"Geoffrey S. Mendelson" wrote in message
...
I made a 300 ohm twinlead folded dipole that is resonant at around 15mHz.
It was cut because I wanted to try some 20m operation with an indoor
antenna
and that fit exactly the space.

The ham I wanted to reach was km away, across a valley. I figured with a
tuner and a few watts, I could reach him.

I never used it for that, he moved before we ever got together.

I put the antenna up outside to use for an SWL antenna. It is fed with
about 6 feet of twinlead and then 75 ohm coax. It worked best at 15mHz,
and slowly degraded as frequencies got lower. It was useable at 7mHz for
reception.

At MW frequencies it's basicly a noise pickup and no signals could be
received.

I made a balun from 9 trifilar turns of wire that I had (.5mm plastic
insulated). The instructions I was following said to use 10 turns of
#14 enamel on a wider core, but 9 were all that fit on the core I had.
The core is 8mmx80mm with a permeability of 400.

When I hooked it up to the antenna, I found that the resonant frequency
shifted to 14mHz. My guess is that the feedline now is part of the
antenna.
However at 7Mhz it is totally dead. So dead that a signal that reads S5 on
my receiver using a 2m JPole hung from the near end of the folded dipole
as an antenna does not move the s-meter at all. The null extends from
around 6950 kHz up to around 7300.

The question is why and what can I do to improve it?


I think I would not go with a folded dipole and balun. Especially if you
want to use it to transmitt with.

If you do not have enough space for a full size antenna you may want to try
what is called an inverted U antenna. YOu run the horizontal elements as
far as you can and drop the ends down. Somewhere I saw a way to stack
several like this for multibands. It is difficult to make a dipole operate
on a much lower frequency. That is if you cut one for 20 meters, it is
difficult to make it opwerate on 40 meters.