Re: Re: Optoisolation for a modem

Remember, when you make a perfectly terminated and protected phone line to ground and the transient comes in on the AC line it
will use the modem phone line as ground return. Result: blown modem.

You also need to protect the line with a common ground point at the PC itself, not just at the house entry point.
Bertho
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> From: James Eckman <fugu@...>
>
> > From: "Harrison, Doug" <dharrison@...>
> >
> > Does anyone know of a good way to protect a modem from spikes on the phone
> > line?
>
> 10 ohm carbon COMPOSITION resistors in series with the tip and ring and
> followed by a 170 volt MOV, about quarter sized, across tip and ring.
> This combination can take multiple FCC part 15 test strikes.
>
> Of course, finding carbon comps may require a search of surplus stores,
> I think everything nowadays is carbon film or metal film.
>
> Jim Eckman