I have read that these old knife switches have very poor RF insulation
qualities. Perhaps this effect is frequency and/or power sensitive (for
want of better terminology) to some extent.

Doc.

"Holger 'Geri' Kinzel, DK8KW" wrote:

Tom, G3OLB:

>Years ago I remember my grandfather having a wireless aerial (as it was
>known then) down his garden which came through an insulator in the
>window frame and was connected to a ceramic knife switch on the window-
>sill. This allowed changeover of the aerial from the wireless to earth
>during thunder storms. Does anyone know of a source of such switches
>these days?

... have a look at

http://www.surplussales.com/Antennas/Antennas-4.html

... the second item is similar to the switch that I use to ground my
umbrella antenna whenever not in use. Is this the kind of switch you are
looking for?

Best 73

Geri, DK8KW (W1KW)