Getting matching transformer from telephone

[krw]

On Sat, 03 Jan 2009 07:26:23 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

tony sayer wrote:

Eeyore wrote:

And Pin 1 on an XLR is ALWAYS the cable shield. It may also be GROUND -
but
that's another story. It certainly isn't used to provide phantom power
under
ANY circumstances.#

Apart from providing the -return path- for the current sent over the
balanced pair...


Don't confuse him with facts. He has trouble breathing and typing at
the same time.

Oh he can do that, albeit through the mouth. Because Dumb Donkey is a
mouth breather, he drools as he types (loses control over other bodily
functions, as well). The result is what you see here.

 

[Stuart]

In article <OXUAL6K1f7XJFw2S@bancom.co.uk>,
tony sayer <tony@bancom.co.uk> wrote:

Because until the 1980s (I think it was) The GPO/BT didn't have a monopoly
on telecommunications,

Kingston telecoms anyone..

...alright not that much of the UK!....

Actually I did have them in mind whilst composing my reply but forgot
while I was typing.

--
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:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

Look, I've designed line interfaces FFS. For Xerox. I've already
mentioned it once.

You can say anything you like, but when you make up all
the ridiculous garbage you are posting to this thread
there is little doubt that you haven't got even the
faintest clue how telecommuncations equipment works.

Want to to see the schematics ? I'm sure I still have them here
somewhere.

Yes, I would like to see them. Probably better than the
Sunday funny paper.

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

You have that backwards. If you use a properly designed
pad with the correct impedance it will maximized common
mode rejection of induced currents.

As far as to how using correctly designed pads are
unsafe, I'll pass on that one and let you explain what
you think you are saying. (Because I just can't imagine
how a proper pad, or even an improper one, is unsafe.)

"Howls of derisive laughter" Bruce:

So you admit you cannot support your claims.

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

 

[Michael A. Terrell]

Eeyore wrote:

"Michael A. Terrell" wrote:

Eeyore wrote:
"Michael A. Terrell" wrote:

Here is the donkey's 'Civilized World'
http://www.dailymail.co.uk/news/article-1103843/Boozy-Britains-bloody-New-Year-A-999-seven-seconds-alcohol-induced-mayhem.html

At least we don't kill thousands of our fellow citizens each year with GUNS.

You prefer car bombs.

And when do you we last had one of those ?

When was the last time you wrote a coherent question?


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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]

"Floyd L. Davidson" wrote:

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

You have that backwards. If you use a properly designed
pad with the correct impedance it will maximized common
mode rejection of induced currents.

As far as to how using correctly designed pads are
unsafe, I'll pass on that one and let you explain what
you think you are saying. (Because I just can't imagine
how a proper pad, or even an improper one, is unsafe.)

"Howls of derisive laughter" Bruce:

So you admit you cannot support your claims.

He can't even support his three chins.


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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]

krw wrote:

On Sat, 03 Jan 2009 07:26:23 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


tony sayer wrote:

Eeyore wrote:

And Pin 1 on an XLR is ALWAYS the cable shield. It may also be GROUND -
but
that's another story. It certainly isn't used to provide phantom power
under
ANY circumstances.#

Apart from providing the -return path- for the current sent over the
balanced pair...


Don't confuse him with facts. He has trouble breathing and typing at
the same time.

Oh he can do that, albeit through the mouth. Because Dumb Donkey is a
mouth breather, he drools as he types (loses control over other bodily
functions, as well). The result is what you see here.

That's why he thinks its easy to fill potholes. Unfortunately, his
fill is foul.


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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.

 

[Jamie]

Eeyore wrote:

Stuart wrote:


Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

It isn't. Not for about 45 years.

45 years ago it certainly was!


Minority use even then.

Try and think WHY.

Graham

Really?

Minorities were allowed to use them back then?

http://webpages.charter.net/jamie_5"

 

[ingvald44]

Floyd L. Davidson wrote:

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

Not all telephone cable can run ADSL.
In civilised parts of the world with proper infrastructure it can.

How would you know that?

I think he is referring to a part of the world that is about to adopt

sharia law..

 

[Archimedes' Lever]

On Sat, 03 Jan 2009 17:36:13 -0500, ingvald44 <noone@nowhere.com> wrote:

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

Not all telephone cable can run ADSL.
In civilised parts of the world with proper infrastructure it can.

How would you know that?

I think he is referring to a part of the world that is about to adopt
sharia law..

