In article , dxAce
wrote:
bpnjensen wrote:
Telamon wrote in
message
odigy.co m...
In article ,
(bpnjensen) wrote:
(RHF) wrote in message
. com...
BJ,
I would venture to say 'if' you are using the Loop Antenna
for both Receiving and Transmission then a 1:1 or 2:1 Balun
would work well with a Coax Cable Lead-in-Line. An Antenna
Tuner would be required for Multi-Band operation.
"IF" the Loop Antenna is going to be used as a Receive "Only"
Antenna with a Coax Cable Feed-in-Line; then a 4:1 or even a
9:1 Balun could be used with good Multi-Band results.
~ RHF
Thanks RHF, and everyone else too - these are great ideas and
links. I have managed to obtain quite good results on most of
the bands from 6 MHz and up, and so I was going to concentrate
my efforts with this loop on the tropicals. I was going to
start with about 220' of wire in a loop around my rooftop and
off into some backyard trees.
Based on what I've seen here and on the websites, it looks as
though a 2:1 balun might be perfect, but a 4:1 may work about
as well for a slightly broader frequency coverage on a
receive-only antenna; so I may try these two first and then
compare. One website says not to use a balun at all (why?),
so maybe I'll try it unmatched too.
The impedance changes according to the length of the loop
relative to the wavelength received. A full wave length loop
within a wavelength of ground is around 100 ohms so you would
want to use a 2:1 BALUN to 50 ohm coax. If the loop is closer to
half wave length then it will be closer to 50 ohms and you would
want to use a 1:1 BALUN.
Thanks for this, Telamon - I intend to use this antenna for
reception only on several lower frequency HF bands (really about 3
through 6 MHz), so I'm not sure that I want or need a
BALUN/transformer that will match the impedance so closely.
Ultimately, I may end up extending the length of the wire up to 340
feet and making it's shape weird so that it will fit in my limited
space, just to see if I can achieve better results on 90m...but it
weould still be used on 49, 60 and 75.
It has been my experience in years past that horizontal loops are
great for close in work, say on 160, 75 and 80 meters. However, they
do not seem to support long haul DX. And that is why many amateur
users of those bands love them, makes for a great, close in range
signal, firing up, and then down.
Yes, great for reducing QRM sources, but that is because they
concentrate on vertically arriving signals, rather than the more
commonly horizontally polarized QRM.
Now, if you had the loop in the vertical plane, that would of course
change things dramatically.
Just my opinion, of course.
I generally agree with what you stated. My horizontal loops generally
seem to work better evenings as opposed to daytime where the lower
frequencies are favored. Generally, I get a stronger signal response
from a vertical loop daytime but they are directional where the
horizontal loop is not.
Remember that for a one-wavelength or more loop the response is in and
out of the loop so a horizontal loop is looking straight up. The pattern
changes, as the loop becomes half wave where the response is from the
edge. For a fixed horizontal loop then at high frequencies it looks up
and at low frequencies, it looks more toward the horizon in one
direction.
The BALUN will most likely only help you with local noise coming from
the AC power through your radio up the coax to the antenna and then back
to the radio input.
--
Telamon
Ventura, California