I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art

In article .com, art
wrote:

I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art


Good stuff, but 75 ohms.

--
Namaste--

I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art

That's nothing real new. Yes, is air dielectric and slightly less lossy
than regular foam dielectric heliax. Since you described the outer
conductor as aluminum, I suspect it is 75 ohm cable.... but not
necessarily. There should be info printed onto the outer plastic jacket
material mthat would help in specifically identifying that cable.


Ed K7AAT

"Ed" wrote in message
. 92.175...


I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art

That's nothing real new. Yes, is air dielectric and slightly less lossy
than regular foam dielectric heliax. Since you described the outer
conductor as aluminum, I suspect it is 75 ohm cable.... but not
necessarily. There should be info printed onto the outer plastic jacket
material mthat would help in specifically identifying that cable.


Ed K7AAT


In a "Hints and Kinks" book - I believe - or maybe it was an Antenna
Handbook from the ARRL - they described how to make a matching network to
take that sort of heliax to use for 50 ohm purposes.

Lou

It's a common misconception that the use of disks or foamed dielectric
reduces loss because of reduced dielectric loss.

But, up to a frequency of somewhere around 1 - 10 GHz or so, that isn't
true.

Below 1 - 10 GHz, the conductor skin effect loss is much greater than
the dielectric loss of solid PE or PTFE (the common coax insulating
materials), so further reduction of dielectric loss makes no appreciable
difference.

BUT, going to disks or foamed dielectric does reduce the effective
dielectric constant of the insulator. This results in the requirement of
a larger diameter center conductor for the same Z0 and cable diameter.
The cable does have lower loss, but because of the larger center
conductor, not because of decreased dielectric loss.

Roy Lewallen, W7EL

Ed wrote:
I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art


That's nothing real new. Yes, is air dielectric and slightly less lossy
than regular foam dielectric heliax. Since you described the outer
conductor as aluminum, I suspect it is 75 ohm cable.... but not
necessarily. There should be info printed onto the outer plastic jacket
material mthat would help in specifically identifying that cable.


Ed K7AAT

The fact that it is 75 ohm really doesn't bother me. I use 1inch dia Andrews
hard line at the moment
for a 200 foot run but this other stuff was used for cable T.V. and computor
stuff before they changed out to
fiberglass ,so I wondered if it was better than what I was using now and if
so how much !
It does not have a plastic covering on it so no numbers are visible.
Regards
Art


"Lou" wrote in message
o.verio.net...

"Ed" wrote in message
. 92.175...


I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art

That's nothing real new. Yes, is air dielectric and slightly less lossy
than regular foam dielectric heliax. Since you described the outer
conductor as aluminum, I suspect it is 75 ohm cable.... but not
necessarily. There should be info printed onto the outer plastic jacket
material mthat would help in specifically identifying that cable.


Ed K7AAT


In a "Hints and Kinks" book - I believe - or maybe it was an Antenna
Handbook from the ARRL - they described how to make a matching network to
take that sort of heliax to use for 50 ohm purposes.

Lou

Thank you Roy. That puts the whole question in perspective.
I suppose the long runs that are required for country locations
would not benefit from serial amplification so prevention of
loss would be more beneficial
Regards
Art


"Roy Lewallen" wrote in message
...
It's a common misconception that the use of disks or foamed dielectric
reduces loss because of reduced dielectric loss.

But, up to a frequency of somewhere around 1 - 10 GHz or so, that isn't
true.

Below 1 - 10 GHz, the conductor skin effect loss is much greater than the
dielectric loss of solid PE or PTFE (the common coax insulating
materials), so further reduction of dielectric loss makes no appreciable
difference.

BUT, going to disks or foamed dielectric does reduce the effective
dielectric constant of the insulator. This results in the requirement of a
larger diameter center conductor for the same Z0 and cable diameter. The
cable does have lower loss, but because of the larger center conductor,
not because of decreased dielectric loss.

Roy Lewallen, W7EL

Ed wrote:
I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art


That's nothing real new. Yes, is air dielectric and slightly less lossy
than regular foam dielectric heliax. Since you described the outer
conductor as aluminum, I suspect it is 75 ohm cable.... but not
necessarily. There should be info printed onto the outer plastic jacket
material mthat would help in specifically identifying that cable.


Ed K7AAT

Art,
It's chief advantage is that it's cheaper to make. Not
much, but some. One of it's disadvantages is that you will
have to seal it (makes a good garden hose otherwise).
'Doc

"art" wrote in message
oups.com...
I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art


Look on Google for "fused disc" AND "cable".

Most Cable TV companies stopped using it when they started using frequencies
above 300 MHz.

This cable acts as a filter around 350 MHz.

On Sat, 08 Jan 2005 19:30:03 GMT, "Phil" wrote:


"art" wrote in message
roups.com...
I was just given a coil of 7/8 hardline coax that I have not seen
before.
It has plastic discs inside to separate the core from the outer
aluminum tube which I suppose uses air as the dielectric. Anybody got
any info on this stuff
and any advantages it may have over the normal hardline cable?
Regards
Art


Look on Google for "fused disc" AND "cable".

Most Cable TV companies stopped using it when they started using frequencies
above 300 MHz.

This cable acts as a filter around 350 MHz.

I used to use a lot of the 3/4 " foam filled CATV line and still have
probably 200 to 300 feet left. At HF it works well and does not
require matching sections unless the operator is a perfectionist.

It's much more rugged than the fused disk stuff and water isn't
normally a problem.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com