Topband: Detuning towers and K9AY loops

[Tom Rauch]

> OK, I can visualize how this might work, but I'm missing a couple of
> steps.  On a shunt fed tower, for example, where is the "drop wire"
> connected to the system?  Is it tuned by changing the length, or by
> adding capacitance or inductance somewhere?  

In general you want a modest length of drop wire, something that uses 
a fairly large capacitor for tuning. The drop wire connects someplace 
above the point where the system ties to the tower.

That keeps the Q low, and bandwidth wider. Multiple drops also have 
more bandwidth, because they use larger C values for a given drop 
wire length.

You adjust the capacitor's reactance to tune the system. In BC 
systems we used a small variable L in series with a fixed 
capacitor...but for amateur use a conventional air variable would 
work just fine.

By the way, if anyone can e-mail me a file that shows severe or even 
modest interaction of a K9AY antenna with a metal mast I'd appreciate 
it.  I'm stumped about why that would happen, and could not duplicate 
that effect here. Maybe I just haven't hit the bad combination.
73, Tom W8JI
W8JI@contesting.com