Re: [time-nuts] Thunderbolt reception problems
Warren, Thanks for the Tbolt tips. The power supply was a good linear supply so I doubt that was causing what I see. The room temp was cycling a degree, maybe two, I did sometime see some quick shifts that were not coincident with temperature but they were all less than 10 nS. The largest swings always followed temperature excursions. Even after putting it in a box and lowering the temp. drift to fractions of a degree, I would see swings if as much as 30 nS in 5 minutes. I thought that this was just too much to fool with and decided to use it as a reference for a 900 MHz ham repeater. It will be interesting to see how it does in a room with no heat or air conditioning. I hope to get on next week. I have another one and may, at some time try putting a double oven oscillator to see how it does. I thought about trying an LPRO but I think the Tbolt would just make it worse rather than better. ___ 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] Thunderbolt reception problems
John Thanks, that puts things a bit more in perspective. Sometimes One persons 'A lot' is another persons 'almost Great'. 5 min = 300 sec As much as 30 ns / 300 sec = 0.1ns /sec = less than 1e-10 freq shift A lot of NON broken things can cause that kind of small drift. With under 1e-10 shifts over 5 minutes, see below for some addition comments. ws - Original Message - From: John Green wpxs...@gmail.com To: time-nuts@febo.com Sent: Wednesday, November 25, 2009 9:47 AM Subject: Re: [time-nuts] Thunderbolt reception problems Warren, Thanks for the Tbolt tips. The power supply was a good linear supply so I doubt that was causing what I see. ws) Make sure it is not line sensitive, OR Temperature sensitive. A few mv change on the +12 V could cause that kind of error. Plug the PS into a variac and blow a hair driver at it to make sure that + - 15 % line change 15+ deg does not effect the Tbolt over the 5 min time span. ** The room temp was cycling a degree, maybe two. ws) 1 deg F can cause a 1e-10 freq shift, More important is how fast it is changing. Keeping the changes down to about 1 deg C per hr AT The Tbolt sensor is a conservative overkill that will keep temp from being an issue. ** I did sometime see some quick shifts that were not coincident with temperature but they were all less than 10 nS. ws) This Sounds like the typical Tbolt satellite switching problem. Solution is one or all of the following: Better signal or antenna view, better Position setting, lower AMU, Higher TC, higher elevation setting. The problem is that although these small fast phase jumps do not effect the Peak Phase much, They can cause a great deal of short term Freq noise. ** The largest swings always followed temperature excursions. Even after putting it in a box and lowering the temp. drift to fractions of a degree, I would see swings if as much as 30 nS in 5 minutes. ws) When you first put the Tbolt in a new environment (a box) it will take a couple hours for it to adjust to its new environment. After That, the important thing is what kind of temp change per time does the Tbolt see. Unfortunately, due to the two different kind of sensors used in Tbolts, (one type with high resolution, one is low resolution) this may not always be easy to see. One solution that gives you less phase shift error with 'quick' temp change is to lower the TC, The compromise is Less PP pahse error but you get more ADEV noise at 1 and 10 second tau. With slow changes at 'a fraction of a degree' (a fraction is 1/10 F or less), NOT likely it is the Tbolt drfting unless yours does not have a working Oven Osc at all. Check the current draw of the +12 volts with changing temp to see. More likely it is the Power supply changing IF you are holding the TBOLT constant while the room is changing. OR ANY of your other test equipment that is outside the BOX, and subject ot the quick temp change. ** I thought that this was just too much to fool with and decided to use it as a reference for a 900 MHz ham repeater. It will be interesting to see how it does in a room with no heat or air conditioning. I hope to get on next week. I have another one and may, at some time try putting a double oven oscillator to see how it does. I thought about trying an LPRO but I think the Tbolt would just make it worse rather than better. ws) There are easier ways to get the performance of a double oven Osc without the cost and trouble ... John Green said: mine got a lot worse with TC set to 500 sec. Depends if that was Short term Osc Freq noise or long term Phase drift? Short answer: A TC of 500 can causes a LOT more (x10 +) long term Phase shift error if the temp is changing, especially when the Dac_Gain and Damping are not also set correctly. Here comes those darn Tbolt setting trade offs again. First point is: If you are a battery backed cell site or the average Ham that just wants to know that the in house freq reference is within 1e-9 (1ns drift per second) the default Tbolts settings are fine and make an OK plug and play unit. On the other hand if you are a NUT would like 10 ns per day (1e-13 freq) then the factory defaults are not so good (Said). Another major trade off is if you want the best 1 sec ADEV numbers OR the lowest long term Phase errors. Takes different settings. Using the TC and Damping settings, different trade offs or compromises can be made. BUT until the Dac_Gain is set correctly (which the default setting is NOT), their proper setting And interaction is just a shot in the dark. Dac_gain is the sensitivity of the OXCO EFC input in Hz per Volt. Basic way to find the correct value is to disable the tracking, then output a + and - 0.1 volt Dac difference from its nominal tracking value using Tboltmon S/W, Average the measured + - HZ freq change of the 10 MHZ, multiply by 10, and update the Dac_Gain AND SAVE (sign
Re: [time-nuts] Thunderbolt reception problems
I have been following the discussion regarding Tbolt performance closely. I have 2 of them and have not seen performance even close to what others report. I don't seem to have sensitivity related issues that others have reported. I am feeding Tbolt and Z3801 from a common antenna through a purpose made GPS splitter. The Tbolt seems to see more sats quicker than the Z3801. The Tbolts I have are extremely temperature sensitive. Even putting them in a box to shield them from room temperature variations, they seem to wander around a lot. This sounds crazy and is not in line with what others have reported but when I changed the TC to 500 seconds, mine got a lot worse. I found that a TC of around 10 seconds with a damping of 1 made for the least amount of phase slip compared to a Z3801. ___ 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] Thunderbolt reception problems
John Green said: mine got a lot worse with TC set to 500 sec. Depends if that was Short term Osc Freq noise or long term Phase drift? Short answer: A TC of 500 can causes a LOT more (x10 +) long term Phase shift error if the temp is changing, especially when the Dac_Gain and Damping are not also set correctly. Here comes those darn Tbolt setting trade offs again. First point is: If you are a battery backed cell site or the average Ham that just wants to know that the in house freq reference is within 1e-9 (1ns drift per second) the default Tbolts settings are fine and make an OK plug and play unit. On the other hand if you are a NUT would like 10 ns per day (1e-13 freq) then the factory defaults are not so good (Said). Another major trade off is if you want the best 1 sec ADEV numbers OR the lowest long term Phase errors. Takes different settings. Using the TC and Damping settings, different trade offs or compromises can be made. BUT until the Dac_Gain is set correctly (which the default setting is NOT), their proper setting And interaction is just a shot in the dark. Dac_gain is the sensitivity of the OXCO EFC input in Hz per Volt. Basic way to find the correct value is to disable the tracking, then output a + and - 0.1 volt Dac difference from its nominal tracking value using Tboltmon S/W, Average the measured + - HZ freq change of the 10 MHZ, multiply by 10, and update the Dac_Gain AND SAVE (sign is negative) If you don't have a external counter with enough resolution, You can find the Dac_Gain using the Tbolt 'turnover test'. Even putting them in a box to shield them from room temperature variations, they seem to wander around a lot. My answer depends on what you mean by 'a lot' , but some general comments. It would seem that there are many different OXCO used in Tbolts, from no oven to double oven. Even with my very small sampling, I've seen units where case temp change does not matter much at all to where the temp should be held to under 0.1 deg C change per hr. You may have one of the poor Temperature performing units, BUT more likely what is causing it to wonder around a lot is the GPS. We know the GPS wonders around a lot short term, much more than Temperature can, over short periods of time like 10 seconds. It is safe to say that there is something 'broken' somewhere, if a TC setting of 10 secs works better than a setting of 100 + secs. Just a guess on what is broken is the Data or setup. BUT if you are using a common PS on both units, check it, especially the +12 volts, It should be stable to better than 1mv. Yours may be changing by a volt, to cause the type of errors you are seeing. Also be sure the units are not jumping in and out of holdover due to a high AMU setting and low GPS signal level or indoor antenna. If you can post or send me a plot of what your errors look like, I could make a better guess of what is broken. For those that do not want to fiddle, or customize their settings, but want a better performing Tbolt than the Default settings, For an average NON cell site unit that is in a nice environment, using an outdoor antenna, inside with stable temp, not under the heater outlet, and not being bounced or moved around, A compromise set of values better than the Defaults are: 1) Dac_Gain -3.5 Hz/Volt (default is -5) BUT best to set it to the correct measured value. (If off, the values below will not be correct) Range, unknown, 2) TC of 500 nominal, (default is 100), Range 250 to 750 seconds, Lower numbers give better results if the temp is changing and not controlled, Higher numbers give better weak signal answers. 