Getting matching transformer from telephone

[Floyd L. Davidson]

"Don" <me@ntlworld.invalid> wrote:

In news:5015e0eccbSpambin@argonet.co.uk,
Stuart <Spambin@argonet.co.uk> typed:

What was the "test match" effect?


I'm intruiged! Go on - tell us!

This should be real interesting...

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Floyd L. Davidson]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Al wrote:

A real hybrid uses 2 transformers to get the 2-4 wire.

Or a couple of op-amps suitably configured.

Or one transformer with three windings. Or, for that
matter, a network of resistors can make a nice hybrid too.

http://www.telephonecollectors.org/library/weco/2500dm.pdf

An example of a typical telephone set designed for customer
premise use.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Floyd L. Davidson]

John Livingston <null@spambin.com> wrote:

Floyd L. Davidson wrote:
Stuart <Spambin@argonet.co.uk> wrote:
In article <87prj9kiqc.fld@apaflo.com>,


In the UK these cables went underground from studio, via as many exchanges
and repeater stations as necessary, to transmitter and never overhead.
^^^^^^^^^^^^^^^^^^^^^

You also apparently don't know what "repeater stations"
are when dealing with analog carrier systems.

Repeater Stations were not limited to FDM carrier systems. "Repeater"
refers primarily to amplification. Plenty baseband amplified circuits as
well (2 wire and 4 wire).

But 600 miles of "baseband amplified circuits" at VF
frequencies will leave you with nothing but noise.

It appears that you worked at the customer premise
location and saw only the drop equipment.

Yes, we did send program feeds from London to Burghead in Scotland via
landline.

Correct. I've worked on circuit equalisation at Burghead end. It was
baseband audio - not carrier.

And you have no idea what was in between.

You sent them that distance via FDM carrier systems, not
via landlines, even in the 1930's.

Very rarely - most carrier channels were 300-3400Hz.

Yes, most were. But not all. It was relatively easy to
use a double wide channel, or use a groupband device
that took up 48 KHz.

The noise and
distortion figures came nowhere near the requirements for broadcast
audio.

So you think an equalized audio channel over cable
would, after 600 miles????

ISTR there were attempts to use carrier, but with all sorts of
problems, not the least being that the CCITT carrier frequency plans
(Groups-Supergroups-Hypergroups) are based on 4KHz channel spacing - not
10KHz. Single Sideband translations are also problematic with music
(broadcast) circuits, as the frequency stability requirements are MUCH
higher than telephone-quality speech. Master oscillators DID go off
frequency ....

Even by the 1930's they were using phase locked
oscillators (for example L carrier systems used a 64 KHz
pilot to for frequency synchronization).

I worked for about 20 years on carrier systems designed
in the 1930's, and never saw a single instance of a
system going off frequency.

Yes, although different impedences are *now* used under different
circumstances, the cables *were* /all/ 600 ohms twisted pair.
Twisted pair cables are not 600 Ohms.

WRONG!!!!!

The characteristic impedance of a transmission line(Zo)varies by
frequency. At audio the influence of series resistance and parallel
conductance outweighs the ratio of inductive to capacitive reactance,
and the Zo rises as the frequency falls. A twisted pair will be
typically 600 ohms at 800Hz.
At RF the reactances become much more significant than the
conductance/resistance, and the Zo will level out at the figure usually
quoted as Characteristic Impedance. The same twisted pair will be about
140 ohms at RF.

I have a book here that is definitive. It is the 1938
edition of the Bell System publication "Principals of
Electricty Applied to Telephone and Telegraph Work".

A fold out chart (page unnumbered) between pages 192 and
193 shows cable characteristics for just about every
common cable used at the time. The highest
characteristic impedance shown (at 1000 Hz) for a non
loaded cable is 19 gauge NLS at 470.1 Ohms.

There is not one single cable shown as +/- 10% of 600 Ohms.

On the other hand, on page 190 there is a chart showing
open wire characteristics, and more than a third of the
configurations shown have an impedance within 10% of 600
Ohms.

Open wire might be though... ;-)

See above.

Do see above!

