Electronics > Beginners
First Spectrum Analyzr HP 8590A
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Crambone:
Well I replaced the mixer diodes in the first converter today they did test good but figured while I had it out I would just pop in the new ones. Got it back together ran the cal and it was very close to being on frequency. I was feeding 27.5 MHz AM 30% at .5watts. My peak on the analyzer was 27.67. Let it track marker for about an hour and it drifted down to 26.5 MHz with Span set at 3 MHz.
Wondering were to look next? What can be causing that drift?
Crambone:
Correct after diode replacement
MarkL:
The drift spec for the 8590A is <50kHz over 5 minutes after a two-hour warmup (from the service manual in the performance verification section).  Did you meet the warmup and time requirements?  The full list of frequency and other specs are split between the service manual and the installation/verification manual.

There's going to be some drift and you're not going to get super-accurate results, like you would from a frequency counter.  Later models in the 859x family have a counterlock feature to combat drift and provide more accurate frequency results.
Crambone:
Yes I allowed a full 2 hr warmup and test was performed directly after calibration. I noticed the drift after a few minutes so I’m thinking it’s in spec
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