The ULTIMATE coaxial cable???

[Andrew Thornett]

For those with deep pockets, maybe this is the ultimate coaxial cable for your station:

LMR-1200.......at £63.25 per metre!!!!

Andy

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[Marcus D Leech]

Would be a waste of money. But yeah. 

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On Jan 11, 2025, at 11:06 AM, 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



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[Marcus D Leech]

When I visited the Stanford dish many years ago they had something like 4” heliax going up to the feed. 

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On Jan 11, 2025, at 11:06 AM, 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



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[Jim Brown]

There are thousands of feet of (at least) 3" Andrew heliax in big spools at Green Bank and they have no use for them.  They've been on spools down by the old interferometer for the past 20 some years. 

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[Marcus D. Leech]

On 11/01/2025 11:23, 'Jim Brown' via Society of Amateur Radio Astronomers wrote:

There are thousands of feet of (at least) 3" Andrew heliax in big spools at Green Bank and they have no use for them.  They've been on spools down by the old interferometer for the past 20 some years. 

I have some Phelps-Dodge type-N adaptors for 7/8" hardline that I've had for, oh crap, maybe 35 years.  Never found a use for
  them, but when they were sitting on that table in the "flea" at Dayton, I couldn't resist....

The problem with heliax is that it will get contaminated if the ends are left open in the environment, since it's basically
  a hollow core, with a helical support thingy for the center conductor, there's nothing that really prevents water incursion.
  Had a run of it going up to the roof of the Dunton Tower at Carleton U back in the 1980s.  For our bit-regenerating repeater
  on 220MHz.  Started failing.  When I pulled the connector off on the lower end to check things, about 1.5L of water ran
  out of it :(

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[Jim Brown]

They used this for the inteferometer.  I didn't look closely but at the time I would think the engineers would have sealed the ends with future use in mind.  Next SARA conference someone go down and look.  There are one or maybe two spools probably 5 feet in diameter.  Some of it has to still be good.  There is a lot of it in a cable trace as well.  The SARA conference has gotten out my retirement fixed income so going down isn't in the cards anymore.

JB

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[Anthony]

LMR 1200, isn't that burial coax, I thought

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[Anthony]

600" is $279.99...

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[Anthony]

Oops, disregard that,mistaken for LMR 600

On Sat, Jan 11, 2025, 11:06 AM 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

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[Lester Veenstra]

Always use Heliax with positive dry air/Nitrogen system.

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

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[Brian Ramey]

Curious what coax is commonly used by Amateur Radio Astronomy enthusiasts if you have a fairly long run?  LMR-400's attenuation is typically 3dB per 100'  at 450MHz while 1/2" Heliax is 1 dB per 100'.  I guess with an LNA at the feedhorn it's not such a big issue, but I still hate to lose that 3 dB with LMR-400!  

Brian  

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[Marcus D. Leech]

On 11/01/2025 19:11, Brian Ramey wrote:

Curious what coax is commonly used by Amateur Radio Astronomy enthusiasts if you have a fairly long run?  LMR-400's attenuation is typically 3dB per 100'  at 450MHz while 1/2" Heliax is 1 dB per 100'.  I guess with an LNA at the feedhorn it's not such a big issue, but I still hate to lose that 3 dB with LMR-400!  

Brian 

The system Tsys (which basically determines your ultimate SNR) is almost *completely dominated* by the gain and noise figure of
  your first stage LNA.  Loss after that mostly just lowers the levels of signals, but doesn't noticeably negatively affect
  SNR.

See "Friis noise chain analysis".

Granted, if you have a LOT of loss after the LNA, this can be a problem.

At the CCERA observatory, we use RG6-DS and RG6-Q from the feedpoint down into the receiver/elevation cabin.  About 15m
  of cable.  Our estimated Tsys is around 90K, sometimes a bit better.   Granted, RG6 is 75-ohm,  but, again, after the first LNA
  stage, this makes very little difference--a small attenuation at the receiver can help damp-out any (very small) reflections that
  can cause spectral artifacts.

RG6 is convenient for us because you can literally buy it in 500' reels at Home Depot and the like, and the connectors and
  tooling for those connectors is available just about everywhere.   Although this will slowly start to "go away" as the world
  moves away from SatTV and Cable TV, and just uses the Internet for everything.

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[fasleitung3]

We use Ecoflex 10 for longer runs. Exoflex 10 is very similar to LM400. For connections where high flexibility is required Aircell 7 is our primary choice.

We have runs of > 50m with Ecoflex 10, one just have to make sure that there is a line amplifier in front of the cable to compensate for the loss.

Wolfgang

[Brian Ramey]

Thanks for the info, Marcus. Makes sense! 

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[Andrew Thornett]

There is always the attached - 3 inch wide air spaced coax!

Andy

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Sent: Sunday, January 12, 2025 4:15:10 PM
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Subject: Re: [SARA] The ULTIMATE coaxial cable???

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