[time-nuts] Z3805 two frequency maxima

Azelio Boriani azelio.boriani at screen.it
Sun Nov 18 14:53:24 UTC 2012


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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