[time-nuts] Thunderbolt Harmonics

Rhys D heyrhys at gmail.com
Wed Jan 18 15:17:40 EST 2017


Thanks all for the extremely educational replies.

On 19 January 2017 at 07:08, 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
>
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