[[email protected]]

Hi Wise men..........
Could you tell me somethin' more about the history of the use of 600
ohm lines in audio technology?????
Do you know books or articles that explain this topic.....
cheers great MAGISTERS

[Richard Crowley]

wrote ...
Hi Wise men..........
Could you tell me somethin' more about the history of the use of 600
ohm lines in audio technology?????
Do you know books or articles that explain this topic.....
cheers great MAGISTERS

Direct descendent of the domestic telephone system.

[Rick Ruskin]

On 20 Nov 2006 09:04:15 -0800, wrote:

Hi Wise men..........
Could you tell me somethin' more about the history of the use of 600
ohm lines in audio technology?????
Do you know books or articles that explain this topic.....
cheers great MAGISTERS


It's my understanding that it originated with Bell Telephone for line
transmission and that they wrote the standards we still use today.




Rick Ruskin
Lion Dog Music - Seattle WA
http://liondogmusic.com

[Mike Rivers]

wrote:
Hi Wise men..........
Could you tell me somethin' more about the history of the use of 600
ohm lines in audio technology?????

To give you the right answer would be to ask why the telephone company
decided to make this their standard, as we got a lot of our standards
and practices from telephony. I don't know why they chose 600 ohms
other than that's what was what they made at the time. It's actually a
reasonable compromise between having a high enough voltage to get above
the noise level, being able to supply the required power with
reasonable components, and having a low enough impedance so that high
impedance noise sources would be divided down to a negligable voltage.

Just a reasonable compromise, like just about everything else in audio.

[Scott Dorsey]

Mike Rivers wrote:

To give you the right answer would be to ask why the telephone company
decided to make this their standard, as we got a lot of our standards
and practices from telephony. I don't know why they chose 600 ohms
other than that's what was what they made at the time.

It's because an open-wire transmission line with five inches between
18 ga. conductors has a characteristic impedance of 600 ohms.

On long cross-country telephone circuits you care about characteristic
impedance because you don't want to see reflections from the termination
hundreds of miles away. Transmisson line effects DO become a big deal
when you're running a line from New York to LA.

Of course, the phone company stopped using open-wire transmission lines
by the 1920s, and went to twisted pair systems. That's why you ALSO
see the 150 ohm standard (as used at CBS radio). 150 ohms happens to
be the characteristic impedance of typical cotton-insulated 20 ga.
twisted pair.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers]

Scott Dorsey wrote:

It's because an open-wire transmission line with five inches between
18 ga. conductors has a characteristic impedance of 600 ohms.

Darn! Why didn't I remember that. Maybe because before 1920 I was still
sending smoke signals and hadn't graduated to electricity.

[Scott Dorsey]

Mike Rivers wrote:
Scott Dorsey wrote:

It's because an open-wire transmission line with five inches between
18 ga. conductors has a characteristic impedance of 600 ohms.

Darn! Why didn't I remember that. Maybe because before 1920 I was still
sending smoke signals and hadn't graduated to electricity.

Because you didn't take Dr. Feeney's transmission line theory class.

There are actually some AM stations out there still using 600 ohm open
wire ladder line for antenna feeds. Not many, though.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Steve King]

"Scott Dorsey" wrote in message
...
Mike Rivers wrote:

To give you the right answer would be to ask why the telephone company
decided to make this their standard, as we got a lot of our standards
and practices from telephony. I don't know why they chose 600 ohms
other than that's what was what they made at the time.

It's because an open-wire transmission line with five inches between
18 ga. conductors has a characteristic impedance of 600 ohms.

On long cross-country telephone circuits you care about characteristic
impedance because you don't want to see reflections from the termination
hundreds of miles away. Transmisson line effects DO become a big deal
when you're running a line from New York to LA.

Of course, the phone company stopped using open-wire transmission lines
by the 1920s, and went to twisted pair systems. That's why you ALSO
see the 150 ohm standard (as used at CBS radio). 150 ohms happens to
be the characteristic impedance of typical cotton-insulated 20 ga.
twisted pair.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

The telcos may have stopped installing open-wire transmission lines in the
20s, but the existing ones remained in use well into the 50s. Some here may
recall that that was when the deluge of green glass telco insulators in
their myriad shapes and sizes hit the collectible markets. As the wires
came off the poles to be replaced by multi-twisted pair cables the
insulators were often left in place. They were then scavanged by
enterprising people for their own collections or for re-sale. This
continued through the 60s in various parts of the country.

Steve King

[[email protected]]

Steve King ha scritto:

"Scott Dorsey" wrote in message
...
Mike Rivers wrote:

To give you the right answer would be to ask why the telephone company
decided to make this their standard, as we got a lot of our standards
and practices from telephony. I don't know why they chose 600 ohms
other than that's what was what they made at the time.

It's because an open-wire transmission line with five inches between
18 ga. conductors has a characteristic impedance of 600 ohms.

On long cross-country telephone circuits you care about characteristic
impedance because you don't want to see reflections from the termination
hundreds of miles away. Transmisson line effects DO become a big deal
when you're running a line from New York to LA.

Of course, the phone company stopped using open-wire transmission lines
by the 1920s, and went to twisted pair systems. That's why you ALSO
see the 150 ohm standard (as used at CBS radio). 150 ohms happens to
be the characteristic impedance of typical cotton-insulated 20 ga.
twisted pair.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

The telcos may have stopped installing open-wire transmission lines in the
20s, but the existing ones remained in use well into the 50s. Some here may
recall that that was when the deluge of green glass telco insulators in
their myriad shapes and sizes hit the collectible markets. As the wires
came off the poles to be replaced by multi-twisted pair cables the
insulators were often left in place. They were then scavanged by
enterprising people for their own collections or for re-sale. This
continued through the 60s in various parts of the country.

Steve King




An interesting point of view......Bill Whithlock wrote a paper called
"trasmission lines : why 600 ohm"......
Thanks to everybody...........
Scott, Mike How old are You????????
Thanks

[[email protected]]

"Steve King" writes:

The telcos may have stopped installing open-wire transmission lines
in the 20s, but the existing ones remained in use well into the 50s.
Some here may recall that that was when the deluge of green glass
telco insulators in their myriad shapes and sizes hit the
collectible markets. As the wires came off the poles to be replaced
by multi-twisted pair cables the insulators were often left in
place. They were then scavanged by enterprising people for their
own collections or for re-sale. This continued through the 60s in
various parts of the country.

Some years ago they totally got rid of the line along the Trans line
from Kalgoolie to Port Augusta. Not only did they salvage all the
wire, not much, a lot of it was SWER, but also the poles as well. This
was a disaster for the eagle population, as they used the poles for
nesting. So they had to build towers every mile or so for nesting.

That was a VERY expensive salvage job!

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

[Adrian Tuddenham]

Mike Rivers wrote:

wrote:
Hi Wise men..........
Could you tell me somethin' more about the history of the use of 600
ohm lines in audio technology?????

To give you the right answer would be to ask why the telephone company
decided to make this their standard, as we got a lot of our standards
and practices from telephony. I don't know why they chose 600 ohms
other than that's what was what they made at the time.

It was the correct terminating impedance for the cross-sectional
dimensions of the long-distance overhead circuits they were already
using.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk