[time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp

Chris Albertson albertson.chris at gmail.com
Sun Dec 7 14:27:31 EST 2014

> Bob,
> can you explain more about the effect of antenna performance on a GPSDO
> system?
> Now you have told me it is important,  I would like to know more! My lab
> has an East facing window.

Physically what is happening here is that the error bars on the fix your
GPS gets will cycle over a 12  hour period because of the sats all have 12
hour orbital periods.   If you can only see part of the sky the amplitude
of this is greater.

As an example thing of the worst possible case where you antenna can only
see a few degrees of the sky.  Every 12 hours one GPS satellite comes into
view and your GPS gets a decent "fix" but then for 8 hours the GPS sees
nothing and drifts off.  Now think about moving the antenna to a marginally
better place where it always sees at last ONE GPS stiletto but for 8 hours
there are two and for 2hours there are three satellites.   The quality if
the "fix" would still vary but would be better.   In the best case your 12
channel GPS receiver ALWAYS is able to select the 12 BEST places GPS
satellites that are in view.

This is not a great effect as long as there is enough sky that there are
always some in view.

t worry about listening strike on your antenna.  If is FAR MORE likely that
lighting will strike some utility pole within 1/4 mile of your house and
the surge will come in through the AC mains power.  So if you want to fix a
problem fix that one first, then worry about less and less likely things.
This is not to say not to take normal precautions and ground the iron pipe
with a $7 aluminum ground wire just like you would do to an old fashioned
TV antenna.


Chris Albertson
Redondo Beach, California

More information about the time-nuts mailing list