On 1/18/17 8:56 AM, Bob Camp wrote:
HI
the first time we ran the test (using a Keysight 33622 signal
generator) we saw significant 2nd and 3rd harmonics (50-60 dB down,
but easily detectable). A quick review of the data sheet.. Oh, the
signal generator spec is only -43 dBc for frequencies above 10
MHz.
So even a pretty expensive signal generator still has “loud”
harmonics if judged at the -60 dbc level ….
that's actually an inexpensive ($7.4k) function generator (with good
performance for a function generator that does a lot of stuff, except
generate chirps at the right rate)..
A $8k Keysight N9310 is -30dBc
A R+S SMA100 specs -30dBc (actually does better)
A $23k Keysight 8663D specs -55dBc (at 1 GHz)
Another case where low harmonic content is when doing two tone IMD
tests - if the sources have significant harmonic content, you might
be seeing intermod between the harmonics of the source, rather than
intermods between the fundamental of the source.
Which is one of the reasons a lot of IMD test setups have a variety
of filters in them.
These also are a pretty common item on eBay, at ham fest, and in your
typical RF junk box. 10.7 MHz IF filter cans can fairly easily be
tuned down to 10 MHz to custom roll bandpass filters.
Yeah, but it's easier (cheaper if you're paying for labor) just to buy a
box of 10 filters at $30/each and stack them
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