3) Damping 0.7 nominal (Default is 1.2) Range 0.5 to 1.5 Lower numbers give less long term phase error, Higher numbers lower short term Osc ADEV noise. 4) AMU 2.5 (default is 4), Range 1 to 4, Lower numbers if weak GPS signal. 5) Elevation mask to 15 deg (default is 5) A band-aid compromise setting so that the unit does not lock onto low level signals. ( better to use elevation than AMU because of the behavior of Tbolts control loop) Also important, be sure the unit is in fixed position and not 3D, position tracking or survey mode, AND that it has the antenna's correct location loaded and saved. ws ** - Original Message - From: John Green wpxs...@gmail.com To: time-nuts@febo.com Sent: Tuesday, November 24, 2009 7:45 AM Subject: Re: [time-nuts] Thunderbolt reception problems I have been following the discussion regarding Tbolt performance closely. I have 2 of them and have not seen performance even close to what others report. I don't seem to have sensitivity related issues that others have reported. I am feeding Tbolt and Z3801 from a common antenna through a purpose made GPS splitter. The Tbolt seems to see more sats quicker than the Z3801. The Tbolts I have are extremely temperature sensitive. Even putting them in a box to shield them from room
Re: [time-nuts] Thunderbolt reception problems
Hi Warren, yes, I do think I need to insulate the unit(s) from the room heater. That would probably help, but is a hassle to do. Double OCXO's rule! bye, Said In a message dated 11/23/2009 22:10:33 Pacific Standard Time, warrensjmail-...@yahoo.com writes: Note the plot does not look like the typical Too Hi of TC drift. On his plot, something is causing some pretty quick Phase jumps every 3 hrs or so, that are them being pulled back in. I'm thinking temperature is the most likely cause, which a faster TC will lower the PEAK to Peak by turning some of the long term noise into lower level higher freq noise. Damn always a trade off to made somewhere. ___ 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] Thunderbolt reception problems
Hi Tom, Warren, for now I am planning to identify the two best references I have, then go into fine-tuning these with TC's, damping factors, etc. May not be the best way to do it, but should get me some results close to what I am looking for. What I am looking for is to get a similar measurement capability of the ADEV that Tom measured on the Fury DOCXO on his analyzer: _http://www.leapsecond.com/pages/gpsdo/_ (http://www.leapsecond.com/pages/gpsdo/) bye, Said In a message dated 11/23/2009 21:29:18 Pacific Standard Time, t...@leapsecond.com writes: That could be part of the problem. 8 hours seems really long to me for a PRS10. I mean, it would not surprise me to see a PRS10 time drift by 10's of ns over 1/3 to 1/2 of a day. So I wonder what a TC of just 1 hour would look like. A one-day run using PRS10 alone (no M12 gps) would also settle it one way or another. ___ 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] Thunderbolt reception problems
Said Double OCXO's rule! Agree, Should have a talk with Mark Sims, He has a neat, simple, No cost, double oven solution for the Tbolt using Software... There goes your plug and play, Can't have everything (Yet) ws ** - Original Message - From: saidj...@aol.com To: warrensjmail-...@yahoo.com ; time-nuts@febo.com Sent: Tuesday, November 24, 2009 12:25 PM Subject: Re: [time-nuts] Thunderbolt reception problems Hi Warren, yes, I do think I need to insulate the unit(s) from the room heater. That would probably help, but is a hassle to do. Double OCXO's rule! bye, Said In a message dated 11/23/2009 22:10:33 Pacific Standard Time, warrensjmail-...@yahoo.com writes: Note the plot does not look like the typical Too Hi of TC drift. On his plot, something is causing some pretty quick Phase jumps every 3 hrs or so, that are them being pulled back in. I'm thinking temperature is the most likely cause, which a faster TC will lower the PEAK to Peak by turning some of the long term noise into lower level higher freq noise. Damn always a trade off to made somewhere. ___ 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] Thunderbolt reception problems
Hi Warren, that is correct, I care to make best use of the environment I have, not the one I would like to have (sounds like Rumsfeld, doesn't it?!). It works now with the AMU changes, and I did change the TC to 500 as well. I am comparing against my PRS-10 Rubidium (driven by an M12+ receiver) and phase-measured on my 5370B. Will post a drift plot sometime later today. bye, Said In a message dated 11/22/2009 23:10:53 Pacific Standard Time, warrensjmail-...@yahoo.com writes: Said's situation: 2) How to make the Tbolt work the best that it can with a less than optimized existing setup. Answer: Lower the AMU to 1, rise the elevation to 15or20, increase the TC setting to 500 sec. (It will work better than when the factory defaults are use with the #1 case above) ___ 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] Thunderbolt reception problems
Said I know this is not something that you really want to have to fiddle with, but you may find some of it useful information. More Default changes you may want to consider are: With the default Dac Voltage setting of 0 and the Default Survey setting of DO NOT save position If the power fails, then things have to start all over which can take a ling time. Solution: sorry I do not remember the exact names that tbolt monitor uses, but I think you can get the idea of what is needed from: 1) save the default startup Dac voltage using the current Dac voltage reading. 2) Save the current location (may have to manually copy it, don't remember) OR do a re-survey with the 'save survey location to eeprom' flag set. That and the other default changes you have made Now ALMOST make it a plug and play. Unfortunately still without an sink indicating Led, But With these setting I have never seen mine loose sink or go into holdover unless the power went off or I disconnected the antenna. And then if you really want to make it better, when comparing Phase to your PRS-10, There are other default setting that you can change that will improve it from two to ten times. Without going into the details, the most important are: 1) Let it age a month, 2) ReSet the Dac gain, default is -5Hz/volt mine measured around -3/volt 3) Set the damping, default is 1.2,0.707 works better , Then set TC to 750 sec 4) Don't let the Temperature change fast (or at all), I'm using an active temperature controller, But a big passive 'brick thing' will help. 5) insure the + 12 power supply is real good and does not change or have noise on it. have fun ws *** Hi Warren, that is correct, I care to make best use of the environment I have, not the one I would like to have (sounds like Rumsfeld, doesn't it?!). It works now with the AMU changes, and I did change the TC to 500 as well. I am comparing against my PRS-10 Rubidium (driven by an M12+ receiver) and phase-measured on my 5370B. Will post a drift plot sometime later today. bye, Said *** In a message dated 11/22/2009 23:10:53 Pacific Standard Time, warrensjmail-one at yahoo.com writes: Said's situation: 2) How to make the Tbolt work the best that it can with a less than optimized existing setup. Answer: Lower the AMU to 1, rise the elevation to 15or20, increase the TC setting to 500 sec. (It will work better than when the factory defaults are use with the #1 case above) ___ 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] Thunderbolt reception problems
WarrenS wrote: Some of the disagreement has to do with the fact that Two similar topics, each with a different answer are being mixed together here. Magnus's point: 1) How to make the Tbolt the best that it can be? Answer: Start with a good strong signal and a quiet environment. Actually, that was not my point. My point was that the signal levels is lower than what is the normally recommended level and worse performance may be expected otherwise. Said's situation: 2) How to make the Tbolt work the best that it can with a less than optimized existing setup. Answer: Lower the AMU to 1, rise the elevation to 15or20, increase the TC setting to 500 sec. (It will work better than when the factory defaults are use with the #1 case above) I rather viewed it as, when things isn't as optimal... lower the level to get more sats to play with and thus a more stable situation. These things isn't really in conflict... one is being aware that you left stable ground and the other is how to best handle that situation. Interesting enough, I have both cases with optimized setting running on my bench now and although the #1 is generally about 25% to 50% quieter, It is not always so. About 25% of the time the #2 case is as quiet or quieter. So the less than perfect #2 case is not really a big deal to most. There are much more important things that can be done if one likes to 'tweak fiddle'. Lowering the AMU limit would hopefully get sufficient sats in place, but it can be used to find a balance so that the effective constallation doesn't change, so weak potential dropouts can be cleared off while many reliable (altought maybe just a thad weak) remain in the solution. The AMU limit is a two-edged sword... at least. I was trying to warn about the fact that you now accept lower power signals, and is not just a magical twist of knobs that makes everything good again. There is a benefit in lowering that limit given the situation, and I happilly agree with that. concerning: that you may not get the performance of the spec-sheet. Not a problem, cause they seem careful not to include any specs concerning this except for the 1e-12 per day average. TvBs measurements could be another source... it's just so you know that beyond that point your milage may vary... 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] Thunderbolt reception problems
