[RTTY] RadioShack isolation transformer replacement

[Ed Muns]

Great advice and well-summarized.  Isolation transformers are a work-around
for system grounding problems.  However, isolation transformers are useful
when it is not easy or quick to do these two things.  I keep a supply of
them handy for quick "fixes" when a ground loop problem arises.  Ultimately
fixing the ground loop problem is the better approach.

The same thing is true of ferrites to work-around RFI problems in the shack.

Ed W0YK

 

Bill, W6WRT, wrote:
> Another approach, if you feel a bit experimental, is to 
> eliminate the ground loop in the first place. Do that and no 
> transformer is needed at all.
> 
> The kind of ground loop that causes hum with soundcard 
> digital applications is caused because the chassis of the 
> computer and the chassis of the radio are not at the same AC 
> potential. It takes only a few millivolts of difference 
> between the two chassis to cause 60 Hz AC current to flow 
> between the two chassis via the audio cables and the I 
> squared R voltage drop in the cable shield causes hum to be 
> generated and coupled into the audio.
> 
> There are two cures:
> 
> 1. Most important, place the computer and radio physically 
> close to each other and run a short, heavy wire between the 
> two chassis. This shorts out almost all the voltage 
> difference. No voltage difference = no ground loop current. 
> As a bonus, this wire will often help a lot with EMI problems 
> as well. Without this wire, the cables between the computer 
> and radio form a small loop antenna. It's usually 
> non-resonant and not very efficient of course, but in the 
> presence of a strong RF field, the loop can pick up enough RF 
> to cause trouble. The ground wire shorts out the "feedpoint" 
> of the loop.
> 
> 2. The AC power plug for the computer and the one for the 
> radio should be plugged into the same AC outlet. This 
> connects the "third wire" of the two power supplies together 
> at the AC source. Different AC sockets throughout your house 
> can have minutely different AC potentials on the third wire 
> ground and those differences go directly to the two chassis.
> 
>   I have used these two methods for nearly 20 years now and I 
> have never needed an isolation transformer anywhere.