[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
>> 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>)
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 
another project.

Re the time-nuttery:  Only 1E-14.  Can't afford better (yet).








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