Getting matching transformer from telephone

[Eeyore]

I'm laughing at YOU !

Have you NO understanding how phones work ? Apparently NOT ! Ringing voltage is
around 100V AC or chopped DC. How's your matching transformer going to deal with
THAT ?

http://en.wikipedia.org/wiki/Ringing_voltage#Ringing_signal

 

[tony sayer]

Unfortunately has has NO CLUE about the characteristic impedance of twisted pair
cable as used for telecoms.

http://en.wikipedia.org/wiki/Twisted_pair#Unshielded_twisted_pair_.28UTP.29

"UTP is also finding increasing use in video applications, primarily in security
cameras. Many middle to high-end cameras include a UTP output with setscrew
terminals. This is made possible by the fact that UTP cable bandwidth has
improved to match the baseband of television signals. While the video recorder
most likely still has unbalanced BNC connectors for standard coaxial cable, a
balun is used to convert from 100-ohm balanced UTP to 75-ohm unbalanced."

*** 100-ohm balanced UTP ***

Graham

I seem to remember from another time that Old Floyd worked for some
Alaskan phone company..

Anyways what was the original question .. seems to have fallen off the
news server?...

 

[tony sayer]

Quite so !



Absolutely not. About 100 ohms.



Via 'Post Office Telecommunications'.



He has made that evidently apparent.

Graham

Course there are misunderstandings and some terminology shift in
broadcast/telecoms and all related to the way various operators used to
and now do things etc at different times..

But its all good for a slanging match...

 

[Eeyore]

I seem to remember from another time that Old Floyd worked for some
Alaskan phone company..

Anyways what was the original question .. seems to have fallen off the
news server?...

A slightly obscure question as to effectively (not sure if the OP realised) whether
impedance or voltage matching was important. Needless to say, many IDIOTS think
everything audio HAS to be 600 ohms which is an irrelevant ancient standard anyway
but lingers on in the minds of the long brain-dead.

Here's the original.

" I am looking for some 1-to-1 matching transformers to connect varioua
audio devices to my PC. I usually get noises and hum.

These line matching transformers are not so cheap at about £6 or 7
each.

Telephones seem to suppress line noise and hum rather well so I
figure the components they use are probably of half-decent quality.

If I strip down some landline phones I 've got here, then will there
be a matching transformer in each one? Or is their technology
different now? "

Graham

 

[tony sayer]

A slightly obscure question as to effectively (not sure if the OP realised)
whether
impedance or voltage matching was important. Needless to say, many IDIOTS think
everything audio HAS to be 600 ohms which is an irrelevant ancient standard
anyway
but lingers on in the minds of the long brain-dead.

Here's the original.

" I am looking for some 1-to-1 matching transformers to connect varioua
audio devices to my PC. I usually get noises and hum.

These line matching transformers are not so cheap at about £6 or 7
each.

Telephones seem to suppress line noise and hum rather well so I
figure the components they use are probably of half-decent quality.

If I strip down some landline phones I 've got here, then will there
be a matching transformer in each one? Or is their technology
different now? "

Graham

Right..

Wonder what's he actually trying to do .. in practice?..

If he's still there?...

 

[krw]

US trade name.

Beta blocker ! Ticker problem ? Not surprised with your temper.

A-fib. "Temper"? There is nothing here important enough to get
excited about, certainly not you.

Mine are MUCH more exciting ! Hopefully the physio (suspected trapped
nerve) will remove the need for the opiates.

A drugie, I suspected as much.

Going in for a CT on 14th Jan too btw. They're really giving me the
working over this time. And all for FREE on the National Health System !
You might learn something from that. Hillary's not wrong.

If you lived in the US you'd have had it done by now. CT scans
aren't something rare here. There is *nothing* free in this world.
You're simply taxed through the nose, to wait.

 

[krw]

He didn't have the opportunity, as they didn't exist in his lifetime.

History's never been your strong suit has it ?

Reading has never been your strong suit, eh Dumbass Donkey?

 

[krw]

I have found ebay to be an EXCELLENT place to shop. Many of the best
deals are to be had there. Why run a shop with overheads when you can do
it all online and they even provide the invoicing tools !

It is a good place for bottom feeders to congregate, sure.

And I know shops who do have traditional outlets AND they sell on ebay
too, often at a lower cost. Saved someone several pounds exactly that
way recently in fact.

No one said bottom feeders didn't have "traditional outlets".

 

[Franc Zabkar]

In european specifications (for Finland etc..) I have seen this
that complex reference impedance Z = 270 + (750 //150 nF)

750 ohm
_____
270 ohm +--|_____|--+
_____ | |
--|_____|---+ +-----
| || |
+----||-----+
||
150 nF

I'd just like to contribute a couple of references which I found
useful in the past.

This [old] document talks about complex impedances (see page 37):
http://web.archive.org/web/20001001070243/http://www.midcom-inc.com/pdf/TN69.pdf

International Digital Access Arrangements:
http://groups.google.com/group/comp.dcom.modems/msg/232247c06425cc1d?dmode=source

- Franc Zabkar

 

[daestrom]

s/arrogance/dung/

Wouldn't the correct syntax be:

s/arrogance/dung/g

?? So it replaces more than one occurance on each line??

Sed, gotta love it

daestrom

 

[Salmon Egg]

For a long time I believe the term actually used for this transformer
was "induction coil."

Now we're getting to the point.

'Loading coils' were used to boost voice levels on long line circuits by
loading the line to compensate for line capacitance IIRC.

NOT needed in your average city. And certainly NOT a *transformer*.[/QUOTE]

I was NOT referring to loading coils. I was referring to the
transformers inside telephones that impressed ac signals onto the pair
of conductrs forming the subscriber line.