Hi Warren, et. al, here is a plot (about 20hrs long) of my PRS-10 (driven by a M12+) compared against my Thunderbolt both running from the same antenna feed. Comparison done on the 10MHz outputs, at maximum sample rate on my 5370B counter. Both units have been running for 6+ months now, the Thunderbolt has only been locked for a day+ though. Standard deviation is 7.6ns, and the mean is 1.5ns. Peak to Peak is ~ -15ns to +19ns. I was hoping for slightly better. Not sure who is the better of the two (yet). Bye, Said In a message dated 11/23/2009 11:22:27 Pacific Standard Time, saidj...@aol.com writes: Will post a drift plot sometime later today. bye, Said inline: PRS-10_Thunderbolt.gif___ 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] Thunderbolt reception problems
Said Not bad at around + - 15 ns Peak over a day, IF I got the scaling right it is about 2 hrs division AND there are around 3 hr cycles (10k sec) in the phase (along with lots of other stuff) If it is the Tbolt which is likely, then it is due to some of the other things I warned about like room temp cycling. The Tbolt can get down to the 3 ns RMS range with care and luck. Hate to have to say it cause I know you don't want to add yet more software BUT If you want to know if it is the Tbolt, and how to fixed it. One the way to tell is to use Lady Heather and plot the phase error and Dac voltage at the same time as the PS10 phase difference. If Lady heather shows about the same long term Phase noise then it's the Tbolt, If not its external. If external, and if PS10 is a Stanford Research Systems Rubidium PSR 10 Osc then could be because the TC of the PSR10 is set to the wrong TC, It should be around 10K sec. Something to be aware of, but does not really change how or what you are doing here. Because you are using the same reference for both units (the GPS system), very low freq noise in the reference (GPS) which is much slower than either's TC will not be seen. I was hoping for slightly better. That is asking a lot, If you still feel that way, you should update the other Defaults also and use Mark's Lady heather to check for the other possible causes. Have fun, ws ** - Original Message - From: saidj...@aol.com To: time-nuts@febo.com ; warrensjmail-...@yahoo.com Sent: Monday, November 23, 2009 5:52 PM Subject: Re: [time-nuts] Thunderbolt reception problems Hi Warren, et. al, here is a plot (about 20hrs long) of my PRS-10 (driven by a M12+) compared against my Thunderbolt both running from the same antenna feed. Comparison done on the 10MHz outputs, at maximum sample rate on my 5370B counter. Both units have been running for 6+ months now, the Thunderbolt has only been locked for a day+ though. Standard deviation is 7.6ns, and the mean is 1.5ns. Peak to Peak is ~ -15ns to +19ns. I was hoping for slightly better. Not sure who is the better of the two (yet). Bye, Said In a message dated 11/23/2009 11:22:27 Pacific Standard Time, saidj...@aol.com writes: Will post a drift plot sometime later today. bye, Said ___ 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] Thunderbolt reception problems
The Tbolt can get down to the 3 ns RMS range with care and luck. - over approx what time frame was that RMS average taken? - what frequency reference did you compare against? /tvb ___ 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] Thunderbolt reception problems
Standard deviation is 7.6ns, and the mean is 1.5ns. Peak to Peak is ~ -15ns to +19ns. I was hoping for slightly better. Not sure who is the better of the two (yet). Bye, Said Remember the phase plot that you made is the combined phase wander of both GPSDO: the PRS10/M12 and the TBolt. It could be that the performance of either one individually is slightly better that what you see in your plot, even if they are running off the same antenna. To be sure you would make a run of each against a 3rd standard. Cesium would be good. But lacking that, either GPSDO in free-run mode might shed a little light on the situation. Especially the PRS10 alone vs. the TBolt. TBolt free-run, and TBolt gps-locked. Let me see if I have PRS10/M12 data somewhere. /tvb ___ 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] Thunderbolt reception problems
Hi Tom, in progress now PRS-10 against a FireFly-IIA... The PRS-10 is set to a very long time-constant, more than 8 hours if I remember correctly.. The Thunderbolt is set to 500s TC. bye, Said In a message dated 11/23/2009 20:58:02 Pacific Standard Time, t...@leapsecond.com writes: To be sure you would make a run of each against a 3rd standard. Cesium would be good. But lacking that, either GPSDO in free-run mode might shed a little light on the situation. Especially the PRS10 alone vs. the TBolt. TBolt free-run, and TBolt gps-locked. Let me see if I have PRS10/M12 data somewhere. /tvb ___ 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] Thunderbolt reception problems
Hi Warren, checking the PRS-10 against a FireFly-IIA now, and later this month against a Fury GPSDO. That should clarify which unit has the best performance in my setup, including temperature cycling, the antenna/splitter challenge, etc.. I suspect the PRS-10 with an 8+ hour TC is going to be the best. BTW: the test data is very close to 10 samples/s. bye, Said In a message dated 11/23/2009 20:21:00 Pacific Standard Time, warrensjmail-...@yahoo.com writes: If external, and if PS10 is a Stanford Research Systems Rubidium PSR 10 Osc then could be because the TC of the PSR10 is set to the wrong TC, It should be around 10K sec. Something to be aware of, but does not really change how or what you are doing here. Because you are using the same reference for both units (the GPS system), very low freq noise in the reference (GPS) which is much slower than either's TC will not be seen. ___ 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] Thunderbolt reception problems
/tvb - over approx what time frame was that RMS average taken? a day or so, or forever? if nothing disturbs anything. - what frequency reference did you compare against? GPS, For the most part Using Lady heather plots. Which is Just comparing it to the filtered GPS, and does not take into account GPS drift. (which is similar to what Said is plotting). AND I have checked Lady heather plots against my 10811 set up and they agree very well when a high TC setting is used in the Tbolt, over times longer than the TC setting and shorter than the drifting rate of the 10811. I think the bigger deal is that Said is comparing a cheap little Tbolt using a 'poor' antenna feed, and has not been optimized except for some basic guess defaults and now can't tell if it is the $1,500 + GPS tracked Rubidium or the Tbolt that is in error. I'd say the Tbolt is doing Great. ws The Tbolt can get down to the 3 ns RMS range with care and luck. - over approx what time frame was that RMS average taken? - what frequency reference did you compare against? /tvb ___ 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] Thunderbolt reception problems
I just completed a 4 hour run with a Tbolt pimped out with the optimized AMU (1.0), elevation mask (25 deg), DAC gain (3.458 Hz/V), TC (500 sec), and damping (1.2 ... could be better) settings along with the active temperature control. And I wasn't using the fancy pants Sunday go-to-meetin' antenna. Results were PFDG (pretty freqin' darn good) none the less: RMS of PPS error 2.53 ns, rms of osc error 14 ps, rms of temperature error 26 microdegrees C, max temperature deviation 3.7 millidegrees C (not too shabby for a cardboard box, a little waffle foam, and a PWM modulated fan) All values were based upon the Tbolts self-reported data values. Due to my horrible location issues, there were some satellite constellation and signal dropouts... things could have been better. --- - over approx what time frame was that RMS average taken? - what frequency reference did you compare against? _ Windows 7: I wanted simpler, now it's simpler. I'm a rock star. http://www.microsoft.com/Windows/windows-7/default.aspx?h=myidea?ocid=PID24727::T:WLMTAGL:ON:WL:en-US:WWL_WIN_myidea:112009 ___ 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] Thunderbolt reception problems
