Getting matching transformer from telephone

[Floyd L. Davidson]

"Phil Allison" <philallison@tpg.com.au> wrote:

"Floyd LUNATIC AUTISTIC Davidson"


"Phil Allison"

The term " isolation transformer " has a specific meaning in electronics
and
electrical work = "galvanic isolation".

That is not true.

** Fraid it damn well is - FUCKHEAD.

Hey, look at that... it *still* isn't true! Amazing,
eh?

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

Your cited source does not support you statement. It
merely says that is one type of "isolation transformer".
(Regardless, Wikipedia is not a credible source.)

http://www.leonaudio.com.au/line_iso.htm

Again, that is not a definitive source, but in fact it
does not support your claim anyway.

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

 

[Ross Herbert]

On Mon, 29 Dec 2008 16:07:31 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:"Phil Allison" <philallison@tpg.com.au> wrote:
:>"Floyd L. Davidson"
:>> Eeyore
:>>>
:>>>> Historically they *all* had such a transformer, and even
:>>>> today many of them do (it's cheap).
:>>>
:>>>Transformers are not cheap and I haven't ever seen a phone with one in,
:>>>even
:>>>going back 30+ years. There's simply no need.
:>>>
:>>
:>> Get a diagram of any given telset you wish that works
:>> without active components (amplifiers), and you *will*
:>> find a transformer.
:>>
:>> And trust me, they *are* cheap!
:>>
:>> Going back 30+ years, they *all* had transformers.
:>
:>** But not the 1:1 matching/ isolating kind the OP asked about - dickhead.
:
:I'm sorry, but the nickname your mother uses for you is
:not appropriate in reference to other people.
:
lease not that I have not said it is a matching
:transformer, nor have I said that it is necessarily
:appropriate for the OP. All I did was properly describe
:what it actually is.
:
:> The " hybrid " circuit couples the earphone and mic to the line but is
:>generally not even isolating.
:
:Wrong again. It provides isolation. As I mentioned in
:another post, a POTS loop needs to isolate the VF signal
:from the DC signal, and also to isolate the transmit
:signal from the receive signal.
:
:It's primary purpose is isolation. It does not provide
:impedance matching (in typical telsets, though I assure
:you there are special ones that do have exactly that
:function built into the hybrid network).


I have to agree with Phil on this one. The so called "transformer" you are
referring to in a POTS telephone is NOT for isolation at all. In fact in its
main function is to act as a hybrid matching transformer. Most of these
transformers will have 3 inductive windings and may also include non-inductive
windings to act as resistors (such as for the balance arm of the hybrid). The
windings are not generally galvanically isolated from one another and the device
generally conforms as a type of "auto-transformer".

Here is some text from an old BPO training document which describes the function
of the hybrid transformer in a POTS telephone. Despite it being old doesn't mean
that the theory is outdated. Incidentally, the schematic included shows all 3
windings connected in series, ie. NOT galvanically isolated.

QUOTE:
It is only possible for the transmitter, receiver, and line of a telephone
circuit to be interconnected so that each is electrically matched to the
remainder of the circuit, thus ensuring maximum transfer of sent and received
power, when an additional power consuming impedance is included in the
circuit. The power consuming impedance is termed a 'balance'.

The sense of the three windings of the induction coil and the electrical
characteristics of the other components are such that, ideally

(a) when transmitting, the output power is shared only between the line and
balance,

and;

(b) when receiving, the output power from the line is shared only between the
receiver and the transmitter.
UNQUOTE

 

[Ross Herbert]

On Mon, 29 Dec 2008 16:03:16 -0900, 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.

 

[Ross Herbert]

On Mon, 29 Dec 2008 16:07:31 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:
:It's primary purpose is isolation. It does not provide
:impedance matching (in typical telsets, though I assure
:you there are special ones that do have exactly that
:function built into the hybrid network).


