RadioBanter - View Single Post

December 10th 05, 07:26 PM posted to rec.radio.shortwave

In article .com,
wrote:

Yes, the field that the coax sees is not the same as the antenna, but
the coax is still another antenna.

You prevent the coax lead-in from becoming another antenna by
terminating it in its characteristic impedance on both ends.

If the coax lead-in is terminated by the loop on one end and the radio
on the other end it will not behave as an antenna. Most people do not
understand this termination requirement and that is just one reason a
impedance matching UNUN is important on a single wire antenna for
example.

Telamon wrote:
In article .com,
wrote:

I agree on the choke, but it seems to me the right angle coax would be
an antenna, but not aimed with the rest of the loop. For instance, a
horizontal loop connected to vertical coax would fit your description,
but I would still say the coax unbalanced the loop.

The electrical fields on the coax lead-in with be decoupled from the
same on the antenna elements when it is at right angles to it.

FWIW, I get better results with vertical loops than horizontal.

I've seen the same thing generally.

One advantage to making a loop antenna out of coax is that it is about
a third larger in electrical length than the single wire due to the
dielectric in the coax causing the velocity factor to be .6 to .7 of
air in most cases.

Telamon wrote:
In article . com,
"RHF" wrote:

M... - " The loop will be unbalanced if you don't use a balun. "

Please Educate me as to Why the Loop Antenna
would be Un-Balance without using a Balun ?

i want to know - cause -iane ~ RHF

Any time you connect a transmission line directly to a antenna the coax
shield can affect the antenna unless you decouple it.

You can:
1. Run the coax at a right angle from the antenna elements.
2. Use a choke of some type on the coax.

Otherwise the coax shield become part of the antenna.

--
Telamon
Ventura, California

--
Telamon
Ventura, California

--
Telamon
Ventura, California