[GPS_Standard] No joy here

[Chris Howard w0ep]

I think the control circuit of my oscillator must be
faulty.  I have watched the controller card go rail to
rail with the control voltage and it doesn't seem to
make any difference with the output frequency.

I went in and manually set the DAC to skip ahead;
I still get the same mixture of sample frequencies,
still the same general frequency offset in the same direction.
It's like I didn't do anything.

I've tested the voltage on the pin of the oscillator.
The controller is changing the voltage, it just doesn't
have any effect.

My oscillator is an HP 10811-60111.

Chris



On 2/13/2012 9:28 AM, Chris Howard w0ep wrote:
> Thanks! I appreciate the encouragement.
>
> I have made a couple of changes that gave me
> quick improvement:
>
> 1) I worked up a small amp to boost my 1 PPM up to 5 volts.
> 2) I "discovered" that the HP oscillator needs negative
>     tuning slope.
>
> Now I am "locked" and chasing the warming up oscillator
> back toward mid-range of the DAC voltage.
>
>
>
>
>
> On 2/13/2012 7:11 AM, Bert, VE2ZAZ wrote:
>> Hi Chris,
>>
>> Welcome to the world of accurate frequency. Here are a few comments.
>> First you should reduce the S sampling period to something like 16 to
>> let the system find the sweet spot much faster. When you notice that the
>> DAC adjustments alternate  (more or less) between going upward and
>> downward, you are ready to use a much larger value. You are currently
>> just wasting time slowly going through the DAC values. Note that you
>> won't have to do this every time, just at the first time start up.
>>
>> I don't know for how long you have had the OCXO powered up, but you can
>> expect to see it drift (re-trace) for several days before stabilizing.
>> This is typical of an OCXO that has been powered down for some time.
>>
>> Did you try to center the OCXO with the coarse adjustment while
>> zero-beating the 10MHz WWV station (with DAC value set to center)?
>> Remember that the HP OCXOs can only tune electronically to +/- 0.5 Hz
>> (if my memory does not fail me), so you may be sitting outside of the
>> electronic tuning range. With WWV, you can do better than that with a
>> bit of patience.
>>
>> Have Fun.
>>
>> Bert, VE2ZAZ
>> http://ve2zaz.net
>>
>>
>> On 02/12/2012 10:12 AM, Chris Howard w0ep wrote:
>>> After two years, I finally focused on getting this
>>> GPS standard working.  I have had all the parts
>>> for the past few months, but just didn't get
>>> around to putting it all together until yesterday
>>>
>>> I'm using the oscillator from a defunct HP counter,
>>> a Resolution-T GPS, built into a  2-U chassis which I picked
>>> up at a university's junk sale awhile back.
>>>
>>> The chassis was from some sort of heater controller from
>>> Kodak. It included a digital volt meter on the front panel
>>> which I have incorporated to watch the DAC voltage.
>>>
>>> I used power supply parts from the HP counter
>>> and the Kodak controller.  I am using a separate +/-5v
>>> supply from the Kodak unit instead of using
>>> the +5v derived onboard.
>>>
>>> It has been plugged in and running for 800 16-second
>>> samples and DAC voltage is slowly moving upward.
>>> No lock yet.
>>>
>>> I have a switchable RS-232 port that allows me to
>>> connect to either the GPS or the controller card.
>>>
>>> Still needed:  better GPS antenna connection (need
>>> to buy a crimper), better GPS antenna, bring bi-color
>>> LED to the front panel, and buy or make some 50 ohm
>>> BNC terminators for the unused ports.
>>>
>>>
>>>
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>>
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