"Priz" wrote in message
ups.com...
On Nov 12, 11:38 am, "Tam/WB2TT" wrote:

An open loop is supposed to be 1/2 wavelength. A closed loop is supposed
to
be 1 wavelength +. A closed loop will sort of work on EVEN harmonics.
Using
a 4:1 balun is probably wrong, as is the 300 Ohm line. For 20 meters you
would need about 72 feet of wire in a closed loop, 1:1 balun, and 1/4 WL
of
RG11, feeding into a random length of RG8. SWR will be less than 1.5:1 at
resonance. For 40 meters you could use about 65 feet of wire in an open
loop, fed with RG8; haven't tried this, but I think the SWR will be less
than 2:1.

Tam/WB2TT

I used 300ohn twinlead because I plan to use this as a multiband
antenna and twinlead wouldn't have as much loss as coax in such a
situation plus I had a big roll of it lying around. The open loop
design was so I could get to a frequency as low as possible with the
amount of space I had. I know I fell a few feet short on 40 meters,
but it was the best I could do under the circumstances. As for the
balun, I bought the switchable balun because I knew some instances
might work better with 4:1, others with 1:1.

I did manage to get the SWR down a little on 40 meters by not using
the balun and just connecting the twinlead with one lead to the single
wire feed and one to the ground, but I had to use almost maximum
inductance and one of the capacitors at max as well, but didn't work
anyone.

The tuner I have was homebrewed by another ham and was built so he
could load up single wire feed antennas for low band and Top Band QRP
work. He told me the capacitors came out of a broadcast receiver and
he found the roller inductor at a hamfest while the second inductor he
made. I used it alot for tuning single wires in the past and it
worked well, although I did have some problems when I went above 17
meters with RF in the shack. Perhaps it was suitable for those kind
of applications, but not for this one and I may need to get a
commecial tuner of figure out how to modify this one to get it to work
better.

I also wonder if the feedline length could have something to do with
the strange characteristics this antenna is exhibiting. It's probably
30 feet or so.

The joys of trying to get on HF in limited space.

30 feet is around 1/4 wavelength at 40 m. So, if the impedance at the
feedpoint is less than 300 Ohms, the twin lead will transform it to a higher
impedance. It will almost certainly work better if you connect the coax
directly to the antenna. With or without a balun.

Tam/WB2TT