In article , wrote:

"RM" == Ralph Mowery writes:

RM Check for a loose wire somewhere in the circuits that are affected.
Check
RM the voltages at the affected devices to see if they change when the frying
RM pan is cut on and off.

Thanks but a ham told me (in Chinese) that this is a well known
phenomenon with cheap current limiters, that take a bite out of each
crest of the AC sine wave as their method of limiting. That's why such
appliances cause power supplies in the same house to hum when such
appliances are switched to LOW or MEDIUM, but not HIGH. If only I
could find the English name of this phenomenon, I could look up what
to do about it.


You've got a cheezy SCR-based control in the electric blanket. When it
turns on, you get a fast current spike. IR products in your power
wiring turn this into a voltage spike (drop), and since it's a
reasonably fast, sharp edge, it's rich in harmonics.

Now let's look at your power transformers, such as the one in your ham
radio supply, or in the UPS. When they're getting nice clean sine
waves, they hum along merrily (they hum because they don't know the
words).

But when that spike from the SCR wanders in, the windings in the
transformer try to reproduce it, humming now at harmonics of the power
line, and humming a different and more irritating tune.

When the electric blanket is on high, the SCR is essentially turned on
through the entire cycle (or half-cycle depending on topology).
Turning on at close to zero voltage minimizes the switching spike.

Fixes:

Brute force filter at the electric blanket, and/or a snubber on the SCR.

Get an electric blanket that uses a (zero-crossing) triac control.

Heavier, shorter power wiring to the electric blanket, the UPS and ham
radio gear, or both.

Ditch the electric blanket and get a live-in friend!

Before we rebuilt our house, when the fuser heater in the laser printer
in the office kicked on (another cheap SCR switch), the fluorescent
lights in the room would flicker. After rebuilding, and replacing all
the wiring, going from AWG 14 to AWG 10 and 12, that laser printer
didn't make the lights flicker any more. Replacing it with a more
efficient laser printer helped a lot, too.

--
Namaste--