[time-nuts] Cable length calibration
usenet at teply.info
Wed Jun 29 16:18:07 EDT 2016
Am Wed, 29 Jun 2016 12:28:50 -0700
schrieb Hal Murray <hmurray at megapathdsl.net>:
> brooke at pacific.net said:
> > At one point they were looking into making a GPS time receiver
> > where the cable length calibration would be built-in.
> How would you do that?
> The obvious way is to compare the time you get with a known-good
> time, but if you had that, why would you want this new GPS with an
> unknown cable length.
> You might be able to do it by measuring the DC drop. Getting enough
> accuracy seems tough.
Possibly a bit far-fetched, but Time-Domain Reflectometry might work
out. It wouldn't directly yield the physical cable length but rather
twice the propagation time, but as the time delay is what this all
would be about, this seems a fair deal. I'm sure this could in
principle be done, but haven't thought about it for long enough to have
an idea on how to address some more or less obvious obstacles.
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