Pumpkin UM-20, Руководство пользователя

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User Manual
UM-20 Low-cost Oven-controlled Crystal Oscillator (OCXO) Assembly 7
Using an external frequency standard physically ties an instrument
to that standard, and makes it less portable, etc. We wanted to have
an inexpensive, desktop frequency counter with an input range of
up to ca. 100MHz, with a relatively accurate and stable internal
oscillator. Additionally, we wanted to become more
knowledgeable on the matter of oscillators.
OCXO Replacement
The XL Microwave line of microwave frequency counters satisfied
our frequency counter requirements, and provides a high-frequency
power meter, to boot. These frequency counters have a
1/2/5/10MHz external reference oscillator input, and a 10MHz
reference output. Via eBay and other sources, Pumpkin purchased
the following models in good to excellent condition:
•
Model 3030-6 Options: D S/N 950823357
2
•
Model 3120 Options: 115 S/N 981025390
3
•
Model 3080 Options: 115 S/N 120825142
4
Figure 2: XL Microwave Model 3120 frequency counter
By comparing this particular Model 3080’s reference output to a
GPS-disciplined 10MHz, we discovered that its internal OCXO
was wildly out-of-range at 9,887,XXXHz.
Option 115’s OCXO (the second of four progressively better
internal oscillator options for these frequency counters) has the
following performance:
•
Aging/second: E-11 root Allan variance
•
Aging/day: 5E-10 after 72 hours
2
Built in 1995, warrantied by XL Microwave for 2 years until 1997.
3
Built in 1998, warrantied by XL Microwave for 5 years until 2003.
4
Built in 2002, warrantied by XL Microwave for 5 years until 2007. Unknown why
the S/N code is not consistent with the other two …