[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Paul Babiak" wrote:

By definition, dBm is a power ratio, referenced to 1 mW into 600 ohms,
which is 0.775v across that same 600 ohm load.

When 600 ohm source and load impedances were no longer common in
professional audio, a new term was introduced, the dBu.

The dBu is a voltage ratio, referenced to 0.775v, and since it is a
voltage ratio, it is impedance-independant.


Hi Paul. Two points.

You seem to have fallen into the usual trap.
Unlike the dB, from which it is derived, dBm is *not* a
ratio but a unit, with a specific reference.

dBu was certainly not a *new* term.

Eh ?

Yes it was. It dates from the 1970s.

I am told it existed long before that. I will try to find some references
in earlier books.

'What to use to replace the dBm' was quite
a long winded process that the industry agonised over for some years. The
dBV
was no good since it meant changing all the references and for a while the
dBv
was promoted as a voltage based reference that wasn't 1 Volt but it was
considered confusing since it could easily be mis-typed as dBV which it
wasn't.
Hence dBu which I understand as 'decibel unit' not 'decidel unloaded' as
some
have suggested.

Many understand it as "decibel unspecified" (i.e.unspecified load)
This seems clearer.

Iain

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Andre Jute wrote:
"Iain Churches" wrote:
"Eeyore" wrote

I've been in pro-audio some 34 years now

Only 34 years, Graham? I can beat that by eight. Now pull yourself
together lad, and fetch us a cup of tea. Milk and two sugars:-)


Iain, I'll remind you again that it is company policy, when you send
the junior apprentice to make the tea, to instruct him to wash the
mugs first!

You forgot the bit about polishing the jacks on the patch cords.

If you were smart, you would use Tuchel connectors, not jacks.

You are quite mad.

Has anyone ever fitted a Tuchel 'patch bay' ?

Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:

dBu was certainly not a *new* term.

Eh ?

Yes it was. It dates from the 1970s.

I am told it existed long before that.

By whom ?


I will try to find some references in earlier books.

Forget the books. Ask the AES.

I recall the discussion well. It was extensively covered in the industry
magazine 'Studio Sound'.

Graham

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote
Andre Jute wrote:
"Iain Churches" wrote:
"Eeyore" wrote

I've been in pro-audio some 34 years now

Only 34 years, Graham? I can beat that by eight. Now pull yourself
together lad, and fetch us a cup of tea. Milk and two sugars:-)


Iain, I'll remind you again that it is company policy, when you send
the junior apprentice to make the tea, to instruct him to wash the
mugs first!

You forgot the bit about polishing the jacks on the patch cords.

If you were smart, you would use Tuchel connectors, not jacks.

You are quite mad.

Has anyone ever fitted a Tuchel 'patch bay' ?

Yes indeed. They were common both in studios and broadcast facilities
in Germany and Scandinavia.

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

Iain

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote
Andre Jute wrote:
"Iain Churches" wrote:
"Eeyore" wrote

I've been in pro-audio some 34 years now

Only 34 years, Graham? I can beat that by eight. Now pull yourself
together lad, and fetch us a cup of tea. Milk and two sugars:-)


Iain, I'll remind you again that it is company policy, when you send
the junior apprentice to make the tea, to instruct him to wash the
mugs first!

You forgot the bit about polishing the jacks on the patch cords.

If you were smart, you would use Tuchel connectors, not jacks.

You are quite mad.

Has anyone ever fitted a Tuchel 'patch bay' ?

Yes indeed. They were common both in studios and broadcast facilities
in Germany and Scandinavia.

I can't think of anything more unpleasant to use.

How do they deal with switched contacts (normalling) for example ?


What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

They are a purely a Germanic curiosity.

Graham

[Iain Churches[_2_]]

"Eeyore" wrote in message
...

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

My mentor Arthur Bannister used to say that the Germans lost WWII
while they were fiddling with their Tuchel connectors. But they *are*
100% reliable.

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Iain

[Iain Churches[_2_]]

"Eeyore" wrote in message
...

Iain wrote:
If you disagree, please post your definition of 0dBm.
That was my reason for starting this thread, to ask for
suggstions or improvements to the page.

I've been giving some thought to it. Will come back on this.

Looking forward to your version.


The Crowhurst reference to dBu is from circa 1973. It
may have been he who suggested the term.

I have modified the page to read:

dBu

"When 600 ohm source and load impedances were no longer common in
professional audio, an alternative term, the dBu, came into wider use after
much discussion within the audio industry during the 1970s. The dBu may be
used when working into an unknown or unspecified load impedance. It is
referenced to 0.775 Volts into any impedance"

Regards
Iain

[The Phantom]

On Wed, 15 Aug 2007 08:59:48 +0300, "Iain Churches"
wrote:

From e-mail I receive, it seems to me that
the decibel is a misunderstood and widely
abused term.

I have added a page to my website on the
subject mainly constructed from my dog-eared
student notes from the third quarter of the last century.
The page cannot yet be accessed
from the index page, but can be found at:

http://www.kolumbus.fi/iain.churches...heDecibel.html

Any comments or suggestions/additions would
be welcome. I am grateful for the help of my
pals Jim and Richard in the UK for their contributions.

Regards to all
Iain

The second paragraph is a little off. You say:

"The basic unit chosen was the power loss in a standard telephone line over
the distance of one mile, at 1kHz. This was called the Transmission Unit,
but was renamed, after the inventor of the telephone, and became known as
the bel..."

Let me quote from page 9 of the book, "Transmission Circuits for
Telephonic Communication", published by Bell Labs in 1925.

"Three different units have been used to express telephonic volume
efficiencies:

(1) The natural attenuation unit, also designated as a napier or as a hyp;

(2) The mile of standard cable or simply a mile;

(3) The so-called transmission unit or TU."

Regarding a mile of standard cable, they say:

"Standard cable is defined as a cable having uniformly distributed
resistances of 88 ohms per loop mile and uniformly distributed shunt
capacitance of .054 microfarad per mile. Its series inductance and shunt
leakance are assumed to be zero.*

* In England it has been customary to assume an inductance of .001 henry
per loop mile--which assumption reduces the attenuation constant of the
cable by approximately 3 per cent."

