[time-nuts] HP/Agilent 5065A Rubidium Vapour frequency standard problem

Palfreyman, Jim L Jim.Palfreyman at team.telstra.com
Thu May 8 08:42:51 EDT 2008

Thanks Bill for your input.

The second harmonic is at 32 which as I understand is a good reading. The Photo I however is only 18. The original reading was 24 and then 20 some time later - so it seems to have been low anyway.

I cannot change the error reading with either the course or fine control.

Powering off the unit and/or changing oscillators doesn't give me the effect I described earlier anymore.



-----Original Message-----
From: Bill Hawkins [mailto:bill at iaxs.net]
Sent: Thursday, 8 May 2008 4:50 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] HP/Agilent 5065A Rubidium Vapour frequency standardproblem


When a controller drifts out to its limit, the control loop is not closed. Either or both the measurement and output are not working.

For the input:

What is the second harmonic reading on the meter? If it's too low, there's not enough for a measurement.

Does changing the coarse oscillator change the error reading?
Actually, you should be able to see motion if you change the Fine adjustment by 100.

For the output:

Catch the Control reading before it reaches the end of the scale after turn-on. The coarse oscillator adjustment should change the Control reading. Once it reaches the end of the scale it has saturated, and won't necessarily move when you change the coarse frequency.

I expect that A8TP3 provides a clue, but I don't have the book with me.

It's entirely possible that the power cycle on the unit just discharged the control integrating capacitor so it would start from zero again. Swapping oscillators may have nothing to do with it. Of course, a cold oscillator has a different frequency than a hot one.

Tell us what you read on the meter besides Control.

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Palfreyman, Jim L
Sent: Wednesday, May 07, 2008 11:21 PM
To: time-nuts at febo.com
Subject: [time-nuts] HP/Agilent 5065A Rubidium Vapour frequency standardproblem

Hi all,

I'm in need of someone with some experience in fault finding a 5065A.
I'm having a go at repairing my university's old unit which up until a short while ago was working well. I've got the PDF of the manual and I've been testing and trying various things but I need someone with a bit of experience with these units to help diagnose the fault.


A) The unit drifts at about 1 usec/sec.

B)  The CONTROL reading is pegged off the scale.

C) The course oscillator adjustment doesn't affect the CONTROL reading.

D) A8TP3 doesn't seem to produce anything but a straight line, however
A8TP2 is fine.

The fact that the course oscillator didn't seem to do anything made me suspect the 10811-60109 OCXO. I happen to have a spare 10811-60111 and so I powered off the unit, substituted the (cold) 10811-60111 and powered on. The course oscillator control could adjust the CONTROL reading and within a minute or two the unit was drifting at only 80 picosec/sec.

Voila - problem solved!

However, 8 hours later the CONTROL level was pegging the meter again and the unit was drifting at 1 usec/sec.

And now the oscillator course control had no effect on the CONTROL level.

So why is that a luke warm 10811 combined with a hot RVFR allowed the unit to function, but once the 10811 heated up it drifted again?

The Continuous Operation light operates all the time and the Integrator Limit light comes on after a while as expected when the CONTROL voltage is high.

Any hints or tips will be appreciated.

Jim Palfreyman

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