开云体育

I remember running across a web page for a European
company that was building a two-element loop antenna
to cover 80 through 10 meters. A picture shows the
loops with the smaller 20 through 10-meter loop at 90
degrees and inside the large 80 through 30-meter loop.
I personally do not think this would make for a very
good antenna, as there would be interaction between
them and cause problems. I built a single turn loop
using RG-8 coax to experiment with and found that just
the motor control wires running from the capacitor
across the loop to the feed point to cause loss of
efficiency and pattern distortion. I knew the RG-8
coax would be a poor loop element and any problems
would really show up in antenna performance. The less
amount of metal inside the loop the better it will
perform. This tells me that having that small loop
inside the large loop is going to make a very poor
antenna on both elements. After I found the
performance to increase after removing the wires I
removed the motor drive and mount from the capacitor
and placed it at the bottom of the loop and used a
fiberglass drive shaft between them. I also found that
moving the motor drive to the other side of the loop
balanced the antenna and made it much easier to handle
when transporting, assembling, and setting it in it's
tripod ground mount. I have pictures of it in the
photo section.
As for feeding a loop with a Ferrite core, that's
pretty simple. Check out this site….

He goes into detail with all the information you need
to feed a loop this way. Personally, I just use 1/4
inch (6M) copper plumbing pipe. Cut the pipe 1/5 the
circumference of the main loop and flatten the ends
just enough to drill a hole to mount it to whatever
type coax connector you want to use. It supports it's
self and does not flop around like the RG-58 coax you
see most people use. This allows you to turn the loop
inside the main loop so you can get a 1:1 SWR on any
band you operate it on. I have found that on the
highest band the antenna is designed for the feed loop
will be almost exactly in line with the main loop and
as you change to lower bands turning the loop a little
will bring the match back to 1:1 where as if you keep
the feed loop the same you might only get a 1.5:1 or
higher match.

--- aa0ni@y... wrote:

Has anyone tried to build a coplanar loop - one
which consisted of two
loops that shared a common feed point, but were of
different
dimmensions (one built inside the other - sharing
one side)?

I'm thinking about building an 8x8 copper loop for
40m, and building a
4x4 copper loop inside of it. I would tune each loop
using a coax
capacitance stub (for 14060 and 7040). Is such a
design possible? or
would it make things so complex having two loops
together that one
would interfere with the other? It would be a
similar concept to using
two dipoles off of the same feedline - except, using
two tuned loops
instead.

Thanks,
Daniel / AA0NI

p.s. How many of you have used a toroid transformer
to go between your
feedline and single turn compact transmitting loop?
What kind and size
did you use? Iron core or Ferrite? T-50, T-114, ...
?

__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around