John wrote:
> With a voice circuit, the "last mile" is usually copper wire with the
> analog signal directly impressed on the line.  Any noise induced in the
> line within the audio band will appear directly as noise in the telephone
> receiver.  A partial short to ground or from line to line, as with a wet
> cable, produces a lot of noise (a good book on electronics can probably
> give some kind of explanation of why this is so - I certainly don't want to
> get into that here).

Old story:

************************************************
THE BARKING PHONE...
************************************************

It's common practice in England to ring a telephone by signaling extra
voltage accross one side of the two wire circuit and ground (earth in
England). When the subscriber answers the phone, it switches the two wire
circuit for the conversation. This method allows two parties on the same
line to be signalled without disturbing each other.

Anyway, an elderly lady with several pets called to say that her telephone
failed to ring when her friends called; and that on the few occasions when
it did ring, her dog would always bark first.

The telephone repairman proceeded to the scene, curious to see this
psychicdog. He climbed a nearby telephone pole, hooked in his test set,
and dialed the subscriber's house. Sure enough the phone didn't ring.
Then he tried dialing it again. This time the dog barked loudly! And
after a few moments the dogs barking would be followed by a ringing
telephone.

Climbing down from the pole, the telephone repairman found:

a. A dog was tied to the telephone system's ground post via an iron chain
and collar.

b. The dog was receiving 90 volts of signaling current.

c. After several such jolts, the dog would start barking and urinating
on the ground.

d. The wet ground now completed the circuit and the phone would ring.