Jason W0JSB:
Your residential distribution is single phase. Much of the ground wire
current is in the earth.
The 75 stands for 75 KVA transformer rating. The primary voltage might
be 4160, might be 2400, might be 7200, might be 7500, might be 14.4 KV,
might be 15 KV. Probably line to neutral. 220 is still single phase. One
wire has 120 volts to ground, the other wire has 120 volts phase angle
180 degrees to ground, so between them there's 240 volts.
If your 120 volt loads are wandering about, its likely you have a poor
neutral connection and are experiencing neutral shift from changing
(like refrigerator and furnace) 120 volts. That's not a good sign. The
bad connection in the neutral can be in your main panel, the wires from
the pole to your house (overhead or underground, more often a problem
with buried aluminum wires) or out on the pole. On the pole its a
utility problem (and may show at your neighbor's as their changing loads
contribute to the neutral shift), but the service drop and main panel in
the house are your problem. A good electrician can find the problem and
fix it or get it fixed. It will get worse and start damaging stuff from
high voltage, lamps first, electronics later.
Signaling on the power line using audio tones has been going on for at
least 75 years. Sometimes its used to control fixed loads for peak
reduction or to change capacitors correcting system power factor.
My graduate work was applying communications in the audio range to power
lines. Some places when checking for background level, I found volts of
trash from SCR operated induction heaters.
Noises from arcing switches should show up with strong 60 Hz spectral
components because the arcing only happens near the peaks of the line
voltage. That hash could be a poorly RFI protected aquarium thermostat.
Their switches are notorious for slow opening and opening a tiny gap to
arc. The heat of the arc forces them to open better so they get quiet.
If that aquarium heater is on the same side of the transformer as your
transmitter power supply, transmitting may be lowering the line voltage
to cause the heating to be a little slower.
Then it could be a bad door bell transformer with a thermal protector
that opens at intervals making hash as it opens.
And those noise sources could be anywhere in a couple blocks. But as it
seems to be voltage sensitive, it may be in your house with the neutral
shift.
73, Jerry, K0CQ
--
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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