JW wrote:

Whenever there is significant rain or wet snow before the ground has
frozen, the dial tone is accompanied by an annoying hum. Calls can go
out and be received, but it is extremely difficult for parties at
either end to hear. Also, when this occurs, I cannot connect to the
Internet. 10-12 hours later when conditions are dry, the phone works
OK. Diagnosis? Treatment? Thanks




We had exactly this problem in our home a few years ago. We'd get an
annoying hum when it rained, but only on "electronic" phones, ones which
needed power from a wall wart to work all their fancy functions. The
couple of old style non-electronic phones in the house didn't hum at all.

The problem was a "common mode" 60 Hz signal on the incoming phone
lines, probably leakage from the power lines on the poles to the phone
lines.

I put my scope on 'em and there was about a 30 volt p-p 60 Hz signal
relative to ground on all the phone wires when the weather was wet.

The technical explanation for why the electronic phones hummed was that
they didn't have enough "common mode rejection" on their phone input.

The phone company tried switching our lines to different pairs in their
cables, but that wasn't helpful, so we switched our phones over to
Comcast, who also supplies our cable TV and internet service. Been fine
since then.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."