[time-nuts] Re; Req: Decent GPS Antenna Active/PassiveRecommendation
At least for the T-bolt moving the antenna to a super-optimal location is a super waste of effort and money. I suspect this applies to most other GPS DOs. Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or a good crystal) you cannot learn much more or provide better than the short term accuracy of the receiver. Improving on this will require a good local standard running open loop. The location should provide tracking of a few satellites - more than 4 if possible - but it will remain locked with as few as 1 or 2. The glitches you see will always occur as the receiver switches satellites and cannot be avoided with even the most perfect antenna location. So the short term ADEV presented by LH jumps around. Fooling around with the damping factor and time constants will not help this much. Set the DF to 1 and the TC to 200 seconds and leave it there. (or something like those values) The way to get a good standard is to open loop (using you fingers) adjust a local Rb such as the LPRO so it maintains a constant phase difference with the GPS 10 MHz for a period of hours. Using the time for the phase to change a measured number of nanoseconds, the frequency offset between the two is easily calculated. There is a HP ap note on how to do this. Use the GPS calibrated local open loop standard for all critical work - not the GPS output. Due to lightning considerations here is Kansas - my GPS antenna is in the front yard at 6 ft elevation and the N.E FOV is shielded by a 3 story house. Result is that the phase as plotted on a strip chart recorder is unchanging for hours relative to my Rb, but the flat plot shows phase jumps from time to time when the receiver shifts satellites. However the long term phase jump always returns to the previous value after the jump. To make further progress you need a good open loop local standard like the LPRO and some way to measure the 10 MHz Phase difference and record it over a period of hours. As to using the pps - I don't know much about doing it that way - however it seems obvious that the 10 MHz phase is more sensitive and faster due to the greater update rate. I could be wrong! Best regards and don't put the thing on the tower. Total waste of effort. Get a Rb. Do protect the receiver from rapid temp changes - -73 john k61ql ___ 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] Re; Req: Decent GPS Antenna Active/PassiveRecommendation
Hi With a good survey and a good antenna location, you can get the jumps in the TBolt down to under 2 ns. That's a lot better than it is with a poor survey and a bad location. Since the time jumps relate directly to frequency, improving one improves the other. (the pps is simply divided down off of the 10 MHz). Bob On Sep 15, 2013, at 12:50 PM, johncr...@aol.com wrote: At least for the T-bolt moving the antenna to a super-optimal location is a super waste of effort and money. I suspect this applies to most other GPS DOs. Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or a good crystal) you cannot learn much more or provide better than the short term accuracy of the receiver. Improving on this will require a good local standard running open loop. The location should provide tracking of a few satellites - more than 4 if possible - but it will remain locked with as few as 1 or 2. The glitches you see will always occur as the receiver switches satellites and cannot be avoided with even the most perfect antenna location. So the short term ADEV presented by LH jumps around. Fooling around with the damping factor and time constants will not help this much. Set the DF to 1 and the TC to 200 seconds and leave it there. (or something like those values) The way to get a good standard is to open loop (using you fingers) adjust a local Rb such as the LPRO so it maintains a constant phase difference with the GPS 10 MHz for a period of hours. Using the time for the phase to change a measured number of nanoseconds, the frequency offset between the two is easily calculated. There is a HP ap note on how to do this. Use the GPS calibrated local open loop standard for all critical work - not the GPS output. Due to lightning considerations here is Kansas - my GPS antenna is in the front yard at 6 ft elevation and the N.E FOV is shielded by a 3 story house. Result is that the phase as plotted on a strip chart recorder is unchanging for hours relative to my Rb, but the flat plot shows phase jumps from time to time when the receiver shifts satellites. However the long term phase jump always returns to the previous value after the jump. To make further progress you need a good open loop local standard like the LPRO and some way to measure the 10 MHz Phase difference and record it over a period of hours. As to using the pps - I don't know much about doing it that way - however it seems obvious that the 10 MHz phase is more sensitive and faster due to the greater update rate. I could be wrong! Best regards and don't put the thing on the tower. Total waste of effort. Get a Rb. Do protect the receiver from rapid temp changes - -73 john k61ql ___ 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] Re; Req: Decent GPS Antenna Active/PassiveRecommendation