Hi Tom, in progress now PRS-10 against a FireFly-IIA... The PRS-10 is set to a very long time-constant, more than 8 hours if I remember correctly.. The Thunderbolt is set to 500s TC. That could be part of the problem. 8 hours seems really long to me for a PRS10. I mean, it would not surprise me to see a PRS10 time drift by 10's of ns over 1/3 to 1/2 of a day. So I wonder what a TC of just 1 hour would look like. A one-day run using PRS10 alone (no M12 gps) would also settle it one way or another. You might also try a run with the TBolt TC = 100s to see if that makes a difference. The symptom of too large a TC is excessive wander (because you are giving the OCXO too much say over the GPS engine). Sorry if this just makes more work for you. But the matrix of settings to try and the references to use is bounded. So even if each run takes a day, you'll have real data within a week. Unless you're independently sure of your TBolt OCXO and your sky/volt/temp/air lab environment, I'd worry some about a TC that's too long. There's also the issue of the correct damping factor to match the TC you use. Warren can explain that better. /tvb ___ 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] Thunderbolt reception problems
Said I'd sure guess a good disciplined rubidium should win over the Tbolt. But if the Tbolt does not come in a close second, Give me another chance to change some of your other default setting. It would be interesting to see what the ADEV plot looks like using Ulrich's plotter program. . OR email me your raw data file. ws - Original Message - From: saidj...@aol.com Subject: Re: [time-nuts] Thunderbolt reception problems Hi Warren, checking the PRS-10 against a FireFly-IIA now, and later this month against a Fury GPSDO. That should clarify which unit has the best performance in my setup, including temperature cycling, the antenna/splitter challenge, etc.. I suspect the PRS-10 with an 8+ hour TC is going to be the best. BTW: the test data is very close to 10 samples/s. bye, Said In a message dated 11/23/2009 20:21:00 Pacific Standard Time, warrensjmail-...@yahoo.com writes: If external, and if PS10 is a Stanford Research Systems Rubidium PSR 10 Osc then could be because the TC of the PSR10 is set to the wrong TC, It should be around 10K+ sec. Something to be aware of, but does not really change how or what you are doing here. Because you are using the same reference for both units (the GPS system), very low freq noise in the reference (GPS) which is much slower than either's TC will not be seen. ___ 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] Thunderbolt reception problems
Tom said I'd worry some about a TC that's too long. There's also the issue of the correct damping factor to match the TC you use. Too true, this started out to be just an antenna feed issue. and it sounded like Said wanted to keep it simple. I did not know this was going to be a Phase face off, The 500 TC AND a 1.2 damping AND a DAC_Gain that is not set correct will very likely be too long for best phase long term error. It is more optimized to keep the short term Osc Freq noise down due to low signal levels. WITH the correct Dac_gain and Damping, a TC of 500 should be fine, IF he has a good controlled temperature environment. Note the plot does not look like the typical Too Hi of TC drift. On his plot, something is causing some pretty quick Phase jumps every 3 hrs or so, that are them being pulled back in. I'm thinking temperature is the most likely cause, which a faster TC will lower the PEAK to Peak by turning some of the long term noise into lower level higher freq noise. Damn always a trade off to made somewhere. ws ** Hi Tom, in progress now PRS-10 against a FireFly-IIA... The PRS-10 is set to a very long time-constant, more than 8 hours if I remember correctly.. The Thunderbolt is set to 500s TC. That could be part of the problem. 8 hours seems really long to me for a PRS10. I mean, it would not surprise me to see a PRS10 time drift by 10's of ns over 1/3 to 1/2 of a day. So I wonder what a TC of just 1 hour would look like. A one-day run using PRS10 alone (no M12 gps) would also settle it one way or another. You might also try a run with the TBolt TC = 100s to see if that makes a difference. The symptom of too large a TC is excessive wander (because you are giving the OCXO too much say over the GPS engine). Sorry if this just makes more work for you. But the matrix of settings to try and the references to use is bounded. So even if each run takes a day, you'll have real data within a week. Unless you're independently sure of your TBolt OCXO and your sky/volt/temp/air lab environment, I'd worry some about a TC that's too long. There's also the issue of the correct damping factor to match the TC you use. Warren can explain that better. /tvb ___ 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] Thunderbolt reception problems
I just completed a 4 hour run with a Tbolt pimped out with the optimized AMU (1.0), elevation mask (25 deg), DAC gain (3.458 Hz/V), TC (500 sec), and damping (1.2 ... could be better) settings along with the active temperature control. And I wasn't using the fancy pants Sunday go-to-meetin' antenna. Results were PFDG (pretty freqin' darn good) none the less: RMS of PPS error 2.53 ns, rms of osc error 14 ps, rms of temperature error 26 microdegrees C, max temperature deviation 3.7 millidegrees C (not too shabby for a cardboard box, a little waffle foam, and a PWM modulated fan) Mark, I like the temperature control. More on that later. I'd like to see the raw data for the pps and osc figures, maybe once it gets over 24 hours. All values were based upon the Tbolts self-reported data values. You realize that when you use self-reported values what you are measuring is mostly how tight the loop is closed, rather than the true performance of the TBolt 10 MHz output. For short tau the TBoltmon/LH self-reported values are misleading by as much as 100x; but for long tau it's usually within 2x of the correct value, which is good enough for most people. But either way, it sounds like your TBolt is doing very well. One of these days we need to get you a Rb or Cs so you can take data on the real performance of the TBolt, not just the self-reported values. There's an example for you of the difference under: http://www.leapsecond.com/pages/tbolt-tic/ I need to finish that page but even the rough plot tells much of the story. /tvb ___ 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] Thunderbolt reception problems
Magnus said Actually, that was not my point. Yea I know, but I hoped it was close enough to what we do agree on. My point was that the signal levels is lower than what is the normally recommended level and worse performance may be expected otherwise. That is a good example of speculations with possible truth. Myself, I have not seen the recommended signal level, especially for OUR application. And to say the performance will be worse, Maybe, Maybe not. Have you tested it to know where it starts degrading? My thought is JUST because it is a factory default, That is a long way from saying it is the BEST or even a recommended setting for OUR application (which is not a cell site). If you take the idea that the Default is the recommended best logic a bit further then It would seem to say that: A TC of 100, A damping of 1.2, a Dac_startup voltage of zero, NO location stored after a site survey, a Dac gain of -5Hz/V, a survey of 3000, and ... ARE all the best thing to use,... I hope you know none of that is not true. Changing any and ALL of the above INCLUDING AMU, and performance can be improved in our application'. I rather viewed it as, when things isn't as optimal... lower the level to get more sats to play with and thus a more stable situation. Close, BUT not quite correct. Has more do with the Tbolt's control loop design and how it handles when satellites switch in and out, which unfortunately is not optimized for Our application, and the low AMU setting is just a Band-Aid to help that.. These things isn't really in conflict... one is being aware that you left stable ground and the other is how to best handle that situation. Yes, I think we ALMOST agree here, IF you change the 'You left stable ground' statement to You could made it even better.. Lowering the AMU limit would hopefully get sufficient sats in place, but it can be used to find a balance so that the effective constellation doesn't change, so weak potential dropouts can be cleared off while many reliable (although maybe just a thad weak) remain in the solution. The AMU limit is a two-edged sword... at least. Close but only partially true. Its pretty much a single edge ... Lower the AMU and raise the elevation and things will get better for all fix location signal conditions. Only real question is what is the optimum setting of the AMU when there is a good strong signal Answer is probable about 3. One of the faults with your statement, so weak potential dropouts can be cleared off while many reliable remain in the solution. That assumes there are MORE than 8 sat available for it to choose from, which is seldom the case. And during the few times that there are more than 8 to choose from, your statement would indicate that the way they are choosing which to use is not at all based on signal level directly or indirectly. Myself I do not know what their criteria is, I did not see an independent setting like on the Motorola Oncores that say take the highest and strongest ones when in fixed position mode and take the lowest ones when tracking position. I'm going to give them some credit and say they probable got the basics right. I was trying to warn about the fact that you now accept lower power signals, And we fully agree here and is not just a magical twist of knobs that makes everything good again. We agree here, no magic, just need to change the default AMU, which is all 'Said was asking for. There is a benefit in lowering that limit given the situation, and I happily agree with that. And we agree again. So we do not actually disagree on much, just like to argue the Finer points. If you would like to discuss a fix that is better than the AMU band-aid I'm now using, glad to talk about how I plan to modify their control loop to work better. Have fun ws *** - Original Message - From: Magnus Danielson mag...@rubidium.dyndns.org To: WarrenS warrensjmail-...@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, November 23, 2009 4:06 PM Subject: Re: [time-nuts] Thunderbolt reception problems WarrenS wrote: Some of the disagreement has to do with the fact that Two similar topics, each with a different answer are being mixed together here. Magnus's point: 1) How to make the Tbolt the best that it can be? Answer: Start with a good strong signal and a quiet environment. Actually, that was not my point. My point was that the signal levels is lower than what is the normally recommended level and worse performance may be expected otherwise. Said's situation: 2) How to make the Tbolt work the best that it can with a less than optimized existing setup. Answer: Lower the AMU to 1, rise the elevation to 15or20, increase the TC setting to 500 sec. (It will work better than when the factory defaults are use with the #1 case above) I rather viewed it as, when things
