Topband: Effect of DC on Ferrite Toroids?

[Tom Rauch]

> How do you know if you are exposed to such trouble?I think 
> in my small
> property it would be unlikly to develope such a problem 
> but with somebody
> close to a power sub station or heavy industrial power 
> supplies/supply
> lines/tranformers it could be a real problem!
> I know about a case where a powerline engineer was killed 
> because of an
> earting problem 1/2 a mile away, imagine the power
> available to cook your core,excuse the pun. Tom, how do 
> one check on this
> potential problem?

A clamp on current meter with low frequency response. I have 
two types here (for very low frequencies) an "Amprobe" for 
power lines and a homebrew hall cell detector.

You'd also be surprised how much current flows through 
ground leads in the shack when external dc supplies are 
grounded to the same common point as a rig unless the supply 
has a floating negative terminal.

It often isn't a bother, but it is there and can sometimes 
(if you have a grounded audio line external to the rig) 
cause what people think is RF feedback because the 
time-varying current from the 12V supply that follows voice 
peaks on a SSB rig can modulate the mic input.

73 Tom