In more
recent times we've had rep-coils on the incoming lines to match to 150
ohms and 75 ohms but by and large all *main* feeds are now by digital
systems.

"rep-coils"???? WTF ??

Repeat coils. The common designation on the device itself was
"Rep. Coil".

Known as "Transformers" in ever repeater station I ever worked in .....

You've never worked in the telecommunication industy?

By and large? And 75 Ohms??? (Please don't try buzz words...)

See above for why buzz words won't get it in this conversation.

75 Ohm impedances are virtually *only* used for
unbalance coaxial circuits at baseband levels for
carrier systems. It is *never* used for audio, and is
never used with twisted pair cables that extend past the
end of rack a unit is mounted in.

GPO=General Post Office, the organisation in the UK originally responsible
for all telecommunications in the UK.

Been there. Done it.

Obviously not.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Floyd L. Davidson]

Stuart <Spambin@argonet.co.uk> wrote:

In article <495a35f0$0$27152$fa0fcedb@news.zen.co.uk>,
John Livingston <null@spambin.com> wrote:

"rep-coils"???? WTF ??

Known as "Transformers" in ever repeater station I ever worked in .....

It was the term we normally used when referring to the transformer that,
by and large, separated our (BBC) wiring from that of the GPO/BT. GPO/BT
technicians that I talked to seemed fully conversant with the term.

Depending on the size and layout of the station, it might be at the bottom
of a bay or in a seperate "Line termination room"

Plenty of other transformers about at amplifier inputs/outputs.

Your description is quite correct. *Every* cable pair
would have been terminated in a repeat coil of some
kind, for a number of reasons. The primary reason is
longitudinal balance, next would be DC isolation and/or
impedance matching.

An interesting history on that too, as pre-WWII that
type of device was typically far larger than necessary,
but with efforts to save iron the WWII era designs were
all smaller and lighter. After WWII the design criteria
changed to saving space to allow smaller overall size of
equipment.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Phil Allison]

"Archimedes' Wanker"

** Piss off - you stupid wanker.

An 'isolation transformer' is a device which gets attached to the power
feed. It is for power conversion and isolation on AC systems.

It has NOTHING to do with discussions about isolation in a telephone
circuit,

** God, you are one STUPID PIG IGNORANT PUKE !

http://en.wikipedia.org/wiki/Isolation_transformer

http://en.wikipedia.org/wiki/Galvanic_isolation



....... Phil



http://en.wikipedia.org/wiki/Isolation_transformer

So you piss off, you stupid fucking motherless bastard.

 

[Michael A. Terrell]

"Floyd L. Davidson" wrote:

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:
"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Al wrote:

A real hybrid uses 2 transformers to get the 2-4 wire.

Or a couple of op-amps suitably configured.

Or one transformer with three windings. Or, for that
matter, a network of resistors can make a nice hybrid too.

http://www.telephonecollectors.org/library/weco/2500dm.pdf

An example of a typical telephone set designed for customer
premise use.

I figured the Europeans had never seen the wiring of a typical US
desk set. I probably have a couple hundred networks from 2500 series
1A2 series WE & Stromberg phones. I still see a few 1A2 systems in use,
and have been giving away the last ofd the working spares.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Stuart]

In article <87zlidi9tr.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:

"Don" <me@ntlworld.invalid> wrote:
In news:5015e0eccbSpambin@argonet.co.uk,
Stuart <Spambin@argonet.co.uk> typed:

What was the "test match" effect?


I'm intruiged! Go on - tell us!

This should be real interesting...

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.

--
Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

 

[Eeyore]

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
"Floyd L. Davidson" wrote:
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Archimedes' Lever wrote:

Paul B <mail@nomail.invalid> wrote:

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?

It isn't a matching transformer. It is for isolation purposes, and
yes, there is one in all phones that attach to Ma Bell.

Backward Americans as usual ! ;~)

An ignorant statement, to say the least.

As far as it being a matching transformer, the line
impedance varies typically from perhaps 100 Ohms all the
way up to perhaps 2000 Ohms... but you will not find
anything in a telset to adjust it to match. That's because
nobody cares if it is even close to matching the line
impedance.

So you agree it's NOT a matching transformer you TWAT ?

