Boden wrote:
E Z Peaces wrote:
Jeff Wisnia wrote:
The Daring Dufas wrote:
I had a friend some years ago who ran the communications
division of the local power company. This was back when
they had HF radios for communications and the techs actually
had to know something about electronics. They would get
electronic interference complaints which were often traced
to doorbell transformers. It was a very common problem and
one that many people don't even think of today.
TDD
Sorry, but I have a hard time believing that.
If it was "a very common problem", can you offer a cite proving that
a 60 hz transformer and 10-50 feet of unshielded wire with 24 vac on
it can cause interference at radio frequencies?
Wouldn't you expect that if that story was true those big pole pig
transformers and all that higher voltage wiring running on the poles
on nearly every street would have caused the radios to melt? G
Jeff
According to the FCC Interference Handbook, defective doorbell
transformers are often a source of interference to TVs and other
household electronics. It may be a neighbor's transformer. I think
it happens when part of the core comes loose and vibrates.
If the Guberment says so it must be so. I just don't believe it.
There's always something new to learn....
When I asked for a cite I was thinking only of properly operating
doorbell equipment.
I located this FCC cite:
http://tinyurl.com/63ob78
(It's on page 14 of the .pdf document.)
It sayss there's a thermostatic overload inside (some?) doorbell
xformers designed to protect them from overheating and starting a fire
if the doorbell button sticks on - or there's a short in the secondary
side wiring.
The report says that those thermal overloads (which I expect break the
120 volt primary circuit.) cycle off and back on around once every seven
seconds and that the inductive spark at its contacts can propogate
through house wiring and cause flashes of interference on a tv or
"static clicks" in radios.
Who woulda thunk it?
I wonder how long that cycling mode would continue before those thermal
overload contacts got burned enough to stop connecting and leave an open
circuit there.
That's the second time I've made a mistake this year...Thank G_d it's
almost December. G
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.