Re: [time-nuts] Thunderbolt reception problems
b...@lysator.liu.se wrote: Hi Said, With your background, I assumed you would know better... What is your antenna gain? What is your antenna cable loss? Does the Tbolt work correctly connected directly to the GPS antenna? Do you have an inline LNA to add close to the antenna? Do you have a higher gain antenna available? If 10dB is a lot or nost... that DO depend on the circumstances. If you already moved the signal towards the lower end of the input sensitivity range, then adding additional loss is an issue. GPS receivers degrade their performance gracefully with lower input signal to the point where it degrades more and more ungracefully. It's one of the tests that one should do. I have come to realize that my rig suffers severly from cable-loss and the lack of antenna gain to be followed by a passive splitter before it hits an active splitter. I had to build a gain-rig to overcome part of that, but it doesn't feel right to use two LNAs in series. It's just darkness before my eyes but it works. The first fix to this is an inline amplifier to be inserted at the antenna. Another fix would be to use a better antenna cable. 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] Thunderbolt reception problems
Using two Bullet II, Trimble p/n 4155600, antennas with all my receivers for now. They feed two cheap TV satellite splitters 4 receiver ports each, DC power diode steered to the antenna port from each receiver port. Feed line is RG6 50 to 75 feet in length. Never had less than one less than the max number of sats being tracked most of the time at the max. Receiver list: 3 thunderbolts, Lucent cell site GPSDO with resistor to load antenna detecting circuit, 2 Trak System 8820 type station clock GPSDO one with 8 channel one with 6 channel receiver. In the past have used other receivers like Zyfer with no problems. Stanley ___ 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] Thunderbolt reception problems
Hi Guys, changing the AMU thresholds to 2.0 as suggested by Warren fixed the problem, the unit is now working properly, thanks much for the hint. And no, this was not obvious to me. It is always great to get constructive help rather than the you should know better type of comments. In the end, it looks like this turned out to be a configuration issue rather than a receiver sensitivity issue. But this also begs the question: how much performance degradation will I get when using 2.0 as the AMU threshold rather than the factory default. There must have been a reason why Trimble set the default so high, they mention something about multipath rejection in the manual. Why do I want to get this unit up and running: this unit has been tested to have very good phase noise performance. I'll use anyone's low noise source anyday. bye, Said In a message dated 11/22/2009 07:06:00 Pacific Standard Time, mag n...@rubidium.dyndns.org writes: If you already moved the signal towards the lower end of the input sensitivity range, then adding additional loss is an issue. GPS receivers degrade their performance gracefully with lower input signal to the point where it degrades more and more ungracefully. It's one of the tests that one should do. I have come to realize that my rig suffers severly from cable-loss and the lack of antenna gain to be followed by a passive splitter before it hits an active splitter. I had to build a gain-rig to overcome part of that, but it doesn't feel right to use two LNAs in series. It's just darkness before my eyes but it works. The first fix to this is an inline amplifier to be inserted at the antenna. Another fix would be to use a better antenna cable. 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] Thunderbolt reception problems
In a message dated 22/11/2009 19:45:35 GMT Standard Time, saidj...@aol.com writes: changing the AMU thresholds to 2.0 as suggested by Warren fixed the problem, the unit is now working properly, thanks much for the hint. And no, this was not obvious to me. Hi Said Just out of interest, what levels of AMU are you seeing reported? According to Trimble's Thunderbolt Monitor version 2.6 the six satellites I'm tracking right now are showing AMU values of over 40 and another stops tracking when its AMU drops to approx 33 but starts tracking again at a reported AMU of approx 36 to 37. My signal level mask is set to 4.0, and I don't seem to have had any problems because of that, but I'm intrigued as to the actual relationship between the quantity described as the signal level mask and the reported AMU levels. I would have assumed the units to be the same but that doesn't seem to be the case. OK, so I've just dropped the threshold to 2.0 and am now tracking eight satellites, with the reported levels for the one mentioned above still varying as before and another just below 30 with neither dropping out, but I'm still non the wiser as to the actual value of the set threshold in terms of the reported AMU levels. regards Nigel GM8PZR ___ 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] Thunderbolt reception problems
Said changing the AMU thresholds to 2.0 fixed the problem, If 3 was not working, you should be able to go lower than 2, likely 1.0 to 1.5 will be better yet. The way I tell is using Lady Heather, if there are satellites signals with levels between 20 and 30 dBc with good ACCUs that are still not being used, I lower the AMU value using Tboltmon.exe. how much performance degradation will I get when using 2.0 as the AMU threshold rather than the factory default. Here is what I have found, concerning that question. Lowering the AMU will likely improve the noise performance of the typical setup, for some less than oblivious reasons concerning how the Tbolt reacts in holdover mode and when satellites are switched in and out due to their signal level. Much better to use a weak signal than have no signal AND also better not to toggle a satellite in and out that is on the threshold, Better to lower the AMU threshold and rise the elevation mask. Concerning the relation of AMU to dBc, what I've seen is: AMU of 4 is in the high 30, AMU of 3 is in the mid 30, AMU of 2 is in the high 20, AMU of 1 is in the mid 20, A good outdoor antenna will give dBc in the high 40 to 50s and poor indoor antena will give dBc in the mid 30's AND still works fine, and anything above 25 dBc works OK when in the fixed position 'Overdetermined Clock' mode. To the different question of how much will the performance be degraded using a weak antenna signal, Again the not so oblivious answer is typically only a little, and may even help in some cases. Weak signals need the TC to be set higher than the default 100 sec, OR performance will be degraded. The added signal noise needs to be averaged over a longer time period. My experience is that using a standard 'car' antenna indoors, with a properly set TC, Damping and Dac_Gain will out perform a unit on a good view outdoor antenna IF that Tbolt is still set to the default settings, which most seem to be. The difference I see when Both are set up correct is around 25%. The bottom line is that a good signal AND an accurate location, IS required to get the VERY BEST performance from a Tbolt, BUT there are MANY other things that have MUCH more effect that are often overlooked. ws ** Hi Guys, changing the AMU thresholds to 2.0 as suggested by Warren fixed the problem, the unit is now working properly, thanks much for the hint. And no, this was not obvious to me. It is always great to get constructive help rather than the you should know better type of comments. In the end, it looks like this turned out to be a configuration issue rather than a receiver sensitivity issue. But this also begs the question: how much performance degradation will I get when using 2.0 as the AMU threshold rather than the factory default. There must have been a reason why Trimble set the default so high, they mention something about multipath rejection in the manual. Why do I want to get this unit up and running: this unit has been tested to have very good phase noise performance. I'll use anyone's low noise source anyday. bye, Said ___ 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] Thunderbolt reception problems
I am using a Tbolt with a Symmetricom 58432A antenna, half sky view, and a HP 58515A distribution amplifier without any problems, using the default parameters. Geraldo Lino de Campos gera...@decampos.net ___ 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] Thunderbolt reception problems
