[time-nuts] Z3805 initial behaviour after power up

Ulrich Bangert df6jb at ulrich-bangert.de
Wed Jun 17 04:06:00 EDT 2009


Gents,

yesterday I received the Z3805 that I had bought from fluke.I on eBay and
immediately put it to work. I recorded the EFC value as well as the PPS TI
value over about 20 hours. Attached is the graph of thes two values. 

I interprete this graph in this way:

1) Immediately after power up (perhaps up to the end of the site survey) the
regulation loop seems to work with a very short time constant which is able
to bring the PPS TI close to zero although the OCXO has lots of drift at
this time.

2) Then the loop time constant seems to switch to a significant higher value
which does not keep up with the oscillator's drift, which leads to the
negative excursion of nearly 500 ns.

3) This seems to be too much for the regulation which leads to switching
back to the short time constant and to bring the PPS TI back to near zero
and to return to the longer time constant again...

4) ...which lets the procedure repeat again and again: Drift to -500 ns and
pullback. 

5) Note that I thought it was a kind of malfunction and send a
:system:preset command to the device after the last negative PPS TI spike.
The result was, that the total procedure repeated: About 2 hours of PPS TI
close to zero then again the drift and pullback procedure however with a
reduced drift rate.

6) After 11 hours or so the regulation loop's time constant seems to match
the OCXO's drift and a "real" lock of the pll seems to take place. (The lock
led had been on already hours ago...)

Since I do not have an manual for the Z3805: Can any of you Z3801 owners
second this behaviour to be normal or would you think that it is kind of
special for the Z3805 or even a real malfunction (in the sense that the
OCXO's drift is above the specs in the beginning)?

Best regards
Ulrich Bangert  

Ulrich Bangert
www.ulrich-bangert.de
Ortholzer Weg 1
27243 Gross Ippener 
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