Roland:
They don't have to take down the tower, they just have to get to the
feed with the CFA station off the air and install a 3-way switch of an
appropriate power level handling capability. Then, when the CFA rig is
on the air with an AM broadcast, they can change the switch setting to
go from open to short to an impedance of their choice (nominal input
resistance of the tower, for example) and then see if the listeners in
the fringe reception area can hear the changes. The switching rate
could be something interesting, like several times a second. They
could hear a pattern in the fringe area where the AM receivers' AGC is
no longer controlling the level. What say ye?
If there is a big and noticable effect, then the tower is pretty
important to the coverage they are getting. If the currents in the
tower are not making any difference, then interrupting them (with the
open circuit) and modifying them with the short or the resistor should
not make a noticable effect to the listeners. If the tower is a
resonant tower, on the frequency of the current AM station, then it
should have a pretty decent effect. At the tower itself, a current
probe on a tower leg or two that is good for the broadcast frequency
also should let them get some idea of the size of the currents that
are induced in the old tower.
How about that, Jack, instead of moving a tower that they may need to
go back to some day.
George
Roland Mueller wrote:
> Hello Jack,
>
> It was very insightful of you to include the real world effects into
> the CFA antenna model. If the nearby 75 meter tower is no longer
> being used, it would be interesting to see how the broadcast station
> coverage would change if this tower were removed from the actual
> site....
Received on Thu Apr 29 1999 - 18:16:12 EDT
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