An impedance mismatch at the antenna (high reflected power) does not cause
RF to appear on the outside of the coax.
The reason RF is on the shield of the coax is because it is acting as part
of the antenna. Just like a dipole does when no choke is used at the feed
point.
The antenna may also be too close to the rig and radiating directly into the
rig/microphone cable.
73
Gary K4FMX
>
> Placing a bunch of ferrites on the coax feedline will go a long way to
> solving the symptom, RF riding the coax, but not the underlying issue;
> impedance mismatch at the feed point. The elegant way of resolving the
> issue
> is to build a Unun to transform the feedline impedance to the antenna
> impedance, interface the output of the Unun to a 1:1 Balun, and then
> connect
> the output of the Balun to the antenna. This will resolve the impedance
> mismatch and definitely cut back on the reflected RF from riding the cable
> back to the shack. The only caveat with this is that you are now locked
> into a mono-band antenna for the most part. Given his antenna is on a roof
> with coax in the near field on its short run to the shack, I would put the
> ferrites on the shack end to keep the induced RF at bay.
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