[sdiy] Re: radio signal riding on mains

[KA4HJH]

>ANY power cable can have a signal riding upon it! Even when cable tv first
>came out and I was a *very* young kid, I asked my dad "why can't they just
>use the powercord?" After, of course, I watched a cable lineman basically
>blow off his left arm in a nearby park.

Old-fashioned (wire as opposed to optic fiber) cable TV systems in the US
have the signal riding on 30 or 60V, 60Hz square-wave AC. That's right,
square-wave. Requires specially designed power transformers in the power
supplies.

Filtering out the harmonics in the amplifiers is less of a problem than you
might think thanks in part to the fact that the lower corner of the
passband is at 50MHz, and channel two starts somewhat above that.

We had a special power supply and distribution system in the shop when I
worked on this stuff back in the eighties. Variacs were essential for
fixing the power supplies. Lots of water, surge and lightning damage, plus
the occasional bullet hole and damage done by field techs who didn't know
basic electronics.
-- 

Terry Bowman, KA4HJH
"The Mac Doctor"

"By the end of Chuck Statler's 'Rock Videos' of Devo we agreed that even if
Devo did not take the stage it was still the best concert any of us had
ever attended." --Kim Thayil (Soundgardern), 1995