Shielding of key leads is a good idea. I prefer a very flexible
microphone cable so it doesn't break as often and so that the dielectric
is somewhat lossy at RF. A piece of coax just a quarter wave long and
open at the key end when the key is open is a super antenna for picking
up local RF. At 6m and 2m that's a problem. But audio cable is lossier
at those frequencies and so the coax transformer effect isn't nearly as
pronounced. It wouldn't hurt to put a capacitor at the key end of any
such shielded cable.
A lot depends on the antenna and feed line. If the antenna is close to
the rig, shielded key wires are more necessary (also depends on the
rig). If the feedline is close to the key line and unshielded, it all
depends on the balance in the feed line. If its a single wire, its
antenna and the rig will need all the help you can give it to keep from
getting RF back through the connecting cables.
73, Jerry, K0CQ
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