[TowerTalk] grounding elevated vertical for lightning?

[Jeff Blaine]

Spark gap it is, then...  Thanks for all the suggestions.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: Jim Lux
Sent: Friday, February 08, 2013 3:37 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] grounding elevated vertical for lightning?

On 2/8/13 10:36 AM, Jim Brown wrote:
> On 2/8/2013 5:52 AM, K1TTT wrote:
>> What is the best way to ground this antenna?  Can I put a few ground
>> rods at
>> the center base and run them up to the radial junction?
>
> NO! The work of Rudy Severns, N6LF, on the topic of elevated radials
> shows that elevated radials should NOT be grounded, because doing so
> causes radial currents to be unbalanced, which increases loss.  For the
> same reason, a common mode choke must be used on the coax at the 
> feedpoint.
>
Exactly... this was one of the interesting non-intuitive findings when
NEC3 and NEC4 were being validated: antenna performance with radials
alone was better than with the ground rod added.


I assume you want to ground for lightning protection?  Then a spark gap
is your friend. Open circuit for RF, but when lightning strikes, it
closes.  Hook the spark gap to your ground rods and to your antenna, and
you're all set.  A 1/10" gap breaks down at 7kV. Needle gap is more like
2kV.




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