Dear Said, saidj...@aol.com wrote: Hi Guys, changing the AMU thresholds to 2.0 as suggested by Warren fixed the problem, the unit is now working properly, thanks much for the hint. And no, this was not obvious to me. It is always great to get constructive help rather than the you should know better type of comments. I certainly understand that one. In the end, it looks like this turned out to be a configuration issue rather than a receiver sensitivity issue. But this also begs the question: how much performance degradation will I get when using 2.0 as the AMU threshold rather than the factory default. There must have been a reason why Trimble set the default so high, they mention something about multipath rejection in the manual. I kindly disagree... sorry for the long rambling motivation. While I have not been able to conclude exactly what the AMU measure really is (Amplitude Measurement Unit), but it is similar at least to C/N measures. When the receiver has a bad C/N measure from a certain source, it may be wise not to rely on it. The signal level from each sat can be configured to be delivered in either AMU or in dB-Hz where the later allows comparision among other GPSes. The best description of AMU I have is from the Lassen iQ manual where it states: Note – The signal level provided in this packet is a linear measurement of the signal strength after correlation or de-spreading. Units, either AMU or dBHz, are controlled by Packet 0x35. Thus, you can request the 20*log10(AMU)+Const that converts it into dB/sqrt(Hz) measure. The Lassen iQ AMU limit is default at 2 and for extended sensitivity 1.2. The Thunderbolt AMU values may not need to have the same relationship to dB/sqrt(Hz) as the Lassen iQ, but there may be more to it. The Lassen iQ is tailored towards navigation gear (hence the garage startup) where as the Thunderbolt is aimed at timing. Regardless, AMU or C/N measures is an indication of correlation strength and thus a measure of signal quality. It should rightfully contribute to the TDOP measure. The AMU limit is a pre-T-RAIM cleanup protection value. If you needed to lower your AMU limit from 4 to 2, you are feeding the Thunderbolt a signal level below the intended levels. A 6 dB raise and you would not have needed to shift the limit for the same tracking result. Regardless of where the limit is, the lower AMU values will indicate a higher noise level and thus higher uncertainty in time than otherwise obtained. So, the 10 dB loss in the 1-to-4 splitter is significant here. It's just unfortunate that the Thunderbolt is not clearer about it. Why do I want to get this unit up and running: this unit has been tested to have very good phase noise performance. I'll use anyone's low noise source anyday. Which is also why I like to see mine operational, alongside my Z3801, GPS-4 and 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] Thunderbolt reception problems
b...@lysator.liu.se wrote: Hi Nigel, AMU and SNR are two different scales. I do not have a translation. A Kepler award recepient once explained Trimbles AMU as a meaningless unit. That said, SNR or C/N0 values cannot be directly compared between different receivers since the measures might be taken at different points in the receiver. AMU is just a scaled linear correlation measure. Either this is Ip or the vector sum of Ip and Qp. Ip would suffice onces locked in. C/N measure is a combination of that and that of the pre-correlator noise. Wither this has been done or not is unknown. The Trimble monitor program can be made to switch between AMU and SNR in one of the configuration menues. I think you might have switched to SNR. With above uncertanty of specific SNR definitions noted, most receivers are enjoying an excellent signal if the highest elevation receivers have a SNR above 50. If the highest SVs get +45dB that is still decent. This is where C/N excel over AMU, it's easier to compare to other receivers. 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] Thunderbolt reception problems
In a message dated 22/11/2009 21:23:49 GMT Standard Time, b...@lysator.liu.se writes: AMU and SNR are two different scales. I do not have a translation. A Kepler award recepient once explained Trimbles AMU as a meaningless unit. That said, SNR or C/N0 values cannot be directly compared between different receivers since the measures might be taken at different points in the receiver. The Trimble monitor program can be made to switch between AMU and SNR in one of the configuration menues. I think you might have switched to SNR. -- Ah, that explains it, I wasn't aware there were two options but you're quite right. I don't recall switching it, and Thunderbolt Monitor doesn't seem to have the option to switch it anyway, but I found the option in GPSMon 1v05 and 1v6 and it can indeed be toggled. Whereas GPSMon changes the label of the field to suit it doesn't help that Thunderbolt Monitor leaves it described as AMU regardless of the setting:-) regards Nigel GM8PZR ___ 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] Thunderbolt reception problems
In a message dated 22/11/2009 21:48:14 GMT Standard Time, warrensjmail-...@yahoo.com writes: Concerning the relation of AMU to dBc, what I've seen is: AMU of 4 is in the high 30, AMU of 3 is in the mid 30, AMU of 2 is in the high 20, AMU of 1 is in the mid 20, A good outdoor antenna will give dBc in the high 40 to 50s and poor indoor antena will give dBc in the mid 30's AND still works fine, and anything above 25 dBc works OK when in the fixed position 'Overdetermined Clock' mode. -- Hi Warren That's just what I was looking for and the rest of your post was very informative too, definitely one I'll save for reference. Many thanks Nigel GM8PZR ___ 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] Thunderbolt reception problems
gandal...@aol.com wrote: In a message dated 22/11/2009 21:23:49 GMT Standard Time, b...@lysator.liu.se writes: AMU and SNR are two different scales. I do not have a translation. A Kepler award recepient once explained Trimbles AMU as a meaningless unit. That said, SNR or C/N0 values cannot be directly compared between different receivers since the measures might be taken at different points in the receiver. The Trimble monitor program can be made to switch between AMU and SNR in one of the configuration menues. I think you might have switched to SNR. -- Ah, that explains it, I wasn't aware there were two options but you're quite right. I don't recall switching it, and Thunderbolt Monitor doesn't seem to have the option to switch it anyway, but I found the option in GPSMon 1v05 and 1v6 and it can indeed be toggled. The Thunderbolt Monitor does have it, I just ticked the box and had my C/N measures instead. In the Setup menu, select Packet Masks and Options... where you in the Packer 35 Options frame, the Auxiliary (Byte 3) sub-frame find a tick-box for Output dBc/Hz. Tick the tick-box and press the Set Options button and you get dBc/Hz values rather than AMU values. Whereas GPSMon changes the label of the field to suit it doesn't help that Thunderbolt Monitor leaves it described as AMU regardless of the setting:-) A bit confusing indeed, but the values should never really overlap, so values should be a good hint on what to expect. Bottom line, use C/N values whenever you can. 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] Thunderbolt reception problems
In a message dated 23/11/2009 00:06:52 GMT Standard Time, mag...@rubidium.dyndns.org writes: The Thunderbolt Monitor does have it, I just ticked the box and had my C/N measures instead. In the Setup menu, select Packet Masks and Options... where you in the Packer 35 Options frame, the Auxiliary (Byte 3) sub-frame find a tick-box for Output dBc/Hz. Tick the tick-box and press the Set Options button and you get dBc/Hz values rather than AMU values. -- Yes, you're quite correct, obviously one of my not very observant days:-) --- Whereas GPSMon changes the label of the field to suit it doesn't help that Thunderbolt Monitor leaves it described as AMU regardless of the setting:-) A bit confusing indeed, but the values should never really overlap, so values should be a good hint on what to expect. Agreed, once you're actually aware there's more than one option:-) regards Nigel GM8PZR ___ 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] Thunderbolt reception problems
If you needed to lower your AMU limit from 4 to 2, you are feeding the Thunderbolt a signal level below the intended levels. True, You MAY be feeding it a signal that is below what the cell site recommended High gain outdoor antenna will give it. But any conclusion past that sounds like pure speculation. And most of use are not using them in cell sites. I Can not comment on the other units Magnus referred to that don't work if set too low, and I can not say what AMU is in the Tbolt BUT I can say with certainty that setting it to a value of 1 or 2 with 'Tboltmon.exe' version 1.2 works fine and 1 works MUCH BETTER than 4 in some setup. Looks like the Tbolt software is not so dumb as to use sat signals that will screw it up. 'Trimble GPS Monitor V1-2.pdf' instructions on page 13 shows the signal level mask (AMU) set to 0.6 ws said In the end, it looks like this turned out to be a configuration issue rather than a receiver sensitivity issue. But this also begs the question: how much performance degradation will I get when using 2.0 as the AMU threshold rather than the factory default. There must have been a reason why Trimble set the default so high, they mention something about multipath rejection in the manual. I kindly disagree... ... snip If you needed to lower your AMU limit from 4 to 2, you are feeding the Thunderbolt a signal level below the intended levels. ... 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] Thunderbolt reception problems
