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art January 8th 05 02:49 AM

coax from cable company
 
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


artie January 8th 05 03:09 AM

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--

Ed January 8th 05 03:18 AM



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


Lou January 8th 05 03:38 AM


"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



Roy Lewallen January 8th 05 04:09 AM

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


[email protected] January 8th 05 05:02 AM

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




[email protected] January 8th 05 01:31 PM

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




'Doc January 8th 05 05:41 PM

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

Phil January 8th 05 07:30 PM


"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.



Roger January 9th 05 07:58 AM

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


Wes Stewart January 9th 05 01:06 PM

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.

How so?


'Doc January 9th 05 04:00 PM

Ahh! But amplification is used for very long spans
of cable TV.
'Doc

Ian Jackson January 9th 05 04:59 PM

In message , Wes Stewart
writes
On Sat, 08 Jan 2005 19:30:03 GMT, "Phil" wrote:

|
|"art" wrote in message
groups.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.

How so?


The discs have a higher dielectric constant than the air. There is
therefore an increase of capacitance where there are (so the Zo dips
slightly).

As the discs are located at regular interval, where this spacing is one
wavelength, the repetitive higher capacitance adds up in parallel
(although buffered somewhat by the losses loss of the cable). The effect
is to produce a sharp suckout at the frequency of that wavelength (and
at multiples thereof). This effect is also referred to as 'Structural
Return Loss' (well, it's one of the causes). It sets the maximum
frequency at which the coax can be used.

The closer the spacing of the discs, the higher will be the suckout. If
the spacing is zero, the frequency will be infinite. However, you will
have just invented solid dielectric coax!

Ian.
--


W2RAC January 10th 05 05:52 AM

On my links page I have some links on how to adapt normal so239 and N
ends onto this cable.
Can be used for TX just fine.
www.qsl.net/w2rac

On 7 Jan 2005 18:49:53 -0800, "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



Wes Stewart January 10th 05 03:27 PM

On Sun, 9 Jan 2005 16:59:10 +0000, Ian Jackson
wrote:

|In message , Wes Stewart
writes
|On Sat, 08 Jan 2005 19:30:03 GMT, "Phil" wrote:
|
||
||"art" wrote in message
egroups.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.
|
|How so?
|
|
|The discs have a higher dielectric constant than the air. There is
|therefore an increase of capacitance where there are (so the Zo dips
|slightly).

Okay, I guess this stuff doesn't use the compensation that I am
familiar with where either/or/both conductor diameters are modified to
account for the dielectric constant difference and the locations are
*not* at regular intervals.

Some of the missiles I've worked on used beaded coax at 10 Ghz.

|
|As the discs are located at regular interval, where this spacing is one
|wavelength, the repetitive higher capacitance adds up in parallel
|(although buffered somewhat by the losses loss of the cable). The effect
|is to produce a sharp suckout at the frequency of that wavelength (and
|at multiples thereof). This effect is also referred to as 'Structural
|Return Loss' (well, it's one of the causes). It sets the maximum
|frequency at which the coax can be used.

The "suck out" you refer to is primarily due to mismatch loss. For
the case at hand (ham operation, i.e., a narrow-band system) I don't
think this is an issue.

Wes


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