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

Jim Lux jimlux at earthlink.net
Wed Nov 26 17:14:08 EST 2014

On 11/26/14, 2:00 PM, Martin A Flynn wrote:
> The N2MO station has an external GPS antenna on the gable end of the
> building.  It's connected to the polyphaser arrestor with FSJ4-50
> superflex.
> The antenna mounting pipe has a #2 ground wire  (33.6 mm/2)  the
> polyphaser has it's own #2 ground wire.  Both connect to an 8'  x 5/8"
> (2.4m x 16mm) driven ground rod.  The jacket of the superflex is
> grounded with the factoryt Andrew kit as well
> Even with the GPS antenna lower in elevation then the HF beam and other
> antenna (with similar protection)  I have concerns about leaving it
> connected all the time.

AWG #2 seems a tad overkill, the current in a stroke can be carried by 
AWG #10 without melting, but maybe you had a lot of it around for other 
reasons.  I suspect the coax shield has smaller cross sectional area 
than AWG #2 and you'll protect your grounding wire by blowing up the 
coax<grin>. (in fact, looking at the data sheet for FSJ4-50, the DC 
resistance of the outer conductor is 1 ohm/1000 ft = AWG 10.. it's 
actually more resistance than the inner conductor (the inner conductor 
is 0.820ohms/kft, and 0.140 inch in diameter, compare to AWG 10 which is 
very close to 0.100 inch in diameter).

Hopefully your driven ground rod is bonded to the other system grounds?

I'd worry about multipath from the HF beam and tower (although maybe 
you're not using that GPS for time-nuts 1E-20 precision...<grin>)

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