[time-nuts] Thunderbolt Harmonics

[Bob Camp]

Hi

> On Jan 18, 2017, at 1:08 PM, jimlux <jimlux at earthlink.net> wrote:
> 
> 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

Be *very* careful cascading those Min-Circuits filters without putting some sort of isolation between them. You can get all
sorts of wonky results as the reactances in one mis-terminates the reactances in another.

Bob


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