I agree with John that it is a super waste of effort and money or at the very least can be for many. But for the extreme time-nut, so what? Being an extreme TBolt nut, and having done this many times before, I have to point out where a large amount of time and effort can help Do protect the receiver from rapid temp changes This is always a good idea and easy to do for the most part, If you want to go total-nuts, and improve things even more, don't let the temp change at all. (LH temp controller) The glitches you see will always occur as the receiver switches satellites and cannot be avoided with even the most perfect antenna location If there are glitches of any kind at any level, that is an indication that something are less than optimal, because the 'glitches can be eliminated with a lot of time, effort, and money Some of the more typical causes of the big of phase jumps glitches that happen when satellites switch are due to: a) wrong antenna location saved b) multipath signals, c) Not enough signal strength d) Az set too low letting in poor signals, or too high not letting in enough satellites e) allowing satellites with too low of signal strength to be included. f) GPS not in fixed location mode. g) A non choke ring antenna that is letting in signals from below. f) others ... Set the DF to 1 and the TC to 200 seconds and leave it there. Good idea for most with a typical TBolt setup, and good enough for most applications, But it can be made more than a decade better with a lot of time, effort, and/or money don't put the thing on the tower. Total waste of effort. Unless you want to get rid of those glitches when the satellites change. Get a Rb. Good idea for most, unless you care more about the ADEV noise from 10ms to 10sec, which is decades worse in the typical small RB than even a stock TBolt. Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or a good crystal) you cannot learn much more or provide better than the short term accuracy of the receiver. Improving on this will require a good local standard running open loop. While having the proper tools will make things faster and easier, they are not necessary. With an extreme amount time, effort, and experience, It can be done using only LadyHeather. LH has the options that will let you set up a TBolt good enough to be able to test most any Rb or Cs. There is no single magic bullet fix. To make a real difference, there is a long list of things that must be done and optimized, and unless you do many things, all of which takes spending a lot of time and effort on, then spending too much time or effort on just one item can be a super waste of time, effort and money even for the extreme Time-Nut. With enough time, effort and/or money, the TBolt's performance can be improved to be decade or two better than the typical stock set-up. So it all depends on now nutty you want to get and how much time to you have to spend to make it better. ws From: johncroos at aol.com Sent: Sunday, September 15, 2013 9:50 AM Subject: [time-nuts] Re; Req: Decent GPS Antenna Active/PassiveRecommendation At least for the T-bolt moving the antenna to a super-optimal location is a super waste of effort and money. I suspect this applies to most other GPS DOs. Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or a good crystal) you cannot learn much more or provide better than the short term accuracy of the receiver. Improving on this will require a good local standard running open loop. The location should provide tracking of a few satellites - more than 4 if possible - but it will remain locked with as few as 1 or 2. The glitches you see will always occur as the receiver switches satellites and cannot be avoided with even the most perfect antenna location. So the short term ADEV presented by LH jumps around. Fooling around with the damping factor and time constants will not help this much. Set the DF to 1 and the TC to 200 seconds and leave it there. (or something like those values) The way to get a good standard is to open loop (using you fingers) adjust a local Rb such as the LPRO so it maintains a constant phase difference with the GPS 10 MHz for a period of hours. Using the time for the phase to change a measured number of nanoseconds, the frequency offset between the two is easily calculated. There is a HP ap note on how to do this. Use the GPS calibrated local open loop standard for all critical work - not the GPS output. Due to lightning considerations here is Kansas - my GPS antenna is in the front yard at 6 ft elevation and the N.E FOV is shielded by a 3 story house. Result is that the phase as plotted on a strip chart recorder is unchanging for hours relative to my Rb, but the flat plot shows phase jumps from time to time when the receiver shifts satellites. However the long term phase jump
