View Full Version : A Different Cordless Phone Puzzle

04-14-2000, 12:33 PM
We have one phone line. Whenever we dial out to connect to the Interent, our cordless phone rings once! Why? (Other brands of cordless phones do not do this.)

"They're coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time... :)" - Napoleon IV

04-14-2000, 12:42 PM
The voltage potential of an on-hook (hung-up) line is about 4V, An off-hook line is 50V, and a ringing line is 90V. When someone calls you, the line goes from 4V to 90V. At the peak voltages, phones are supposed to ring.

When your modem picks up the line to make a call, the line goes to 50V. It sounds like your cordless base is overly sensitive and rings when it detects 50V rather than 90V.

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04-14-2000, 12:47 PM
Ok, but...Can you explain this?

When I go to place a call on a different phone, why DOESN'T the cordless phone ring then? (Note: We only have one cordless - the others are wired to a jack...if it matters.)

"They're coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time... :)" - Napoleon IV

04-14-2000, 02:30 PM
My WAG is that this is because a modem is powered by the computer (i.e. it has electrical power) and a hardwired phone does not. So, when the computer picks up the modem it could be applying more voltage to the line?

Hmmm... Sounds kinda ridiculous, actually.

04-14-2000, 05:31 PM
My modem usually causes the phone to chirp when it hangs up rather than when it picks up.

I think it has to do with the speed with which the voltage changes. The changing voltage induces a current briefly. Picking up a phone closes a cheap (two strips of metal) hook switch slowly, while the modem uses a fast-acting relay. Try taking the phone off-hook, then depressing the switch for a moment. Release the switch very suddenly and see if your cordless rings.

Also, if the "different phone" is on the other end of the house, the extra length of wiring has the resistance to reduce the effects of the voltage jump.

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