On Mon, 23 Jan 2006 19:37:34 GMT, "Eric"
wrote:

Richard,
Thanks for your detailed answer.
I am not really set upon combining. I am glad to run another wire. I gather
from your response I am better off with the coax and two transformer setup
than with using 300 ohm twin wire for the strictly AM radio purpose.
Thanks,

Hi Eric,

Why you would use 300 Ohm twin wire for AM antennas is odd, but not
prohibited. However, it does demand all the attention to keeping the
line balanced (like I said, move away from coax, and problems become
compounded). If there are 300 Ohm issues both at the antenna and at
the radio, you must preserve them through transformers if you do
migrate to coax.

Balanced goes by many requirements, none of which can be ignored. An
unbalanced condition is a tacit allowance for the intrusion of noise.
As you describe a problem with noise - well, you see where this leads,
an absolute exercise in driving out the imbalance.

Where does it occur? How do you find it? The problems are stacking
up already. It happens at the antenna itself when it is mounted near
conductive materials. This observation only leads to more questions,
what might be conductive that is nearby, and how near is nearby? The
same problem exists with coax feeds, but you can solve those easier
with the coiled lead at the end (you probably could do the same with
twin lead - and winding either lead 4 or 5 times through a ferrite
core could be equivalent fixes). However, this is only at the antenna
end, and that may not be the source of the imbalance. For twin leads,
it could be as easily that the lead traces up against metal ducting,
or along house wiring.

If you are scrupulous about these kind of details, twin lead may
indeed work fine.

Another method of tackling the problem is to carry a small transistor
radio around the house, and try to locate the noise itself. Killing
the source is a one pound cure for a ten pound problem. If the noise
comes from outside the house, then you have antenna issues, and all
the wishing in the world in trying to avoid a different antenna will
come to naught.

73's
Richard Clark, KB7QHC