[SML] Tele-Q & Practical Phones

[Mick Alderson]

Carla wrote:

> I think what y'all need for getting a live phone line from point A to 
> point B is what's called a 'telephone line simulator'. We used one long 
> ago in developing a modem product and the reasonably good ones simulate 
> a telephone central office and generate all the voltages and tones 
> really well.

Back before Clearcom became universal, we used carbon-mic operator-type telephone headsets in series with a DC source for show com. A 6 volt lantern battery was sufficient to drive up to six headsets, after which signal started to fade. I did a similar thing when my kids were young. I hooked two '60's era dial phones in separate rooms in series with a 9 volt transistor radio battery and they talked to each other on the phones until they got bored. No ringer or dial tone of course, but the handsets worked fine.

I looked at it on a scope once. Assuming I read the thing properly, talking on the handset created an AC signal of about one volt on the DC carrier. As I understand it, the ringer voltage is somewhere about 90 VAC (at low amperage) but the voice carrier voltage only needed to can be a bit more than the variance the mic imposed. Mind you, I've never tried this trick with a more modern touch tone phones, but the voltage and current required for the voice circuit really can't be that great.

Mick Alderson
TD Fredric March Theatre
alderson at uwosh.edu