[time-nuts] Z3805 two frequency maxima
Bob Camp
lists at rtty.us
Sun Nov 18 02:51:27 UTC 2012
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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>>>>
>>>>
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