. Facts and thoughts: 1. The time and frequency attendees at CENAM`s time and frequency forum is reluctant to use GPS antenna splitters for a number of reasons I couldn't conceive. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical GPS receivers each one with it's own antenna, could eventually cause spatial diversity reception for a system of two receivers conceptually set as one for comparison purposes. Different satellites being tracked on each receiver if not connected to a common antenna. Even if antennas and transmission lines are identical. Question is: Am I wrong doing the above mentioned assumptions while considering the use of GPS transmission line splitters? I which scenarios are the splitters recommended? In which cases they are rather not to be considered? Better ask as to start buying more antennas or feel comfortable with my original RF distribution design using splitters. Your kind comments and expert advise is always welcome. Thank you! Best regards, Edgardo Molina Dirección IPTEL www.iptel.net.mx T : 55 55 55202444 M : 04455 20501854 Piensa en Bits SA de CV Información anexa: CONFIDENCIALIDAD DE INFORMACION Este mensaje tiene carácter confidencial. Si usted no es el destinarario de este mensaje, le suplicamos se lo notifique al remitente mediante un correo electrónico y que borre el presente mensaje y sus anexos de su computadora sin retener una copia de los mismos. Queda estrictamente prohibido copiar este mensaje o hacer usode el para cualquier propósito o divulgar su en forma parcial o total su contenido. Gracias. NON-DISCLOSURE OF INFORMATION This email is strictly confidential and may also be privileged. If you are not the intended recipient please immediately advise the sender by replying to this e-mail and then deleting the message and its attachments from your computer without keeping a copy. It is strictly forbidden to copy it or use it for any purpose or disclose its contents to any third party. Thank you. ___ 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] To use or not to use transmission line splitters for GPS receivers
Hi all, In my shack I have a single antenna with two power splitter in series because I need several ports for the four GPSDO and spare port for occasional testing. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. any cross talk depends on the circuit and layout of the splitter. Some crosstalk can happen with two close antenna cable. I suppose the first question have to be : What is my time stability target? Important is a stable electrical and mechanical configuration and port connection. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range I have the same dubt and for this reason I have powered my Agilent splitter not from the GPS but from separate port is present (ac and backup du power).This also for the smart splitter. 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. I agree, the new receivers have comparable performance.Some more difference are in PLL OCXO and firmware. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical GPS receivers each one with it's own antenna, could eventually cause spatial diversity reception for a system of two receivers conceptually set as one for comparison purposes. Different satellites being tracked on each receiver if not connected to a common antenna. Even if antennas and transmission lines are identical. Question is: Am I wrong doing the above mentioned assumptions while considering the use of GPS transmission line splitters? I which scenarios are the splitters recommended? In which cases they are rather not to be considered? I think a standard calibration lab have to setting up with two antenna system and two receivers as recovery plan in case of fault. One system can be single antenna plus GPSDO (recovery reference). The other can use a splitter connected to second receiver and several more ports for testing. All my ports are with a blocking capacitors in series to avoid any antenna or active splitter interaction. Luciano timeok ___ 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] To use or not to use transmission line splitters for GPS receivers
Is there any difference between what a GPS receiver can receve via crosstalk or receive directly from the antenna? In my opinion crosstalk is absolutely less than the last argument about GPS antenna splitters. On Tue, Oct 9, 2012 at 9:58 AM, Timeok tim...@timeok.it wrote: Hi all, In my shack I have a single antenna with two power splitter in series because I need several ports for the four GPSDO and spare port for occasional testing. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. any cross talk depends on the circuit and layout of the splitter. Some crosstalk can happen with two close antenna cable. I suppose the first question have to be : What is my time stability target? Important is a stable electrical and mechanical configuration and port connection. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range I have the same dubt and for this reason I have powered my Agilent splitter not from the GPS but from separate port is present (ac and backup du power).This also for the smart splitter. 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. I agree, the new receivers have comparable performance.Some more difference are in PLL OCXO and firmware. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical GPS receivers each one with it's own antenna, could eventually cause spatial diversity reception for a system of two receivers conceptually set as one for comparison purposes. Different satellites being tracked on each receiver if not connected to a common antenna. Even if antennas and transmission lines are identical. Question is: Am I wrong doing the above mentioned assumptions while considering the use of GPS transmission line splitters? I which scenarios are the splitters recommended? In which cases they are rather not to be considered? I think a standard calibration lab have to setting up with two antenna system and two receivers as recovery plan in case of fault. One system can be single antenna plus GPSDO (recovery reference). The other can use a splitter connected to second receiver and several more ports for testing. All my ports are with a blocking capacitors in series to avoid any antenna or active splitter interaction. Luciano timeok __**_ 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] To use or not to use transmission line splitters for GPS receivers
