Re: Commodore Modems - C1660 and C1670

From: Groepaz (
Date: 2004-01-30 14:21:57

On Friday 30 January 2004 13:52, Marko Mäkelä wrote:

> A semiconductor or an inductive or capacitive load can be viewed as a
> voltage source.  Maybe Mr. Levak was referring on that?

mmmh ok, maybe :=P

> Has anyone measured the voltage when doing pulse dialing?  I think that
> there can be high spikes.  In the early 1990s, when I used a 2400 bps modem
> (the only modem I have ever owned and still own), I remember seeing garbage
> on the screen that could have been caused by a neighbour calling with pulse
> dialing.  I also remember hearing dial pulses when talking on the phone.
> Back then, the phone exchange didn't understand touch tone dialing (or it
> did, but it apparently internally converted DTMF to dial pulses, because
> DTMF calls were actually slower to connect than pulse dialed calls).

pulse dialing is nothing else than interrupting the on-hook voltage for a
defined period of time (thus the dialer in the phone is called "interrupter").

the spikes come from the fact that the interrupter infact toggles the phone
beeing on-hook and off-hook, which means connecting and disconnecting the
bell from the line => inductive load here ... resulting in spikes :)

you can easily prove that to yourself by "dialing" using just the hook...mmh
or maybe that doesnt work anymore on modern lines :) it was a neat trick
in certain countries to dial with the hook in public phones... *cough* :=P


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