Products > Test Equipment
TM4313 GPSDO: strange behavior after a night of poor reception
shapirus:
--- Quote from: shapirus on April 10, 2024, 09:16:14 am ---The next thing to test is to bring the antenna, without disconnecting it, further into inside of the room to simulate a signal level degradation.
--- End quote ---
This test is passed too.
1) antenna moved deep indoors:
--- Code: ---Ph = -16, D = 552276, GL = 0, LOS = 3, ST = 552, AF = 37, RT = 2005
Ph = -15, D = 552269, GL = 0, LOS = 3, ST = 553, AF = 37, RT = 2006
Ph = -15, D = 552263, GL = 0, LOS = 3, ST = 554, AF = 37, RT = 2007
Ph = -15, D = 552256, GL = 0, LOS = 3, ST = 555, AF = 37, RT = 2008
Ph = -14, D = 552254, GL = 0, LOS = 3, ST = 556, AF = 37, RT = 2009
Ph = -14, D = 552247, GL = 1, LOS = 3, ST = 557, AF = 37, RT = 2010
Ph = -14, D = 552247, GL = 1, LOS = 4, ST = 0, AF = 37, sK = 0.00000, RT = 2011
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 1, AF = 37, RT = 2012
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 2, AF = 37, RT = 2013
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 3, AF = 37, RT = 2014
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 4, AF = 37, RT = 2015
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 5, AF = 37, RT = 2016
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 6, AF = 37, RT = 2017
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 7, AF = 37, RT = 2018
--- End code ---
2) antenna brought back to the window:
--- Code: ---Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 156, AF = 37, RT = 2167
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 157, AF = 37, RT = 2168
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 158, AF = 37, RT = 2169
Ph = -14, D = 551097, GL = 1, LOS = 4, ST = 159, AF = 37, RT = 2170
Ph = 0, D = 551097, GL = 1, LOS = 4, ST = 160, AF = 37, RT = 2171
Ph = 0, D = 551097, GL = 1, LOS = 4, ST = 161, AF = 37, RT = 2172
Ph = 0, D = 551097, GL = 1, LOS = 4, ST = 162, AF = 37, RT = 2173
Ph = 0, D = 551097, GL = 1, LOS = 4, ST = 163, AF = 37, RT = 2174
Ph = -1, D = 551097, GL = 1, LOS = 4, ST = 164, AF = 37, RT = 2175
Ph = 1, D = 551097, GL = 1, LOS = 4, ST = 165, AF = 37, RT = 2176
Ph = 3, D = 551097, GL = 1, LOS = 4, ST = 166, AF = 37, RT = 2177
Ph = 4, D = 551097, GL = 1, LOS = 4, ST = 167, AF = 37, RT = 2178
Ph = 5, D = 551097, GL = 0, LOS = 4, ST = 168, AF = 37, RT = 2179
Ph = 0, D = 551097, GL = 0, LOS = 3, ST = 0, AF = 37, RT = 2180
Ph = 2, D = 551097, GL = 0, LOS = 3, ST = 1, AF = 37, RT = 2181
Ph = 3, D = 551097, GL = 0, LOS = 3, ST = 2, AF = 37, RT = 2182
Ph = 5, D = 551097, GL = 0, LOS = 3, ST = 3, AF = 37, RT = 2183
Ph = 6, D = 551097, GL = 0, LOS = 3, ST = 4, AF = 37, RT = 2184
Ph = 7, D = 550771, GL = 0, LOS = 3, ST = 5, AF = 37, RT = 2185
Ph = 10, D = 550656, GL = 0, LOS = 3, ST = 6, AF = 37, RT = 2186
--- End code ---
The output frequency remained stable during the entire length of this test.
So, I guess, no night-time frequency reference for me, for now :). At least without an outdoors antenna.
Yes it would be interesting to test how other GPSDO behave in this scenario, but the level of this curiosity is not high enough to justify the expense required to get another unit.
shapirus:
I took it apart to change the jumpers to connect to the GPS module's serial port and took some pictures while I was there.
OCXO:
Date and HW revision:
The 1 PPS output is connected like so (i.e., not to the GPS module):
Zenith:
--- Quote from: tverbeure on April 09, 2024, 05:21:59 pm ---There's very little literature on the TM4313 other than my blog post, and other than you and me, I don't think anyone has gone father in their analysis of the TM4313 log messages.
--- End quote ---
I'm glad this thread has appeared. I've had a TM4313 for about three years. It came with no instructions and until now I couldn't find anything about it on the WWW, although I hadn't looked for some time. It sits there with the antenna on a window sill, not outside, and agrees with a Racal 1992 with the better OCXO (04E) option, to within a few ppb over the course of a week. I'd always wanted to explore its data reporting features. It's lost lock a couple of times when the antenna has been covered up with something or other.
I assume that for practical purposes, calibrating synthesised sig gens and adjusting frequency counters with ancient OCXOs, (so no better than 1 part in 10^8) that the TM4313 is perfect.
One thing that has surprised me is how good the AliExpress ex-equipment CTI OCXOs are.
tverbeure:
--- Quote from: shapirus on April 10, 2024, 10:02:51 am ---The 1 PPS output is connected like so (i.e., not to the GPS module):
--- End quote ---
Yeah, that’s expected. The 1PPS coming out of the GPS module is way too jittery.
shapirus:
Update.
I cannot reproduce this lock-up when the jumpers are set to receive messages from the GPS module!
Yesterday in the evening it was running with the jumpers set for the MCU's UART output. The GPSDO locked up as described in first post. I disconnected and reconnected the antenna, it started tracking, but then went into that unstable state again. Then I changed the jumpers and let it run again. Guess what, no issues. It's tracking just fine. Yes it did lose tracking a couple of times at some point, but then resumed it properly.
Right now, and it was a second (non-consecutive though) night with no lock-up issues, it's generating a good output frequency with no "seeking" oscillation.
I wonder what do the jumpers have to do with it and how could it affect things. At this point it does not look like a coincidence.
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