I agree, Luciano timeok Il 2012-10-09 10:41 Azelio Boriani ha scritto: Is there any difference between what a GPS receiver can receve via crosstalk or receive directly from the antenna? In my opinion crosstalk is absolutely less than the last argument about GPS antenna splitters. On Tue, Oct 9, 2012 at 9:58 AM, Timeok tim...@timeok.it wrote: Hi all, In my shack I have a single antenna with two power splitter in series because I need several ports for the four GPSDO and spare port for occasional testing. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. any cross talk depends on the circuit and layout of the splitter. Some crosstalk can happen with two close antenna cable. I suppose the first question have to be : What is my time stability target? Important is a stable electrical and mechanical configuration and port connection. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range I have the same dubt and for this reason I have powered my Agilent splitter not from the GPS but from separate port is present (ac and backup du power).This also for the smart splitter. 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. I agree, the new receivers have comparable performance.Some more difference are in PLL OCXO and firmware. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical GPS receivers each one with it's own antenna, could eventually cause spatial diversity reception for a system of two receivers conceptually set as one for comparison purposes. Different satellites being tracked on each receiver if not connected to a common antenna. Even if antennas and transmission lines are identical. Question is: Am I wrong doing the above mentioned assumptions while considering the use of GPS transmission line splitters? I which scenarios are the splitters recommended? In which cases they are rather not to be considered? I think a standard calibration lab have to setting up with two antenna system and two receivers as recovery plan in case of fault. One system can be single antenna plus GPSDO (recovery reference). The other can use a splitter connected to second receiver and several more ports for testing. All my ports are with a blocking capacitors in series to avoid any antenna or active splitter interaction. Luciano timeok __**_ 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. -- timeok ___ 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] To use or not to use transmission line splitters for GPS receivers
When GPS first started to be fitted to light aircraft it was found that LO leakage from some VHF navigation recivers blocked the GPS when the NAV was on certain channels. You can buy a BNC T adaptor where the leg of the T is a 1.5GHz coax stub notch filter. They go on the NAV RX antenna connector. Robert G8RPI. From: gary li...@lazygranch.com To: time-nuts@febo.com Sent: Tuesday, 9 October 2012, 8:51 Subject: Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers I was wondering about that myself, but my guess is the crosstalk would be from whatever grunge was coming from the other GPS. Every amplifier has reverse parameters, so a small amount of the crud (circuitry noise) from one GPS will reach the other GPS. Not much, but some people are nuts about time. This is a bigger problem with radios, where the locals from one radio can reach the input to the other radio. I was also confused on the notion of a transmission line splitter. Is this a Wilkinson or something else? On 10/9/2012 12:40 AM, Azelio Boriani wrote: Crosstalk? With the same signal? ___ 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] To use or not to use transmission line splitters for GPS receivers
Lots of comments. Indeed it sounds like a great discussion for pizza and beer. The more beer the more lively. Did they bring beer? Fact I have used a 8 way splitter Sat/TV for 5 years now. Port to port loss is something like 16 db or 26 db as I recall. It has dc blocking on all but 1 port built in. The loss was as advertised. The cost was pretty high at $7. To make up for the loss I used a amplifier. A Mar circuit and only enough gain to cover the splitter loss since the single antenna has 30db of gain and feed 1/2 hardline. So if all of things discussed are happening its not at all apparent from the 6 rcvrs on the system. Some old like odetics austrons some newer like 3801s and Tbolt...Plus I never have to hunt for a port for experimenting. There is one catch and this can apply to all splitters some rcvrs need a dc load so that they think they have an antenna. I think about 430 ohms. As I say its been 5 years and it just works. Total investment $10?? Though it doesn't say HP on it. Regards Paul WB8TSL On Tue, Oct 9, 2012 at 7:14 AM, Robert Atkinson robert8...@yahoo.co.ukwrote: When GPS first started to be fitted to light aircraft it was found that LO leakage from some VHF navigation recivers blocked the GPS when the NAV was on certain channels. You can buy a BNC T adaptor where the leg of the T is a 1.5GHz coax stub notch filter. They go on the NAV RX antenna connector. Robert G8RPI. From: gary li...@lazygranch.com To: time-nuts@febo.com Sent: Tuesday, 9 October 2012, 8:51 Subject: Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers I was wondering about that myself, but my guess is the crosstalk would be from whatever grunge was coming from the other GPS. Every amplifier has reverse parameters, so a small amount of the crud (circuitry noise) from one GPS will reach the other GPS. Not much, but some people are nuts about time. This is a bigger problem with radios, where the locals from one radio can reach the input to the other radio. I was also confused on the notion of a transmission line splitter. Is this a Wilkinson or something else? On 10/9/2012 12:40 AM, Azelio Boriani wrote: Crosstalk? With the same signal? ___ 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] To use or not to use transmission line splitters for GPS receivers
