Re: Weird modem problem
- From: Fred McKenzie <fmmck@xxxxxxx>
- Date: Sat, 02 Jun 2007 21:06:19 -0400
In article <MPG.20c94f4c6b6a785b98968d@xxxxxxxxxxxxxxxxx>,
Charlie Wilkes <charlie_wilkes@xxxxxxxxxxxxxxxxxx> wrote:
Telco did not do this damage.
Are you sure about that?
Charlie-
If you measure voltage across the phone lines, it should be around 48
volts DC with the phone on-hook. The positive side may be grounded back
at the phone company's battery facility.
When your phone rings, the line has about a 90 volts AC, 20 Hz ringing
voltage. Therefore, your modem must be capable of withstanding these
voltages, plus a bit more to be sure it won't break down.
When the phone or modem goes off-hook, a small amount of current is
drawn from the line. That causes the phone company's equipment to turn
on the dial tone. If two phones or modems are off-hook at the same
time, you should still hear the dial tone but at a reduced level.
If you are listening to the dial tone on a phone, and it disappears when
the modem goes off-hook, then you either have a short-circuited modem
(which you might be able to measure with an Ohm meter), or a pulse was
generated on the line causing the dial tone generator to turn off (as if
you were dialing from a rotary phone).
If you measure the voltage on the line with a DC meter, a short circuit
in your modem would cause the voltage to go to near zero, compared to
several volts across the telephone when it is off-hook.
Fred
.
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