They don't even have phones. Only limb chopping sabers, commissioned
by their saber wielding fucktard they think became a god.

 

[Ross Herbert]

On Fri, 02 Jan 2009 22:54:04 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

:
:
:Ross Herbert wrote:
:
:> Since your PC is mains powered and it may not have the required isolation
:> between the mains side and the sound card input you can do your own thing
using
:> an approved 600:600 transformer with 3kV isolation rating to interface the
:> telephone line to the sound card input.
:
:He DOES NOT need a 600 ohm transformer since the input impedance of the sound
card
:is not 600 ohms <sigh> !

Since the application is merely detecting signal "voltage" it hardly matters
that the secondary impedance of the transformer is 600 ohms and the input
impedance of the sound card is more like 10Kohms. The only reason one tries to
match impedances is where one needs to maximise "power transfer" and that
doesn't apply in this case.


:
:It's more likely to be in the tens of kilohms.
:
:What he really wants is something like a 10k:10k 'line bridging' transformer.
In
ractice, using a '600 ohm' transformer will probably be ok, but being
incorrectly
:loaded will degrade the sound quality (freq resonse may be peaky etc).
:
:Graham
:

Not true!

 

[Phil Allison]

"Ross Herbert"

Since the application is merely detecting signal "voltage" it hardly
matters
that the secondary impedance of the transformer is 600 ohms and the input
impedance of the sound card is more like 10Kohms.

** Fact is, it will be an advantage as the load across the phone line
needs to be high as possible so the level there is not affected.

The only reason one tries to
match impedances is where one needs to maximise "power transfer" and that
doesn't apply in this case.

** Nonsense.

Audio and other wide band transformers have rated ( ie optimum) source and
load impedances.

This relates *directly* to them both operating efficiently AND exhibiting
their specified frequency response curve.

Eg, a 600:600 ohm type operating into 10 kohms may well have a large
response peak at high frequencies while a 10k:10k type operating into 600
ohms will likely have serious roll off from a few kHz upwards.

With transformers that have 1:10 or 1:20 step-up ratios for mic-input to a
valve stage, both load and source impedances become quite critical just to
stay within a +/- 2dB corridor across the audio band.



...... Phil

 

[Michael A. Terrell]

"Floyd L. David son" wrote:

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

Ross Herbert wrote:

Since your PC is mains powered and it may not have the required isolation
between the mains side and the sound card input you can do your own thing using
an approved 600:600 transformer with 3kV isolation rating to interface the
telephone line to the sound card input.

He DOES NOT need a 600 ohm transformer since the input impedance of the sound card
is not 600 ohms <sigh> !

It's more likely to be in the tens of kilohms.

What he really wants is something like a 10k:10k 'line bridging' transformer. In
practice, using a '600 ohm' transformer will probably be ok, but being incorrectly
loaded will degrade the sound quality (freq resonse may be peaky etc).

An 'audio expert' would put a 600 ohm resistor across the secondary
to provide proper loading but no expects you to know that.

That would be true *if* he wanted to load the circuit
down to 600 Ohms, but he almost certainly does not.
Doing so would reduce the level available to the
telephone set user by 3 dB. What he probably wants to
do is bridge across the "600 Ohm" telephone set with
something that is at least 6000 Ohms.

That would work, but a 600 ohm load would give the flattest frequency
response, and a -3 dB change would be equal to someone picking up an
extension. Some signal loss, but not outside the design limits. The
best choice would be a telephone interface like those used for radio
stations. They are bi-directional, and allow the host to talk to the
listeners, and the caller at the same time. They will work reliably,
even if there is a -20 dB change in line level. I have seen it happen
when a SLIC feeding a station goes bad. The problem is that they are
thousands of dollars for a small system. Sometimes you can find the
Dictaphone interface for 911 loggers surplus. They are cheap, and
usually work fairly well.

http://www.jkaudio.com/inline-patch.htm is a cheap version of the
multiple line radio station units. These are used to give the best
match, and eliminate the need for a separate telephone. The multiple
line units have adjustments for each channel for sidetalk, so both sides
are at the same level for each phone line. I don't remember the model
numbers, since it's been over 10 years since I had to clean up a nasty
installation. Someone tried to use a 75 foot piece of 27 pair shielded
audio cable instead of 25 pair telco cable and it wouldn't balance on
any line. I ran a new 25 pair cable from the demark to the interface,
and everything was in spec. All audio cabling in AM radio stations can
be a pain, when there are multiple towers in a phased day/night array.