Paul, I am convinced your realization work very well and it is a lower cost in the market. But depend what kind of user have to use the device. For a standard laboratory or a company I am sure is not sufficent your realization, for an hobbist yes, can be. Business or research company want to have a datsheet with temperature range, technical characteristic, a repair service. In one word a professional package. Me for example, am an hobbist and I am started from the tv sat splitter but now, I have bought on ebay a low cost professional splitter.It is better than mine at least as mechanical realization ad impedance matching. That's all. All the people in time-nuts community want to improve day by day the hw and sw they have at home. yes, yesterday night I have bring a bier. Cirio! Luciano timeok Il 2012-10-09 15:15 paul swed ha scritto: Lots of comments. Indeed it sounds like a great discussion for pizza and beer. The more beer the more lively. Did they bring beer? Fact I have used a 8 way splitter Sat/TV for 5 years now. Port to port loss is something like 16 db or 26 db as I recall. It has dc blocking on all but 1 port built in. The loss was as advertised. The cost was pretty high at $7. To make up for the loss I used a amplifier. A Mar circuit and only enough gain to cover the splitter loss since the single antenna has 30db of gain and feed 1/2 hardline. So if all of things discussed are happening its not at all apparent from the 6 rcvrs on the system. Some old like odetics austrons some newer like 3801s and Tbolt...Plus I never have to hunt for a port for experimenting. There is one catch and this can apply to all splitters some rcvrs need a dc load so that they think they have an antenna. I think about 430 ohms. As I say its been 5 years and it just works. Total investment $10?? Though it doesn't say HP on it. Regards Paul WB8TSL On Tue, Oct 9, 2012 at 7:14 AM, Robert Atkinson robert8...@yahoo.co.ukwrote: When GPS first started to be fitted to light aircraft it was found that LO leakage from some VHF navigation recivers blocked the GPS when the NAV was on certain channels. You can buy a BNC T adaptor where the leg of the T is a 1.5GHz coax stub notch filter. They go on the NAV RX antenna connector. Robert G8RPI. From: gary li...@lazygranch.com To: time-nuts@febo.com Sent: Tuesday, 9 October 2012, 8:51 Subject: Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers I was wondering about that myself, but my guess is the crosstalk would be from whatever grunge was coming from the other GPS. Every amplifier has reverse parameters, so a small amount of the crud (circuitry noise) from one GPS will reach the other GPS. Not much, but some people are nuts about time. This is a bigger problem with radios, where the locals from one radio can reach the input to the other radio. I was also confused on the notion of a transmission line splitter. Is this a Wilkinson or something else? On 10/9/2012 12:40 AM, Azelio Boriani wrote: Crosstalk? With the same signal? ___ 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. -- timeok ___ 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] To use or not to use transmission line splitters for GPS receivers
Hello All - I do not believe there is a hard Yes or No answer for this question. It depends upon the performance specification of the system elements and the system requirements. For instance if the leakage of noise and discrete signals from each receiver out of the antenna port combined with the port to port isolation of the power divider is below the level of harm to the associated receivers then the answer is yes. Otherwise NO. The issue of antenna power is simply solved by placing a DC block in the line from the splitter to all but one of the receivers. It then powers the antenna for all of them. I use this system with a 3 way splitter and 3 T bolts. More elaborate and redundant schemes are possible with a bit of engineering. I have several of the receivers developed by Novatel for the early WASS project experiments. These boxes used 3 receivers as both L1 and L2 were involved. A standard Mini Circuits power splitter was employed to feed the antenna to all 3. Apparently that sufficed for what was a pretty demanding requirement. Finally - Anyone advocating a hard Yes or No to this question without first considering the performance numbers for the system elements has been smoking their view-graphs. With proper design it is totally feasible to feed a number of receivers from one antenna. -john k6iql ___ 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] To use or not to use transmission line splitters for GPS receivers
Hi If you look at the way NIST sets up one of their time modem installations, they do indeed worry a lot about this sort of stuff. There's a major choke / isolator between the antenna and the feed line. The claim is that they see in building grunge causing trouble without it. I'm sure that will be a variable depending on your building. The next claim is that without the isolation and a choke antenna, there is a possibility of multi-path issues. Since most of us do not have a choke ring antenna the isolator may be overkill. The NIST site in Bolder is definitely multipath challenged. They probably have some pretty good data on that. If you are after sub ns level timing, things are a bit different than if you are happy with tens of ns error. Few of us have an adequate survey of our location to *really* worry about sub ns numbers. If you are one of those lucky few that can worry about sub-ns, yes mismatch and voltage and a whole long list of things matter. The temperature coefficient of your antenna also gets onto that list at some point. Receivers are often designed with an I'm by my self approach. Some designs do indeed feed crud back up towards the antenna. Digitization clocks and all sorts of other things can be a source of these signals. Given the high gain of the antenna preamp, they can get away with a certain degree of sloppy design. I suspect that there are cases of GPS A not liking the spurs from GPS B. For most of us, none of this matters. If we're 10 ns off, we'll never know it. If our whole setup varies 2 or 3 ns over a day, we simply don't have the gear to spot the problem. It also does not matter to most of the people who use GPSDO's in systems. I have yet to see a surplus GPSDO arrive with a non-zero cable delay in it's eeprom. I doubt that people have zero delay cables. Without measuring the cable delay and compensating for it, you can easily be off 100's of ns. Yes, you can get out your TDR and come up with a cable number to 100ps or less. You can get a survey that's good to centimeters. You can get a good antenna (cheap if you are lucky or patient). Do all that and more, you can get into the sub ns range. Calculated cables based on length, estimated location based on self survey, easy to get antennas, not going to cut it. As always, the answer is it depends on what you are doing. