[time-nuts] Z3805 two frequency maxima

Volker Esper ailer2 at t-online.de
Sun Nov 18 02:12:38 UTC 2012


I'm impressed - but what law is behind this?


Am 17.11.2012 21:26, schrieb Bob Camp:
> Hi
>
> 60 db isn't to bad a number. More or less:
>
> 100 ns ->  100 ps is 1000:1. 20 log of that is 60 db. 100 ps to 60 ps is about 4.4 db. That would sum up to -64.4 dbc. The main gotcha is that you *might* also have some 15 MHz (and higher) energy in the signal as well. Also phase gets into the calculation.  Still, pretty close.
>
> Bob
>
> On Nov 17, 2012, at 12:50 PM, Volker Esper<ailer2 at t-online.de>  wrote:
>
>>
>> So let's have a look into the machine... and what do we see? There's a nice little Symmetrcom oven, with the sign reading "5.000 MHz" - bingo!
>>
>> May be there's a time saving way to determine the energie of the sub harmonic: using my spectrum analyzer. It tells me, that there's a 5 MHz subharmonic at the level of -62dBc.
>>
>> How would you have calculated the energy? What would be your ansatz?
>>
>> Thanks so far
>>
>> Volker
>>
>>
>> Am 17.11.2012 17:55, schrieb Bob Camp:
>>> Hi
>>>
>>> That's what you get if you have "sub harmonic" energy in the output of your OCXO. I'd bet you a warm glass of beer that you have a 5 MHz / doubled to 10 MHz MTI OCXO in your Z3805.  If you have a lot of time on your hands, you can calculate the likely level of the energy from the amount of jitter (spacing between the two peaks) you get.
>>>
>>> Bob
>>>
>>> On Nov 17, 2012, at 11:41 AM, Volker Esper<ailer2 at t-online.de>   wrote:
>>>
>>>> Hi,
>>>>
>>>> while playing with my recently aquired TIC (SR620) and measuring the period time of some oscillators I discovered something I hadn't expect at all:
>>>>
>>>> The output of my GPSDO (Z3805) writes two maxima in the period histogram (at a spacing of 60ps).
>>>>
>>>> I didn't believe that result and assumed an inherent error in my measuring setup or the counter itself.
>>>>
>>>> So I plugged another oscillator, the reference TCXO of my signal generator (R&S SMX), and that result made me happy and uneasy at once: The TCXO hat only one maximum.
>>>>
>>>> I havn't calculated the ADEV curve, yet.
>>>>
>>>> See pictures.
>>>>
>>>> Why does my GPSDO produce such a weird result?
>>>>
>>>> Cheers
>>>>
>>>> Volker - DF9PL
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>>>
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>>
>>
>>
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