If the line input this transformer is attached to is 6k
Ohms or higher, a 1:1 transformer will do. Otherwise he
has two choices, one of which is a transformer with a
more suitable turns ratio, which will provide maximum
signal level. However, at that point there is almost
certainly an excess of gain, and hence another possible
solution is to merely put a pair of resistors in series
with the side connecting to the telephone set, or on the
side of the transformer connecting to his recording
device (if it is single ended, it requires only a single
resistor).

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

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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.

 

[Floyd L. Davidson]

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

"Ross Herbert"


Since the application is merely detecting signal "voltage" it hardly
matters
that the secondary impedance of the transformer is 600 ohms and the input
impedance of the sound card is more like 10Kohms.

** Fact is, it will be an advantage as the load across the phone line
needs to be high as possible so the level there is not affected.

No, it merely needs to be "high enough", not "high as
possible". If the bridging device has ten times the
circuit impedance, there will be a 0.3 dB drop in levels
on the circuit, and a 30 dB loss across the bridging
device.

That is considered satisfactory for virually all
applications. In this instance it would probably be
satisfactory if the bridging impedance where half that.

Regardless, you 10k Ohm value is absurd.

The only reason one tries to
match impedances is where one needs to maximise "power transfer" and that
doesn't apply in this case.

** Nonsense.

Audio and other wide band transformers have rated ( ie optimum) source and
load impedances.

This relates *directly* to them both operating efficiently AND exhibiting
their specified frequency response curve.

Eg, a 600:600 ohm type operating into 10 kohms may well have a large
response peak at high frequencies while a 10k:10k type operating into 600
ohms will likely have serious roll off from a few kHz upwards.

So read what you just wrote, and tell us how that affects a telecom
circuit that is specified at 400-2800 kHz?

With transformers that have 1:10 or 1:20 step-up ratios for mic-input to a
valve stage, both load and source impedances become quite critical just to
stay within a +/- 2dB corridor across the audio band.

At perhaps 15-20 kHz. So just who cares, in this case?

--
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. David son" wrote:

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

Ross Herbert wrote:

Since your PC is mains powered and it may not have the required isolation
between the mains side and the sound card input you can do your own thing using
an approved 600:600 transformer with 3kV isolation rating to interface the
telephone line to the sound card input.

He DOES NOT need a 600 ohm transformer since the input impedance of the sound card
is not 600 ohms <sigh> !

It's more likely to be in the tens of kilohms.

What he really wants is something like a 10k:10k 'line bridging' transformer. In
practice, using a '600 ohm' transformer will probably be ok, but being incorrectly
loaded will degrade the sound quality (freq resonse may be peaky etc).

An 'audio expert' would put a 600 ohm resistor across the secondary
to provide proper loading but no expects you to know that.

That would be true *if* he wanted to load the circuit
down to 600 Ohms, but he almost certainly does not.
Doing so would reduce the level available to the
telephone set user by 3 dB. What he probably wants to
do is bridge across the "600 Ohm" telephone set with
something that is at least 6000 Ohms.

That would work, but a 600 ohm load would give the flattest frequency
response,

Not true. It won't necessarily change the frequency
response at all, much less significantly.

and a -3 dB change would be equal to someone picking up an
extension. Some signal loss, but not outside the design limits.

Not necessarily! You have no way to know how close it
already is to design limits, and therefore you cannot
make the assumption that using up the entire "slack"
allowed for will not instead put it exactly that far out
of specs.

The
best choice would be a telephone interface like those used for radio
stations.

Assuming money is no object, nor is space.

They are bi-directional, and allow the host to talk to the
listeners, and the caller at the same time. They will work reliably,
even if there is a -20 dB change in line level.

And did you note the price tag on a good one? That is
necessarily a non-trivial design. (Try it sometime! They
are fun, especially if you want to be able to bridge
multiple lines.)

I have seen it happen
when a SLIC feeding a station goes bad. The problem is that they are
thousands of dollars for a small system. Sometimes you can find the
Dictaphone interface for 911 loggers surplus. They are cheap, and
usually work fairly well.

So if you already knew these are not suitable...

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

 

[PCPaul]

On Sat, 03 Jan 2009 11:03:29 -0500, Michael A. Terrell wrote:

Gun control is for morons and cowards. England is the perfect example
of a nation governed by cowards who are afraid of armed citizens.

