[Elecraft] Open wire feeder protection

[Geoffrey Mackenzie-Kennedy]

Chris, K6DBG wrote:

> But winter is coming and I want to feed the signals inside. I have a nice
> steel box and DPDT knife switch to act as ground disconnect. I bought
> some electric fence spark gaps to provide some lightning protection.
> I was planning to 1M 1/2W resistors across the gaps as a bleed ... but
> now I'm thinking that I should use a choke instead?
>
> There seem to be lots of differing opions on this :-)

---------------------------------------------------------------------------

Chris,

If you do use chokes, before installing them check that neither has a series 
resonance at or close to any band on which you operate, if they do you will 
in most cases lose power on both Tx and Rx . You can make this check with a 
grid dip oscillator or an antenna analyzer. As seen by the antenna feeder 
they should be transparent, and your antenna tuner should not have to find 
another match after the chokes are installed.

In the days when tube PAs used pi networks with the DC fed via a choke at 
the tube end of the network, the choke was often wound in sections to avoid 
this series resonance problem, and it is always a good idea to check any 
choke for series resonances before using it in any circuit.

73,
Geoff
GM4ESD