[time-nuts] Temperature weirdness with Thunderbolt & Lady Heather 5
kb8tq at n1k.org
Fri Dec 16 07:47:51 EST 2016
> On Dec 16, 2016, at 3:21 AM, Pete Stephenson <pete at heypete.com> wrote:
> 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).
With multiple things going nuts at the same time, power would be the first
thing on my list. Second would be the serial i/o stuff. In both cases things
like connectors and cables are very much on the suspect list.
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