[time-nuts] Z3805 two frequency maxima
Volker Esper
ailer2 at t-online.de
Wed Nov 28 00:36:54 UTC 2012
Now, that you ask: the measurements are in that range, yes, though it's
not exactly the values.
time shift 12ns -> spacing 10ns
28ns 35ns
66ns 55ns
0ns 8ns
and yes, the peaks get closer while reducing the amplitude of the 5MHz,
it's almost exactly linear:
With the 10MHz at 200mV and a time shift of 66ns, I measured the
following spacings:
5MHz voltage in mV spacing in ns
200 55
100 27.5
50 13.0
25 6.5
12.5 3.3
6.3 1.6
3.2 0.86
1.6 0.44
0.8 0,24
The functional relation of voltage ratio and spacing is quite obvious.
I have to admit, that my counter is not at it's optimal calibration. I
will adjust it first before I can tell you more.
To be precise: all these findings were made while trying to adjust the
trigger circuits of the counter. To do that I needed a well designed 180
degrees power splitter - but I didn't have one at the time. I've
received a Mini Circuits ZSCJ-2-2 recently, now I can go on with my
adjustments.
Though the SR620 TIC is a great instrument when hunting the pico seconds
we have to realize, that it's a thermal design desaster (I have to
apologize to all sr620 friends). I have to run it for at least 12 hours
if not 24 to be shure, that every single part is at a more or less
stationary thermal state. Some (NERC) say "...never switch it off".
I can't do that during the week, we have to wait till weekend.
Thanks for your response
Volker
Am 28.11.2012 00:25, schrieb Azelio Boriani:
> Very interesting indeed. Two questions: after adding the 66nS phase shift,
> were the two peaks at 66nS when at the same amplitude? Then, while reducing
> the amplitude of the 5MHz, were they getting closer (until the 240pS)?
>
> On Tue, Nov 27, 2012 at 9:21 PM, Bob Camp<lists at rtty.us> wrote:
>
>> Hi
>>
>> Phase does indeed matter, it just messes up the math. Most multiplier /
>> filter combinations have significant phase shift between the sub-harmonic
>> and the carrier. You rarely know what the phase shift is, but you can read
>> the sub-harmonic. The simple db to jitter ratio gets you close enough to
>> make rational decisions on how much filtering you need. You could play with
>> filter phase but I've never seen that done in practice.
>>
>> Bob
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Volker Esper
>> Sent: Tuesday, November 27, 2012 2:34 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Z3805 two frequency maxima
>>
>>
>> I followed your argument and tried to synthesize such a signal. I built
>> a simple power combiner (3 times 18 ohms resistors) and combined the 10
>> MHz reference output of my signal generator with a 5 MHz signal from the
>> same generators regular output at the same amplitude. My oscilloscope
>> showed the locked phase of the two signals.
>>
>> I applied this combo signal to the SR620 and observed a wonderful
>> two-maxima histogram. When reducing the amplitude of the 5 MHz signal
>> (while keeping the 10 MHz amplitude) the peaks distance decreased
>> linearly with the voltage reduction, until the peaks melted togehter at
>> about -20dBc.
>>
>> On the one hand it was a success, but why only 20dBc? My experiences
>> with the Z3805 showed a 5 MHz subharmonic at 62dBc and the peaks spaced
>> at 60 ps.
>>
>> So I startet to add phase delay to the 5 MHz signal by looping-in some
>> meters of coax cable.
>>
>> When coming to a delay time of 66 ns I could distinguish the two peaks
>> at a spacing of 240 ps down to an amplitude ratio of about 1000, that
>> is, 60dB.
>>
>> Volker
>>
>>
>>
>>
>>
>> Am 18.11.2012 03:36, schrieb Bob Camp:
>>> 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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