A cable with a resistance of 88 ohms per loop mile is made of standard 19
gauge wire. Later in the book they talk of long distance line composed of
10 or even 8 gauge wires spaced a foot apart.

"The mile of standard cable is based upon the constant percentage
decrease in current (or in power) per mile which takes place when an e.m.f.
of a frequency, such as f cycles (f = w/2pi = 5000/2pi), is impressed at
one end of an infinite length of such a cable."

The measurement frequency here is 796.4 Hz (w = 5000).

They also say:

"Due to the objection that the attenuation constant of standard cable
varies with frequency and also to the fact the use of a frequency of 796.4
Hz is not universally agreed upon, there has recently been adopted a new
transmission unit which (1) does not vary with frequency, (2) is of a
convenient size or magnitude--avoiding one of the chief objections to the
napier or natural attenuation unit--and (3) has a simple physical
significance so that its eventual universal adoption would appear probable.

This new transmission unit (referred to for the sake of convenience as a
TU) is defined by the relation

Ntu = 10*LOG10(W1/W2)

in which Ntu is the number of TU by which any two powers W1 and W2 are said
to differ."

They apparently had not yet decided to call it a decibel, and of course,
one Bel = 10 TU. This text was written in 1924 and published in 1925.

There is a table of conversions:

Relations between various types of units

Multiply by to obtain

miles .947 TU
miles .109 napiers
napiers 9.175 miles
napiers 8.686 TU
TU 1.056 miles
TU .115 napiers
---------------------------------------------------

So, we see that the attenuation of a mile of standard cable was not
called a transmission unit; it was just called a "mile". The transmission
unit (TU) was what would later be called a decibel; it was not a Bel, it
was a tenth of a Bel.

The Wikipedia article says, "Devised by engineers of the Bell Telephone
Laboratory to quantify the reduction in audio level over a 1 mile
(approximately 1.6 km) length of standard telephone cable, the bel was
originally called the transmission unit or TU." This is wrong, as the
quotations I've given show.

The TU was indeed devised to quantify the reduction in audio level, but
it wasn't intended to represent the attenuation in one mile of cable, as
you can see from the conversion table. The TU was defined as
10*LOG10(W1/W2), which wasn't the attenuation of a mile of cable; it was
close (1 mile = .947 TU), and that is why a TU was defined as
10*LOG10(W1/W2) and not just LOG10(W1/W2). They wanted a conveniently
sized unit.

From the conversion table we see that a mile was an attenuation of .947
decibels, to answer John Byrns' question.

[Phil Allison]

"The Phantom"

( snip lots of good stuff )


"Standard cable is defined as a cable having uniformly distributed
resistances of 88 ohms per loop mile and uniformly distributed shunt
capacitance of .054 microfarad per mile.


** That is not too dissimilar to modern twisted pair cables, like Cat 5.

The resistance is about half, due to thicker gauge capper wires and
similarly the capacitance per meter about half.

No doubt due to use of much thicker insulation than the modern, very thin,
PVC kind.

An overall, average voice band, loss of only 1dB mile represents darn good
engineering - for 1925 !!




........ Phil

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

My mentor Arthur Bannister used to say that the Germans lost WWII
while they were fiddling with their Tuchel connectors. But they *are*
100% reliable.

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Well yes. I've never come across one myself. Plenty of Studer tape machines of
course but never a console. I got the impression they only ever sold inside
continental Europe.

Graham

[Iain Churches[_2_]]

"The Phantom" wrote in message
...

The second paragraph is a little off. You say:

"The basic unit chosen was the power loss in a standard telephone line
over
the distance of one mile, at 1kHz. This was called the Transmission Unit,
but was renamed, after the inventor of the telephone, and became known as
the bel..."

Let me quote from page 9 of the book, "Transmission Circuits for
Telephonic Communication", published by Bell Labs in 1925.

(huge snip)

Excellent info. many thanks indeed.


From the conversion table we see that a mile was an attenuation of .947
decibels, to answer John Byrns' question.

John seems to have assumed that the loss over 1 mile was one unit (i.e.
one Bel)

Regards
Iain

[jim Gregory]

Does this mean, traditionally, telephone cable tx loss should be measured
with
a stimulus of centre freq @ 800Hz (near enough to 5000/2pi) in preference to
using 1kHz?
I seem to remember that in '80s-'90s, BT's Private Wires testers often
measured atten of lines at 800Hz.
Jim

"The Phantom" wrote in message
...
On Wed, 15 Aug 2007 08:59:48 +0300, "Iain Churches"
wrote:

From e-mail I receive, it seems to me that
the decibel is a misunderstood and widely
abused term.

I have added a page to my website on the
subject mainly constructed from my dog-eared
student notes from the third quarter of the last century.
The page cannot yet be accessed
from the index page, but can be found at:

http://www.kolumbus.fi/iain.churches...heDecibel.html

Any comments or suggestions/additions would
be welcome. I am grateful for the help of my
pals Jim and Richard in the UK for their contributions.

Regards to all
Iain

The second paragraph is a little off. You say:

"The basic unit chosen was the power loss in a standard telephone line
over
the distance of one mile, at 1kHz. This was called the Transmission Unit,
but was renamed, after the inventor of the telephone, and became known as
the bel..."

Let me quote from page 9 of the book, "Transmission Circuits for
Telephonic Communication", published by Bell Labs in 1925.

"Three different units have been used to express telephonic volume
efficiencies:

(1) The natural attenuation unit, also designated as a napier or as a hyp;

(2) The mile of standard cable or simply a mile;

(3) The so-called transmission unit or TU."

Regarding a mile of standard cable, they say:

"Standard cable is defined as a cable having uniformly distributed
resistances of 88 ohms per loop mile and uniformly distributed shunt
capacitance of .054 microfarad per mile. Its series inductance and shunt
leakance are assumed to be zero.*

* In England it has been customary to assume an inductance of .001 henry
per loop mile--which assumption reduces the attenuation constant of the
cable by approximately 3 per cent."

A cable with a resistance of 88 ohms per loop mile is made of standard 19
gauge wire. Later in the book they talk of long distance line composed of
10 or even 8 gauge wires spaced a foot apart.