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Edgardo Molina Sent: Monday, October 08, 2012 10:31 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] To use or not to use transmission line splitters forGPS receivers Dear Group, Good evening. I just arrived home after the first day of conferences at the Electrical Metrology Forum 2012 at Mexico's metrology center CENAM. I attended several presentations of time and frequency, very interesting indeed. At last I understood some concepts hard to land in theory. I will be attending the whole week long and half of next week. I will have the pleasure and honour to meet Dr. Judah Levine from NIST, who has shown a very nice attitude towards me and accepted to talk a little bit around my thesis in network synchronization. Now to the point if you kindly allow. I got involved in a round table discussion around the use of GPS antennas for time and frequency GPS receivers. I tried to make some points from my personal perspective. I got resistance from the audience and the topic went hot very quickly and didn't set at the end. Honestly I would like to share my doubts and opinions with you in order to enhance my experience about the topic. In the end it could also be beneficial to close this debate tomorrow while attending to CENAM's time and frequency forum. Facts and thoughts: 1. The time and frequency attendees at CENAM`s time and frequency forum is reluctant to use GPS antenna splitters for a number of reasons I couldn't conceive. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical
Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers
Yes indeed its a depends since in the original thread there was not a specific requirement. But as you say its a design. If you do not want to design makes more sense to grab a ebay wonder I suspect. For me I had fun designing and saving a buck. 8 ports verses 2... Regards Paul WB8TSL On Tue, Oct 9, 2012 at 12:10 PM, johncr...@aol.com wrote: Hello All - I do not believe there is a hard Yes or No answer for this question. It depends upon the performance specification of the system elements and the system requirements. For instance if the leakage of noise and discrete signals from each receiver out of the antenna port combined with the port to port isolation of the power divider is below the level of harm to the associated receivers then the answer is yes. Otherwise NO. The issue of antenna power is simply solved by placing a DC block in the line from the splitter to all but one of the receivers. It then powers the antenna for all of them. I use this system with a 3 way splitter and 3 T bolts. More elaborate and redundant schemes are possible with a bit of engineering. I have several of the receivers developed by Novatel for the early WASS project experiments. These boxes used 3 receivers as both L1 and L2 were involved. A standard Mini Circuits power splitter was employed to feed the antenna to all 3. Apparently that sufficed for what was a pretty demanding requirement. Finally - Anyone advocating a hard Yes or No to this question without first considering the performance numbers for the system elements has been smoking their view-graphs. With proper design it is totally feasible to feed a number of receivers from one antenna. -john k6iql __**_ 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] To use or not to use transmission line splitters for GPS receivers
I believe it is possible for splitters to be invisible to your system. My first choice would be multiple Antennas. But if you have multiple GPS receivers and require outputs to your test bench, splitters are the logical choice. That said the splitter adds complexity to the system and exponentially multiplies your potential for problems. I have found that equipment placement, grounding, lightning protection can all affect the signal at the receiver and contribute to problems. Although you always want sound theory the complexity of splitter set-up quickly goes beyond what is reasonable to mathematically model. It sound like you are approaching this the way I would by testing different system configurations starting with a simple antenna and coax. You have already seen the difference just antennas can make. Coax model, length, and run will also have a substantial effect. Now is where MATS law kicks in. (More Art Then Science). When you add the splitter the best performing Ant and Coax may no longer the best combination. But applying best practices, logic, and a few hours of trial and error and you will begin to understand your system. If over time you set up a number of systems you will start to know from experience what will work. You see this experience based knowledge in many NIST researchers and dare I say a number of Time-Nuts. I am still on the steep part of the learning curve myself. If I can only learn a little from each of my mistakes. Thomas Knox To: time-nuts@febo.com From: johncr...@aol.com Date: Tue, 9 Oct 2012 12:10:15 -0400 Subject: Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers Hello All - I do not believe there is a hard Yes or No answer for this question. It depends upon the performance specification of the system elements and the system requirements. For instance if the leakage of noise and discrete signals from each receiver out of the antenna port combined with the port to port isolation of the power divider is below the level of harm to the associated receivers then the answer is yes. Otherwise NO. The issue of antenna power is simply solved by placing a DC block in the line from the splitter to all but one of the receivers. It then powers the antenna for all of them. I use this system with a 3 way splitter and 3 T bolts. More elaborate and redundant schemes are possible with a bit of engineering. I have several of the receivers developed by Novatel for the early WASS project experiments. These boxes used 3 receivers as both L1 and L2 were involved. A standard Mini Circuits power splitter was employed to feed the antenna to all 3. Apparently that sufficed for what was a pretty demanding requirement. Finally - Anyone advocating a hard Yes or No to this question without first considering the performance numbers for the system elements has been smoking their view-graphs. With proper design it is totally feasible to feed a number of receivers from one antenna. -john k6iql ___ 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] To use or not to use transmission line splitters for GPS receivers
