Elecraft

RG-8X

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john@kk9a.com

RG-8X

I believe all RG8X has a .242 diameter PVC jacket and about the same loss.
Certainly some brands are better made, I use only Belden 9258.

Perhaps the question should be what is the best coax with a diameter less
than ??? or weight less then ???, for ??? MHz, good for ??? watts for a
portable/permanent installation? There might be some interesting options.

John KK9A

Mon Feb 26 12:07:16 EST 2018

Hi Richard,

Please provide a little more information so that your question can
be answered more accurately.

At what frequencies will you be using your coax?

Will your coax be buried or laid on the ground, or will it not be
in contact with the ground at all?

Many coaxial cables have a vinyl jacket which is very susceptible
to moisture penetration if buried or laid on moist ground.

Are rodents (squirrels, mice, etc) a problem in your area?

Vinyl jacketed coax is very susceptible to rodent damage which
will quickly increase your coax loss.

73
Frank
W3LPL

From: Richard <FlatHat at comcast.net>
To: Elecraft Reflector <elecraft at mailman.qth.net>
Sent: Monday, February 26, 2018 8:35 AM
Subject: [Elecraft] RG-8X

I’m seeking recommendations for RG-8X coax with the lowest loss. The total
run will be about 100 feet.

Cheers!

Richard Kunc — W4KBX

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Jim Brown-10

Re: RG-8X

On 2/26/2018 9:28 AM, [hidden email] wrote:
> I believe all RG8X has a .242 diameter PVC jacket and about the same loss.
> Certainly some brands are better made, I use only Belden 9258.

Not quite. First, for at least 40 years, RG-numbers are NOT a
specification, but only a generic description of cable, mostly telling
us the approximate outer diameter and the characteristic impedance (Zo).
Below about 500 MHz, loss in coax is all due to I squared R, which
depends entirely on the combined resistance of the center conductor and
the shield at the frequency of interest.

Zo depends on conductor diameters, spacing, and the dielectric material.
Coax with a foam dielectric allow the center conductor to be larger for
the same shield diameter. THAT'S why foam cables have lower loss, NOT
because of lower loss in the dielectric -- dielectric loss doesn't show
up until we're well into the UHF region. Shield resistance is reduced by
a larger diameter for two reasons -- more copper and skin effect. Many
coax cables don't use copper for center or shield or both. Loss will be
greater at low frequencies if the center is copper-coated steel, which
is often done for both cost and physical strength. Loss will also be
greater if the shield uses less copper or is made from aluminum.

As usual, Frank has asked the right questions -- there are important
"applications-related" differences between coax types, even from the
same manufacturer.

In general, it's best to use bigger coax from a trusted manufacturer,
and with the best quality shield. Larger coax has less loss. Don't buy
smaller coax because you're running low power -- our Field Day team runs
QRP, and all of our coax is RG8-size with a foam dielectric for low loss
and a robust copper braid shield!

There's a tutorial on this topic at http://k9yc.com/Coax-Stubs.pdf

73, Jim K9YC

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NK7Z

Re: RG-8X

Thanks for sharing! Very interesting.

73s and thanks,
Dave
NK7Z
https://www.nk7z.net

On 02/26/2018 10:10 AM, Jim Brown wrote:

> There's a tutorial on this topic at http://k9yc.com/Coax-Stubs.pdf
>
> 73, Jim K9YC
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Bob McGraw - K4TAX

Re: RG-8X

I did inquire as to the application. To feed a 6M yagi being a 6OWL6W. My thinking, I would cringe at putting up a nice yagi such as this and not use the feedline with the lowest loss possible. Most likely Andrew LDF4-50A hardline.

Bob, K4TAX

Sent from my iPhone

> On Feb 26, 2018, at 12:21 PM, Dave Cole (NK7Z) <[hidden email]> wrote:
>
> Thanks for sharing! Very interesting.
>
> 73s and thanks,
> Dave
> NK7Z
> https://www.nk7z.net
>
>> On 02/26/2018 10:10 AM, Jim Brown wrote:
>>
>> There's a tutorial on this topic at http://k9yc.com/Coax-Stubs.pdf
>> 73, Jim K9YC
> ______________________________________________________________
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Jim Brown-10

Re: RG-8X

On 2/26/2018 11:02 AM, Bob McGraw K4TAX wrote:
> I did inquire as to the application. To feed a 6M yagi being a 6OWL6W. My thinking, I would cringe at putting up a nice yagi such as this and not use the feedline with the lowest loss possible. Most likely Andrew LDF4-50A hardline.

Me too! The 350 ft run from my shack to the 3-el SteppIR is 7/8-in
hardline, transitioning to a short length of flexible coax for the
rotator loop. Scrounged the hard line used for roughly $1/ft. Loss is
about 1 dB on 6M.

73, Jim K9YC

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Jim Brown-10

Re: RG-8X

In reply to this post by Jim Brown-10

On 2/26/2018 10:45 AM, Tom Georgens wrote:

> HI Jim
>
> Thanks for your informed commentary
>
> One question I have had is, if loss is dominated by resistive losses at HF,
> does coax actually get more lossy with age? If so, what is the mechanism.
> Does the dielectric change properties, or do the copper surfaces corrode or
> break down? If the dielectric breaks down, then the impedance should
> change as well
>
> Most info on cable life deal primarily with the UV, heat, and moisture
> resistance of the jacket but I have seen very little about aging of the
> internal components.