"The mile of standard cable is based upon the constant percentage
decrease in current (or in power) per mile which takes place when an
e.m.f.
of a frequency, such as f cycles (f = w/2pi = 5000/2pi), is impressed at
one end of an infinite length of such a cable."

The measurement frequency here is 796.4 Hz (w = 5000).

They also say:

"Due to the objection that the attenuation constant of standard cable
varies with frequency and also to the fact the use of a frequency of 796.4
Hz is not universally agreed upon, there has recently been adopted a new
transmission unit which (1) does not vary with frequency, (2) is of a
convenient size or magnitude--avoiding one of the chief objections to the
napier or natural attenuation unit--and (3) has a simple physical
significance so that its eventual universal adoption would appear
probable.

This new transmission unit (referred to for the sake of convenience as a
TU) is defined by the relation

Ntu = 10*LOG10(W1/W2)

in which Ntu is the number of TU by which any two powers W1 and W2 are
said
to differ."

They apparently had not yet decided to call it a decibel, and of course,
one Bel = 10 TU. This text was written in 1924 and published in 1925.

There is a table of conversions:

Relations between various types of units

Multiply by to obtain

miles .947 TU
miles .109 napiers
napiers 9.175 miles
napiers 8.686 TU
TU 1.056 miles
TU .115 napiers
---------------------------------------------------

So, we see that the attenuation of a mile of standard cable was not
called a transmission unit; it was just called a "mile". The transmission
unit (TU) was what would later be called a decibel; it was not a Bel, it
was a tenth of a Bel.

The Wikipedia article says, "Devised by engineers of the Bell Telephone
Laboratory to quantify the reduction in audio level over a 1 mile
(approximately 1.6 km) length of standard telephone cable, the bel was
originally called the transmission unit or TU." This is wrong, as the
quotations I've given show.

The TU was indeed devised to quantify the reduction in audio level, but
it wasn't intended to represent the attenuation in one mile of cable, as
you can see from the conversion table. The TU was defined as
10*LOG10(W1/W2), which wasn't the attenuation of a mile of cable; it was
close (1 mile = .947 TU), and that is why a TU was defined as
10*LOG10(W1/W2) and not just LOG10(W1/W2). They wanted a conveniently
sized unit.

From the conversion table we see that a mile was an attenuation of .947
decibels, to answer John Byrns' question.

[Arny Krueger]

"Iain Churches" wrote in message
i.fi...

"Eeyore" wrote in message
...


jim Gregory wrote:

Even nowadays, 600 Ohm terminations are regularly applied to feeds via
studio audio distribution amps, or the gain control at each destination
gear
may have

Simply not true. I've been in pro-audio some 34 years now and 600 ohm
terminations were already 'old hat' back when I entered the industry.
(snip)

Only 34 years, Graham? I can beat that by eight. Now pull yourself
together lad, and fetch us a cup of tea. Milk and two sugars:-)

Based on Iain's technical opinions, he didn't so much have 42 years of
experience as 1 year's experience 42 times.

[bill ramsay]

Yes it does.

I used to be a transmission technical officer with British Telecom.
This is going back about 30 yeras. In this role I used to set up
private wires, or lines.

the spot frequencies we used for equalisation were

300, 500, 800, 1.2k, 1.6k, 2.0k, 2.2,.2.4, 2.6, 2.8,3.0,3.2

I am a bit vague on the exact values but they look right, the 1.2k
might be dodgy.

We used equalisation boxes with RLC ccts in them. Nearly always we
managed to equalise using the standard C with a variation of R for the
local conditions.

Bill




On Fri, 17 Aug 2007 16:30:46 GMT, "jim Gregory"
wrote:

Does this mean, traditionally, telephone cable tx loss should be measured
with
a stimulus of centre freq @ 800Hz (near enough to 5000/2pi) in preference to
using 1kHz?
I seem to remember that in '80s-'90s, BT's Private Wires testers often
measured atten of lines at 800Hz.
Jim

"The Phantom" wrote in message
.. .
On Wed, 15 Aug 2007 08:59:48 +0300, "Iain Churches"
wrote:

From e-mail I receive, it seems to me that
the decibel is a misunderstood and widely
abused term.

I have added a page to my website on the
subject mainly constructed from my dog-eared
student notes from the third quarter of the last century.
The page cannot yet be accessed
from the index page, but can be found at:

http://www.kolumbus.fi/iain.churches...heDecibel.html

Any comments or suggestions/additions would
be welcome. I am grateful for the help of my
pals Jim and Richard in the UK for their contributions.

Regards to all
Iain

The second paragraph is a little off. You say:

"The basic unit chosen was the power loss in a standard telephone line
over
the distance of one mile, at 1kHz. This was called the Transmission Unit,
but was renamed, after the inventor of the telephone, and became known as
the bel..."

Let me quote from page 9 of the book, "Transmission Circuits for
Telephonic Communication", published by Bell Labs in 1925.

"Three different units have been used to express telephonic volume
efficiencies:

(1) The natural attenuation unit, also designated as a napier or as a hyp;

(2) The mile of standard cable or simply a mile;

(3) The so-called transmission unit or TU."

Regarding a mile of standard cable, they say:

"Standard cable is defined as a cable having uniformly distributed
resistances of 88 ohms per loop mile and uniformly distributed shunt
capacitance of .054 microfarad per mile. Its series inductance and shunt
leakance are assumed to be zero.*

* In England it has been customary to assume an inductance of .001 henry
per loop mile--which assumption reduces the attenuation constant of the
cable by approximately 3 per cent."

A cable with a resistance of 88 ohms per loop mile is made of standard 19
gauge wire. Later in the book they talk of long distance line composed of
10 or even 8 gauge wires spaced a foot apart.

"The mile of standard cable is based upon the constant percentage
decrease in current (or in power) per mile which takes place when an
e.m.f.
of a frequency, such as f cycles (f = w/2pi = 5000/2pi), is impressed at
one end of an infinite length of such a cable."

The measurement frequency here is 796.4 Hz (w = 5000).

They also say:

"Due to the objection that the attenuation constant of standard cable
varies with frequency and also to the fact the use of a frequency of 796.4
Hz is not universally agreed upon, there has recently been adopted a new
transmission unit which (1) does not vary with frequency, (2) is of a
convenient size or magnitude--avoiding one of the chief objections to the
napier or natural attenuation unit--and (3) has a simple physical
significance so that its eventual universal adoption would appear
probable.

