[TowerTalk] 160m shunt feed followup

[Pete Smith]

After trying to use my Autek RF-1 to adjust the shunt feedpoint on my
tower, I reported getting a Z minimum in the band by putting in series C,
but the indicated SWR remained off-scale high.

Just for fun, I decided to substitute a small roll of RG-8X as the series
capacitor (440 pf measured) and see what SWR my VFD measures at the shack
end of 200 feet of 75-ohm CATV hardline.  To my pleased surprise, it
indicates an SWR minimum of ~2.1, at the same frequency where the Autek
indicated a Z minimum, and the radio's internal tuner found it very easy to
match.

Realizing that the CATV hardline presents some imponderables, it looks to
me as if:

a) something (a BC station?) was interfering with the Autek's SWR measurement.

b) I potentially have a workable feed situation, though I may want to
experiment with using a UNUN to do an impedance stepdown for a better
match, particularly if adding a radial field brings the feedpoint impedance
down.

Can I declare victory and start laying down radials, or do I need to drag a
radio out to the base of the tower to verify what I think I'm seeing in the
shack?

73, Pete N4ZR






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