[time-nuts] Help with LPRO 101

John Ackermann N8UR jra at febo.com
Tue Oct 9 18:05:40 EDT 2007

Geraldo Lino de Campos said the following on 10/09/2007 05:42 PM:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+jra=fluffles.febo.com at febo.com RETRY
> New to the list, I got a used LPRO 101 and developed a GPS-based
> counter to check accuracy of calibration. I found it is almost on the
> spot, freq=9.99999998 MHz.
> However, I can not adjust the frequency neither by adjusting the
> external C-field potentiometer nor by applying a voltage at the EXT.
> Am I missing something, or do I have a faulty unit? In this case are
> there schematics somewhere, or someone have experience repairing the
> unit?

Hi Geraldo.  Welcome to the list!

I would suspect either the counter or the LPRO to be faulty.  Can you
check either against another device?

My reason for saying so is that the 9 digit number you gave us provides
resolution only to parts in 10e-9, and the last digit of most counters
is ambiguous by nature.

A typical Rb may have a total adjustment range of only a couple of parts
in 10e-9, so your counter resolution plus last digit ambiguity pretty
much hides any change that you might see.  If you can extend your gate
time by 10, that would add another digit of resolution and with that,
you should be able to see a change over the Rb tuning range.  (But note
that if you are clocking the counter directly from GPS, any gate time
shorter than thousands of seconds will have jitter measured in nanoseconds.)

I would not have been surprised if your counter read either 1 count
below 10 MHz, or 1 count above -- that would be expected due to the last
digit ambiguity.  But given the adjustment range, reading 2 counts low
with no change over the adjustment range does seem to indicate a problem
as that is (probably) out of the adjustment range.  However, unless we
can verify that the counter is in proper order, we can't tell whether
the problem is the counter or the Rb.

Hope this helps.


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