My 160 meter shunt fed tower project is essentially done. However, I
have an issue with the 80 meter antennas hung off that tower. In a
nutshell, the current baluns (ferrite beads) feeding these antennas
don't have enough common mode impedance on 160 meters. They heat up, and
the SWR of the shunt fed tower changes as they heat up.
After some reading, I think what I need are some RG8X toroid baluns,
wound on #31 ferrite material. If they are going to replace the existing
bead baluns, then they will need to be placed at the feedline/antenna
junction. However, if I want to completely isolate the 160 shunt fed
tower from the 80 meter feedlines, shouldn't I place the new baluns as
close to the tower-mounted antenna switch as possible, and leave the
bead baluns in place at the end of the feedline to choke off the 80
meter common mode energy ?
To add more complications for adding the RG8X toroid balun, my 80 meter
antennas are switchable 2 element wire beams, with each element fed with
18' of RG-8. That dimension is critical, as it provides the proper
amount of capacitive reactance at the feedpoint to make the element a
director.
Comments ?
73,
Steve, N2IC
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Topband reflector - topband@contesting.com
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