Suppose I wanted to do an experiment with GPS receivers: Is setup A better than setup B? But they share some parts, say the antenna, so I can't run them both at the same time. How long do I have to collect data for each setup to tell which is better? Is that even the right question? I'm thinking of things like satellites in view changing so if I run for an hour, then switch and run for another hour one run could get lucky and have lots of satellites in the right place while the other run was unlucky. -- 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] To use or not to use transmission line splitters for GPS receivers
On 9 Oct, 2012, at 12:48 , Bob Camp li...@rtty.us wrote: If you are after sub ns level timing, things are a bit different than if you are happy with tens of ns error. Few of us have an adequate survey of our location to *really* worry about sub ns numbers. If you are one of those lucky few that can worry about sub-ns, yes mismatch and voltage and a whole long list of things matter. The temperature coefficient of your antenna also gets onto that list at some point. I think you can get sub-nanosecond time (if you can arrange for a proper equipment calibration) and sub-centimeter positioning on your own using the IGS products and GPS Precise Point Positioning techniques. The gotchas are that you need to have a high-priced dual-frequency, carrier phase tracking receiver and the software you need seems to only be available to the very rich (though there are free online services which will process your data to determine the location for you). The antenna temperature thing is kind of indicative of just how much lore and black art seems to be involved in arranging equipment for fine timing, however. I have the ITU 2010 Handbook for Satellite Time and Frequency Transfer and Dissemination. In Chapter 12, when discussing GPS Common View techniques, the document says this about antenna temperature 12.5.2 Temperature stabilized antennas It is now well documented, and generally admitted, that GPS time-receiving equipment, and more specifically its antenna, is sensitive to environmental conditions [Lewandowski and Tourde, 1990]. For conventional GPS time-receiving system this sensitivity could be expressed by a coefficient of about 0,2 ns/°C and can approach 2 ns/°C. This was a major precluding obstacle, as it did, the goal of 1 ns accuracy announced earlier for GPS time transfer. and goes on to recommend using an antenna with an oven keeping the temperature of the electronics constant. In Chapter 13, on the other hand, when discussing GPS PPP, it says this: There have been some poorly supported claims of strong variations of geodetic clock estimates with temperature changes in some GPS antennas, together with recommendations to use temperature-stabilized units. While this might apply to certain low-end, single-frequency units, direct tests of a standard AOA Dorne Margolin choke ring antenna have failed to detect any sensitivity of the clock estimates to antenna temperature variations. Ray and Senior [2001] placed an upper limit of 2 ps/°C on the short-term (diurnal) temperature sensitivity and later extended this to 10.1 ps/°C for any possible long-term component [Ray and Senior, 2003]. Even smaller sensitivities, 0.17 ps/°C or less, were determined by [Rieck et al., 2003] for an Ashtech choke ring model. So Chapter 13 says that what Chapter 12 said is bogus. It appears that Chapter 12 may have written been written by a European while Chapter 13 is an American effort, so this may be some sort of cultural thing. Chapter 13 does later go on to point out how crappy the Canadian IGS stations are in the winter and blames this on snow and ice in the near field below the antenna, so even Chapter 13 does find a use for heating at the antenna. Both chapters do agree that keeping the temperature of the receiver constant is good. I think the antenna splitter thing is probably the same kind of issue. Someone, somewhere, may have had a problem with an antenna splitter and published a paper on that, and this in turn reinforces the conservative assumption that you should leave anything out that doesn't absolutely need to be there, so it has become common wisdom that you should avoid splitters. Or something. Dennis Ferguson ___ 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] To use or not to use transmission line splitters for GPS receivers
Boy all I can say is I measured the $7 satellite splitter and it matched the specs for fwd and rtn loss. Port to port loss using an HP network analyzer. So what can I say it worked and well. Actually surprisingly so. Regards Paul. On Tue, Oct 9, 2012 at 2:38 PM, Dennis Ferguson dennis.c.fergu...@gmail.com wrote: On 9 Oct, 2012, at 12:48 , Bob Camp li...@rtty.us wrote: If you are after sub ns level timing, things are a bit different than if you are happy with tens of ns error. Few of us have an adequate survey of our location to *really* worry about sub ns numbers. If you are one of those lucky few that can worry about sub-ns, yes mismatch and voltage and a whole long list of things matter. The temperature coefficient of your antenna also gets onto that list at some point. I think you can get sub-nanosecond time (if you can arrange for a proper equipment calibration) and sub-centimeter positioning on your own using the IGS products and GPS Precise Point Positioning techniques. The gotchas are that you need to have a high-priced dual-frequency, carrier phase tracking receiver and the software you need seems to only be available to the very rich (though there are free online services which will process your data to determine the location for you). The antenna temperature thing is kind of indicative of just how much lore and black art seems to be involved in arranging equipment for fine timing, however. I have the ITU 2010 Handbook for Satellite Time and Frequency Transfer and Dissemination. In Chapter 12, when discussing GPS Common View techniques, the document says this about antenna temperature 12.5.2 Temperature stabilized antennas It is now well documented, and generally admitted, that GPS time-receiving equipment, and more specifically its antenna, is sensitive to environmental conditions [Lewandowski and Tourde, 1990]. For conventional GPS time-receiving system this sensitivity could be expressed by a coefficient of about 0,2 ns/°C and can approach 2 ns/°C. This was a major precluding obstacle, as it did, the goal of 1 ns accuracy