Hi The OCXO on the 73090 does not have an internal mechanical trimmer. It is a 0 to 5V tune range.
Bob > On Jan 11, 2021, at 8:17 PM, Scott Newell <[email protected]> wrote: > > TL, DR: Trimble 73090 5V OCXO won't tune to 10 MHz (9.999 989 MHz at 0 VDC > EFC, 9.999 997 MHz at 4.88 VDC EFC). Worth fixing? Maybe an internal > mechanical trim? > > > I've got one of those China special GPSDOs (thanks again, Paul!) built around > a surplus Trimble UCCM 57964 (or 57963?) board. PPS driving NTP went wonky > the other day--turns out the GPSDO had lost lock. Due to WFH I didn't have LH > running, so I can't see what the DAC was at before it unlocked. I did examine > the Trimble logs after the fact and noticed this: > > L73:20/12/22.19:05:24 Phase over 10 microsecond > L74:20/12/22.19:16:39 Phase over 100 microsecond > L75:20/12/22.20:32:11 Phase over 1 millisecond > > Late December is when I noticed the problem, so the log looks reasonable. > > I now have my hands on it and can test. DC supply current and 10 MHz output > from cold shows that the oven is working and the output frequency rises > during warm-up (9.999 668 MHZ cold, 9.999 993 MHz hot), so SC cut rock, > right? (Tbolt 10 MHz used as counter ref.) > > With no antenna connected, LH lets me fiddle the DAC voltage: > 0 DAC = -100% = 9.999 989 MHz = 0 VDC EFC > 524287 DAC = 0% = 9.999 994 MHz = 2.50 VDC EFC > 1048575 DAC = 100% = 9.999 997 MHz = 4.88 VDC EFC > > I thought these 5V GPSDOs were using +/- 5 volt tuning, but that's not what > I'm seeing. Not that it would help this unit... Tuning range from 0-5 V is > about 8 Hz, or +/- 0.4 PPM. Does that seem reasonable? > > UCCM-P >*IDN? > TRIMBLE,57964-80,60498844,V2.0.1.6-01 > > Datecode on the OCXO is 0948. Paul gave it to me back in March of 2016, and > it's run pretty much continuously since then. LH shows phase error > accumulating, which makes sense for an off-frequency clock. > > Thought or suggestions? > > thanks! > newell N5TNL > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