This new transmission unit (referred to for the sake of convenience as a
TU) is defined by the relation

Ntu = 10*LOG10(W1/W2)

in which Ntu is the number of TU by which any two powers W1 and W2 are
said
to differ."

They apparently had not yet decided to call it a decibel, and of course,
one Bel = 10 TU. This text was written in 1924 and published in 1925.

There is a table of conversions:

Relations between various types of units

Multiply by to obtain

miles .947 TU
miles .109 napiers
napiers 9.175 miles
napiers 8.686 TU
TU 1.056 miles
TU .115 napiers
---------------------------------------------------

So, we see that the attenuation of a mile of standard cable was not
called a transmission unit; it was just called a "mile". The transmission
unit (TU) was what would later be called a decibel; it was not a Bel, it
was a tenth of a Bel.

The Wikipedia article says, "Devised by engineers of the Bell Telephone
Laboratory to quantify the reduction in audio level over a 1 mile
(approximately 1.6 km) length of standard telephone cable, the bel was
originally called the transmission unit or TU." This is wrong, as the
quotations I've given show.

The TU was indeed devised to quantify the reduction in audio level, but
it wasn't intended to represent the attenuation in one mile of cable, as
you can see from the conversion table. The TU was defined as
10*LOG10(W1/W2), which wasn't the attenuation of a mile of cable; it was
close (1 mile = .947 TU), and that is why a TU was defined as
10*LOG10(W1/W2) and not just LOG10(W1/W2). They wanted a conveniently
sized unit.

From the conversion table we see that a mile was an attenuation of .947
decibels, to answer John Byrns' question.

[bill ramsay]

On Fri, 17 Aug 2007 16:30:46 GMT, "jim Gregory"
wrote:

Does this mean, traditionally, telephone cable tx loss should be measured
with
a stimulus of centre freq @ 800Hz (near enough to 5000/2pi) in preference to
using 1kHz?
I seem to remember that in '80s-'90s, BT's Private Wires testers often
measured atten of lines at 800Hz.
Jim

"The Phantom" wrote in message
.. .
On Wed, 15 Aug 2007 08:59:48 +0300, "Iain Churches"
wrote:

From e-mail I receive, it seems to me that
the decibel is a misunderstood and widely
abused term.

I have added a page to my website on the
subject mainly constructed from my dog-eared
student notes from the third quarter of the last century.
The page cannot yet be accessed
from the index page, but can be found at:

http://www.kolumbus.fi/iain.churches...heDecibel.html

Any comments or suggestions/additions would
be welcome. I am grateful for the help of my
pals Jim and Richard in the UK for their contributions.

Regards to all
Iain

The second paragraph is a little off. You say:

"The basic unit chosen was the power loss in a standard telephone line
over
the distance of one mile, at 1kHz. This was called the Transmission Unit,
but was renamed, after the inventor of the telephone, and became known as
the bel..."

Let me quote from page 9 of the book, "Transmission Circuits for
Telephonic Communication", published by Bell Labs in 1925.

"Three different units have been used to express telephonic volume
efficiencies:

(1) The natural attenuation unit, also designated as a napier or as a hyp;

(2) The mile of standard cable or simply a mile;

(3) The so-called transmission unit or TU."

Regarding a mile of standard cable, they say:

"Standard cable is defined as a cable having uniformly distributed
resistances of 88 ohms per loop mile and uniformly distributed shunt
capacitance of .054 microfarad per mile. Its series inductance and shunt
leakance are assumed to be zero.*

* In England it has been customary to assume an inductance of .001 henry
per loop mile--which assumption reduces the attenuation constant of the
cable by approximately 3 per cent."

A cable with a resistance of 88 ohms per loop mile is made of standard 19
gauge wire. Later in the book they talk of long distance line composed of
10 or even 8 gauge wires spaced a foot apart.

"The mile of standard cable is based upon the constant percentage
decrease in current (or in power) per mile which takes place when an
e.m.f.
of a frequency, such as f cycles (f = w/2pi = 5000/2pi), is impressed at
one end of an infinite length of such a cable."

The measurement frequency here is 796.4 Hz (w = 5000).

They also say:

"Due to the objection that the attenuation constant of standard cable
varies with frequency and also to the fact the use of a frequency of 796.4
Hz is not universally agreed upon, there has recently been adopted a new
transmission unit which (1) does not vary with frequency, (2) is of a
convenient size or magnitude--avoiding one of the chief objections to the
napier or natural attenuation unit--and (3) has a simple physical
significance so that its eventual universal adoption would appear
probable.

This new transmission unit (referred to for the sake of convenience as a
TU) is defined by the relation

Ntu = 10*LOG10(W1/W2)

in which Ntu is the number of TU by which any two powers W1 and W2 are
said
to differ."

They apparently had not yet decided to call it a decibel, and of course,
one Bel = 10 TU. This text was written in 1924 and published in 1925.

There is a table of conversions:

Relations between various types of units

Multiply by to obtain

miles .947 TU
miles .109 napiers
napiers 9.175 miles
napiers 8.686 TU
TU 1.056 miles
TU .115 napiers
---------------------------------------------------

So, we see that the attenuation of a mile of standard cable was not
called a transmission unit; it was just called a "mile". The transmission
unit (TU) was what would later be called a decibel; it was not a Bel, it
was a tenth of a Bel.

The Wikipedia article says, "Devised by engineers of the Bell Telephone
Laboratory to quantify the reduction in audio level over a 1 mile
(approximately 1.6 km) length of standard telephone cable, the bel was
originally called the transmission unit or TU." This is wrong, as the
quotations I've given show.

The TU was indeed devised to quantify the reduction in audio level, but
it wasn't intended to represent the attenuation in one mile of cable, as
you can see from the conversion table. The TU was defined as
10*LOG10(W1/W2), which wasn't the attenuation of a mile of cable; it was
close (1 mile = .947 TU), and that is why a TU was defined as
10*LOG10(W1/W2) and not just LOG10(W1/W2). They wanted a conveniently
sized unit.

