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| OCXO tuning screws not working on old equipment |
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| Gertjan:
Yes, those screws are covers :) Under the "Fine" cover screw you will find the trim capacitor you are looking for. Be very gentl with it! On my Racal-Dana 1998 I only have to touch it for a change in frequency... And I have to wait 10...15 minutes before the oscillator does not drift anymore. So, this OCXO does take some time to fine-tune.... regards, Gertjan. |
| Thomas:
Yep, Gertjan is spot on. Adjusting the screws didn't seem to do anything, and after a day or two I thought "sod it, I'm going in" and removed them. THERE are the trimmers :o NOW we're getting somewhere ;D I really should have taken the hint, because my 1992 has brown fiber washers on the covers :-[ |
| tverbeure:
--- Quote from: Thomas on July 07, 2023, 10:37:50 am ---Yep, Gertjan is spot on. Adjusting the screws didn't seem to do anything, and after a day or two I thought "sod it, I'm going in" and removed them. THERE are the trimmers :o NOW we're getting somewhere ;D I really should have taken the hint, because my 1992 has brown fiber washers on the covers :-[ --- End quote --- Amazing! I'm starting to think that this could explain the symptoms of what I'm seeing! ;D Just my luck that the two counters that I'm trying to calibrate are using trimmer obfuscation techniques. |
| GigaJoe:
im measure Freq quite rare and very dissatisfied with all internal oscillators. as it need many hours to stabilize when turn ON, and even 8D direct counter most likely 2 last digits will be incorrect. cheap OCXO well insulated with Vref like LT1021-5 , after a reasonable time to age , gives -10 per year stability and no jitter. high stability OCXO inside an equipment, required constant ON condition, so like meter off but not a reference. in my case usage are few times per year , and it doesn't make sense to keep it running. so i decided to build external 10M ref that constantly on, well Insulated OCXO consume around 20ma on 12V vs 120mA open space, and significantly lower jitter, as a thermal loop control do it much more precise, due to less heating loss. as well as I noticed for quartz oscillators need approximately a week to get stabilized (stop drifting) after extended offline period. so adjustment better do after long period of ON or STANDBY . |
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