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'OT:modem back to back.'
1998\09\10@155704 by ogerio Odriozola

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Sorry for the OT message. Is it possible to hook 2 standard modems like the
ones intendend for computers directly (back to back) or thru an audio link
(full range 20hz-20Khz) without using a phone line? I have spare audio
links and no data links left.
One will be hooked to a PIC  :- )

1998\09\10@162104 by Peter L. Peres

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Add a 12 V battery or wall wart in series with the 2 modems and issue ATO
and ATA respectively at each end. Ring won't work.

For a more elaborate scheme search dejanews with my email address and the
word 'phone' in it, I have posted an ASCII art schematic once in response
to a query.

Peter

1998\09\10@163423 by David VanHorn

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>Add a 12 V battery or wall wart in series with the 2 modems and issue ATO
>and ATA respectively at each end. Ring won't work.



Limit the battery current to <=100mA with a light bulb or some such, and
toss a large-ish electrolytic across that mess to keep the AC impedance
down. I made boxes like that for our products using three 9V batteries.
We needed to see >20V for idle line detect.

Some modems, including ones I've designed, need loop current to bias the
diodes in their line interfaces on, otherwise the distortion is huge, and
they may not work at all.

1998\09\10@163650 by William Chops Westfield

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   Is it possible to hook 2 standard modems like the ones intendend for
   computers directly (back to back) or thru an audio link (full range
   20hz-20Khz) without using a phone line? I have spare audio links and
   no data links left.

See if your modem has "analog leased line mode."  If so, that should
do the trick...

BillW

1998\09\10@170701 by Peter L. Peres

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On Thu, 10 Sep 1998, David VanHorn wrote:

> >Add a 12 V battery or wall wart in series with the 2 modems and issue ATO
> >and ATA respectively at each end. Ring won't work.
>
> Limit the battery current to <=100mA with a light bulb or some such, and
> toss a large-ish electrolytic across that mess to keep the AC impedance
> down. I made boxes like that for our products using three 9V batteries.

Ahh, the ASCII art schematic that I have posted on USENET months ago uses
a bulb too, and a cap ;) Small world I guess.

Anyway I've noticed that the 'leased line' option is missing from most
off-the-shelf modems.

Peter

1998\09\10@174616 by paulb

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David VanHorn wrote:

> Limit the battery current to <=100mA with a light bulb or some such,
> and toss a large-ish electrolytic across that mess to keep the AC
> impedance down.

 Aw come on, do a *decent* job!  For phone circuits, use a regulator,
e.g. 78L08 (as well as a couple of electrolytics).

> Some modems, including ones I've designed, need loop current to bias
> the diodes in their line interfaces on, otherwise the distortion is
> huge, and they may not work at all.

 You've got me there!  The only diodes a modem would normally have are
those in the ring detector, and those are DC isolated by a capacitor
anyway.  You are talking of line-*powered* (PCMCIA) modems?
--
 Cheers,
       Paul B.

1998\09\10@213710 by David VanHorn

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>  Aw come on, do a *decent* job!  For phone circuits, use a regulator,
>e.g. 78L08 (as well as a couple of electrolytics).

A light bulb isn't noisy, is cheap, and will survive line transients. A
kilometer of wire has some significant inductance.  I've done the constant
current approach too, but I kept loosing reg chips.

>> Some modems, including ones I've designed, need loop current to bias
>> the diodes in their line interfaces on, otherwise the distortion is
>> huge, and they may not work at all.
>
>  You've got me there!  The only diodes a modem would normally have are
>those in the ring detector, and those are DC isolated by a capacitor
>anyway.  You are talking of line-*powered* (PCMCIA) modems?


We did line voltage sensing, so we had a bridge on the input. Some also use
optoisolated interfaces (no transformer) and they also require loop current
to run. You gotta light the LEDs with something.
The telco never gives you a specific voltage, but they do guarantee a
minimum 20mA, and you have to draw at least 20mA off hook to assure that
they see you.  It's a current-oriented world.

1998\09\11@033829 by Mark Willis

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I had pretty decent luck with a pair of ZyXel modems a while back on
one project, using a telco-provided leased line;  5 Mi is IIRC *Too far*
for a straight "long haul modem" current loop setup.  I've seen 14.4
ZyXel's on occasion, surplus around here <G>  The pair I had definitely
had leased line mode.

 Mark Willis, spam_OUTmwillisTakeThisOuTspamnwlink.com

1998\09\11@034426 by Sean Breheny

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Hi all,

I have figured out 95% of the abreviations that are used on the list, but I
still need to ask, what does IIRC mean?

Thanks,

Sean

At 12:36 AM 9/11/98 -0700, you wrote:
>I had pretty decent luck with a pair of ZyXel modems a while back on
>one project, using a telco-provided leased line;  5 Mi is IIRC *Too far*
>for a straight "long haul modem" current loop setup.  I've seen 14.4
>ZyXel's on occasion, surplus around here <G>  The pair I had definitely
>had leased line mode.
>
>  Mark Willis, .....mwillisKILLspamspam@spam@nwlink.com
>
+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
shb7spamKILLspamcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\09\11@035045 by Lynx {Glenn Jones}

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If I Recall Correctly

------------------------------------------------------------------------------
A member of the PI-100 Club:
3.1415926535897932384626433832795028841971693993751
058209749445923078164062862089986280348253421170679

On Fri, 11 Sep 1998, Sean Breheny wrote:

{Quote hidden}

1998\09\11@035258 by Sean Breheny

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Thanks.