announced earlier for GPS time transfer. and goes on to recommend using an antenna with an oven keeping the temperature of the electronics constant. In Chapter 13, on the other hand, when discussing GPS PPP, it says this: There have been some poorly supported claims of strong variations of geodetic clock estimates with temperature changes in some GPS antennas, together with recommendations to use temperature-stabilized units. While this might apply to certain low-end, single-frequency units, direct tests of a standard AOA Dorne Margolin choke ring antenna have failed to detect any sensitivity of the clock estimates to antenna temperature variations. Ray and Senior [2001] placed an upper limit of 2 ps/°C on the short-term (diurnal) temperature sensitivity and later extended this to 10.1 ps/°C for any possible long-term component [Ray and Senior, 2003]. Even smaller sensitivities, 0.17 ps/°C or less, were determined by [Rieck et al., 2003] for an Ashtech choke ring model. So Chapter 13 says that what Chapter 12 said is bogus. It appears that Chapter 12 may have written been written by a European while Chapter 13 is an American effort, so this may be some sort of cultural thing. Chapter 13 does later go on to point out how crappy the Canadian IGS stations are in the winter and blames this on snow and ice in the near field below the antenna, so even Chapter 13 does find a use for heating at the antenna. Both chapters do agree that keeping the temperature of the receiver constant is good. I think the antenna splitter thing is probably the same kind of issue. Someone, somewhere, may have had a problem with an antenna splitter and published a paper on that, and this in turn reinforces the conservative assumption that you should leave anything out that doesn't absolutely need to be there, so it has become common wisdom that you should avoid splitters. Or something. Dennis Ferguson ___ 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] To use or not to use transmission line splitters for GPS receivers
Hi In the context of the original post, probably the right question is: do you have a hydrogen maser and an ensemble of cesiums to compare it to? That's the environment that gets front and center at these conferences. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of paul swed Sent: Tuesday, October 09, 2012 2:43 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers Boy all I can say is I measured the $7 satellite splitter and it matched the specs for fwd and rtn loss. Port to port loss using an HP network analyzer. So what can I say it worked and well. Actually surprisingly so. Regards Paul. On Tue, Oct 9, 2012 at 2:38 PM, Dennis Ferguson dennis.c.fergu...@gmail.com wrote: On 9 Oct, 2012, at 12:48 , Bob Camp li...@rtty.us wrote: If you are after sub ns level timing, things are a bit different than if you are happy with tens of ns error. Few of us have an adequate survey of our location to *really* worry about sub ns numbers. If you are one of those lucky few that can worry about sub-ns, yes mismatch and voltage and a whole long list of things matter. The temperature coefficient of your antenna also gets onto that list at some point. I think you can get sub-nanosecond time (if you can arrange for a proper equipment calibration) and sub-centimeter positioning on your own using the IGS products and GPS Precise Point Positioning techniques. The gotchas are that you need to have a high-priced dual-frequency, carrier phase tracking receiver and the software you need seems to only be available to the very rich (though there are free online services which will process your data to determine the location for you). The antenna temperature thing is kind of indicative of just how much lore and black art seems to be involved in arranging equipment for fine timing, however. I have the ITU 2010 Handbook for Satellite Time and Frequency Transfer and Dissemination. In Chapter 12, when discussing GPS Common View techniques, the document says this about antenna temperature 12.5.2 Temperature stabilized antennas It is now well documented, and generally admitted, that GPS time-receiving equipment, and more specifically its antenna, is sensitive to environmental conditions [Lewandowski and Tourde, 1990]. For conventional GPS time-receiving system this sensitivity could be expressed by a coefficient of about 0,2 ns/°C and can approach 2 ns/°C. This was a major precluding obstacle, as it did, the goal of 1 ns accuracy announced earlier for GPS time transfer. and goes on to recommend using an antenna with an oven keeping the temperature of the electronics constant. In Chapter 13, on the other hand, when discussing GPS PPP, it says this: There have been some poorly supported claims of strong variations of geodetic clock estimates with temperature changes in some GPS antennas, together with recommendations to use temperature-stabilized units. While this might apply to certain low-end, single-frequency units, direct tests of a standard AOA Dorne Margolin choke ring antenna have failed to detect any sensitivity of the clock estimates to antenna temperature variations. Ray and Senior [2001] placed an upper limit of 2 ps/°C on the short-term (diurnal) temperature sensitivity and later extended this to 10.1 ps/°C for any possible long-term component [Ray and Senior, 2003]. Even smaller sensitivities, 0.17 ps/°C or less, were determined by [Rieck et al., 2003] for an Ashtech choke ring model. So Chapter 13 says that what Chapter 12 said is bogus. It appears that Chapter 12 may have written been written by a European while Chapter 13 is an American effort, so this may be some sort of cultural thing. Chapter 13 does later go on to point out how crappy the Canadian IGS stations are in the winter and blames this on snow and ice in the near field below the antenna, so even Chapter 13 does find a use for heating at the antenna. Both chapters do agree that keeping the temperature of the receiver constant is good. I think the antenna splitter thing is probably the same kind of issue. Someone, somewhere, may have had a problem with an antenna splitter and published a paper on that, and this in turn reinforces the conservative assumption that you should leave anything out that doesn't absolutely need to be there, so it has become common wisdom that you should avoid splitters. Or something. Dennis Ferguson ___ 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
Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers
