Getting matching transformer from telephone

[Eeyore]

Tomi Holger Engdahl wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> writes:
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.

The twisted pair cable as used for telecoms has a nominal 100-120 ohm
impedance for high frequecies the ADSL system uses. The ADSL
system uses frequencies between 138 kHz and 1.1 MHz for downstream
data (and 25 kHz to 138 kHz ofr upstream). This 100-120 ohm
impedance holds pretty well for those frequencies above 100 kHz.

True.

For lower frequencies the the impedance of the telephone cable
is not anymore that 100-120 ohm, but something else.
For voice frequencies used on on normal telephone (300-3400 Hz)
the impedance is normally considerable higher than 120 ohms.

But that is NOT the 'characteristic impedance' and will vary depending whether
you're 100m from the exchange / C.O. or 5km !

I appreciate your other information but it sure isn't the way we do things here
in the UK.

Graham

 

[Eeyore]

Phil Allison wrote:

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

** Huh ??

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

I think he was having a laugh !

USA and back via either underground cable or satellite can (did) do some weird
stuff, but even that has gone now with IP telephony which is becoming near
universal now. I can make certain calls to the USA from the UK for LESS than the
cost of certain types of UK call.

In fact a US call for me from the UK to a landline OR CELLPHONE costs 7.5c to
connect and 1.5c / minute.

Graham

 

[Michael A. Terrell]

Eeyore wrote:

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 ***

WHat does that have to do with what Floyd was discussing? As usual,
you change the subject in an attempt to cover your ignorance.

Any other time you damn anyone for using Wikipedia as a reference,
but when it suits some of your ignorance...


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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.

 

[Michael A. Terrell]

Eeyore wrote:

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

You really are stupid.


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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.

 

[Michael A. Terrell]

Eeyore wrote:

I appreciate your other information but it sure isn't the way we do things here
in the UK.

No, you build monstrosities, then brag about them.


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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.

 

[Michael A. Terrell]

Eeyore wrote:

Phil Allison wrote:

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

** Huh ??

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

I think he was having a laugh !

I have had severe echo on as little as ten miles of underground
telephone cable on an old mechanical exchange. The phone company had
run new lines out to rural areas, then connected some downtown
businesses to the trunk a block from the C.O. We had one of the first
digital alarm monitoring services, and had trouble decoding some numbers
because of the echo. Ohio Bell refused to correct their problem stating
it would be done on schedule in six years so we had to move the business
to another town that had recently undergone a full rebuild. The line
ran about ten miles from the C.O. to the end.


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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]

Phil Allison wrote:

"Lostgallifreyan"
"Phil Allison"
LYING

Posted after last post in a subthread does not mean aimed at last poser,
when the new post is a useful read for all posting. Got that? Read it,
it's a
lot more interesting than you are right now.

** Oxygen thieves like this anencephalic turd need shooting.

I have to agree.

Plus think of the advantage in reduction of methane emissions !

Graham

 

[Stuart]

In article <495B6C81.4B8FCB38@hotmail.com>,
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

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

Oh dear, you need educating.

http://www.telephonesuk.co.uk/images/232_cct.jpg

What do you think "Coil,Induction No20" is?

--
Stuart Winsor

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Telephone cable is twisted pair

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

Except of course when it has loading coils in it, and
then it is something much higher.

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

 

[krw]

In article <495B66E1.C1EE782C@hotmail.com>,
rabbitsfriendsandrelations@hotmail.com says...

krw wrote:

Not much of a difference, eh?

What meds are YOU on ?

Metoprolol and aspirin why? Is your inferriority getting the better
of you again?

--
Keith

 

[krw]

In article <oqydnaMeppa09cbUnZ2dnUVZ_gidnZ2d@earthlink.com>,
mike.terrell@earthlink.net says...

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.

s/arrogance/dung/

--
Keith

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

Twisted pair cables are not 600 Ohms.

Absolutely not. About 100 ohms.

Cable type Impedance at 1000 Hz

19NLS 470
19NLP 262
19H50P 675
16B22 806
19H245S 1882

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

He has made that evidently apparent.

So have you.

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

Bill Janssen wrote:
Eeyore wrote:
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.

Not true, as has been discussed elsewhere.

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'.

Not true, as has been shown conclusively in other posts.

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.

