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Author Topic: MSF5000 UHSO Crystal Oven  (Read 7705 times)
K4JJL
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Posts: 480




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« on: March 08, 2013, 09:27:15 AM »

I've got an MSF with a 14.4 MHz signal from the hi stab osc that's about 500 Hz off.  When I checked the output of the 5 MHz oven, it showed it was about 500 Hz off, as well.  I don't have enough tuning range in the oven adjustment to get it to bend down that far.  Is it possible the heater died?  It's pretty much a sealed box that will probably require a torch to open.  Anybody had any experience with these?
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WB6DGN
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« Reply #1 on: March 11, 2013, 05:53:55 AM »

A comment from a factory FTR years ago about the HI Stab. stations, "If your service monitor says its off frequency, have your service monitor repaired."

That said, they DO fail and its entirely possible that yours has a problem.  I'm not familiar with the Motorola unit as I've never had a problem with one but the HP is a double oven unit (an oven within an oven).  If the Motorola is similar to that, then I doubt that a failed oven (one of the two) would cause it to go that far off frequency.  I'd look at a possible bad crystal or some part of the frequency determining network (capacitors) first.  I assume that you've verified the accuracy of your measuring device as the FTR warned?
Tom
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K4JJL
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« Reply #2 on: March 11, 2013, 08:50:43 AM »

Yeah.  It's an HP8920 calibrated at a friend's house with his GPS reference 6 month ago.  I picked up another oven from a Micor at a hamfest over the weekend.  I'm gonna try that tonight.  If it's still off, I'll drag the monitor back to his house for another calibration.  I really wish I had kept that rubidium standard I sold a couple years ago Sad

The FTR probably didn't take into account that this crap might just happen to be a little off 25 years later.  However, if the crystals were fine-tuned at the factory with graphite, they will age.

Just dawned on me that I could check the heater lines with a amprobe.  Might try that first to see if it's working.
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WB6DGN
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« Reply #3 on: March 11, 2013, 09:06:57 AM »

Quote
I really wish I had kept that rubidium standard I sold a couple years ago...

They're maintenance intensive too; actually more so than a crystal oscillator.  GPSDO is arguably the best compromise but they fail too.  Face it, if the stuff kept working constantly, it would be awful boring.
Tom
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K4JJL
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« Reply #4 on: March 11, 2013, 11:10:05 AM »

it would be awful boring.

I'm getting to the point where I prefer the equipment I maintain to be "awful boring" now.  Seems to be cutting into my motorcycle time.
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