[time-nuts] Fwd: FE-5680A Physics package

Peter Bell bell.peter at gmail.com
Mon Oct 31 09:41:57 EDT 2011


That FE-5680A (the "non-programmable" one) is the same as the 2 units
I have - I have seen the "heat a lamp with a heat gun" trick before
when I was playing with the FRSs - but in this case the actual lamp is
fine - the problem seems to be with the absorption cell (or possibly
the other one, which I suspect may be a filter). I've never seen these
go bad in any of the other units I've seen.  I guess I could try
re-consolidating the Rb into that little pinch and see what happens.

I'm also not sure the heat gun trick is going to be very practical for
the lamps on these units - the RF exciter coil seems to have been
stuck onto the lamp with RTV and then the whole assembly stuck into
the lamp housing using a big dollop of RTV at the back.  You possibly
could release the lamp, but it looks like you would have a good chance
of destroying the drive coil in the process.

I've also been trying to figure out what the RF architecture of these
units is - it certainly seems to be different from the older ones; for
a start, the DDS chip is now an integral part of the control loop and
is generating at least part of the modulation used to interrogate the
resonance cell (the DDS is clocked with 20MHz and generating
~5.312MHz, but the Fselect pin is being driven by a 416.6...Hz square
wave coming from the Xilinx PLD and it's output is mixed with the
60MHz from the VCXO and fed to the snap diode on the physics package
multiplier assembly.

Once I get a better handle on how it all works, I guess I should write
it up for the benefit of anyone else trying to fix these things - but
right now it's in the "unannotated photographs and cryptic notes"
phase :)

Regards,
Pete

On Mon, Oct 31, 2011 at 8:32 PM, J. L. Trantham <jltran at att.net> wrote:
> That's it!  Plus, more information.
>
> I knew most everyone would be better organized than I am.
>
> Joe
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Mark Detering
> Sent: Monday, October 31, 2011 7:22 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Fwd: FE-5680A Physics package
>
>
> Here is a page that has some information on the FE-5680.
> http://vk3um.com/Rubidium%20Intro.html
> Near the bottom the is a link to an article by VK3GJM that talks about
> rejuvinating Rb lamps. This may be of help.
>
>> Peter,
>>
>> Somewhere, I have read an article about 'resurrecting' a 'dead' Rb
>> bulb.  I think it was done with heating but I do not recall.  I
>> probably have the article squirreled away somewhere and I can probably
>> chase it down if someone else on the list does not come up with the
>> link first.
>>
>> Are you familiar with what I am talking about?
>>
>> Joe
>>
>
>
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