Bill

 

[Salmon Egg]

Have you NO understanding how phones work ? Apparently NOT ! Ringing voltage
is
around 100V AC or chopped DC. How's your matching transformer going to deal
with
THAT ?

It does not have to. With the phone on hook, the ringing takes place in
a circuit that disappears when the phone goes off hook.

Bill

 

[Archimedes' Lever]

I'm waiting to see your guesses to *both* questions

Hint: both answers relay on the fact that the lines are straight analogue
from end to end.

Freudian shlip? 'relay'? rely

 

[Keith]

Wouldn't the correct syntax be:

s/arrogance/dung/g

Could be. My backgound isn't DEC, rather IBM, so...

?? So it replaces more than one occurance on each line??

....where your version would be "c/arrogance/dung/al"l. However there
was only one occurance in the post I was replying to.

Sed, gotta love it

;-)

 

[Archimedes' Lever]

They are still softening you up to accept it.

I thought that was what the country was doing to us by putting Obama in
office.

Softening us up for the royal screwing we are in the process of
getting.

 

[Paul B]

Right..

Wonder what's he actually trying to do .. in practice?..

If he's still there?...

Hello Tony and everyone, I am the OP.

I've been away for a few days and I see there's so many posts that
now I'm trying to get through them all!


MY OBJECTIVE

My aim is to take voice recordings made on various equipment and save
them to a PC. Some of the voice recordings are of telephone
conversations made onto tape. I would prefer to have fed the phone
signal direct to the PC but I get a lot of noise.

I want to preserve as much quality as possible because it will
probably be necessary for a third party to identify the person
speaking.

------

Secondly and quite separately from the above....

I didn't raise this problem in my first post. I am getting hum and
noise when I record using a purpose build connector (Retell model 156
~ see link below) to a hand-held battery-powered flash-memory
recorder even when the phone is on hook. I can't see where the hum
is coming from unless it is on the phone line because there can't be
a ground loop this time.

http://www.telephonerecorder.co.uk/recording/connectors/156.htm

I do know my landlines don't have all the hum and noise so they must
be doing something which I want for my recorder! I thought may be a
transformer to better terminate the Virgin Media phone line might
help but I am out of my depth here and line termination may be the
wrong idea altogther.


DEFINITIONS

I guess my use of the word "matching" is not a very good electrical
description. I'm not seeking to match impedances and I get the
feeling that in electrical engineering, "matching" is often shorthand
for impedence matching. So apologies for any confusion I have
caused.

I want to minimise any ground loop to reduce hum and other spuriae so
perhaps I should have said "isolating" transformer.

Retell have a model (the 157) which connects direct to a PC and I
believe it is identical to the 156 except it has the additional
transformer I am asking about.

 

[Archimedes' Lever]

I want to minimise any ground loop to reduce hum and other spuriae so
perhaps I should have said "isolating" transformer.

According to Roy, you want a ground loop.

He is such an electrical genius!


NOT!

bwuahahahahahahahahahahahahaha!

 

[Phil Allison]

"Paul B"

My aim is to take voice recordings made on various equipment and save
them to a PC. Some of the voice recordings are of telephone
conversations made onto tape. I would prefer to have fed the phone
signal direct to the PC but I get a lot of noise.

** Hey pal.

YOU already know what to do ( ie use a proper 600:600 ohms ISOLATION
transformer or a device incorporating same) ) and are just objecting to a
price of a few pounds or dollars.

Make you a fucking PITA wanker.

**** OFF.



...... Phil

 

[Archimedes' Lever]

It's true that isolation is not important for a well-insulated telephone.

A 10kV arc from a 2MV lightning strike *COULD* make it all the way into
the handset, and OUT of the perforations in the handset, through the
earpiece or mouthpiece, and hit the user. The microphone and the
earpiece transducer both use metal cans, making the distance to the user
a mere 1/4" through air. Not good.

This is ONE of the many reasons that isolation elements are
incorporated at VARIOUS locations in the system. One of which is at the
CABLE connection to the phone itself, which is why isolation elements can
be found at these positions. This is a standard element of device design
where human contact is present, and has nothing to do with it being in a
plastic case. It isn't your Dad's AC fed two wire drill motor with an
un-phased power cord and metal case. It is, however, in close
(electrical) proximity (potentially) with lightning events, and that is
why arresting elements have been incorporated.

Most incorporations are overkill, as it were, but I am happy that our
scientists and engineers of decades past were concerned about such
things.

Idiots today seem to think everything is low voltage and harmless.

 

[Phil Allison]

"Phil McKerracher"

Interesting thread (not the childish abuse, the technical stuff!).

** So you post more tech BS & childish stuff - great .

This is true ...

** Make sure you get attributitions correct - pal.


- someone (not sure who, sorry) commented earlier that this

doesn't matter because the speed of light is so high, and that's true for
local calls but not for long distance ones.

** The comment was:

" Audible echoes on a few miles of twisted pair ??? "

Which excludes all longer lines, of course.

These days there is packet delay to worry about as well. There are echo
cancellers but they're not perfect. Mismatches also affect loudness.

** But *audible echoes* on a line are not caused by transmission line
behaviour.

They are caused by problems with the hybrid to line impedance match so that
signals get retransmitted back to the exchange PLUS there has to be a
significant time delay caused by a very long link - ie thousands of miles.

It's true that isolation is not important for a well-insulated telephone.
It's also true that differential amps are a cheap alternative to
transformers for the hybrid part. But I have definitely seen phones with
transformers in them in the past (the 80s).

** What you claim you saw without proof is irrelevant

- seen any Martians lately ?

Exceptional cases are also irrelevant to the original matter.

And I have designed interfaces myself (for modems) that used transformers
..

** Modems are not the topic.

Different animals to ordinary phones.



...... Phil