Topband: sloper puzzler

[Earl W Cunningham]

A bit from my own on-the-air experience with slopers:

When I returned to the air in 1996 after a long hiatus (I QRT'd in 1984
after achieving 160m DXCC), I needed an antenna for 80m to go after
5BDXCC.  I installed an 80m sloper on one of the towers and used it for
about a month.  Results were only mediocre at best.  Also, it screwed up
that 160m shunt fed tower, so to QSY to 160m I had to bring the 80m
sloper straight down and short its far end to the tower base so that it
did not affect the 160m shunt feed system.

After about a month of this hassle, I decided to try shunt feeding the
same tower on 80m.  It worked quite well, so I 80m shunt fed the other
tower and use them as a 2-el phased array (spacing 1/2 wavelength on 80m,
so two I have bi-directional patterns with gain over a single vertical). 
This array is red hot on 80m and seldom do I have to call the DX more
than once or twice in a pileup.  So, in my case, the shunt-fed tower is
head and shoulders above the sloper on 80m.  80m DXCC was achieved that
same winter season to complete my 5BDXCC.

With the top-loading Yagis on my towers (TH6DXX on one, 402BA on the
other), they are both self-resonant at about 2100 kHz.  Therefore they
are approximately 3/8 wave on 80m and high angle radiation is not a
problem.  The only top loading in addition to his TH6DXX on SP5EWY's
tower is a17/12 meter dualband beam and his tower is still slightly
shorter than 1/2 wave electrically, so I doubt that high-angle radiation
on 80m is his problem.  I suggest that he re-try using a single-capacitor
method (rather than his Omega match).  Being close to 1/2 wave, the shunt
wire tap point will be quite high above ground for 80m -- perhaps near
the top of the tower.

I also have shunt feeds on both of my towers for 160m which works quite
well as a phased array on that band.  Addition of the 80m shunt feeds
does not appear to have degraded the 160m signal at all.

73, de Earl, K6SE