[time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp
Martin A Flynn
maflynn at theflynn.org
Wed Nov 26 17:56:27 EST 2014
On 11/26/2014 5:14 PM, Jim Lux wrote:
> 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
>> 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>)
The #2 copper was recycled. The main RF grounding trapeze is tied to
the grounding electrode system with 1/0, which was also recycled from
Re the time-nuttery: Only 1E-14. Can't afford better (yet).
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