.... my RFI
> tutorial.
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
*** This is excellent. It reminds me of the importance of ground loops.
Ground loops and me - we have a history.
Once upon a time, when I was in high school, somebody gave me a Heathkit
OM-1 oscilloscope. This was a primitive machine, uncalibrated in any way.
I got it home, powered it up - and saw a 60Hz sine wave - with nothing
connected to the scope. When I shorted out the input, it went away.
I fought with it and fought with it, replacing filter capacitors - and
increasing them beyond all reason. No difference. Then I had a
breakthrough - I borrowed another scope from a friend. Poking and
prodding around, I found that there was an AC voltage on one part of the
chassis - as compared to another part!
How could this be? Well, Heathkit used to use a lot of self-tapping
sheetmetal screws to put their aluminum chassis together. This would
work great for some years, then dissimilar metal corrosion would create
resistances between the various panels. Hence ground loops, and
voltages on pieces of metal seemingly solidly bolted to other pieces of
metal. I cleaned the aluminum, bolted things back up and had a working
OM-1 scope.
The lesson in ground loops was worth far more than the scope :).
- Jerry Kaidor
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