Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Hi Ok, what do you know / have a pretty good guess at? 1) There’s an SC (or similar) cut crystal in there 2) That crystal has a curve that looks something like the “0” or “1” curve in figure 7 of: https://coloradocrystal.com/applications/ 3) It

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

On 1/15/2021 8:30 PM, paul swed wrote: Not sure how hard it might be to get a thermocouple into the oven. That would give you a hint. Regards Paul Seems to me you already have a temperature sensor in the OCXO. If you temperature soak it overnight and monitor the frequency as power is applied,

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Hi There is both short term and long term noise on the GPS PPS signal out of a GPS module. Some of the short term noise can be reduced by software using the “sawtooth correction” out. That assumes the module you are using provides this output. The uBlox M8T is one of many that provide this

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Hi Simple answer is to do a general search on eBay for “OCXO” then take a look at the pictures. The descriptions often are a bit off …. Bob > On Jan 15, 2021, at 11:46 PM, Scott Newell wrote: > > At 07:49 PM 1/15/2021, Bob kb8tq wrote: >> then indeed, the temperature sensitivity will go way

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

If the gpsdo output pps signal does not drift, but the gps pps signal drifts slowly, it is bound that after a period of time, the gpsdo pps signal will have a very large beat in order to follow the gps. How to solve this problem? In tens of nanosconds, I see that the pps of the gps are always

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

At 07:49 PM 1/15/2021, Bob kb8tq wrote: then indeed, the temperature sensitivity will go way up. Most of the OCXO’s off these boards are a sub $20 sort of item on eBay. How good are they? Who Any suggestions for a SC-cut 5V OCXO? Searching for "Trimble 73090" or "73090 OCXO" just brings

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Not sure how hard it might be to get a thermocouple into the oven. That would give you a hint. Regards Paul On Fri, Jan 15, 2021 at 8:51 PM Bob kb8tq wrote: > Hi > > One of the options is that the EFC has an issue. > > Another option is that the oven control circuit has a problem. > > Either

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Hi One of the options is that the EFC has an issue. Another option is that the oven control circuit has a problem. Either one *could* put the center frequency someplace odd. If it’s the heater control (or heater set point) then indeed, the temperature sensitivity will go way up. Most of

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Quick update: tried using an AD780 reference + op-amp to offset the EFC voltage. Worked great, until I slid everything back into the enclosure and it was tuning the OCXO too high! After several disassembly/mod/reassembly passes (all tuning too high once boxed up), I punted and went back to

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

One thing I forgot to mention, is that the EFC sensitivity isn't necessarily the same in this new range as it was before. In other words, having more gain may not be a big deal, or even beneficial. You're way past the steeper dC/dV slope anyway, so the actual effect of the varicap on the net

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Scott, it looks like you have already proven the tune voltage can go much higher than specified, and sufficient to get in-range for 10 MHz ideal. The currents noted show there's probably a pull-down resistor on the tune line - maybe 75-100 k. The reverse leakage of the varicap diode should be

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Thats fantastic to see. Yes you have it. Use an opamp to insert an offset of 6-7V so the DAC itself still uses its normal range of 0-5V. Opamp output would be 6-11V or something. You just may have the unit for a while longer. Regards Paul WB8TSL On Tue, Jan 12, 2021 at 8:19 PM Scott Newell

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

At 01:27 PM 1/12/2021, paul swed wrote: Granted at 5V the varicaps may be at minimum. Use a 2K R. That should be pretty safe. Current limited bench supply though 4.7 k and an inline DMM to monitor current. Made quick-n-dirty measurements of EFC voltage, EFC current, and output frequency.

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Newell it will give you a hint as to how bad is bad. Granted at 5V the varicaps may be at minimum. Use a 2K R. That should be pretty safe. Good luck. Regards Paul WB8TSL On Tue, Jan 12, 2021 at 12:01 PM Scott Newell wrote: > At 08:14 AM 1/12/2021, Bob kb8tq wrote: > >Hi > > > >The OCXO on the

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

At 08:14 AM 1/12/2021, Bob kb8tq wrote: Hi The OCXO on the 73090 does not have an internal mechanical trimmer. It is a 0 to 5V tune range. Thanks! That saves me the effort of opening the can. I think I'll cut the EFC trace and see how far I can pull it past 5 VDC (with a series resistor to

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

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 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?

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Newell its all a gamble at this point so go with the 6V and see if you gain a few hz. Its a serious cheat. But it just gives you a sense of how bad is bad. Does a olid volt maybe move you 1 hz or 5 hz? In the can you could actually look at the crystal and in general several caps around it. One of

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

At 09:01 PM 1/11/2021, paul swed wrote: Can you see what the xtal unit actually is. Trimble "73090". I suspect there is not a hole to a trimmer cap. But potentially if you can I peeled the sticker from the top--no holes hidden there or on the four sides. open it you could get to a cap

Re: [time-nuts] GPSDO won't lock: OCXO aged out?

Newell Thois is a different Paul. Can you see what the xtal unit actually is. I suspect there is not a hole to a trimmer cap. But potentially if you can open it you could get to a cap or at least see the xtal and what caps are around it. Other more difficult approach is to insert a purposeful

[time-nuts] GPSDO won't lock: OCXO aged out?

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