From the conversion table we see that a mile was an attenuation of .947
decibels, to answer John Byrns' question.

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:

dBu was certainly not a *new* term.

Eh ?

Yes it was. It dates from the 1970s.

I am told it existed long before that.

By whom ?

Though I cannot as yet find the article, I
am told that Crowhurst made reference to it.


I will try to find some references in earlier books.

Forget the books.

If it referred to in an earlier book then it does
not originate from the 1970's altough that was
indeed the time when the subject was under discussion.


Iain

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

My mentor Arthur Bannister used to say that the Germans lost WWII
while they were fiddling with their Tuchel connectors. But they *are*
100% reliable.

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Well yes. I've never come across one myself. Plenty of Studer tape
machines of
course but never a console. I got the impression they only ever sold
inside
continental Europe.

Gosh. There cannot be many studio professionals (nor probably rival
console manufacturers) who have not carefully examined a Studer or Lawo
console.

The EBU chose Lawo as the console contractor for Eurovision 2007
from a long list of companies offering leading-edge technology
Sadly, Studiomaster was not among them:-))

I understand that the BBC have a number of Lawo
consoles on order. They may well have been delivered
by now. According to a press release, the BBC also
ordered a Lawo router in March 2006.

Cheers
Iain

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

My mentor Arthur Bannister used to say that the Germans lost WWII
while they were fiddling with their Tuchel connectors. But they *are*
100% reliable.

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Well yes. I've never come across one myself. Plenty of Studer tape
machines of course but never a console. I got the impression they only ever
sold
inside continental Europe.

Gosh. There cannot be many studio professionals (nor probably rival
console manufacturers) who have not carefully examined a Studer or Lawo
console.

What gives you that idea ? I know plenty of 'studio professionals' and none have
ever met them either AFAIK. I doubt you'll find an example of either in the UK.


The EBU chose Lawo as the console contractor for Eurovision 2007
from a long list of companies offering leading-edge technology
Sadly, Studiomaster was not among them:-))

EBU (as opposed to BBC) says a lot.

RTE (Ireland) used a Studiomaster P7 console in one of their studios btw.


I understand that the BBC have a number of Lawo
consoles on order. They may well have been delivered
by now. According to a press release, the BBC also
ordered a Lawo router in March 2006.

Possibly because they no longer have a tame Neve to supply their requirements ?

Graham

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Well yes. I've never come across one myself. Plenty of Studer tape
machines of course but never a console. I got the impression they only
ever
sold
inside continental Europe.

Gosh. There cannot be many studio professionals (nor probably rival
console manufacturers) who have not carefully examined a Studer or Lawo
console.

What gives you that idea ? I know plenty of 'studio professionals' and
none have
ever met them either AFAIK. I doubt you'll find an example of either in
the UK.

To quote you, Graham: "You are raving mad!" I can think of a dozen
facilities in the UK that have Studer consoles. The BBC have at least two
Studer Vista 8's of 72 channels each. TVM has a Studer Vista 5, and
there is a 52 channel Studer at Maidstone. That's just for starters. The
Studer console owned by one of my colleagues came from the UK.

By then end of this year there will be some 20 Lawo consoles in the UK.
This number excludes those ordered by the BBC.


The EBU chose Lawo as the console contractor for Eurovision 2007
from a long list of companies offering leading-edge technology
Sadly, Studiomaster was not among them:-))

EBU (as opposed to BBC) says a lot.

Do you hold the BBC on a pedestal?

The BBC is a member of the EBU, but has no more say in
matters than the rest of the members. Germany, France, and
Sweden in particular. As far as classical broadcasting is
concerned, there are several German stations, and
also Sverige radio who can give the BBC a very good
run for their money.

RTE (Ireland) used a Studiomaster P7 console in one of their studios btw.'

And Granada had a Soundcraft . But how is that relevant?

I understand that the BBC have a number of Lawo
consoles on order. They may well have been delivered
by now. According to a press release, the BBC also
ordered a Lawo router in March 2006.

Possibly because they no longer have a tame Neve to supply their
requirements ?

There are still plenty of others from which to have chosen.
Lawo fully met their requirements. The ergonomics of their
current designs are unsurpassed.

Cheers
Iain

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Well yes. I've never come across one myself. Plenty of Studer tape
machines of course but never a console. I got the impression they only
ever sold inside continental Europe.

Gosh. There cannot be many studio professionals (nor probably rival
console manufacturers) who have not carefully examined a Studer or Lawo
console.

What gives you that idea ? I know plenty of 'studio professionals' and
none have ever met them either AFAIK. I doubt you'll find an example of
either in
the UK.

To quote you, Graham: "You are raving mad!" I can think of a dozen
facilities in the UK that have Studer consoles.

What sort of facilities ?


The BBC have at least two
Studer Vista 8's of 72 channels each. TVM has a Studer Vista 5, and
there is a 52 channel Studer at Maidstone. That's just for starters. The
Studer console owned by one of my colleagues came from the UK.

How long have they been there ?


By then end of this year there will be some 20 Lawo consoles in the UK.
This number excludes those ordered by the BBC.

So the Lawos don't actually exist over here yet.

That simply confirms what I said.

Graham

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:

What have you been doing in those 34 years? - Never heard of
Studer or Lawo consoles, or seen a Tuchel routing bay? :-)))

They are a purely a Germanic curiosity.

Hopefully you are not referring to Studer or Lawo!

Well yes. I've never come across one myself. Plenty of Studer tape
machines of course but never a console. I got the impression they
only
ever sold inside continental Europe.

Gosh. There cannot be many studio professionals (nor probably rival
console manufacturers) who have not carefully examined a Studer or
Lawo
console.

What gives you that idea ? I know plenty of 'studio professionals' and
none have ever met them either AFAIK. I doubt you'll find an example of
either in
the UK.

To quote you, Graham: "You are raving mad!" I can think of a dozen
facilities in the UK that have Studer consoles.

What sort of facilities ?
Take your pick. The Studer is, and always has been a very expensive
console, so they are not to be found in budget studios.

The BBC have at least two
Studer Vista 8's of 72 channels each. TVM has a Studer Vista 5, and
there is a 52 channel Studer at Maidstone. That's just for starters. The
Studer console owned by one of my colleagues came from the UK.