Afraid of armed Yanks, definitely.

24% of the US casualties in the first Gulf War were down to 'friendly
fire'.

24%.

 

[Michael A. Terrell]

"Floyd L. Davidson" wrote:

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

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

Ross Herbert wrote:

Since your PC is mains powered and it may not have the required isolation
between the mains side and the sound card input you can do your own thing using
an approved 600:600 transformer with 3kV isolation rating to interface the
telephone line to the sound card input.

He DOES NOT need a 600 ohm transformer since the input impedance of the sound card
is not 600 ohms <sigh> !

It's more likely to be in the tens of kilohms.

What he really wants is something like a 10k:10k 'line bridging' transformer. In
practice, using a '600 ohm' transformer will probably be ok, but being incorrectly
loaded will degrade the sound quality (freq resonse may be peaky etc).

An 'audio expert' would put a 600 ohm resistor across the secondary
to provide proper loading but no expects you to know that.

That would be true *if* he wanted to load the circuit
down to 600 Ohms, but he almost certainly does not.
Doing so would reduce the level available to the
telephone set user by 3 dB. What he probably wants to
do is bridge across the "600 Ohm" telephone set with
something that is at least 6000 Ohms.

That would work, but a 600 ohm load would give the flattest frequency
response,

Not true. It won't necessarily change the frequency
response at all, much less significantly.

That depends on what you consider significant. Even though the telco
bandwidth is limited, there is little reason to make it worse.

and a -3 dB change would be equal to someone picking up an
extension. Some signal loss, but not outside the design limits.

Not necessarily! You have no way to know how close it
already is to design limits, and therefore you cannot
make the assumption that using up the entire "slack"
allowed for will not instead put it exactly that far out
of specs.

So you are saying that there are lines in use that can't have a
working extension in use with the main phone? The sound card he intends
to use has far more than 3 dB gain for the line level inputs.

I have seen network feeds via Telco plant that were so bad that they
hit the building at more than -20 dB. At one they insisted it was
leaving their C.O. at 0 dB, but we had to turn everything wide open to
get even close to 100% modulation. I used a spare magnetic phono preamp
to bring it up closer to 0 dB, and had to put up with the RIAA
equalization for the network feed. When people complained, we told them
why the network sounded so bad. BTW, that feed was through White Alice.

The
best choice would be a telephone interface like those used for radio
stations.

Assuming money is no object, nor is space.

I'm a former Radio & TV broadcast engineer. Both were
considerations, but performance and reliability were more important.
Dead air is very, very expensive. It can cost you advertisers as well
as listeners. Enough of it can cost you your license.

They are bi-directional, and allow the host to talk to the
listeners, and the caller at the same time. They will work reliably,
even if there is a -20 dB change in line level.

And did you note the price tag on a good one? That is
necessarily a non-trivial design. (Try it sometime! They
are fun, especially if you want to be able to bridge
multiple lines.)

I have. The design isn't that difficult, but the market is tiny so
the engineering costs don't have millions of units to defray the costs.
Electron hybrids are a handful of op-amps and the concept has been
around for a long time. Try designing a high performance AGC system for
tracking satellites. The last one I worked with had 14 op-amps and less
than 1.5 mV error over a 0 to 5 volt range. This was used to combine
(similar to bridging) two unmatched video sources to a proper 0 dBm
output with less than a .01 dB tracking error. That is something you
would never try to do with a couple phone lines.

The radio station equipment I mentioned can bridge all the lines, as
desired. That is 20 lines or so. Since the interfaces are
bi-directional, its simple to do the bridging at the station side by
simply connecting them together in any combination. A simple on
line/Off line button connects each line to the board. Punching up
additional lines also bridges them. Even if the telco lines aren't
perfect, it works. Each line can be trimmed for best performance, as
long as the telco plant is fairly stable.


The packaging and documentation for niche market equipment can cost
more than the actual electronics. The highest cost is still the
engineering.

I have seen it happen
when a SLIC feeding a station goes bad. The problem is that they are
thousands of dollars for a small system. Sometimes you can find the
Dictaphone interface for 911 loggers surplus. They are cheap, and
usually work fairly well.

So if you already knew these are not suitable...

By who's definition? This thread has wandered all over the place.

If you want cheap, some stations with a 1A2 system would take a spare
phone and remove the handset. They would connect the receiver terminals
to a 200 to 600 ohm input on their console and use the phone to select
the line to go live.

