[time-nuts] Thunderbolt Harmonics

jimlux jimlux at earthlink.net
Wed Jan 18 13:08:43 EST 2017

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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