By then end of this year there will be some 20 Lawo consoles in the UK.
This number excludes those ordered by the BBC.

So the Lawos don't actually exist over here yet.

Oh. I think there already may be quite a few, and their numbers will
be expanded to twenty by the end of this year.

That simply confirms what I said.

Nonsense. I will not call you an ignorant f*ckw*t (which is the
term by which you addressed me) I am far too much of a gentleman:-)

Best regards
Iain

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote

So the Lawos don't actually exist over here yet.

Oh. I think there already may be quite a few

But you don't know ? Is it just a broadcast console ?


and their numbers will be expanded to twenty by the end of this year.

Fine but that doesn't mean they're here now.

Graham

[John Byrns]

In article ,
Eeyore wrote:

John Byrns wrote:

That would imply a 50 dB loss between my home and the central
office, if I called the neighbor across the street, the total loss would
be 100 dB and I doubt conversation would be possible with that sort of
loss. The original statement on the web page just doesn't pass the
smell test.

Your mistake is thinking that the dBs add.

Don't they, and if not why not?

5 miles would simply be 5 times the resistance or ~ 1500 ohms. That's NOT
50dB
attenuation. Probably about 20dB.

Telephone cable is not equivalent to a simple resistor as you would have
us believe, there is also a large amount of shunt capacitance, whose
effect you seem determined to ignore.

Note that I am not claiming that the local loop serving my telephone,
actually the one that did in an earlier day, has anywhere near 50 dB
attenuation, or even 20 dB, I was simply illustrating what the
nonsensical result would be applying the information on Iain's web page.

Some loss could be ameliorated using 'loading coils' AIUI.

Oops I guess I misspoke, you seem to recognize the shunt capacitance
after all, as loading coils are only of use because of the capacitance.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article ,
Eeyore wrote:

John Byrns wrote:

Eeyore wrote:
jim Gregory wrote:

If 5 miles of wiring @ hypothetical loss of 10dB/mile are a continuous
path, in cascade, that's got to be 50dB loss in my book.

As I explained, no-one said it was like a transmission line with a dB/km
loss. A cable has to be much much longer to have transmission line
behaviour at
audio
frequencies. What really matters at these lengths is cable resistance and
this increases LINEARLY with distance.

Actually the book I am reading on Telephony theory, which gives all the
"sums", says it is like a transmission line, which has always been
obvious to me in the case of loaded lines, but much less so in the case
of non loaded lines.

In which case I suggest you throw that book in the trash where it belongs.

What exactly is your definition of a "transmission line"?

It really said that about 5 km runs ?

Not that it makes any difference, but I said 5 miles, not 5 km.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article ,
Eeyore wrote:

John Byrns wrote:

If all there was to a telephone line was series resistance then you
would have a point, I think the main point you are missing is the effect
the capacitance has.

I'm not missing anything.

It appears that you are missing the effect of the distributed shunt
capacitance that is a characteristic of telephone lines. Are you trying
to say that telephone lines have no shunt capacitance?

Equipment interconnects don't behave like transmission lines either.

Sure they do, its just that the effects of such short transmission lines
are very small and can only be detected by the most golden eared of
audiophiles.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article i,
"Iain Churches" wrote:

"The Phantom" wrote in message
...

From the conversion table we see that a mile was an attenuation of .947
decibels, to answer John Byrns' question.

John seems to have assumed that the loss over 1 mile was one unit (i.e.
one Bel)

Yes, that is exactly what I assumed after reading you web page, which
said; "In the early days of telephone engineering, a unit was needed to
measure the loss of signal over distance. The basic unit chosen was the
power loss in a standard telephone line over the distance of one mile,
at 1kHz. This was called the Transmission Unit, but was renamed, after
the inventor of the telephone, and became known as the bel circa 1924."

It is hard for me to see how anyone could come to a different conclusion
as a result of reading your web page? This quote from your web page
also implies that a "Transmission Unit" = a "bel", is that correct?

Also, the bel and decibel are simple logarithmic relations and it is
hard to believe that they would exactly match up as units with the loss
characteristics of a particular pre existing "standard line. I would
guess that the decibel was simply close to the loss of the "standard"
line, as illustrated by the 0.947 dB figure quoted above.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Iain Churches[_2_]]

"John Byrns" wrote in message
...
In article ,

Note that I am not claiming that the local loop serving my telephone,
actually the one that did in an earlier day, has anywhere near 50 dB
attenuation, or even 20 dB, I was simply illustrating what the
nonsensical result would be applying the information on Iain's web page.


John. The result is not nonsensical. What does *not* make sense
is your interpretation of the information given in the book published
by Bell Telephones in 1925, which was quoted chapter and verse earlier
in this thread by The Phantom.

Regards
Iain

[Iain Churches[_2_]]

"John Byrns" wrote in message
...
In article i,
"Iain Churches" wrote:

"The Phantom" wrote in message
...

From the conversion table we see that a mile was an attenuation of
.947
decibels, to answer John Byrns' question.

John seems to have assumed that the loss over 1 mile was one unit (i.e.
one Bel)

Yes, that is exactly what I assumed after reading you web page, which
said; "In the early days of telephone engineering, a unit was needed to
measure the loss of signal over distance. The basic unit chosen was the
power loss in a standard telephone line over the distance of one mile,
at 1kHz. This was called the Transmission Unit, but was renamed, after
the inventor of the telephone, and became known as the bel circa 1924."

Hi John.

I posted the link to this provisional page inviting comments.
In the case of their being errors, I thought that someone as
smart as yourself would be delighted to point them out :-)

It is hard for me to see how anyone could come to a different conclusion
as a result of reading your web page? This quote from your web page
also implies that a "Transmission Unit" = a "bel", is that correct?

Also, the bel and decibel are simple logarithmic relations and it is
hard to believe that they would exactly match up as units with the loss
characteristics of a particular pre existing "standard line. I would
guess that the decibel was simply close to the loss of the "standard"
line, as illustrated by the 0.947 dB figure quoted above.

I took what I wrote from some very old student notes. A search
under "dB" came up with Wiki, and the same information, which
I therefore took as being correct. It was not clear that the TU
was roughly equivalent to the dB not the bel.

