Topband: Shunt Fed Tower

[Jim Brown]

On Sat, 11 Oct 2008 07:54:33 -0400, Herbert L. Schoenbohm wrote:



>mike stokes wrote:
>> I plan on shunt feeding my 88' Rohn 45 Tower for 160M.  It has 12 feet of
>> mast out the top.  The only antenna is an 40M Inverted Vee @ 80' 
>>
>> My question is, is this tall enough to shunt feed on 160M without any Yagis
>> for for the Tophat effect ?
>>
>>
>> Suggestions:

>   1. Make sure the inverted V is not going to interact and distort  the
>      vertical TOA.

Use one of my coaxial chokes (use the instructions for 80M-160M) on the feedline 
of the 40M antenna, placing it roughly halfway between the top of the antenna and 
the earth. This will take the feedline out of the picture. The 40M wires are too 
short to matter on 160M. 

To make the 40M antenna quieter on RX, I would also use a choke (wound for 40M) at 
the feedpoint. 

>   2. Try to at least get a 30 foot horizontal  boom on the mast in the
>      mean time. This will bring you very close to a 1/4 wave.

Or run wires out from either the boom or the top of the tower. Make sure that ALL 
of these connections are very solid electrical connections. 

>   3. Use a 3 wire cage to make the feed a bit more manageable and
>      broaden the B/W.
>   4. A 100 foot standing alone is overall a very good radiator low
>      angle radiator on 1.8 if the ATU can be perfected.

I agree. 

73,

Jim K9YC