Topband: Half Slopers
RadioIR at charter.net
Mon Feb 4 23:17:25 EST 2008
I have to modify some of my quick answers.
1. Other than the tower itself, exactly which components contribute to the
radiated field? I understand that the minimal contribution of the sloping
wire is high angle radiation, but what about the yagis used for top loading?
Do they actually radiate?
I answered this question a little too quickly and without details. The
Yagis don't contribute any significant radiation to the total if they
are symmetrical (most of the fields cancel). They mostly act like top
loading for the mast and tower which is the part that radiates the most,
but they are a very important part of the antenna, and there are
currents in the Yagis.
3. I understand how to decouple or detune a classic shunt-fed tower for use
with a nearby RX antenna. How would you best detune a tower-fed half sloper?
I could easily switch in additional length to the bottom end of the sloping
wire, or switch in a reactive component at the tower feedpoint. Would this
You could switch it out at the feedpoint with a relay or detune it by
lengthening or shortening the sloper wire.
Correct again Jim. I was thinking he was asking if a different length
sloping wire would do it. Well no, not if it's there all the time, but
if it is switched when changing from transmit to receive that would do
it, provided the tower by itself is not resonant. I would first try to
find a method that doesn't require a T/R relay.
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