Topband: grounded tower detuning

[K9AY]

> Gary Nichols KD9SV wrote:
>> Has anyone on this reflector been able to detune a grounded tower using 
>> one or two drop wires instead of the Usual three.

> Greg, ZL3IX replied:
> With the tower only 70 ft high, you should get enough detuning simply by 
> disconnecting the coax from the shunt feed with a relay, when on Rx.
_____

I have a nearly identical situation to Gary -- 72' tapered self-supporter, 
but currently there are no antennas installed, and very little re-radiation. 
However, this tower will approach resonance at 160M when a 10 ft. mast, 
large tribander and 40M beam are installed. I will need to detune it, since 
it is only 150 ft. from the 160M vertical.

My tower tapers from 36" to 11" -- I expect one drop wire to make a large 
improvement, probably needing a second drop wire to further reduce 
re-radiation. I don't think this tower is wide enough to require a 3-wire 
"skirt."

In my pre-1985 broadcast days, a single drop wire worked well for detuning 
grounded 25G and 45G style towers. These were usually 2-way radio towers 
with little top-loading (pre-cell site era). Since these towers were rarely 
1/4-wave at the BC freq., insulating the guy wires made a big improvement, 
and the detuning circuit did the rest of the work. The only towers requiring 
a 3-wire skirt were CATV or microwave relay towers, which were taller, 
fatter, and had the extra loading of multiple antennas.

Gary
K9AY