Warren, WarrenS wrote: If you needed to lower your AMU limit from 4 to 2, you are feeding the Thunderbolt a signal level below the intended levels. True, You MAY be feeding it a signal that is below what the cell site recommended High gain outdoor antenna will give it. But any conclusion past that sounds like pure speculation. And most of use are not using them in cell sites. True, but lowering this value should be a warning-sign that you may not get the performance of the spec-sheet. There where some debate on wither the signal level was an issue or not. Lowering the AMU limit only lowers the acceptance level of signal strength for a sat in view to be accepted for tracking. Regardless how AMU is cooked up (an issue we could ponder over as a side-track), it remains a signal strength measure. I Can not comment on the other units Magnus referred to that don't work if set too low, and I can not say what AMU is in the Tbolt BUT I can say with certainty that setting it to a value of 1 or 2 with 'Tboltmon.exe' version 1.2 works fine and 1 works MUCH BETTER than 4 in some setup. Looks like the Tbolt software is not so dumb as to use sat signals that will screw it up. It uses the AMU limit to select among the available sats. It then uses the T-RAIM to cancel out any outliners among that subset of sats to churn out which sats is being used for positioning/timing solution. The AMU limit is nothing magic, it's only that we don't have a good reference to what the AMU value is in detail, but we do know that high values is good and low values is bad. Lowering the AMU value as you did is good in the sense that you got more sats to actively track. It is bad that the signal levels the Thunderbolt is experience is so low that you need to take that action. Low signal values means more timing noise and thus more timing instabilty. Having a few sats is better than none. So it is an indication that the unit would like some more gain... 10 dB or so. 'Trimble GPS Monitor V1-2.pdf' instructions on page 13 shows the signal level mask (AMU) set to 0.6 If the statement that AMU is a linear scale is correct, that would mean that the C/N limit is set 16,5 dB lower than normally, i.e. that C/N being 16,5 dB lower can be accepted. It would be fun to play around with a variable damper to see what relationship to level the AMU value is on the Thunderbolt. 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] Thunderbolt reception problems
Hi Nigel, et. al., I just changed the setting to C/No with the help of the instructions posted here; learned yet something else. With that I now get between 30 and 36dBc/Hz C/No (at night, which usually results in higher values than during daylight). I am impatient, and expect my equipment to be plug-and-play, this is what cause my frustration and surprise in the first place, since I did not have a problem with this antenna feed in the past. Due to the lack of a lock LED, and these issues, I guess I will have to dedicate an RS-232 to constantly monitor the unit, and be content with it's performance when connected to the splitter. That's better than drilling another hole into the wall and mounting another antenna on the roof. Thanks for everyone's help, bye, Said In a message dated 11/22/2009 12:14:01 Pacific Standard Time, gandal...@aol.com writes: Just out of interest, what levels of AMU are you seeing reported? According to Trimble's Thunderbolt Monitor version 2.6 the six satellites I'm tracking right now are showing AMU values of over 40 and another stops tracking when its AMU drops to approx 33 but starts tracking again at a reported AMU of approx 36 to 37. ___ 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] Thunderbolt reception problems
Something in the last post got cut off... Anything you can do to minimize satellite constellation changes is good. If reducing the signal level cutoff threshold or changing the elevation mask angle works for your installation, go for it. It appears that the effects of constellation changes is worse than the effects of low signal levels. _ Bing brings you maps, menus, and reviews organized in one place. http://www.bing.com/search?q=restaurantsform=MFESRPpubl=WLHMTAGcrea=TEXT_MFESRP_Local_MapsMenu_Resturants_1x1 ___ 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] Thunderbolt reception problems
Mark Sounds like the same problem I had when I had the AMU set TOO high. ( I don't think it can be set with LH, Need Tboltmon to change it) I have not seen the condition that you describe where the Tbolt will switch satellites just because it has found a better one. (I don't think that happens) Mine will hold all eight and will not release any unless the signal level goes below the AMU setting. I do not know of any other way that will causes a satellite to switch out in only a few minutes when tracking under 8. When I had the AMU set too high, and the signal level was right at the bounty, then the satellites would tend to toggle in and out as you described. The solution for me was to set the AMU to one so that the Tbolt did not release a satellite once it got it, and I also raised the elevation mask so that it did not pick up the satellite until the satellite got higher and stronger in the sky. In my location which sounds similar to yours, with Elevation set high and the AMU set low it no longer toggles. As you said the worse thing for noise is when the Tbolt toggles the satellites in and out. This is much worse than holding a low level noisy signal. My unit works fine now with the TC set to 750+ seconds when there is ANY signal at least in the high 20s, which is always the case at my location. The High TC setting of 500+ and a damping setting of 0.7 (and Dac gain set correct) greatly helps in reducing the noise cause by satellites switching. ws ** Mark Sims said: I have considerable experience operating Thunderbolts in less than optimum conditions (my house is in an urban jungle, surrounded by Jurassic trees and nasty multipath monsters). Lady Heather defaults to the dBc setting since that seems to be the most understandable and better defined system. Signal levels above 40 are very good. There seems to be little to be gained with signals above 40. Above 35 are OK-ish. From 32-35 are usable, if you are not too picky about your system. Below 32 are just plain craptastic and pretty much unusable. The most problematic and intractable source of Tbolt output errors seem to be the result of satellite constellation changes as the unit constantly switches between satellites in an effort to track the best available satellites. If you plot the satellite count and DAC voltage (and along with the PPS error estimate) you will see that the DAC voltage changes with every satellite constellation change. This causes the oscillator to change frequency. The better your signal levels, the less reason the unit has to switch tracked satellites and the better will be your oscillator and PPS outputs. The Tbolt firmware supplies few tools for minimizing its annoying habit of tracking the supposedly best satellites of any given instant. At my location, I am doing real good if the tracked satellite constellation stays fixed for over a minute... ___ 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] Thunderbolt reception problems
Some of the disagreement has to do with the fact that Two similar topics, each with a different answer are being mixed together here. Magnus's point: 1) How to make the Tbolt the best that it can be? Answer: Start with a good strong signal and a quiet environment. Said's situation: 2) How to make the Tbolt work the best that it can with a less than optimized existing setup. Answer: Lower the AMU to 1, rise the elevation to 15or20, increase the TC setting to 500 sec. (It will work better than when the factory defaults are use with the #1 case above) Interesting enough, I have both cases with optimized setting running on my bench now and although the #1 is generally about 25% to 50% quieter, It is not always so. About 25% of the time the #2 case is as quiet or quieter. So the less than perfect #2 case is not really a big deal to most. There are much more important things that can be done if one likes to 'tweak fiddle'. concerning: that you may not get the performance of the spec-sheet. Not a problem, cause they seem careful not to include any specs concerning this except for the 1e-12 per day average. ws - Original Message - From: Magnus Danielson mag...@rubidium.dyndns.org To: WarrenS warrensjmail-...