I am grateful to The Phantom for taking the trouble to type the
large extract from the Bell Telephone publication.

Regards
Iain

[John Byrns]

In article ,
"Iain Churches" wrote:

"John Byrns" wrote in message
...
In article ,

Note that I am not claiming that the local loop serving my telephone,
actually the one that did in an earlier day, has anywhere near 50 dB
attenuation, or even 20 dB, I was simply illustrating what the
nonsensical result would be applying the information on Iain's web page.


John. The result is not nonsensical.

Sure it is, your web page says, unless you have since corrected it, that
"In the early days of telephone engineering, a unit was needed to
measure the loss of signal over distance. The basic unit chosen was the
power loss in a standard telephone line over the distance of one mile,
at 1kHz. This was called the Transmission Unit, but was renamed, after
the inventor of the telephone, and became known as the bel circa 1924."
What you are implying with that statement is that the loss in a mile of
"standard" telephone line is one bel, which equates to 10 dB, which
means that a "standard line 5 miles long would have a loss of 5 x 10 dB
or 50 dB. The loss in a 5 mile long local loop would be even greater
because the wire gauge used in local loop is higher numerically than the
wire gauge of the "standard" line.

What does *not* make sense
is your interpretation of the information given in the book published
by Bell Telephones in 1925, which was quoted chapter and verse earlier
in this thread by The Phantom.

What is wrong with my interpretation of what the "Phantom" posted? As
far as I can see the Phantom's post supports what I said, not what your
web page says. The Phantom explicitly says of the quotation on your web
page "This is wrong, as the quotations I've given show."

He also says that the attenuation of a mile of "standard" line is 0.947
dB, which is much more reasonable than the one Bel your quote implies.

Note also that the "Phantom" makes a distinction between the "TU" and
the later "Ntu" or "New TU" which later became the decibel, although I
think he then fails to maintain the distinction throughout his writing.

I suggest you reread what the "Phantom" wrote once again and try to
understand what he really is saying, making allowances for the
inevitable typos and muddled language.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Iain Churches[_2_]]

"John Byrns" wrote in message
...
In article ,
"Iain Churches" wrote:

"John Byrns" wrote in message
...
In article ,

Note that I am not claiming that the local loop serving my telephone,
actually the one that did in an earlier day, has anywhere near 50 dB
attenuation, or even 20 dB, I was simply illustrating what the
nonsensical result would be applying the information on Iain's web
page.


John. The result is not nonsensical.

Sure it is, your web page says, unless you have since corrected it, that
"In the early days of telephone engineering, a unit was needed to
measure the loss of signal over distance. The basic unit chosen was the
power loss in a standard telephone line over the distance of one mile,
at 1kHz. This was called the Transmission Unit, but was renamed, after
the inventor of the telephone, and became known as the bel circa 1924."
What you are implying with that statement is that the loss in a mile of
"standard" telephone line is one bel, which equates to 10 dB, which
means that a "standard line 5 miles long would have a loss of 5 x 10 dB
or 50 dB. The loss in a 5 mile long local loop would be even greater
because the wire gauge used in local loop is higher numerically than the
wire gauge of the "standard" line.

What does *not* make sense
is your interpretation of the information given in the book published
by Bell Telephones in 1925, which was quoted chapter and verse earlier
in this thread by The Phantom.

What is wrong with my interpretation of what the "Phantom" posted? As
far as I can see the Phantom's post supports what I said, not what your
web page says. The Phantom explicitly says of the quotation on your web
page "This is wrong, as the quotations I've given show."

He also says that the attenuation of a mile of "standard" line is 0.947
dB, which is much more reasonable than the one Bel your quote implies.

Note also that the "Phantom" makes a distinction between the "TU" and
the later "Ntu" or "New TU" which later became the decibel, although I
think he then fails to maintain the distinction throughout his writing.

I suggest you reread what the "Phantom" wrote once again and try to
understand what he really is saying, making allowances for the
inevitable typos and muddled language.


John. I now have access to a copy of the original Bell text, and have
made some changes to the page.

http://www.kolumbus.fi/iain.churches...heDecibel.html


Thanks for your comments.
Iain

[John Byrns]

In article i,
"Iain Churches" wrote:

John. I now have access to a copy of the original Bell text, and have
made some changes to the page.

http://www.kolumbus.fi/iain.churches...heDecibel.html

You should set the Wikipedia people straight and share this new
information with them.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Eeyore]

John Byrns wrote:

Eeyore wrote:
John Byrns wrote:

That would imply a 50 dB loss between my home and the central
office, if I called the neighbor across the street, the total loss would
be 100 dB and I doubt conversation would be possible with that sort of
loss. The original statement on the web page just doesn't pass the
smell test.

Your mistake is thinking that the dBs add.

Don't they, and if not why not?

What happens when you add logarithms ? That's what you're suggesting.

Graham

[John Byrns]

In article ,
Eeyore wrote:

John Byrns wrote:

Eeyore wrote:
John Byrns wrote:

That would imply a 50 dB loss between my home and the central
office, if I called the neighbor across the street, the total loss would
be 100 dB and I doubt conversation would be possible with that sort of
loss. The original statement on the web page just doesn't pass the
smell test.

Your mistake is thinking that the dBs add.

Don't they, and if not why not?

What happens when you add logarithms ? That's what you're suggesting.

Yup, it's one of the marvels of modern math.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Arny Krueger]

"Eeyore" wrote in message
...


John Byrns wrote:

A Bel or 10 dB seems like an awfully large loss for "a standard
telephone line over the distance of one mile, at 1kHz", is this really
correct?

I suggest you consider the DC resistance of a mile (and a mile back) of
thin
wire.

Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case:

26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is
a low resistance ground.

Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB.

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote:
John Byrns wrote:

A Bel or 10 dB seems like an awfully large loss for "a standard
telephone line over the distance of one mile, at 1kHz", is this really
correct?

I suggest you consider the DC resistance of a mile (and a mile back) of
thin wire.

Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case:

26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is
a low resistance ground.

The reurn is a length of the same wire.


Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB.

The load is rarely 600 ohms AIUI.