That was nothing more than a telephone network across the line, and
using the isolated receiver circuit to feed the console. It was common
until the '80s when stations wanted cleaner audio and better control of
each phone line. Some of the electronic interfaces also allow computer
control so the 'talent' can click on a button on the screen with the
mouse to select a line. The same way they select commercials, station
IDs and PSAs. The screen will list the callers name and information
from the call screener, if desired. Click another button and it will
display every piece of music in the station's library for listeners
request type shows.


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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]

PCPaul wrote:

On Sat, 03 Jan 2009 11:03:29 -0500, Michael A. Terrell wrote:

Gun control is for morons and cowards. England is the perfect example
of a nation governed by cowards who are afraid of armed citizens.

Afraid of armed Yanks, definitely.

24% of the US casualties in the first Gulf War were down to 'friendly
fire'.

24%.

'Friendly fire' accidents do happen. Mostly due to the troops of
various countries not following the instructions for proper ID, correct
passwords, or keeping up with the proper communications for the day or
mission. Some are simply where they were told not to be. Either they
ignored the orders, or the command chain was so slow it never arrived.

Would you rather they be captured and tortured to death by the enemy?


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The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Stuart]

In article <87r63pi7wq.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:

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????

I now have some more information on this.

To quote:

"Studio Engineering for Sound Broadcasting" Illife 1955.
Chapter 7 "Programme circuits on Post Office Lines" G Stannard, Bsc
A.M.I.E.E - Lines department.

p142. "The distribution of BBC Light Programme to Burghead at the time of
writing contains 693 miles of 16mH/1.136m. and the estimated delay
distortion relative to 1kc/s is:
50 c/s 50m.sec
100 c/s 9.5m.sec
7 kc/s 7.3 m.sec"

16mH/1.136m describes a loaded line and m, in this case, would be miles.
Elsewhere a table gives the following information for this type of line:

Weight of conductor 40lb/mile, Approx characteristic impedance 490 ohms,
Cut-off frequency 9.3kc/s, maximum useable frequency 7.44kc/s.

The book further goes on to discuss carrier circuits

p131 (Same chapter)

"In 1938 the Post Office began a big expansion in their communication
network by laying 12-channel carrier cables. These are low capacitance
cables specifically designed for the transmission of frequencies up to 60
kc/s and subsequently up to 120kc/s"

Two schemes are discussed for using carrier circuit lines but they are
described (p155) as inferior to circuits obtained by more conventional
methods.

--
Stuart Winsor

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

 

[John Livingston]

Stuart wrote:

In article <87r63pi7wq.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:
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????

I now have some more information on this.

To quote:

"Studio Engineering for Sound Broadcasting" Illife 1955.
Chapter 7 "Programme circuits on Post Office Lines" G Stannard, Bsc
A.M.I.E.E - Lines department.

p142. "The distribution of BBC Light Programme to Burghead at the time of
writing contains 693 miles of 16mH/1.136m. and the estimated delay
distortion relative to 1kc/s is:
50 c/s 50m.sec
100 c/s 9.5m.sec
7 kc/s 7.3 m.sec"

16mH/1.136m describes a loaded line and m, in this case, would be miles.
Elsewhere a table gives the following information for this type of line:

Weight of conductor 40lb/mile, Approx characteristic impedance 490 ohms,
Cut-off frequency 9.3kc/s, maximum useable frequency 7.44kc/s.

The book further goes on to discuss carrier circuits

p131 (Same chapter)

"In 1938 the Post Office began a big expansion in their communication
network by laying 12-channel carrier cables. These are low capacitance
cables specifically designed for the transmission of frequencies up to 60
kc/s and subsequently up to 120kc/s"

Two schemes are discussed for using carrier circuit lines but they are
described (p155) as inferior to circuits obtained by more conventional
methods.

Thanks Stuart - this fits exactly with my memories of the time. It was a
while back though ......
The BBC now has its own digital audio distribution systems, and no
longer requires the widespread use of BT programme circuits.

To reiterate for those who have generated all the heat and the
fabulously inaccurate rantings - The programme circuits were BASEBAND
AUDIO all the way - amplified en route. As Stuart quotes - carrier is
possible, but provides worse noise and distortion standards.

Carrier was not generally used for main UK programme distribution (sorry
Floyd - you may be right about American practice, but not UK).

John