On Tue, Oct 9, 2012 at 10:33 AM, Hal Murray hmur...@megapathdsl.net wrote: Suppose I wanted to do an experiment with GPS receivers: Is setup A better than setup B? But they share some parts, say the antenna, so I can't run them both at the same time. How long do I have to collect data for each setup to tell which is better? Is that even the right question? I'm thinking of things like satellites in view changing so if I run for an hour, then switch and run for another hour one run could get lucky and have lots of satellites in the right place while the other run was unlucky. The satellites are in 12 hour orbits. Everything repeats every 12 hours. But the sun is on a 24 hr. period and if you did two 12 hour tests you don't want to do one at night and one in day. So start each test at the same time of day let it run for 12+ hours. Chris Albertson Redondo Beach, California ___ 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] To use or not to use transmission line splitters for GPS receivers
Here's a link to a USNO paper that measured the tempco of three GPS amplifiers: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA490830 They found that amplifier filtering was the prime cause of tempco, and the narrowest bandpass amplifier they looked at had a group delay range of 4 nanoseconds over the range of -15 to +45 degrees C. And for what it's worth, I used a VNA to measure the electrical length of an ~80 foot piece of LMR-400 laying on the dark roof of my Georgia house, and saw no measurable difference between cool pre-sunrise and hot mid-afternoon on a sunny summer day. There's also a brief paper about coax tempco from Haystack: http://www.haystack.mit.edu/tech/vlbi/mark5/mark5_memos/069.pdf John On 10/9/2012 2:38 PM, Dennis Ferguson wrote: On 9 Oct, 2012, at 12:48 , Bob Camp li...@rtty.us wrote: If you are after sub ns level timing, things are a bit different than if you are happy with tens of ns error. Few of us have an adequate survey of our location to *really* worry about sub ns numbers. If you are one of those lucky few that can worry about sub-ns, yes mismatch and voltage and a whole long list of things matter. The temperature coefficient of your antenna also gets onto that list at some point. I think you can get sub-nanosecond time (if you can arrange for a proper equipment calibration) and sub-centimeter positioning on your own using the IGS products and GPS Precise Point Positioning techniques. The gotchas are that you need to have a high-priced dual-frequency, carrier phase tracking receiver and the software you need seems to only be available to the very rich (though there are free online services which will process your data to determine the location for you). The antenna temperature thing is kind of indicative of just how much lore and black art seems to be involved in arranging equipment for fine timing, however. I have the ITU 2010 Handbook for Satellite Time and Frequency Transfer and Dissemination. In Chapter 12, when discussing GPS Common View techniques, the document says this about antenna temperature 12.5.2 Temperature stabilized antennas It is now well documented, and generally admitted, that GPS time-receiving equipment, and more specifically its antenna, is sensitive to environmental conditions [Lewandowski and Tourde, 1990]. For conventional GPS time-receiving system this sensitivity could be expressed by a coefficient of about 0,2 ns/°C and can approach 2 ns/°C. This was a major precluding obstacle, as it did, the goal of 1 ns accuracy announced earlier for GPS time transfer. and goes on to recommend using an antenna with an oven keeping the temperature of the electronics constant. In Chapter 13, on the other hand, when discussing GPS PPP, it says this: There have been some poorly supported claims of strong variations of geodetic clock estimates with temperature changes in some GPS antennas, together with recommendations to use temperature-stabilized units. While this might apply to certain low-end, single-frequency units, direct tests of a standard AOA Dorne Margolin choke ring antenna have failed to detect any sensitivity of the clock estimates to antenna temperature variations. Ray and Senior [2001] placed an upper limit of 2 ps/°C on the short-term (diurnal) temperature sensitivity and later extended this to 10.1 ps/°C for any possible long-term component [Ray and Senior, 2003]. Even smaller sensitivities, 0.17 ps/°C or less, were determined by [Rieck et al., 2003] for an Ashtech choke ring model. So Chapter 13 says that what Chapter 12 said is bogus. It appears that Chapter 12 may have written been written by a European while Chapter 13 is an American effort, so this may be some sort of cultural thing. Chapter 13 does later go on to point out how crappy the Canadian IGS stations are in the winter and blames this on snow and ice in the near field below the antenna, so even Chapter 13 does find a use for heating at the antenna. Both chapters do agree that keeping the temperature of the receiver constant is good. I think the antenna splitter thing is probably the same kind of issue. Someone, somewhere, may have had a problem with an antenna splitter and published a paper on that, and this in turn reinforces the conservative assumption that you should leave anything out that doesn't absolutely need to be there, so it has become common wisdom that you should avoid splitters. Or something. Dennis Ferguson ___ 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] To use or not to use transmission line splitters for GPS receivers
