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

Mark Spencer mark at alignedsolutions.com
Wed Nov 26 19:33:25 EST 2014

Sweet.   I settled on #3 copper for my antenna grounding system on economic grounds and had a "debate" with a residential electrical contractor about bonding the antenna ground to the electrical service ground.   The city inspector passed the system with the bond installed.

I haven't used poly phasers but do hope to at least stop the house from burning down in the event of a lightning strike on the roof mounted antennas.   

I also found that the metallic city water supply pipe is by far the best ground I have (at least for 60 cycle AC.) (Using a clamp on meter I can measure an appreciable current thru it, unlike the other two grounds.   I presume the current is being diverted from the utility neutral and is eventually making it's way back to the transformer that powers my house.) I'm glad the water pipe is also bonded to the electrical service ground.   I'm happy that I don't have any appreciable currents flowing thru my antenna ground.    This might be something to carefully consider (or possibly have looked at by a pro) if you have a really low impedance ground.   I've heard anecdotal accounts of sparks occurring when low impedance antenna grounds are connected to an electrical service ground.

My usual disclaimer of I'm not an expert in this field, the preceding is only my opinion,  and don't rely on this applies.

Mark Spencer

On 2014-11-26, at 2:56 PM, Martin A Flynn <maflynn at theflynn.org> wrote:

> 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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