[TowerTalk] Elevated vertical

[K8RI on Tower talk]

<snip>
>> > Elevated radials SHOULD have the feedpoint decoupled
> through
>> > a common mode choke. if you ground the radial common
> point
>> > is causes increased loss as well as current on the
> feedline
>> > shield.
>>
>> How would you go about this with an antenna like the
> AV-640 which has a
>> built in tuning network that is grouneded.  Isolate the
> entire antenna from
>> the tower, feed it through a choke, and atach the radials
> to the bottom of
>> the antenna where it would normally atach to the mast
> driven into the
>> ground?
>
> To be truly unbalanced a system should have equal and
> opposite currents flowing into the shield and center
> conductor at both ends, and the shield has to have
> essentially zero voltage to the environment around the
> antenna including the feedline.

Would you then create a group of 1/4 wave radials tied together at the 
center, but floating above ground as the antenna is grounded to the tower? 
The antenna has its own matching and isolation network for ground, but the 
bottom of the antenna mount is still realy ground with the isolation inside.

This is just a back up system and I don't expect performance approaching my 
big antennas, or sloping half wave dipoles, but I would like it to at least 
work on 20.  Thing is, if I put in 20 meter radials will it still work on 
the other bands?  It seems to work well on 40 and 6-meters. I've not tried 
it on any of the others except 20 as I've not found those bands open while 
I've been in the shop.  15 and 10 tend to be relatively quiet at 3:00 AM.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com