Re: [time-nuts] Z3805 two frequency maxima

[Volker Esper]

@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.bori...@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<li...@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<li...@rtty.us>  wrote:

Hi

Just good old Fourier series.

Bob

On Nov 17, 2012, at 9:12 PM, Volker Esper<ail...@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<ail...@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<ail...@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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