@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, November 22, 2009 5:03 PM Subject: Re: [time-nuts] Thunderbolt reception problems Warren, WarrenS wrote: If you needed to lower your AMU limit from 4 to 2, you are feeding the Thunderbolt a signal level below the intended levels. True, You MAY be feeding it a signal that is below what the cell site recommended High gain outdoor antenna will give it. But any conclusion past that sounds like pure speculation. And most of use are not using them in cell sites. True, but lowering this value should be a warning-sign that you may not get the performance of the spec-sheet. There where some debate on wither the signal level was an issue or not. Lowering the AMU limit only lowers the acceptance level of signal strength for a sat in view to be accepted for tracking. Regardless how AMU is cooked up (an issue we could ponder over as a side-track), it remains a signal strength measure. I Can not comment on the other units Magnus referred to that don't work if set too low, and I can not say what AMU is in the Tbolt BUT I can say with certainty that setting it to a value of 1 or 2 with 'Tboltmon.exe' version 1.2 works fine and 1 works MUCH BETTER than 4 in some setup. Looks like the Tbolt software is not so dumb as to use sat signals that will screw it up. It uses the AMU limit to select among the available sats. It then uses the T-RAIM to cancel out any outliners among that subset of sats to churn out which sats is being used for positioning/timing solution. The AMU limit is nothing magic, it's only that we don't have a good reference to what the AMU value is in detail, but we do know that high values is good and low values is bad. Lowering the AMU value as you did is good in the sense that you got more sats to actively track. It is bad that the signal levels the Thunderbolt is experience is so low that you need to take that action. Low signal values means more timing noise and thus more timing instabilty. Having a few sats is better than none. So it is an indication that the unit would like some more gain... 10 dB or so. 'Trimble GPS Monitor V1-2.pdf' instructions on page 13 shows the signal level mask (AMU) set to 0.6 If the statement that AMU is a linear scale is correct, that would mean that the C/N limit is set 16,5 dB lower than normally, i.e. that C/N being 16,5 dB lower can be accepted. It would be fun to play around with a variable damper to see what relationship to level the AMU value is on the Thunderbolt. 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] Thunderbolt reception problems
Maybe something too basic many too say, but did you lower the Tbolts signal level mask AMU setting? Default is 3, set to 1 or 2 so that it will accept lower level signals - Original Message - From: saidj...@aol.com To: time-nuts@febo.com Sent: Saturday, November 21, 2009 11:40 AM Subject: [time-nuts] Thunderbolt reception problems Hi guys, some weeks ago we talked about reception problems on Trimble Thunderbolt units. I finally took the time to download the Trimble monitor again, and get my unit locked again. Here is what I found: The unit was running continuously for the last months, but wasn't locked. Using the Trimble monitor, I restarted the unit, now connected directly to my antenna, then after the survey was done let it run from my antenna splitter. This works, but just barely. I use an Agilent 58512A amp, followed by a Mini Circuits ZB4PD1-152-75+ 1-to-4 passive splitter. In the attached plot a JLT FireFly-IIA and the Thunderbolt are both running from the same Mini Circuits splitter. The Antenna sense circuit in the Thunderbolt is happy, but the signal strength is just at the threshold of working. The Sats kick in and out. Please see the attached screen shot. At the same time the FireFly-IIA receiver is tracking 11 Sats with perfect signal strengths (up to 45dB+ C/No), from the same feed. The difference in receiver performance is quite clear. Unfortunately I have only a single antenna, so need to run the Thunderbolt from a splitter. One can also see two more interesting tid-bits in the screen shot: the FireFly-IIA is tracking and using WAAS Sat PRN 48 (PRN 51 goes in and out of lo ck due to a chimney being in the way), and it is showing true MSL rather than just GPS Height. Thanks for the help, bye, Said ___ 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] Thunderbolt reception problems
Hi Said, As we talked about some weeks ago... your test is unfair to the Tbolt, but that is perhaps intentional. The Tbolt will need more gain to work. You are giving it a signal that is out of spec. -- Björn Hi guys, some weeks ago we talked about reception problems on Trimble Thunderbolt units. I finally took the time to download the Trimble monitor again, and get my unit locked again. Here is what I found: The unit was running continuously for the last months, but wasn't locked. Using the Trimble monitor, I restarted the unit, now connected directly to my antenna, then after the survey was done let it run from my antenna splitter. This works, but just barely. I use an Agilent 58512A amp, followed by a Mini Circuits ZB4PD1-152-75+ 1-to-4 passive splitter. In the attached plot a JLT FireFly-IIA and the Thunderbolt are both running from the same Mini Circuits splitter. The Antenna sense circuit in the Thunderbolt is happy, but the signal strength is just at the threshold of working. The Sats kick in and out. Please see the attached screen shot. At the same time the FireFly-IIA receiver is tracking 11 Sats with perfect signal strengths (up to 45dB+ C/No), from the same feed. The difference in receiver performance is quite clear. Unfortunately I have only a single antenna, so need to run the Thunderbolt from a splitter. One can also see two more interesting tid-bits in the screen shot: the FireFly-IIA is tracking and using WAAS Sat PRN 48 (PRN 51 goes in and out of lo ck due to a chimney being in the way), and it is showing true MSL rather than just GPS Height. Thanks for the help, bye, Said ___ 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] Thunderbolt reception problems
Hi Bjoern, I respectfully disagree. I measured the loss through the GPS amp and Mini Circuits splitter at only 10.1dB. That's really not a lot. I couldn't find a loss-spec in the Thunderbolts' specification. The Agilent amp has GPS filters in it that improve signal quality by filtering out all non-GPS signals. Someone else had the same problem here (that's how the discussion initially started) thinking his Symmetricom splitter was dead. I think it's safe to say a GPSDO can be expected to work with a name-brand GPS splitter (which it did not either for the other gentleman). So if the M12+, M12M, and all other GPS receivers I have can all handle this signal without a hitch, except the Thunderbolt, then this means the Thunderbolt requires special attention (or in my case possibly it's own GPS antenna). I will try to change the AMU settings as Warren suggested, that makes sense. Maybe this is what we should have tried from the beginning to make our Thunderbolts work? bye, Said In a message dated 11/21/2009 14:18:51 Pacific Standard Time, b...@lysator.liu.se writes: Hi Said, As we talked about some weeks ago... your test is unfair to the Tbolt, but that is perhaps intentional. The Tbolt will need more gain to work. You are giving it a signal that is out of spec. -- Björn ___ 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] Thunderbolt reception problems
I think I was the one that started this. My problem was the Tbolt did not work when connected to the Symmetricom splitter alone (except for the antenna of course) but worked great when the splitter was also connected to a Z3816A. I think it must have to do with lack of appropriate power from the Tbolt to power the splitter though I have not taken any detailed measurements. If anyone wants a particular measurement, let me know. I contacted Symmetricom to try to get a schematic of the splitter without any luck. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of saidj...@aol.com Sent: Saturday, November 21, 2009 10:03 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt reception problems Hi Bjoern, I respectfully disagree. I measured the loss through the GPS amp and Mini Circuits splitter at only 10.1dB. That's really not a lot. I couldn't find a loss-spec in the Thunderbolts' specification. The Agilent amp has GPS filters in it that improve signal quality by filtering out all non-GPS signals. Someone else had the same problem here (that's how the discussion initially started) thinking his Symmetricom splitter was dead. I think it's safe to say a GPSDO can be expected to work with a name-brand GPS splitter (which it did not either for the other gentleman). ___ 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] Thunderbolt reception problems
Hi Said, With your background, I assumed you would know better... What is your antenna gain? What is your antenna cable loss? Does the Tbolt work correctly connected directly to the GPS antenna? Do you have an inline LNA to add close to the antenna? Do you have a higher gain antenna available? If 10dB is a lot or nost... that DO depend on the circumstances. -- Björn Hi Bjoern, I respectfully disagree. I measured the loss through the GPS amp and Mini Circuits splitter at only 10.1dB. That's really not a lot. I couldn't find a loss-spec in the Thunderbolts' specification. The Agilent amp has GPS filters in it that improve signal quality by filtering out all non-GPS signals. Someone else had the same problem here (that's how the discussion initially started) thinking his Symmetricom splitter was dead. I think it's safe to say a GPSDO can be expected to work with a name-brand GPS splitter (which it did not either for the other gentleman). So if the M12+, M12M, and all other GPS receivers I have can all handle this signal without a hitch, except the Thunderbolt, then this means the Thunderbolt requires special attention (or in my case possibly it's own GPS antenna). I will try to change the AMU settings as Warren suggested, that makes sense. Maybe this is what we should have tried from the beginning to make our Thunderbolts work? bye, Said In a message dated 11/21/2009 14:18:51 Pacific Standard Time, b...@lysator.liu.se writes: Hi Said, As we talked about some weeks ago... your test is unfair to the Tbolt, but that is perhaps intentional. The Tbolt will need more gain to work. You are giving it a signal that is out of spec. -- Björn ___ 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.