WRONG! It does provide impedance matching between the line, transmitter,
receiver and balance network. If these elements are not effectively balanced
during the various transmission and receiving phases then signal power transfer
would be severely degraded and efficiency would be poor.

Do NOT confuse SIGNAL isolation with GALVANIC isolation. The hybrid in a phone
provides the former but NOT the latter.

 

[Archimedes' Lever]

On Tue, 30 Dec 2008 12:09:03 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"Floyd Lunatic Davidson"
Eeysore


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???


** Don't be such a pompous bloody prick.

Of course he meant the phone itself.


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.


** Don't be such a pompous bloody prick !!

Any "isolation " transformer has " galvanic isolation" .

Look it up on Google, if you are still completely clueless.

Wot a Wanker.

I do not recall giving it the moniker of "isolation transformer". I
merely mentioned the function of electrical isolation.

 

[Stuart]

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!

Telegraph wires were typically a #11 rusty wire, not a twisted pair.

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

--
Stuart Winsor

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

 

[Tomi Holger Engdahl]

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.

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.

Normal telephone subscriber lines in USA (0.4-0,6mm subscriber PE
insulated vaseline filled cable) are 770 ohm resistor (with 2uf series
capacitor) and 47nF parallel capacity.


2 uF
||
----+-----||--------+
| || |
| | |
--- | | 770 ohms
--- 47 nF | |
| |
----+---------------+

This diagram is referred to 800Hz, but impedance is rather complex,
and varies from high value at low frequency and drops to ca. 150 ohm
on 10kHz and 120-125 ohm above 100kHz.

Some telephone lines can have higher impedance (typically 1100 ohms in
lines with loading coils or telephone air cables).

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

Typical cable used in for subscriber lines has following
characteristics: 0.5 mm diameter wire, loop
resistance 182 ohm/km and pair capacitance 39 nf/km.


TRANSMISSION SYSTEMS FOR COMMUNICATIONS, revised 4th edition, Bell
Telephone Laboratories (1971) gives the followign information on
typical cable characteristics:

"The primary constants of twisted pair cables are subject to
manufacturing deviations, and change with the physical environment
such as temperature, moisture, and mechanical stress. The inductance,
L, is of the order 1 mH/mile for low frequencies and the capacitance,
C, has two standard values of 0.066 and 0.083 uF per mile although
lower capacitance cables are under development.

Of the primary constants, only C is relatively independent of
frequency; L decreases to about 70 percent of its initial value as
frequency increases from 50 kHZ to 1 MHz and is stable beyond; G is
very small for PIC (polyethylene insulated cables) and roughly
proportional to frequency for pulp insulation; and R, approximately
constant over the voiceband, is proportional to the square root of
frequency at higher frequencies where skin effect and proximity effect
dominate."

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

600 Ohms is somewhat of a compromise between different real-life
impedances that could be seen. Normal telephone line connections are
theoreticallydesigned to be 600 ohm resistive impedance. This 600
ohm is kept as international reference for designing telephone line
equipment (typically the signal powers are measured to 600 ohm load).
In practice the telephone line does lot look like pure 600 ohm
resistance.

Telephone equipment which is designed to operate with 600 ohm loads
will operate with those real-life lines, but it's performance is worse
than in ideal situation. Typically the modems are designed for 600 ohm
reference impedance because they can handle the sidetone.

The return loss of the terminal equipment must be greater than 10 dB
when compared to 600 ohm reference. This measurement applies to
telephones, modems and other terminal equipments. NET4 technical specs
are European specs and they are used in many European countries (NET4
is actually a collection of different specs in use in different countries).

For best performance the telephones are designed to the exact line
impedance. Matching the hybrid circuit to the real line impedance
(instead of 600 ohm) will improve the feedback typically by
3-6dB. 20dB sidetone is easy to achieve, but 30dB is also not too
difficult provided you can measure the line impedance and take steps
to build a correct balancing network.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

 

[Floyd L. Davidson]

Stuart <Spambin@argonet.co.uk> 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.

