Alex C.J. van Eijk <DXIS@wxs.nl> writes:
"I am wondering how a half-sloper for 80m suspended from a 25m high tower
effects the shunt-fed operation of that same tower for 160m, and
vice-versa?"
=============
About a year ago I put an 80m half-sloper on my 23m tower which already
had a 160m shunt feed. The 80m half-sloper totally detuned the 160m
system and made 160m operation with that tower impossible while the
sloper was in place.
I was able to operate on 160m if I detached the end of the sloper from
its support and ran the sloper wire straight down the tower and grounded
it to the tower near the tower base (the sloper's feedline already ran
down the tower to ground level). This brought the 160m system back in
tune again. It was not an easy way to QSY from one band to another, but
it did work.
Possibly my 160m shunt feed could be retuned with the 80m sloper in
operational position, but that seemingly would unbalance my
near-identical phased/shunt-fed towers on 160m. Instead, I took down the
80m half-sloper and added an 80m shunt feed to that tower. This worked
well and only slightly detuned the 160m shunt feed, which was retuned by
decreasing its gamma wire "tap" height by about 3' (1m). I then added an
80m shunt feed to the other tower and retuned that tower's 160m shunt
feed.
Phasing both towers works quite well on both bands. There is no
noticeable degradation on 160m since adding the 80m shunt feeds (possibly
even an improvement, because the towers are electrically "longer" with
the 80m shunt feeds in place). The array is *very* effective for DX on
80m as well.
With your single tower, you should be able to retune the 160m shunt feed
after adding the 80m half-sloper. I feel that it should work as well as
on 160m as it did before adding the sloper. The main effect the sloper
will have on 160m is that of additional top-loading, with possible
de-circularization of the 160m pattern.
BTW, the 80m half-sloper worked quite well for DX, but the 80m shunt feed
(single tower) seemed to get out even better.
73, de Earl, K6SE
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