Pumpkin UM-20, User Manual

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User Manual
8 UM-20 Low-cost Oven-controlled Crystal Oscillator (OCXO) Assembly
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Aging/year: 1.5E-7 after 7 days, 1E-7 after 30 days
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Warm-up @25C: 2E-8 in 30 minutes
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Temperature (0 to 50C): 1E-8
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±10% MAINS change: 1E-9
S/N ‘357 has a 10MHz IsoTemp Research, Inc. Model
OCXO36-44 10.000MHz large OCXO S/N 9051-61 DATE 9552
that can be tuned down to 1E-10 using the method that compares
the drift of its output to the GPS-derived 10MHz signal. The two
screws on the can – marked Coarse and Fine – are covers for the
pots inside ... the OCXO must be unscrewed from the Model
3030’s chassis in order to get access to these screws … very nice.
Figure 3: IsoTemp OCXO36-44, the "original" Option 115
OCXO for Model 3xxx frequency counters
S/N ‘390 has the same oscillator.
Opening up S/N ‘142 revealed that this unit’s internal OCXO has
an MTI 220-0102-A 5.0000 MHz OCXO module S/N 124463 on a
small PCB, with a trimpot for frequency trimming. This MTI
OCXO puts out a 3V (roughly) sine wave; the reference output
could not be pulled to 10MHz with the trimpot when connected via
J4
to the Model 3080’s frequency input; it was, however, tunable
to 5MHz when there was no load on its output. Contacting MTI for
a replacement revealed that each OCXO cost around $500 new, but
there was a $1500 minimum order.