TV Coax--300 vs 75 ohm

[W. eWatson]

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

I went to use a old TV the other day that I had hooked up to about 25'
of coax, but needed an extension of about 12'. There were zero marking
on the coax, but I'm pretty sure I bought it at The Shack some years
ago. I asked them the ohmage, but they said it didn't matter. They had
some nondescript 25' cable, and said it would be fine.

I did buy it, and it seems OK. Maybe they matched. $24 for 12', so I
bought the same at K-Mart for $8!

 

[Rich Webb]

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
<wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.

--
Rich Webb Norfolk, VA

 

[W. eWatson]

On 1/25/2011 11:52 AM, Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.

Perhaps I should have mentioned that what I have from The Shack uses BNC

at both ends, and that I'm using a yagi.

The really old stuff I suspect is flat like a ribbon.

 

[Michael A. Terrell]

Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.

There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[Don Klipstein]

In article <ihn4dm$div$1@news.eternal-september.org>, W. eWatson wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

I went to use a old TV the other day that I had hooked up to about 25'
of coax, but needed an extension of about 12'. There were zero marking
on the coax, but I'm pretty sure I bought it at The Shack some years
ago. I asked them the ohmage, but they said it didn't matter. They had
some nondescript 25' cable, and said it would be fine.

I did buy it, and it seems OK. Maybe they matched. $24 for 12', so I
bought the same at K-Mart for $8!

300 ohm coax sounds to me not so easy to get. Coax is usually 50-52
ohms or 75, much less commonly other values generally less than 300 ohms.
TV coax is 75. Coax connectors for TV and video are for 75 ohm coax
cable.

300 ohm TV cable is twinlead, not coax. What twinlead connects to is
generally a pair of screws.
--
- Don Klipstein (don@misty.com)

 

[krw@att.bizzzzzzzzzzzz]

On Tue, 25 Jan 2011 17:17:07 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.


There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.

I wired the outlaws' antenna system with that stuff, um, 40 years ago. ;-)

 

[krw@att.bizzzzzzzzzzzz]

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson" <wolftracks@invalid.com>
wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

No. TVs use 75ohm coax. Antiques may have 300ohm twinlead inputs. You can
convert from twinlead to coax, or verse visa, using a Balun.

I went to use a old TV the other day that I had hooked up to about 25'
of coax, but needed an extension of about 12'. There were zero marking
on the coax, but I'm pretty sure I bought it at The Shack some years
ago. I asked them the ohmage, but they said it didn't matter. They had
some nondescript 25' cable, and said it would be fine.

I'm sure they sell RG6. I'd be surprised if RadioShaft sold anything else
these days.

I did buy it, and it seems OK. Maybe they matched. $24 for 12', so I
bought the same at K-Mart for $8!

Good move! You still got ripped a new one, but not quite as large. ;-)

 

[Michael A. Terrell]

"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 17:17:07 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.


There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.

I wired the outlaws' antenna system with that stuff, um, 40 years ago. ;-)

What I saw was early foam insulation over standard twin lead, with a
layer of foil. It was a pain in the dimbulb to work with, and was
quickly replaced by RG59.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[krw@att.bizzzzzzzzzzzz]

On Tue, 25 Jan 2011 21:53:04 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 17:17:07 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.


There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.

I wired the outlaws' antenna system with that stuff, um, 40 years ago. ;-)

What I saw was early foam insulation over standard twin lead, with a
layer of foil. It was a pain in the dimbulb to work with, and was
quickly replaced by RG59.

Same stuff. RG59 was around but I would have needed two baluns and eaten the
insertion loss.

 

[Jasen Betts]

On 2011-01-25, W. eWatson <wolftracks@invalid.com> wrote:

On 1/25/2011 11:52 AM, Rich Webb wrote:
On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.

Perhaps I should have mentioned that what I have from The Shack uses BNC
at both ends, and that I'm using a yagi.

A BNC coax cable from radio shack was probably an old thin ethernat cable
50 ohms. http://en.wikipedia.org/wiki/10BASE2

The really old stuff I suspect is flat like a ribbon.

Yeah this stuff: http://en.wikipedia.org/wiki/Twin-lead

--
⚂⚃ 100% natural

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[Michael A. Terrell]

"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 21:53:04 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 17:17:07 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.


There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.

I wired the outlaws' antenna system with that stuff, um, 40 years ago. ;-)

What I saw was early foam insulation over standard twin lead, with a
layer of foil. It was a pain in the dimbulb to work with, and was
quickly replaced by RG59.

Same stuff. RG59 was around but I would have needed two baluns and eaten the
insertion loss.

A good bauln has less than a half dB loss, but some of the early stuff
was crap. One thing a lot of people don't know is that there was a
balun in the TV tuner so you could use cheap twin lead.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[krw@att.bizzzzzzzzzzzz]

On Wed, 26 Jan 2011 11:22:08 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 21:53:04 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 17:17:07 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.


There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.

I wired the outlaws' antenna system with that stuff, um, 40 years ago. ;-)

What I saw was early foam insulation over standard twin lead, with a
layer of foil. It was a pain in the dimbulb to work with, and was
quickly replaced by RG59.

Same stuff. RG59 was around but I would have needed two baluns and eaten the
insertion loss.

A good bauln has less than a half dB loss, but some of the early stuff
was crap. One thing a lot of people don't know is that there was a
balun in the TV tuner so you could use cheap twin lead.

Half a dB here and a half there and pretty soon you have a snow storm. The
set only had screws on the back. I wasn't about to hack into the set.

 

[Michael A. Terrell]

"krw@att.bizzzzzzzzzzzz" wrote:

On Wed, 26 Jan 2011 11:22:08 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 21:53:04 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


"krw@att.bizzzzzzzzzzzz" wrote:

On Tue, 25 Jan 2011 17:17:07 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:


Rich Webb wrote:

On Tue, 25 Jan 2011 10:22:44 -0800, "W. eWatson"
wolftracks@invalid.com> wrote:

Don't TVs (analog) require 300 ohm coax? Can 300 and 75 be mixed?

[Oh good, something that I know just enough about to be dangerous ;-) ]

The 300 ohm stuff that you remember was not coax, it was the old
twin-lead cable. That configuration has the advantage of somewhat lower
losses than coax, and also a better impedance match to folded dipole
antennas (a common TV antenna configuration). A disadvantage is its
greater susceptibility to interference and also to losses caused by
neighboring conductive surfaces (e.g., aluminum siding).

When TV sets went coax, along with the rise of cable systems, twin-lead
could still be run from an antenna but it needed a balun (balanced
(twin-lead) to unbalanced (coax)) converter between the two.


There was shielded 300 Ohm Twinlead, but it was rare. The last I saw
was 45+ years ago.

I wired the outlaws' antenna system with that stuff, um, 40 years ago. ;-)

What I saw was early foam insulation over standard twin lead, with a
layer of foil. It was a pain in the dimbulb to work with, and was
quickly replaced by RG59.

Same stuff. RG59 was around but I would have needed two baluns and eaten the
insertion loss.

A good bauln has less than a half dB loss, but some of the early stuff
was crap. One thing a lot of people don't know is that there was a
balun in the TV tuner so you could use cheap twin lead.

Half a dB here and a half there and pretty soon you have a snow storm. The
set only had screws on the back. I wasn't about to hack into the set.

The problem was that early RG59 had a copper braid for a shield, and
sold poly insulation with had a lot higher loss than a pair of baluns.
It wasn't undil foil shielded RG59 & RG6 was availible that 75 ohm feeds
made sense. Early VHF CATV systems used RG11 between amplifiers, and
horrible tilt.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.