[time-nuts] Z3805 two frequency maxima

Bob Camp lists at rtty.us
Sun Nov 18 20:23:40 UTC 2012


Hi

This is one of those interesting areas where a broadband measurement (like a counter) and a narrowband measurement (like a DMTD) will give very different results. The counter will see the sub-harmonic, and call it jitter. It can show up in an ADEV calculation. A DMTD will ignore the sub-harmonic, and show no added jitter. With a DMTD, the ADEV will look fine. A PLL multiplier will (likely) also ignore the sub-harmonic, the jitter will not show up if you use the 10 MHz as a counter timebase in a HP counter. 

Which one's right / does it matter - as always, that depends on what you are trying to do with the signal. 

Bob

On Nov 18, 2012, at 1:26 PM, Volker Esper <ailer2 at t-online.de> wrote:

> 
> @Azelio: Yes, (like Bob told) it's the phase lock, that locks the two maxima. Actually the counter is able to look between the 60ps spaced towers, have a look at the pictures in the first mail of this thread. However, there is a smallest time value the counter can determine, but it is much smaller than 60ps.
> 
> Volker
> 
> 
> 
> Am 18.11.2012 17:11, schrieb Bob Camp:
>> 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
>>>>>>>>>> 
>>>> <DSCF1437_bbb.jpg><DSCF1439_bbb.jpg>_______________________________________________
>>>>>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>>>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>>>>>> and follow the instructions there.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> _______________________________________________
>>>>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>>>>> and follow the instructions there.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> _______________________________________________
>>>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>>>> and follow the instructions there.
>>>>>>> 
>>>>>>> 
>>>>>>> _______________________________________________
>>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>>> and follow the instructions there.
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>> and follow the instructions there.
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>> and follow the instructions there.
>>>> 
>>>> 
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>> and follow the instructions there.
>>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
>> 
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.





More information about the Time-nuts_lists.febo.com mailing list