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

Pete Stephenson pete at heypete.com
Fri Dec 16 09:30:18 EST 2016


On 12/16/2016 1:54 PM, wb6bnq wrote:
> Hi Pete,
> 
> Are you really at an altitude of 645 meters ?

Yes. That's the result of multiple surveys over a week a year or two
ago. I'm pretty sure the altitude hasn't changed since then. :)

I think Lady Heather shows the altitude as that above the WGS84 geoid
rather than above sea level, right? I'm trying to resolve some
discrepancies in reported altitude between my handheld Garmin eTrex 20,
Oncore UT+, and Thunderbolt (the Oncore and Thunderbolt share a split
signal from the same antenna).

> Also, it seems that your oscillator gain (currently at -5 Hz/v) may not
> be set right ?

That's the default for the Thunderbolt. I've tried tuning it a bit to
other values but it runs reasonably well at that value so I stick with it.

> Have you checked the power supply voltages and observed them on an
> oscilloscope to see if they are relatively clean and free of spurious
> junk ?

I've checked them with a multimeter and, while not dead-on at +5, +12,
and -12V, they're within the acceptable range mentioned in the
Thunderbolt manual. I have an oscilloscope and will probe them later
today when I get home from work.

> The available number of SATS  is quite low and could be a matter of
> concern.

The antenna is in a poor location, facing to the northwest. It's the
best I can do in this apartment, and the number of satellites seen is
typical for this location.

What's interesting is that the weird transients would occur at least
once every few hours over the last two days, but when I switched to
using a hardware serial port (as opposed to a genuine FTDI USB-to-serial
adapter connected to a hub) there hasn't been anything for the last 7
hours. I made no other changes to the setup.

The adapter had been working fine with no issues for at least a year and
I was using it for other devices as well with no problems. I had turned
off the Thunderbolt for a few months to save electricity (with my PhD
studies nearing a close I needed to focus and take time off from amateur
radio stuff) and just turned it on again in preparation for the leap second.

It's possible this may have simply been a communication error between
the Thunderbolt and the computer. I'll do more tests to find out.

Cheers!
-Pete


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