The RFI is probably due to the fact that your antenna is so close to the
affected equipment. I used to make the bathroom flourescent light go on
with my attic dipole.

A trap design will have its current nodes in different places than a simple
dipole, but if it is working, the field strength in the house will be the
same.

The ARRL antenna book should show you where to tune the traps.


Alternativly:
If your tuner (via balanced line, NOT coax) would not tune the antenna on
multi bands, try making it into a loop. Follow around the house with the
largest size you can. Just staple the wire to the rafters. Don't worry if
your tuner does not have a balanced output, with the loop it won't make much
difference. The "balun" in the tuner would just add losses.

My roof has shingles made from Steel Slag, not gravel. I suspect it has a
much different RF charectaristic than the stone shingles do.

KA9CAR
John

"Bill" wrote in message
. ..
Yes, I agree. I have used open wire dipoles and they work great over all
bands. But, my problem is constrained by wife and housing subdivision
requirements. So my antenna is confined to the attic. I tried to use a
short
version of the open wire dipole and it is not loading at all and the RFI
is
everywhere. So I guess traps are my only option at this point. I just
never
built one before or had experience with coaxial type traps either. Just
need
to know where to tune the traps for maximum impedance on the band of
operation. Your explanation of pruning makes sense.

Thanks for your reply
73, Bill


"WB3FUP (Mike Hall)" wrote in message
...
When building a Trap dipole you start by building from the inside out.
Lets say you want an dipole for 20 and 40. Cut a twenty meter dipole,
hang
it up and adjust it for minimum SWR. Then add the traps and balance of
the
antenna. You will obtain some loading from the coils in the traps so
the
40 meter antenna will be somewhat shorter than you would expect. Prune
for
operation on 40 meters. The problem with traps is that you need a set
for
each band you want to work. You can't sneak by on the odd multiple
halfwave, the traps might be at a bad place on that 20/40 antenna used
on
15. I have a great example of that on a trapped dipole I loaded on 12
to
try the band out..

I regret the years wasted with coaxial fed dipoles. Life is much easier
if
you hang as much wire as you can, as high as you can get it, and feed
with
ladder line. I work all 80 through 10 with a 68' (34' a side) dipole
fed
with 460 ohm ladder line. For portable use I have 75 feet of AWG#22
speaker wire. 34" is split and forms the doublet, the rest is the
transmission line. It is usable from 80 to 10 and works great.

--
73 es cul

wb3fup
a Salty Bear

"Bill" wrote in message
...
Anybody tried to build this trap antenna yet?

http://www.nerc.com/~jdegood/coaxtrap/
http://members.shaw.ca/ve6yp/
http://members.fortunecity.com/xe1bef/hf-antennas.htm

Need some help on where to tune the traps for the bands of operation,
and
pruning the connection wiring. Can this be done with out a major test
equipment investment?