Topband: Feed Line

[Tom Rauch]

> There appear to be at least two other solutions:
> 1. a transmission line stub, similar to the write ups for half squares and
> bobtail curtains. 

A transmission line stub, other than providing matching, radiates. 
We have the very same common-mode current problems we have 
with open wire line right into the shack. We just satisfy the SWR 
issues and make a single band antenna (at least for a fixed length 
stub).  

>2. A tank coil tuned to 160 meters at the feed point
> with a tap or link for 50 ohm coax to the radio and the top or a high tap
> for the high impedance antenna feed point.  The tank coil approach is in
> figure 12-19 of ON4UN's 1994 edition of Low-Band DXing.  Note the inverted
> ground plane is simply the middle part of a bobtail curtain, omitting the
> inverted L portions on either end.

That would solve matching and balance (common mode) problems, 
assuming an isolated link is used and the antenna has a ground 
system at the ground-level feedpoint. But again, it is a single band 
system unless you switch networks outside.

What I used, when I had limited space, was a simple 100 foot long 
dipole with balanced feeders down to the ground. I could feed the 
antenna as a T on 160 and 80, or as a dipole on 80 on up. I had to 
switch networks outside. Of course it needed a ground system, as 
all verticals or antennas near earth do if you want high efficiency.

73, Tom W8JI
W8JI@contesting.com 


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