analog telephone voltages

Guest
Hi all,

I am trying to gain some knowledge on POTS phone systems. I need to
know what the minimum voltages for ring and supply if I have a private
point to point connection using standard telecom interfaces? I really
don't care what the standard is... I am just interested in what it
would take to get a point to point system working (reliably of
course....). I am sure that I mis-worded this question so please ask
for clarification if I messed it up too bad.
Thanks in advance for any help.

Frodo
 
jeff posted:

<< I am trying to gain some knowledge on POTS phone systems. I need to
know what the minimum voltages for ring and supply if I have a private
point to point connection using standard telecom interfaces? I really
don't care what the standard is... I am just interested in what it
would take to get a point to point system working (reliably of
course....). I am sure that I mis-worded this question so please ask
for clarification if I messed it up too bad.
Thanks in advance for any help.
POTS is one thing, and point-to-point is another.

What channel type did you order? Some include network ring voltage, and some
do not. Please describe in the terms you and the telco discussed.

Don
 
Actually, I do not intend to connect the private line to the telco. It
is just between two devices that work on a standard POTS line. I want
to be able to generate off-hook, ring, and on hook so that I can use a
low end modem between two points that expect to be on a telco line. I
hope I have been able to clarify this...if not...give me another shot
at it please...
 
John,

I have seen the specs for one part that seems to indicate it will sense
a ring voltage as low as 17Vac rms. Can I generally depend on that?
 
jeff.mcdaniel@edwards.spx.com wrote:

Hi all,

I am trying to gain some knowledge on POTS phone systems. I need to
know what the minimum voltages for ring and supply if I have a private
point to point connection using standard telecom interfaces? I really
don't care what the standard is... I am just interested in what it
would take to get a point to point system working (reliably of
course....). I am sure that I mis-worded this question so please ask
for clarification if I messed it up too bad.
Thanks in advance for any help.

Frodo
Not interested in the specifications, but do want to know minimum
Click to expand...
requirements???

Oh well, do some digging here:
http://www.discovercircuits.com/T/telephone.htm
 
Jeff posted:

<< Actually, I do not intend to connect the private line to the telco. It
is just between two devices that work on a standard POTS line. I want
to be able to generate off-hook, ring, and on hook so that I can use a
low end modem between two points that expect to be on a telco line. I
hope I have been able to clarify this...if not...give me another shot
at it please...
Over what distance?

If you are within a few hundred feet you can probably ring a phone with 12V, 60
Hz.

12VDC will give you at least 20mA loop current thru the two phones, so that is
adequate.

If the computers are "real close" you could just use No Modem connection,
a.k.a. Null Modem.

Don
 
I read in sci.electronics.design that jeff.mcdaniel@edwards.spx.com
wrote (in <1102983740.755825.244270@z14g2000cwz.googlegroups.com>) about
'analog telephone voltages', on Mon, 13 Dec 2004:
I have seen the specs for one part that seems to indicate it will sense
a ring voltage as low as 17Vac rms. Can I generally depend on that?
Click to expand...
No.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
jeff.mcdaniel@edwards.spx.com wrote:
I am trying to gain some knowledge on POTS phone systems. I need to
know what the minimum voltages for ring and supply if I have a private
point to point connection using standard telecom interfaces?
Click to expand...
Quick specs from memory:

On-hook: -48 VDC
Off-hook: less, down (up?) to maybe -5 VDC
Ring: 90 V, 20 Hz at the phone company, maybe down as far
as 40 V by the time you get it

I have run two phones using a 9 V battery. I'm not sure what the
lower limit is. If you have an AC-powered supply, it has to be
filtered pretty well to keep hum off the phones.

For more details, see pages 935-936 of "The Art of Electronics".

Matt Roberds
 
jeff.mcdaniel@edwards.spx.com wrote:

Hi all,

I am trying to gain some knowledge on POTS phone systems. I need to
know what the minimum voltages for ring and supply if I have a private
point to point connection using standard telecom interfaces? I really
don't care what the standard is... I am just interested in what it
would take to get a point to point system working (reliably of
course....). I am sure that I mis-worded this question so please ask
for clarification if I messed it up too bad.
Thanks in advance for any help.

Frodo
Click to expand...
what POTS are you talking about? USA-Canada?
 
Telephone systems really don't work on voltage.

For US-Centric systems, you'll find that the CO will see you off-hook if you
draw at least 20mA.

There's a book, called "Understanding Telephone Electronics" that is a very
good reference.
 
"Dave VanHorn" <dvanhorn@dvanhorn.org> wrote in message
news:ncmdnRmed_qDo3bcRVn-rw@comcast.com...
Telephone systems really don't work on voltage.

For US-Centric systems, you'll find that the CO will see you off-hook if
you
draw at least 20mA.

There's a book, called "Understanding Telephone Electronics" that is a
very
good reference.
Click to expand...
However voltage is a very important part ... just try having your little
fingers across the ring and tip wires when the telemarketer calls
and you get -48v with a 90 volt 20 hz ringer signal ... your ears
will wiggle at 20 hz !!! ;-)
 
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