[time-nuts] Z3805 two frequency maxima

Sun Nov 18 16:11:54 UTC 2012

Hi

The 5 MHz and 10 MHz are "locked together" by the multiplier. Their relative phase is fixed. The 5 MHz component is not free to wander independently relative to the 10 MHz.  Since it's a doubler, you get a two peak plot. If it was a X3 you would get three peaks.  It really only makes sense if you look at it on a scope. Of course at 60 ps, it would have to be a mighty good scope. Much easier to see when the sub-harmonic is a bit stronger...

Bob

On Nov 18, 2012, at 9:53 AM, Azelio Boriani <azelio.boriani at screen.it> wrote:

> Interesting this, but why exactly 60pS? I would expect also something
> in-between. That is, to have the 5MHz energy 64dB below, in my opinion
> nothing prevents to have the edge to wander not only at 60pS but
> continuously between 0 and 60pS. Maybe the SR620, being a 25pS resolution
> counter, simply doesn't see what's going on in-between and the resulting
> histogram looks that way.
> 
> On Sun, Nov 18, 2012 at 3:51 AM, Bob Camp <lists at rtty.us> wrote:
> 
>> Hi
>> 
>> A little more detail:
>> 
>> What's going on is more clear if you trigger a scope on the positive edge
>> of the 5 MHz and look at the 10 MHz. With an ideal multiplier, both the
>> positive and negative edges of the 5 MHz should line up exactly with a
>> positive edge of the 10 MHz. In reality, negative edge (the one not
>> triggered) does not quite line up. It's a bit ahead (or behind) the ideal
>> location. Since it's a small angle, the delta in phase and delta in
>> amplitude both follow the same basic law.
>> 
>> Bob
>> 
>> 
>> On Nov 17, 2012, at 9:36 PM, Bob Camp <lists at rtty.us> wrote:
>> 
>>> Hi
>>> 
>>> Just good old Fourier series.
>>> 
>>> Bob
>>> 
>>> On Nov 17, 2012, at 9:12 PM, Volker Esper <ailer2 at t-online.de> wrote:
>>> 
>>>> 
>>>> 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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