[TowerTalk] RFI and a new antenna

[Peter Dougherty (W2IRT)]

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