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