[time-nuts] Thunderbolt E failing

[Kevin Schuchmann]

Matthias,
    It was put away for about 3 months, then powered up and ignored for 
about a month as I figured it would have to settle in again.
I then started monitoring it with LH  and saw the abrupt jumps that 
would not go away.

    I pulled the cover off today and the OCXO behaves as expected, cool 
it and the current draw goes up, warm it and current drops.
It is stable as far as I can tell with the equipment I have.

   What I did find is the oscillator for the GPS ingest is incredibly 
sensitive to temp changes, just blowing a little air through a straw at 
it can cause  the unit to no longer find any usable satellites. I then 
started paying more attention to the Doppler values and realized this is 
where the abrupt shifts are coming from, they should be a smooth 
increase or decrease depending on if the sat is approaching or receding.

   I totally missed that they are glitching, if I can hit the sweet spot 
temp wise the GPS Doppler becomes smooth with no quick jumps and the 
chart reflects this with a stable oscillator plot.

  So it looks like my problem is the GPS ingest section, looking at it's 
oscillator it measures 12.5 MHz but I have not been able to find any 
specs so far  based on the numbers on its case.

Thanks
   Kevin




On 9/12/2020 12:52 PM, Matthias Welwarsky wrote:
> Kevin,
>
> how long has it been in storage? I expect the GPSDO doing quite clever things
> to compensate for temperature effects. There may be some parameters stored on
> the device and the characteristics of the OCXO may have changed after being
> turned off for an extended period.
>
> Regards,
> Matthias
>
> On Samstag, 12. September 2020 18:13:35 CEST Kevin Schuchmann wrote:
>> Matthias,
>>      You are correct, having spent hours looking at all the stable areas
>> and cooling and heating the gpsdo I find that when it reports that it is
>> 116.25 F then it is stable.
>> So now I guess I need to figure out why it is so picky. I will measure
>> the current draw from a cold start and see if I see the oven warming up
>> and then stabilizing and then heat and cool it and see how it reacts,
>> and also look at the electronics and see if an area is overly sensitive
>> to temperature.
>>
>> Thanks
>> Kevin
>>
>>

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