That is absolutely untrue. Loading coils were not
uncommon on 1/2 mile loops too! Basically whatever the
design plan was for outside plant, it would be used for
*all* loops.

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.

Well, there you go! You haven't got enough exposure to
how telcom systems function to be telling anyone
anything. You should be asking for help!

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.

Then just exactly how do you think the transmitter got
power in those old phones?

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

Do you have a clue? Do you know what the difference
between "ground start" and "loop start" is?

Interestingly, the "line card" that supplies loop
current, and detects hook supervision, also has a
transformer. In the days of mechanical switching
systems, it was for isolation only. With modern digital
systems, it too is a hybrid.

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

 

[Eeyore]

"Michael A. Terrell" wrote:

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.

So, go on Mr Expert. Why is one *needed* ?

Graham

 

[Eeyore]

krw wrote:

rabbitsfriendsandrelations@hotmail.com says...
krw wrote:

Not much of a difference, eh?

What meds are YOU on ?

Metoprolol

US trade name.

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

and aspirin why? Is your inferriority getting the better of you
again?

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

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.

Graham

 

[Eeyore]

"Michael A. Terrell" wrote:

Alexander Graham Bell despised optocouplers

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

History's never been your strong suit has it ?

Graham

 

[Eeyore]

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Archimedes' Lever wrote:
floyd@apaflo.com (Floyd L. Davidson) wrote:

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.

Which is why I stated its primary purpose as being that of isolation

What exactly needs isolating from what ? Have you noticed they tend to be
made of plastic ?

The transformers are made of plastic??? (I don't think so...)

The PHONES - STUPID ! Even when they bakelite, I doubt it was a good conductor
of electricity.

Graham

 

[Eeyore]

Salmon Egg wrote:

floyd@apaflo.com (Floyd L. Davidson) wrote:

A telephone loop has both VF (voice frequency) and DC
signals going in both directions, all of which need to
be "isolated" from each other. The transmit and receive
VF signals also have to be isolated from each other
(which is why the transformer is commonly called a
"Hybrid Network").

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*.

Graham

 

[Eeyore]

"Floyd L. Davidson" wrote:

Salmon Egg <SalmonEgg@sbcglobal.net> wrote:
floyd@apaflo.com (Floyd L. Davidson) wrote:

A telephone loop has both VF (voice frequency) and DC
signals going in both directions, all of which need to
be "isolated" from each other. The transmit and receive
VF signals also have to be isolated from each other
(which is why the transformer is commonly called a
"Hybrid Network").

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

They are commonly called either "induction coil" or
"repeat coil". However, the ones used in the type of
telephone you would commonly see (in a home or business)
are generally encapsulated, and include a balance
network, midpoint capacitor, and possibly other
components, and is usually but not always called a
"network" of some kind.

Equipment seen in a telephone office would more likely
have been built with individual components, and at least
up into the 1970's would have had a separate transformer
that would indeed have been labeled as "Ind. Coil" or
"Rep. Coil". At least for WECo built equipment that
would have been true, and others at times did the same
or came up with something different just to be
different.

Complete overbuild. You should see a 'BT' one made by GEC or Plessey. No
such things.

Graham

 

[Eeyore]

Ross Herbert wrote:

floyd@apaflo.com (Floyd L. Davidson) wrote:
:Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
:>Archimedes' Lever wrote:
:>> floyd@apaflo.com (Floyd L. Davidson) wrote:
:
:>> >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.
:
:>> Which is why I stated its primary purpose as being that of isolation
:
:>What exactly needs isolating from what ? Have you noticed they tend to be
:>made of plastic ?
:
:The transformers are made of plastic??? (I don't think so...)
:
:A telephone loop has both VF (voice frequency) and DC
:signals going in both directions, all of which need to
:be "isolated" from each other. The transmit and receive
:VF signals also have to be isolated from each other
which is why the transformer is commonly called a
:"Hybrid Network").

The hybrid in a POTS phone can have all windings effectively connected in
series. It is the polarity of the windings and the relative impedances and the
connections of the transmitter, receiver and balance impedance which effectively
provide for SIGNAL ISOLATION (ie. NOT galvanic isolation) depending upon whether
the telephone is transmitting or receiving. The windings don't have to be
galvanically isolated to do this.

Sense at last !

Graham