[time-nuts] Datum 4065A Cs Tube Response
EWKehren at aol.com
EWKehren at aol.com
Mon May 5 22:49:22 UTC 2014
The original price of the STEL1173CL was $ 125 in quantity 10 so $ 65 is a
bargain. I have no idea as to how it is used in the 4065A but if it is
limited to 13 frequencies it may be worth wile to take a look at the AD 9913
it is capable to produce very precise frequencies exceeding its 32 bits, tvb
did run tests on a board we build and I have extra boards available. Has a
PIC on it that may help to emulate. Most likely will it not be the only
STEL failure.
Bert Kehren
In a message dated 5/5/2014 5:15:01 P.M. Eastern Daylight Time,
ed_palmer at sasktel.net writes:
I know very little about today's DDS chips, but I think that emulating
the STEL-1173 would be a challenge. It provides 48 bit frequency
resolution. I counted 13 different frequencies that are used to monitor
the signal to make sure that it's on frequency. Based on the manual,
they were shifting it many times per second. I'm not surprised the chip
died - they worked it to death!
Ed
On 5/5/2014 6:49 AM, paul swed wrote:
> I will agree with Joe. I have a CS tube thats darn near impossible to
read
> the beam current and yet it still locks. That truly amazes me. I seem to
> recall other comments ages ago about that chip failing. There should be a
> way to emulate it these days with all of the DDS chips and such that are
> available.
> Good luck.
> Regards
> Paul.
> WB8TSL
>
>
> On Mon, May 5, 2014 at 8:20 AM, J. L. Trantham <jltran at att.net> wrote:
>
>> Ed,
>>
>> If I have the math correct, and you are measuring the voltage to ground
>> through a 10 MegOhm input impedance DMM, you have about 7.5 nA beam
current
>> which seems a bit low compared to what I remember of the HP 5061A.
>> However,
>> you still have a definable 'peak' with a 'peak to valley' voltage of
about
>> 60 mV or a 'useful signal current' of about 6 nA. If your unit's
circuitry
>> can properly amplify that and keep it a clean signal, it should work.
>> However, I would recommend setting the OCXO precisely on frequency with
a
>> GPSDO before trying to close the loop and 'locking' the signal to the CS
>> tube. It will dramatically lower the work load of getting everything
>> adjusted properly, particularly in a setting of low beam current.
>>
>> Somehow, the value of 40 nA sticks in my mind from the 5061A. The 5061A
>> manual says end of life of the HP CS tube is a peak beam current of 8
nA or
>> less. However, I have units with less current and they still lock.
The HP
>> manual also says to measure the voltage at the output of the tube with
a
>> 100
>> MegOhm or higher input impedance DMM. If yours is less, that may
>> artificially lower your values.
>>
>> EOL of the tube is a multifactor issue, including Signal to Noise ratio
and
>> the 'useful signal current' to 'background current' ratio. The
'background
>> current' is what you see with no RF signal applied to the tube. Have
you
>> measured that? A ratio of 1 is EOL per the HP manual. If yours is
about
>> 4.5 nA, as suggested by the 'off peak' values shown, or less, you still
>> have
>> a useful signal and, hopefully, a useful tube.
>>
>> I'd recommend continuing with the repair.
>>
>> Good luck.
>>
>> Joe
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Ed Palmer
>> Sent: Monday, May 05, 2014 12:46 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] Datum 4065A Cs Tube Response
>>
>> I'm playing with my first Cs standard. It's a Datum 4065A which
appears to
>> have a dead STEL-1173 synthesizer. Before I put too much effort into
>> replacing that, I thought I'd check the tube and see if it has any life
>> left. I've attached a chart showing the response of the central peak.
>>
>> My methodology was similar to TVB's as shown here:
>> http://www.leapsecond.com/pages/cspeak except that I measured the tube
>> output directly with a digital voltmeter. The system is reporting
wildly
>> varying levels for the beam current so I didn't want to use any of it's
>> circuitry.
>>
>> Does this look like a usable tube? Healthy or on it's last legs? What
>> response levels are typical for a Datum 7504A tube? I see that these
>> levels
>> are somewhat lower than those shown on leapsecond for the 5061A tube,
but
>> that could just be the specifics of the measurement.
>>
>> Thanks,
>>
>> Ed
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