You tune for minimum current in the skirt, at least the ones I've had my
hands on. The tuner and RF sampler is connected between the skirt and
ground. I've assumed that the skirt and tower become *one* due to their
close proximity.
The tuning for minimum is quite sharp, which is fine for an AM station
that never moves frequency. Retuning is required when tower
appurtenances are modified substantially.
It seems to me that in your case you would tune for minimum on your
favorite frequency and hope that there is enough detuning effect over
your desired bandwidth.
-Steve K8LX
On 8/31/2013 3:38 PM, Roger Parsons wrote:
Sorry Dave, I guess I didn't make myself clear.
The tower has never had a detuning skirft on it, but I am considering
putting one on. I am aware that detuning skirts are most often used
to prevent some other structure re-radiating ones wanted signal as in
the case of your towers and AM broadcast stations.
What I want to do is slightly different. My antenna is not the actual
tower, but a wire some six feet away from the tower and parallel with
it. It obviously couples very strongly into the tower, and it seems
to me that the tower is just about the right size to be 3/4 wave
resonant on 160m. That is a pretty bad length as (1) it will accept a
lot of power and (2) its major radiation lobe will be upwards - not
what is wanted at all.
I believe that a skirt with a series reactance can change the
resonant point of the tower. What I am very unclear about is how I
can adjust it - I believe that normally the skirt is tuned for
minimum current in the tower or maximum current in the skirt. I don't
think that either of those conditions will necessary be right in my
case!
73 Roger VE3ZI
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