Hi guys,
This afternoon my tower guru replaced an 80m monoband dipole with a
TV Evans 3-band dipole for 40/80/160 at my house, and it looks like
I've just opened a can of RFI-flavored worms.
The old dipole was a full-sized homebrew antenna, fed through a W2DU
current balun via about 100 feet of RG-213. It worked "OK" on 80
(nothing to write home about). Although I could achieve a match
through a tuner on 40 and 160, it was worse than useless on those
bands, of course. With the tuner, I could get it to work OK on 80 CW.
So, this came down and the new Evans dipole went up. From a common
centre insulator (too small to be a voltage balun or current balun),
there are two wires off each side -- one is a full-sized dipole for
80m and the other is a full-size 40, then a resonator and an extra
bit of wire for 160. This is fed with the same coax that the old
monoband dipole was fed with.
Right now it's resonant in the middle of the SSB DX window on 80 but
not on 80 CW (obviously), 160 or 40 (both need to be pruned somewhat
for the latter two bands). I keyed up on 40 CW (with a flat SWR) and
noticed massive key clicks coming through my computer speakers and
the lamps inside my Ten-Tec 238 tuner were lighting 3 times their
normal brightness on key-down. Uh Oh.
Looks like a matter of hours before the neighbours break out the
pitchforks and torches, so I've gotta get to the bottom of this and fast.
Last time I ran into something like this was also on 40 at my old
QTH, with my old Alpha-Delta DX-EE. I never could run it on 40
without an MFJ "artificial ground" in my old apartment building, and
even then, it was of limited use. Seems to me, that 40 is a problem
band for RFI for me. Now, there is no current balun on the new
antenna (not enough coax to make a coax balun either), but I'm not
sure if I'm dealing with radiation off my feedline or what. The
feedpoint of the antenna is at the back of the house (near the shack,
about 25' away horizontally and up 70') and the wires run across the
back and side yards to trees.
There's a 3/4" braid from the shack going to a ground rod right
outside (relatively short run), and connected or not, it makes
absolutely no difference whatsoever - as has always been my
experience with grounding, incidentally.
Unfortunately I can't climb (no equipment plus I've never done it in
my life before -- and I'm not in the kind of physical condition which
would allow it, either), so I really don't know what I can do short
of going QRT below 30m permanently -- and that's really not an option
I want to think of. If there's anybody in northern NJ who may be able
to help me engineer a better solution than I have going here, I'd do
just about anything to make this happen.
- Peter
W2IRT
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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