It always helps to know a little about the specific design of the temp control circuit but let's say counter clockwise CCW reduces the internal oven temp. This can be confirmed by letting the temp and frequency stabilize. Using a counter with good resolution monitoring the output frequency, turn the pot CCW several turns and the frequency should slowly decrease a few cycles (typically positive temp coefficient) as the oven cools. Now slowly turn the pot CW about 1/2 turn on each increment watching the frequency slowly increase due to the internal crystal oven slowly getting hotter. Eventually, the frequency will peak and further CW turning of the pot will start to lower the frequency. That's why it called the turn-over temperature. Now set the pot in the middle of two equal frequency points on either side of the frequency peak. Hopefully you will see a broad frequency peak allowing for a little more margin in the oven temperature. All you need to monitor is the output frequency. This process can be a little faster if you have some type of external analog oven temperature indication but it not necessary.
Don -----Original Message----- From: time-nuts [mailto:[email protected]] On Behalf Of [email protected] Sent: Friday, February 19, 2016 9:02 PM To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] MTI 260-0624-D OCXO I have just about finished trashing this OCXO. I was able to run it outside of its case, and I have repaired the case, but I was unable to reinstall it into the case because I have to patch it on both the top and bottom. I could, perhaps, put it into a larger case and might do that later. For now, I will keep it as a potential future resource. The SC crystal is worth that much - they aren't cheap and nothing wrong with that. Also, just the bottom circuit board has problems, possibly another bad unit could be used for parts. That leaves one final question. The suggestion that the POT adjusts the temperature set point for the crystal sounds very reasonable. It clearly does not significantly affect the frequency. At least, not in the range that would allow for tuning the output frequency. However, the POT is clearly designed to be adjusted AFTER everything is assembled because it is intended to be adjusted through the hole in the case. That assumes some sort of feedback. What feedback? What can it affect on the available five pins that would let you know when the temperature is set correctly? If it is not for setting the temperature, and not for setting the frequency, what is it for? Perhaps output voltage level? I would have to get it working again, but I could test that. Any ideas? Mike _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
