From: dfh@dwroll.att.com (D461-David_F_Haertig(Dave)83040)
Newsgroups: comp.sys.ibm.pc.hardware,comp.dcom.modems
Subject: Re: fax/phone switch
Date: 9 Nov 92 18:07:17 GMT
Reply-To: dfh@dwroll.att.com
Originator: dfh@dwroll

From article <oqByTB1w165w@halcyon.com>, by puma@halcyon.com (puma):
> ray@eecs.nwu.edu (Jim Ray) writes:
>> I recently purchased, and subsequently returned, a faulty fax/phone
>> switch.  It was supposed to automatically route fax calls to the
>> fax/modem board in my PC.
>> Can some kind soul recommend a brand and model of a switch that will
>> reliably route fax/modem calls to the right place?  Are there any
>> special features other than automatic routing for these types of
>> devices?
>> 
> There are, in a basic sense, two different kinds of switches.
> One type answers the call in one ring (can sometimes be programmed),
> and listens for a "CNG" (calling) tone from the originating fax
> machine.  If it hears one, it connects and rings through to the fax,
> otherwise it connects to and rings the voice phone/answering machine.
> The second type uses "selective ringing" from your telephone company.
> This is a feature you purchase that provides you with two different
> telephone numbers that both ring your same phone - only one rings 
> using a normal single ring, the other uses a split, double ring.
> The switch detects the ring type, and connects through to the
> correct device (without answering the call!)

I just received a catalog from DAK that offers what appears to be
a third type of fax switch.  The description in the DAK catalog is
not exceptionally clear (is that a surprise?) but this is what the
thing *appears* to do:

  (1) You answer the call.  If you hear a fax tone, just hang up.
      The fax switch will connect the call to your fax machine/modem.

  (2) If you have an answering machine, the answering machine will
      pick up the call, but the fax switch will detect the fax tone
      and "steal" the call away from the answering machine and route
      it to the fax machine/modem.

  (3) You can answer calls from any phone in your house - you don't
      have to use one connected to the fax switch.

From this description, it appears that the fax switch must either:

  (1) ... constantly monitor the phone line (with a very high
      impedance of course) ...

  - or -

  (2) ... monitor the line for increased current flow (indicating
      a phone - or answering machine - went off hook) and then go
      off hook itself to check for fax tone ...

One statement in the ad made me a bit leary.  It was talking about
using the answering machine.  It said something to the effect of:
"You just leave 3-4 seconds of silence at the start of your answering
machine message ..."  It sounds like the fax switch may tend to get
confused when trying to pick out fax tone mixed with conversation.
Does this also mean that when you answer the phone you must wait
3-4 seconds before saying "hello"?  If so, the thing's not very
useful in my opinion.

Anyway, the price was something like $69, $79, $89, or $99 in typical
DAK fashion.  I don't remember the exact price.

I don't know why I always get these DAK catalogs.  I've never bought
anything from them (speakers called "Thunder Lizards"?  I think I'll
pass!!)  Anybody know if these guys are any good, or just resellers
of poor designs and other assorted junk?

Dave Haertig
haertig@att.com