No it is not. (What is "GPO" ???)

Are you aware that inter-office trunking always used 900
Ohms, not 600?

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!

I hate to tell you, but you don't just feed 600 miles of cable
with a signal and expect anything to be at the end...

Telegraph wires were typically a #11 rusty wire, not a twisted pair.

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

Let me repeat that, just so you'll understand:
"Telegraph wires were typically a #11 rusty wire, not a
twisted pair." Telephone cable is twisted pair, and
sometimes it has been used for teletype service, which
might even have been called "telegraph". But when there
were wires that were "telegraph wires", they weren't
twisted pair.

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

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

 

[Archimedes' Lever]

On Tue, 30 Dec 2008 12:17:10 +0000 (GMT), Stuart <Spambin@argonet.co.uk>
wrote:

In article <87prj9kiqc.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:
Let me repeat that, just so you'll understand:
"Telegraph wires were typically a #11 rusty wire, not a
twisted pair." Telephone cable is twisted pair, and
sometimes it has been used for teletype service, which
might even have been called "telegraph". But when there
were wires that were "telegraph wires", they weren't
twisted pair.

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

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

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.

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.

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.
^^^^^^^^^^^^^^^^^^^^^

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

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

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

 

[Floyd L. Davidson]

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

In article <87prj9kiqc.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:
Let me repeat that, just so you'll understand:
"Telegraph wires were typically a #11 rusty wire, not a
twisted pair." Telephone cable is twisted pair, and
sometimes it has been used for teletype service, which
might even have been called "telegraph". But when there
were wires that were "telegraph wires", they weren't
twisted pair.

(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.

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.

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.)

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

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

 

[Stuart]

In article <87prj9kiqc.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:

Let me repeat that, just so you'll understand:
"Telegraph wires were typically a #11 rusty wire, not a
twisted pair." Telephone cable is twisted pair, and
sometimes it has been used for teletype service, which
might even have been called "telegraph". But when there
were wires that were "telegraph wires", they weren't
twisted pair.

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

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

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.
^^^^^^^^^^^^^^^^^^^^^

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

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

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

--
Stuart Winsor

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

 

[Michael A. Terrell]

krw wrote:

In article <3MKdnV-fQ4mr58TUnZ2dnUVZ_rXinZ2d@earthlink.com>,
mike.terrell@earthlink.net says...

"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.


Now, you are catching on. Eeyore is a british idiot, and Phil is a
mentally ill Aussie who won't take his medication.

Not much of a difference, eh?

Either way, Rotor-Rooter refuses to clean up the mess.


--
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.

 

[Phil Allison]

" Floyd LUNATIC AUTISTIC Davidson"


** Wot a brain dead, lying, know nothing cunt.

Gotta be another demented, ASD fucked code scribbler.




...... Phil

 

[Phil Allison]

"Archimedes' Lever"


** Piss off - you stupid wanker.



.... Phil

I do not recall giving it the moniker of "isolation transformer". I
merely mentioned the function of electrical isolation.

 

[John Livingston]

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).

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.

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

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.

Open wire might be though... ;-)

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 ??

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

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.

Been there. Done it.

John

 

[Stuart]

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.

--
Stuart Winsor

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

 

[Stuart]

In article <87d4f9kf3v.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:

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

But not it seems with practical aspects. If you have you might know about
the following

What is a reversible line and how does it work?
What was the "test match" effect?

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

I have a moderate understanding of telephone systems but a much greater
one of the use of program lines and why they were 600 ohms.

--
Stuart Winsor

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

 

[Don]

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!
--

Don

 

[Archimedes' Lever]

On Wed, 31 Dec 2008 00:30:45 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"Archimedes' Lever"


** Piss off - you stupid wanker.



... Phil



I do not recall giving it the moniker of "isolation transformer". I
merely mentioned the function of electrical isolation.

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, you retarded fuck.

So you piss off, you stupid fucking motherless bastard.

 

[Michael A. Terrell]

"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


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