Hi Roy

Mmmmm, yet another base belief falls screaming from the sky! grin

It would be interesting to know how it happened (the misconception that
is). The low level thinking (for me) on a transmission line is that for
a pair of wires, the signal on one side is always 180 degrees out of
phase with the other. Any noise induced by a magnetic field would be in
the same phase hence common mode rejection means it isnt "seen" by a RX.
I cant help thinking that unbalanced line is somewhat asymetrical in
that the diameter of the outer conductor would *somehow* have a non
trivial width when it comes to the wavelength of the frequency in use.
Needless to say I havent gone to the extent of plotting magnetic lines
and rereading my base theory stuff. Some things one just has to accept!

I get the *feeling* that balanced feeder is less likely to radiate than
unbalanced.

Why does one use triax in some situations? (cable damage and inadvertent
DC supply grounding aside)

One hopes it is a fair statement to say that any inbalance in the
current on either side of the transmission line (or phase shift ne 180
deg) will result in line radiation.. (However one gets it)

I have grabbed the ARRL balun PDF from the Eznec site and will see how I
go... Have to pay some bills first!

I was trying to explain why an antenna (folded dipole or qaud) isnt
really a short circuit at the operating frequency, without referring to
terms like Xc, Xl, and resonance. I see I failed! What I was trying to
portray was that for the amount of time and distance (aka wavelength)
that the electrons had to travel around the antenna any instant in time
and at any specifc place would never see a short circuit. Or of you like
AC is very different to DC.

What I really want to know is whether Paul's FM RX is now working!

Cheers Bob


Roy Lewallen wrote:
-----snips----

You have to think of the antenna as a tuned AC circuit. In fact
completely throw away any thoughts of a DC circuit havning any effect
whatsoever. Same kind of logic as a power transformer not looking like
a short circuit. Think of the antenna as being feed by an
instantaneous voltage that takes a fixed time to get from the
feedpoint to where there is a "short cicruit" in the wire. The signal
from one side of the coax arrives "in phase" with the one from the
other side so no current flows between them. The trick is in the
length of the wire in question. . .


I don't quite follow this, so I might be misinterpreting what was said,
but it doesn't sound quite right.