[time-nuts] Testing the TAC, and a question about ADEV

Fabio Eboli FabioEb at quipo.it
Fri Dec 28 16:26:08 UTC 2012


How could I test the time to analog converter
we talked few posts ago?
Something that can be done with things I have
or can easily find.

I was thinking that would be nice to try to
feed it with signals similar to the real ones,
but that can be controlled: PPS + 10MHz reference,
without the PPS tipical jitter.

To do so I was thinking to use the PPS from
one of the 2 FE5680 and the 10MHz from the
second ad use these to simulate the real signals.

I can tune the frequency of the Rb with the
serial interface (tested and working).
I'd like to verify both the resolution and

I was trying to figure the approx jitter
I will have using the Rb like I said above,
so I'm giving an eye to this diagram from
John Miles page: http://www.ke5fx.com/rb.htm

If I'm understanding correctly, that 5680
at 1s should have most of the jitter (95% +-2sigma)
into an interval +- 3.08x10^-11 wide, i.e. about 62pS
on the PPS signal (non considering the PPS buffer
inside the 5680). Is this how it work, or I'm mistaking?
This is from only one unit, but both unit will have
the jitter, how to take into account the jitter
from both?

Is there a better method to make this test?
I could try to test the TAC alone feeding it
with a 100 to 200nS pulse, but I dont know
from where to start to generate a clean stable
and repeteable pulse.

I have the 2 5680, the counter with it's 10MHz
inputs and outpus, and a Vectron OCXO that came
with one of the 5680, with these markings:
OCXO500-18 63.897600MHz
34537 A0715
soldering iron, solder and scrap electronics :)


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