Graham

[Iain Churches[_2_]]

"John Byrns" wrote in message
...
In article i,
"Iain Churches" wrote:

John. I now have access to a copy of the original Bell text, and have
made some changes to the page.

http://www.kolumbus.fi/iain.churches...heDecibel.html

You should set the Wikipedia people straight and share this new
information with them.

Yes. I will do that.
With the exception of the Bell Telephone publication, I can find no other
written reference to the fact that the TU was replaced by the NTU, smaller
by an order of magnitute, which then itself became known as the TU.
This is the crux of the matter, and the cause of the confusion.

Iain

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote

So the Lawos don't actually exist over here yet.

Oh. I think there already may be quite a few

But you don't know ? Is it just a broadcast console ?

How can I possibly know? I am not in the UK.
The MC2-90 is a very flexible design, and can be supplied
in optimised formats for broadcast, music recording. audio post,
or CD mastering etc.

and their numbers will be expanded to twenty by the end of this year.

Fine but that doesn't mean they're here now.

The use of the word "expanded" leads me to think they
already have a user base (maybe ten or so, who knows)
that will grow to twenty during this year.
It's by no means a cheap console, so pretty good going.

Just had an e-mail from someone in the UK who says:

quote:
""The Studer desks have been shown at IBC for more years
than I care to remember. They were at Brighton, long before the
exhibition was transferred to Amsterdam. So that must be at
least thirty years. I remember seeing a 72 channel Studer console
at the AES when the A80 Mk II multitrack came out.
Maybe Graham spent too much time at the bar when he should have
been looking at the equipment:-)""
unquote

Iain continues. Lawo will be at the AES on 5-8 October, and at
IBC 7-11 Sept. Will you be there, Graham? I will be happy to buy
you a pork pie and a pint.

Cheers
Iain

[The Phantom]

On Tue, 21 Aug 2007 08:41:59 +0300, "Iain Churches"
wrote:


"John Byrns" wrote in message
...
In article i,
"Iain Churches" wrote:

John. I now have access to a copy of the original Bell text, and have
made some changes to the page.

http://www.kolumbus.fi/iain.churches...heDecibel.html

You should set the Wikipedia people straight and share this new
information with them.

Yes. I will do that.
With the exception of the Bell Telephone publication, I can find no other
written reference to the fact that the TU was replaced by the NTU, smaller
by an order of magnitute, which then itself became known as the TU.
This is the crux of the matter, and the cause of the confusion.

Iain

Iain,

Did you get your hands of an actual copy of the Transmission Circuits
book?

I have another book from around 1933 that also explains about these
things. I could scan the relevant pages and make them available.

[Arny Krueger]

"Eeyore" wrote in message
...


Arny Krueger wrote:

"Eeyore" wrote:
John Byrns wrote:

A Bel or 10 dB seems like an awfully large loss for "a standard
telephone line over the distance of one mile, at 1kHz", is this really
correct?

I suggest you consider the DC resistance of a mile (and a mile back) of
thin wire.

Telephone wire in the US is usually 24 or 26 gauge. Taking the worst
case:

26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path
is
a low resistance ground.

The reurn is a length of the same wire.

Yes, the line is usually balanced. So about double the loss to about 5
dB/mile.

Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB.

The load is rarely 600 ohms AIUI.

Do you think it is higher or lower than 600 ohms?

[The Phantom]

On Tue, 21 Aug 2007 07:35:03 -0400, "Arny Krueger"
wrote:


"Eeyore" wrote in message
...


Arny Krueger wrote:

"Eeyore" wrote:
John Byrns wrote:

A Bel or 10 dB seems like an awfully large loss for "a standard
telephone line over the distance of one mile, at 1kHz", is this really
correct?

I suggest you consider the DC resistance of a mile (and a mile back) of
thin wire.

Telephone wire in the US is usually 24 or 26 gauge. Taking the worst
case:

26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path
is
a low resistance ground.

The reurn is a length of the same wire.

Yes, the line is usually balanced. So about double the loss to about 5
dB/mile.

Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB.

The load is rarely 600 ohms AIUI.

Do you think it is higher or lower than 600 ohms?


An example is given on page 69 of the book "Transmission Circuits for
Telephonic Communication".

I quote:

"In order to get a clearer idea of what is meant by transformer and
transition losses as well as to get a more concrete idea of their order of
magnitude, let us consider the case of an e.m.f. E acting through a sending
end impedance Z1 of 240 - j123 ohms and connected to a receiving end
impedance Z2 of 623 - j350 ohms."

Make of it what you will.

On page 70 and 71, they discuss a test set for comparing transmitters
(carbon microphones, I think). The circuit simulates the sending end
circuitry of a telephone and has 8 miles of cable as well as some
transformers and induction coils (as they called them; they were just
inductors). The impedance driving the telephone line wasn't just the
impedance of the microphone; it was modified by the additional circuitry.
They then say:

"In this particular circuit the 800 cycle impedance at the transmitter
terminals is approximately 307 - j74 ohms. It is, therefore, seen that
with present commercial types of transmitters, ranging between 30 and 150
ohms in resistance, this circuit will discriminate in favor of the
transmitter having the higher resistance."
-------------------------------------------------------------------------

On page 149 they have some text and a table:

"At 800 cycles, the velocity of wave propagation on different types of
circuits, as computed by formula (16) and using the circuit constants
commercially encountered, is approximately as follows:

Type of circuit Velocity-miles per second

N.L. No. 12 N.B.S.G. 174,000
N.L. No. 8 B.W.G 178,000
N.L. No. 19 A.W.G. 39,000
N.L. No. 22 A.W.G. 28,000
L. No. 12 N.B.S.G 56,000
L. No. 8 B.W.G. 53,000
X.L.L. 20,000
M.H.L. 10,000

In the above table N.L. designates non-loaded, M.H.L. medium heavy loaded
and X.L.L. extra light loaded. The very low speed of wave propagation on
loaded circuits is often an objection to their use, especially on long
repeatered circuits where echo effects and transients may become serious."

On page 150, they say:

"For example, the 800-cycle iterative impedance of a non-loaded No. 19
gauge cable circuit is approximately 500 @ 45 degrees, and that of a
non-loaded open wire line is about 700 @ 14 degrees ohms."

I had to spell out "degrees", because I can't find a suitable ascii symbol
right now.