So now you finally agree too, eh? Who does that make
into a "TWAT"?

You won't find pointless transformers (dead weight) in WORLD telecoms.

An ignorant statement, to say the least.

An informed one actually. I have NO phone with a transformer. Some analogue
modems yes but even there they found a way round it with optocouplers.

Graham

 

[Eeyore]

"Michael A. Terrell" wrote:

Now, you are catching on. Eeyore is a british idiot

Your ignorance stands out like a shining beacon on a dark night.

There never was or has ever been a need for a transformer in a phone.

Graham

 

[Eeyore]

krw wrote:

Not much of a difference, eh?

What meds are YOU on ?

 

[Eeyore]

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Salmon Egg wrote:

Tomi Holger Engdahl <then@pippuri.niksula.hut.fi> wrote:

600 ohms 1-to-1 matching transformers are quite rare in telephones.
Modern normal telephones are normally "floating" line powered
devices where electronics connect directly to line. The whole
small device is "floating" isolted from everythign else
so that gives good balance.

I know of no situation where something specified as say a 150 ohms
1-to-1 matching transformer would perform significantly different than
something specified as a 600 ohms 1-to-1 matching transformer. This
assumes that they both can support the same voltage over the same
(telephone audio) bandwidth. Am I missing something?

Twisted pair cable as used for telecoms has a nominal 100-110 ohm
inpedance. See the ADSL specs.

For some cables. Not for others.

WRONG ! For all practical cables used on the 'local run' for telecoms it's
100-100 ohms.

It might, for example, be as high as a couple thousand Ohms too.

Utter tripe.

600 ohms is an irrelevant historical nonsense from the days when they used
telegraph wires for phone circuits.

Not at all true. 600 Ohms is somewhat of a compromise,
between the low impedance of an unloaded cable pair and
the higher impedance if loading coils are used.

You haven't a FUCKING CLUE what you're talking about.

Graham

 

[Eeyore]

Stuart wrote:

In article <877i5io50c.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:
Twisted pair cable as used for telecoms has a nominal 100-110 ohm
inpedance. See the ADSL specs.

For some cables. Not for others. It might, for example, be as high
as a couple thousand Ohms too.

600 ohms is an irrelevant historical nonsense from the days when they
used telegraph wires for phone circuits.

Not at all true. 600 Ohms is somewhat of a compromise,
between the low impedance of an unloaded cable pair and
the higher impedance if loading coils are used.

600 ohms was the theoretical impedance of an infinite length of GPO
telephone cable. In the early days of broadcast radio (1930s), when
program was sent to the transmitters by GPO cable, assuming a line
impedance of 600 ohms and matching to it, was found to give the best
overall results. When you're sending program 600 miles from London to a
transmitter in Scotland, it matters!

They weren't using something that resembles a single pair of Cat 5 back then.

As I said, it's HISTORICAL only and of no practical value.

Graham

 

[Eeyore]

"Floyd L. Davidson" wrote:

What is "GPO" ???

General Post Office.

 

[Eeyore]

"Floyd L. Davidson" wrote:

Telephone cable is twisted pair

Which is why it's 100 ohms or so just like Cat 5 etc.

Graham

 

[Michael A. Terrell]

Eeyore wrote:

"Michael A. Terrell" wrote:

Now, you are catching on. Eeyore is a british idiot

Your ignorance stands out like a shining beacon on a dark night.

There never was or has ever been a need for a transformer in a phone.

So much donkey arrogance, so little intelligence.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Eeyore]

Archimedes' Lever wrote:

Hey! Floyd doesn't have an attitude, and is pretty darned good at
accepting other standards and practices, once they are brought to his
attention. I am sure he will concur with you once he realizes from your
post, that the geography and era were different than that he had his
mindset in.

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

 

[Eeyore]

"Floyd L. Davidson" wrote:

Stuart <Spambin@argonet.co.uk> wrote:
Floyd L. Davidson <floyd@apaflo.com> wrote:

(Years ago I worked on telegraph systems...)

Which has nothing to do with the information I am giving here.

It has everything to do with the information we are
discussing.

You don't know the difference between telegraph wire and
telephone wire, just for starters.