Hi Tom. I don't know enough about this issue to say anything useful,
except for this. When N6RZ died something like 8 years ago, I bought a
lot of his stuff and helped his XYL, Kerry, get rid of the rest of it.
He had a lot of coax and some hard line; I bought the hard line, and
took the random lengths of coax to an NCCC meeting, telling members
where it had come from. Almost all of it was good quality stuff, some
used inside, some outside. I even found some stored in a shed. I'd guess
most of it was at least 20 years old. Everyone turned their noses up at
it, so I brought it home, made stubs out of it, and measured their
effectiveness. I didn't have a VNA then, so I used an HP generator and
HP spectrum analyzer (as an RF voltmeter), doing point by point
measurements. Most of the stub data in that Q&A are for that cable.

Since a harmonic stub depends on a low value of impedance to work, that
tells me the cables were still quite good. The only bad piece of cable I
found was one whose interior jacket was green from oxidation of the
shield. I think it had come from that shed.

Until I learn more about it, I go under the assumption that the primary
hazard is moisture. Because dielectric loss doesn't kick in until at
least UHF, I don't buy that being as a factor at HF. A few years ago, I
noticed moisture around the Polyphaser for one of my high dipoles when I
removed it for some reason. I had only recently replaced the dipole and
the coax run (Belden 8213), but hadn't done a good enough job of sealing
the coax around the center insulator. Water penetrated, came down
between the braid and dielectric, and in less than a year, had turned
the shield black. I put that length of coax on the VNA and found that
loss had increased from about 0.4 dB to about 0.45 dB.

I'm copying this to the reflector, hoping that guys like W3LPL will jump
in with more.

73, Jim

>
> Thanks
>
> Tom W2SC
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Jim Brown
> Sent: Monday, February 26, 2018 10:11 AM
> To: [hidden email]
> Subject: Re: [Elecraft] RG-8X
>
> On 2/26/2018 9:28 AM, [hidden email] wrote:
>> I believe all RG8X has a .242 diameter PVC jacket and about the same loss.
>> Certainly some brands are better made, I use only Belden 9258.
> Not quite. First, for at least 40 years, RG-numbers are NOT a specification,
> but only a generic description of cable, mostly telling us the approximate
> outer diameter and the characteristic impedance (Zo).
> Below about 500 MHz, loss in coax is all due to I squared R, which depends
> entirely on the combined resistance of the center conductor and the shield
> at the frequency of interest.
>
> Zo depends on conductor diameters, spacing, and the dielectric material.
> Coax with a foam dielectric allow the center conductor to be larger for the
> same shield diameter. THAT'S why foam cables have lower loss, NOT because of
> lower loss in the dielectric -- dielectric loss doesn't show up until we're
> well into the UHF region. Shield resistance is reduced by a larger diameter
> for two reasons -- more copper and skin effect. Many coax cables don't use
> copper for center or shield or both. Loss will be greater at low frequencies
> if the center is copper-coated steel, which is often done for both cost and
> physical strength. Loss will also be greater if the shield uses less copper
> or is made from aluminum.
>
> As usual, Frank has asked the right questions -- there are important
> "applications-related" differences between coax types, even from the same
> manufacturer.
>
> In general, it's best to use bigger coax from a trusted manufacturer, and
> with the best quality shield. Larger coax has less loss. Don't buy smaller
> coax because you're running low power -- our Field Day team runs QRP, and
> all of our coax is RG8-size with a foam dielectric for low loss and a robust
> copper braid shield!
>
> There's a tutorial on this topic at http://k9yc.com/Coax-Stubs.pdf
>
> 73, Jim K9YC
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html Message
> delivered to [hidden email]
>

John Oppenheimer

Old Coax, was RG-8X

The discussion about old coax reminded me of a recent acquisition. A
couple of weeks ago I went through my old childhood home in FL, just
before it was sold, to look for "stuff" from the past. The property had
a shed, which predated our home, which had old radio stuff in it when I
was young. Looked high and low for something "radio." Finally, up in the
rafters of the shed was a coil for coax with UHF connectors. It predates me.

https://www.icloud.com/sharedalbum/#B0iGhtLJ3GJNmWk

When were those connectors used? Yes, I cleaned off the crud that came
off with a damp cloth.

John KN5L
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Kidder, George

Re: Old Coax, was RG-8X

Those look like military surplus connectors - they were quite common in
the 50's and probably before. A bear to use, but solid.

George W3HBM

On 2/26/2018 6:24 PM, John Oppenheimer wrote:

> The discussion about old coax reminded me of a recent acquisition. A
> couple of weeks ago I went through my old childhood home in FL, just
> before it was sold, to look for "stuff" from the past. The property had
> a shed, which predated our home, which had old radio stuff in it when I
> was young. Looked high and low for something "radio." Finally, up in the
> rafters of the shed was a coil for coax with UHF connectors. It predates me.
>
> https://www.icloud.com/sharedalbum/#B0iGhtLJ3GJNmWk
>
> When were those connectors used? Yes, I cleaned off the crud that came
> off with a damp cloth.
>
> John KN5L
> ______________________________________________________________
> Elecraft mailing list
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>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>