At 12:48 AM 9/11/98 -0700, you wrote:
>If I Recall Correctly
>
>---------------------------------------------------------------------------
---
{Quote hidden}

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
shb7spamspam_OUTcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\09\11@040126 by Mark Willis

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If
 I
 Recall (or Remember)
 Correctly

 I think B&B Electronics has a table of distances vs. Max baud rates
for the long haul modems, http://www.bb-elec.com/, or ask
@spam@supportKILLspamspambb-elec.com (Acrobat's broken here now, I find, or I would have
refreshed my memory!)

 Mark, KILLspammwillisKILLspamspamnwlink.com

Sean Breheny wrote:
{Quote hidden}

1998\09\13@185028 by Dennis Plunkett

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At 08:27 PM 10/09/98 -0500, you wrote:
{Quote hidden}

BUZZT
On this they do! The line voltage is 48V in the specs (Telstra 1563) and it
has a minimum voltage drop (2V) to the tip and ring lines irrespective of
the exchange battery which can be in the range of 42 to 56V. As for the
current, 20mA is the nominal limit, however exchanges must operate down to
17mA (Austel TS002).
As for the current-orientated world, yes! But does your equipment work down
to 3V (This is what providers would like, so that the exchange lines can be
longer), but on this Austel TS002 says that the voltage across the equipment
should not be less than 8V.

As for the light bulb surviving line transients, well unless it is something
like a 6MW bulb, i don't think it would go past a 20KA pulse test!

As for needing voltage, this is correct, as most modems now don't have a
real transformer, and use opamps directly connected to the line (Via some
effective isolation goodies like caps etc.). Again, this depends on the
country that the device is aimed at, Germany and Australia still have some
of the toughest design rules out there


Dennis

1998\09\14@003316 by David VanHorn

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>
>BUZZT
>On this they do! The line voltage is 48V in the specs (Telstra 1563) and it
>has a minimum voltage drop (2V) to the tip and ring lines irrespective of
>the exchange battery which can be in the range of 42 to 56V. As for the
>current, 20mA is the nominal limit, however exchanges must operate down to
>17mA (Austel TS002).

Un-BZZt.  Do you see a spec for OFF-HOOK voltage at the subscriber side?
No you don't.  ON-Hook is easy, and yes, they all spec that. Off-Hook is the
interesting one.

>As for the current-orientated world, yes! But does your equipment work down
>to 3V (This is what providers would like, so that the exchange lines can be
>longer), but on this Austel TS002 says that the voltage across the
equipment
>should not be less than 8V.


All I need is 20mA and about 2.4V across me.

>As for the light bulb surviving line transients, well unless it is
something
>like a 6MW bulb, i don't think it would go past a 20KA pulse test!


I mean in this limited app, to provide a quick hack to link two modems. I
don't design CO equipment in email.

1998\09\14@015126 by Dennis Plunkett

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At 11:22 PM 13/09/98 -0500, you wrote:
>>
>>BUZZT
>>On this they do! The line voltage is 48V in the specs (Telstra 1563) and it
>>has a minimum voltage drop (2V) to the tip and ring lines irrespective of
>>the exchange battery which can be in the range of 42 to 56V. As for the
>>current, 20mA is the nominal limit, however exchanges must operate down to
>>17mA (Austel TS002).
>
>Un-BZZt.  Do you see a spec for OFF-HOOK voltage at the subscriber side?
>No you don't.  ON-Hook is easy, and yes, they all spec that. Off-Hook is the
>interesting one.



BUZZT the Un-BZZt, incorrect go straigt to jail do not pass go do not
collect $200.
Austell TS002 1992 page 40 figure 4 hold signal limits. This is a spec for
CE equipment. As for the no you don't NAR NAR Na NAR NAR yes I do :-)

I think that we have our wires crossed here, in that the CO is not under
this spec, however by default, it must provide greater than 8V when 20mA is
taken from it (This is very different in the case of a public phone where
the current is over 50mA). Note that Austell TS002 is for the subscriber
(CE) equipment, and does cover the terminal voltage when off hook.


Dennnis

1998\09\14@102829 by David VanHorn

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>I think that we have our wires crossed here, in that the CO is not under
>this spec, however by default, it must provide greater than 8V when 20mA is
>taken from it (This is very different in the case of a public phone where
>the current is over 50mA). Note that Austell TS002 is for the subscriber
>(CE) equipment, and does cover the terminal voltage when off hook.
>
>
>Dennnis

That's what I meant. (TS002)  It's been a few years since I did an interface
specifically for down-under.

My only point was that when thinking phones, one should think current,
unless there is specifically a spec that says voltage.  Those phone guys of
youre were smart fellows. Much easier to determine a current at the end of a
loooong wire than a voltage.

1998\09\14@115751 by Tim Economu

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Is this PIC related???

>>
>>BUZZT
>>On this they do! The line voltage is 48V in the specs (Telstra 1563) and
it
>>has a minimum voltage drop (2V) to the tip and ring lines irrespective of
>>the exchange battery which can be in the range of 42 to 56V. As for the
>>current, 20mA is the nominal limit, however exchanges must operate down to
>>17mA (Austel TS002).
>
>Un-BZZt.  Do you see a spec for OFF-HOOK voltage at the subscriber side?
>No you don't.  ON-Hook is easy, and yes, they all spec that. Off-Hook is
the
>interesting one.
>
>>As for the current-orientated world, yes! But does your equipment work
down
>>to 3V (This is what providers would like, so that the exchange lines can
be
{Quote hidden}

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