Quite so !

I have come across your attitude in other groups where americans don't
seem to understand that their way of doing things isn't universal
throughout the rest of the world. Also an inability to read other people's
posts and understand what is being said.

For example, you seem to have entirely missed:

In the UK these cables went underground from studio, via as many exchanges
and repeater stations as necessary, to transmitter and never overhead.
^^^^^^^^^^^^^^^^^^^^^

If that was in reference to the previous paragraph of
yours, then you should have put the information there.
In that case I would have jumped all over your claim
that it makes a difference for the 600 mile distance
mentioned when in fact it is not 600 miles *per* *section*.

You also apparently don't know what "repeater stations"
are when dealing with analog carrier systems.

Yes, we did send program feeds from London to Burghead in Scotland via
landline.

You sent them that distance via FDM carrier systems, not
via landlines, even in the 1930's.

Yes, although different impedences are *now* used under different
circumstances, the cables *were* /all/ 600 ohms twisted pair.

Twisted pair cables are not 600 Ohms.

Absolutely not. About 100 ohms.

Open wire might be though... ;-)

In more
recent times we've had rep-coils on the incoming lines to match to 150
ohms and 75 ohms but by and large all *main* feeds are now by digital
systems.

By and large? And 75 Ohms??? (Please don't try buzz words...)

GPO=General Post Office, the organisation in the UK originally responsible
for all telecommunications in the UK.

Thank you. (I'm familiar with BT, which evolved from
the General Post Office.)

Via 'Post Office Telecommunications'.

Your problem is that you just don't actually understand
the telephone system, at all.

He has made that evidently apparent.

Graham

 

[Eeyore]

John Livingston wrote:

Floyd L. Davidson wrote:

Twisted pair cables are not 600 Ohms.

WRONG!!!!!

RIGHT !

Do the damn sums.

Graham

 

[Michael A. Terrell]

Eeyore wrote:

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

You won't find pointless transformers (dead weight) in WORLD telecoms.

An ignorant statement, to say the least.

An informed one actually. I have NO phone with a transformer. Some analogue
modems yes but even there they found a way round it with optocouplers.

Alexander Graham Bell despised optocouplers as much as he did
demented British donkeys. Something about a 50 year plus lead time for
engineering samples. Someone who actually understood anything about
audio design would have known that though...


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Eeyore]

Bill Janssen wrote:

Eeyore wrote:
Salmon Egg wrote:
Tomi Holger Engdahl <then@pippuri.niksula.hut.fi> wrote:

600 ohms 1-to-1 matching transformers are quite rare in telephones.
Modern normal telephones are normally "floating" line powered
devices where electronics connect directly to line. The whole
small device is "floating" isolted from everythign else
so that gives good balance.

I know of no situation where something specified as say a 150 ohms
1-to-1 matching transformer would perform significantly different than
something specified as a 600 ohms 1-to-1 matching transformer. This
assumes that they both can support the same voltage over the same
(telephone audio) bandwidth. Am I missing something?


Twisted pair cable as used for telecoms has a nominal 100-110 ohm
inpedance. See the ADSL specs.

600 ohms is an irrelevant historical nonsense from the days when they used
telegraph wires for phone circuits.

Impedance for an un-loaded pair varies with frequency. So at DSL
frequencies the impedance is 100 to 110 Ohms.

Correct. It is in fact the classic 'characteristic impedance'.

But for telephone use They preferred to use loaded
pairs and they were designed to be 900 Ohms. And the phone should be a
reasonable match to the line to minimize refections which bother the users as
echoes

Only on long circuits which were treated differently.

The transformers in some sets was not an isolation transformer but a
hybrid and matching transformer.

Only ever seen that in a fax machine I helped develop for Xerox (RXEG) and the
hybrid part was done with differential amps, NOT the transformer. MUCH cheaper.

The carbon mic. used in the old phones
was powered from the line. And many of the newer phones derive power from the
line. So isolation can't be used.

I have never seen a transformer in ANY phone including the carbon mic type which
also 'draws power from the line' to power the mic as you say.

How do the clowns think they determine ON and OFF HOOK ?

Graham