On 5/21/2012 12:55 PM, Richards wrote:
>
>
>
>
> I know you did not intend these examples to be
> all-inconclusive - I believe the comment applies
> equally well to to the so-called or "end fed half-wave
> dipole." The transmission line acts as a counterpoise.
> W8JI agrees on his web site.
That depends on how the end fed half-wave dipole is fed. See my Coax
Chokes Power Point for one form of end fed half wave dipole that does
NOT use the coax as a counterpoise, but DOES use the coax shield as half
of the antenna, using a common mode choke as the end insulator.
http://audiosystemsgroup.com/publish.htm
>
>
>
> > Example -- back when I lived in Chicago, my shack was on the second
>> floor, my antennas were bonded to a station ground, which was bonded to
>> power, telco, some rods, and a big wrought iron fence that ran around
>> the front of my lot.
> * * *
> The big #4 copper that
>> ran from the second floor shack to those grounds and that fence WAS part
>> of the antenna, even though it was CALLED a "ground" wire, and it
>> contributed to the total radiation.
>
>
> I thought a big cable running down from the second
> floor would be seen as a high impedance thing to
> a bolt of lightning... and was ill advised as a safety
> ground. (Ignoring for a moment whether or not it
> will radiate RF and act as part of the antenna system.)
>
> Is that myth, or it is one of those cases where
> something bad is better than nothing at all ?
Not myth at all, but a necessary part of the overall lightning
protection system. For best protection, the coax antenna bonding to
earth, power, telco, etc. would be done at ground level, then extended
back up to the shack. That's not what I did, but it's what I should have
done. :) No damage resulted, but that's the luck of the draw.
73, Jim K9YC
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