K4VUD e-mailed me, copy to the reflector:
>>Should I have a eight to ten turn --six inch diameter-- in line coil of
>>coax at the base feed point of my HyTower all band vertical???
>>
>>My coax is buried from window to base of tower- about 75 feet.
>>
>>BTW, the HyTower is a very good antenna, compared to a dipole inverted vee
>>at 60 feet at center on 160, 75, and 40. Don't have any dipoles on the
>>other bands!!! Works ok on 6meters.
WC1M replied here:
>I think the conventional wisdom says that such a coil, or "lightning loop"
>will
>serve as a lightning suppressor by acting as a choke to the RF component of
>the
>surge. Polyphaser's literature says that might work, but not necessarily. They
>claim that under some circumstances, the coil will actually enhance the
>induction of surge energy into the coax.
In normal performance it probably won't make much difference. FWIW,
I use a coil choke at the base of my vertical, and a clip-on RF current
meter shows exactly equal the currents in the lead to the vertical and
in the ground lead. Current on the coax shield is exactly zero.
Uncoiling the choke and letting the loops lie on the ground, there is
some current on the shield. I simply prefer the choke because it makes
everything work as it should.
As regards lightning, it probably could couple surge energy from the
vertical to the coax if the choke was in a vertical plane. Laying the
choke down flat would minimize this effect, but I think Polyphaser are
right to suggest that the choke may not be a big benefit.
On the other hand, it doesn't introduce any detectable losses in normal
operation, so... why the heck not?
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
|