Dear Edgardo, On 10/09/2012 04:31 AM, Edgardo Molina wrote: Now to the point if you kindly allow. I got involved in a round table discussion around the use of GPS antennas for time and frequency GPS receivers. I tried to make some points from my personal perspective. I got resistance from the audience and the topic went hot very quickly and didn't set at the end. Honestly I would like to share my doubts and opinions with you in order to enhance my experience about the topic. In the end it could also be beneficial to close this debate tomorrow while attending to CENAM's time and frequency forum. Facts and thoughts: 1. The time and frequency attendees at CENAM`s time and frequency forum is reluctant to use GPS antenna splitters for a number of reasons I couldn't conceive. 1.1 They argued that cross talk could happen among ports. I doubt it with the newer models. I have experience with HP and Symmetricom units and they state their products cancel cross talk. Cross-talk can occur, indeed. The main issue should be the connected/unconnected reflections, only very secondary would be leakage of signals from one GPS receiver to another. Both is being handled by measuring and require sufficient port isolation. 1.2 They argued that there could be problems from the power feeding of the antenna and mismatches at the receiver antenna port voltages. Again I doubt it if one uses receivers in the same voltage range There can be. Therefore you should select to use antenna splitters that can 1) Select which port to be feeded from. 2) Back-signal the loss of antenna to the GPS receiver. There are double frequency GPS splitters able to do that. I will soon get some for my private lab. I will measure one I borrowed tomorrow. A third issue would be that passive splitters will give you loss of signal level. Therefore is active splitters recommended. 2. I have been experimenting with GPS constellation coverage with different brands of antennas. I have found different gains, different radiation patterns and as a result different satellites in view for identical GPS receivers. 2.1 I have found that using a single antenna and a two port HP splitter I get the same radiation pattern, gain and identical satellites in view for a set of identical receivers. For comparison purposes I feel this is an adequate scenario. It is easier for me to take care of the transmission line length and errors caused by phase differences, attenuation and delays. 2.2 Two identical GPS receivers each one with it's own antenna, could eventually cause spatial diversity reception for a system of two receivers conceptually set as one for comparison purposes. Different satellites being tracked on each receiver if not connected to a common antenna. Even if antennas and transmission lines are identical. Question is: Am I wrong doing the above mentioned assumptions while considering the use of GPS transmission line splitters? I which scenarios are the splitters recommended? In which cases they are rather not to be considered? Just using a transmission line style Wilkinson power splitter alone is not recommended. The isolation effect between ports is terrible. Using three-port couplers allows for the ports reflection to be loaded into a separate resistor. I think I recall seeing that on the splitters that I have openend up. Thus, it is fairly trivial to isolate the splitter. The Agilent L1 splitters uses resistive power-dividers, which has better isolation at the cost of higher loss, but then they include an amplifier to overcome that, but the amplification is at the input side. If you require isolation between ports, it can be designed in and if you get the devices I have seen, it should be fair isolation. Similarly, the power require similar isolational effects, and again commercial devices addresses these issues. When in doubt, measure the effect. Network analyzers for 1.2-1.7 GHz isn't hard to come by these days. I'll toy around a little with the one at work. Better ask as to start buying more antennas or feel comfortable with my original RF distribution design using splitters. The joy of using multiple antennas is one thing, but if you have a good antenna up, then good cabling in combination with good splitters should work well. Your kind comments and expert advise is always welcome. Thank you! My 2 öre contribution to the discussion. 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] To use or not to use transmission line splitters for GPS receivers
On 10/09/2012 09:27 PM, John Ackermann N8UR wrote: Here's a link to a USNO paper that measured the tempco of three GPS amplifiers: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA490830 They found that amplifier filtering was the prime cause of tempco, and the narrowest bandpass amplifier they looked at had a group delay range of 4 nanoseconds over the range of -15 to +45 degrees C. This is a good paper. I've read it before. It presents three strategies for GPS amplifiers: 1) Wide-band amplifier, represented by the AOA Wideband amplifier 2) Narrow-band amplifier with peaks, represented by the AOA narrow band amplifier 3) Narrow-band amplifier with no peaks, represented by the KW microwave phase-stable narrow band amplifier. The wide-band amplifier has around 4 ns group delay, and it is fairly flat and stable. Since there isn't much delay to start with, it doesn't change a whole lot either. Since the amplifier isn't very flat, it also has some variations in group delay. It's fairly natural. The downside is that it has no suppression of interference, so we should do some damping. The second case tries to achieve just that, but in order to create steep slopes around the pass-band, they have used two resonances, one on each side of the pass-band. You see the peaking effect on the gain curve of figure 1, but oh... they show up clearly in the group delay measurement of figure 2 too. This is expected from the theory, as these two pole-pairs has fairly high Q, their group delay will show this property in the direct vicinity of their respective resonances, just as their contribution to gain will do. So, nice steep slopes and good suppression, but lots of group delay, and by that higher sensitivity to environmental effects, i.e. temperature. The third example shows wider but much flatter amplitude response, and essentially flat group delay. This is what you expect from maximum flat group delay filters such as Bessel/Thompson. No wonders those are specified as measuring filters for digital transmission. Lesser delay, and lesser sensitivity. The downside is that the cost of steep slopes comes from a higher number of needed poles/zeros. Just as I expect from traditional signal theory. Again, you get what you pay for. Now you know why I want a network analyzer reaching this area at home. 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] To use or not to use transmission line splitters for GPS receivers
albertson.ch...@gmail.com said: The satellites are in 12 hour orbits. Everything repeats every 12 hours. But the sun is on a 24 hr. period and if you did two 12 hour tests you don't want to do one at night and one in day. So start each test at the same time of day let it run for 12+ hours. Thanks. After poking around a bit... That's 12 Sidereal hours rather than 12 UTC hours. -- 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.
