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« Last post by DeepLink on Today at 06:49:03 am »
I have several 8903B's and the internal oscillator is ~OK
Remember that you only have 5 digits on the frequency counter
Well, I did design a PLL to lock my 8903 to my house reference (10MHz)
Now the 8903 frequency counter is spot on, as it is directly linked to the reference
But the 8903 generator, is not locked to the internal oscillator, so it will never be precise (it is steered by the internal oscillator)
Not that it is needed for such an instrument
In loop back mode - you should see distortion below -90dB (0,003%) (look in the manual for how to perform the test)
I had one of mine down to -98dB (0,0012%)
I prefer dB for such low levels of distortion
You mention 150mA - but I guess you mean 150mV
Try to increase the output to 6V, 1kHz - then you should see distortion below -80dB (0,01%) if worse, then you instrument is faulty
Also the optional filters is not the best "quality"
So I did my own design with modern components and got the THD better
The filters is also hard to find these days
Also tried to improve the output generator / input circuit with modern Op-Amps and reducing noise in the supply's
Got some marginal gains
HP did make a pretty good Audio Analyzer, and it is my preferred analyzer.
It has "instant on" and is pretty simple to use, high voltage input and good bandwidth (I've measured them to more 500kHz)
If I need better performance I do have some modern FFT analyzers, but they all lack the above features
/Hans