[time-nuts] Temperature weirdness with Thunderbolt & Lady Heather 5

[Pete Stephenson]

On 12/15/2016 7:45 PM, Charles Steinmetz wrote:
> Tom wrote:
> 
>> There's something very odd going on here, either with Pete's TBolt,
>> and/or with Mark's Heather v5.
>>
>> 2) It also shows some truly erratic behavior the last day and a half,
>> with multiple, massive, sudden temperature drops going down several
>> degrees. I've never seen this.
> 
> I think the more revealing trace is the DAC voltage.  There are ~70mV
> plunges, to a dead quiet (at this scale), more negative value.  70mV is
> huge, corresponding to a -35e-9 frequency shift (350mHz).  If the DAC
> voltage actually changed that much, it would pull the OCXO so far off
> frequency during these events that it would take much, much longer than
> shown (indeed, much longer than the width of these events) to
> re-stabilize.  Yet we see clean jumps within seconds, and no settling.
> (Unfortunately, the Tbolt's estimation of frequency is not plotted on
> the posted screen shot.)

Apologies, I did have the frequency plot turned off. I've taken some
more screenshots with the frequency plot turned on.

screenshot.png is a close-up of one of the odd spikes, while
screenshot2.png took place ~10 minutes later (I just scrolled to the right).

The small frequency jumps in screenshot2.png are due to satellites
entering and leaving the field of view. Due to the setup of my
apartment, the antenna location is decidedly sub-optimal and has a clear
view only to the northwest.

> I find it hard to believe that LH does much processing of the reported
> DAC voltage, so I think it's safe to say (1) the LH plot shows
> accurately what the Tbolt is reporting (at least WRT the DAC voltage),
> and (2) the actual DAC voltage is not doing what the Tbolt is reporting.
> 
> Looks like a sick Tbolt to me.

Any idea what might be the issue? I can do SMT rework to replace a bad
temperature sensor or other faulty chips, within reason (super-fine
pitch stuff is a pain).

Cheers!
-Pete

> Best regards,
> 
> Charles
> 
> 
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