cross posting eliminated
Kees:

I am always amused at all the responses one gets on these NGs, and yet no
one answers the question asked. Having said that:

Coaxial cable is supposed to carry signals in electromagnetic wave form
between the shield and inner conductor. It usually does that well.
However, in addition to that, the coax itself looks simply like a big fat
antenna wire on the outside. Now, your job, should you decide to accept it,
is to keep the signals the outside of the coax collects from getting inside.
And where might they get inside? At the top end, where the real antenna is
connected. So, a choke on the outside at the top, which has no effect at
all on the signals inside the coax, tends to isolate the outside of the coax
from the antenna, so these unwanted signals and noises aren't coupled to the
antenna and then on down the inside of the coax. BTW, some radios with poor
shielding will benefit from an additional choke at the receiver end also,
but that depends on the radio. A test to determine whether it is needed:
Disconnect the center conductor of the coax and leave the shield connected.
Hear any signals and/or noise? If so, add a choke.

--
Crazy George
Remove N O and S P A M imbedded in return address