[Antennas] Re: Buried ladder line?

2003年10月16日 09:28:34 -0400

I'm glad the thread has returned to answering the original query and I'd 
like to add my thoughts.
As Tom noted, the concern is minimizing matched-line loss (which quickly 
leads to intolerable loss when the VSWR is high). Unfortunately, as Dick 
noted, the problem is moisture. Ladder line becomes lossy (relative to 
open line under dry conditions) when damp and the losses may be higher 
than coax. I think Dick's solution is the most practical, especially if 
you can find "cut-offs" from a cable TV installation.
Here's another approach. Thread the ladder line through a tube centered 
in the large conduit supported with "spiders" (like a cross between a 
snake and a porcupine?). If you want to get fancy, you can pressurize the 
tube with inert welding gas (commercial installations use dry nitrogen). 
Or it might be good enough to install a stub with desiccant. The 
important thing is to keep it bone-dry; and pitch the ABS conduit so water 
won't accumulate there.
Possible tubes include garden hose, ENT, PB, innerduct, NM liquid-tight 
conduit, plastic pipe with tight joints, and so forth. Some of these will 
have better RF properties than others, so YMMV. Keep the ends of the tube 
away from weather and UV exposure.
I have heard of using garden hose to protect ladder line from rain and 
snow, but I have no experience with it.
> Message: 1
> Date: 2003年10月14日 07:58:18 -0700
> From: Dick Carroll <[email protected]>
> To: [email protected]
> Subject: [Antennas] Re: Antennas digest, Vol 4 #245 - 12 msgs
>> Tom, your problem will be keeping out the water, especially so in 
Oregon.
...
> As to your situation- I'd consider using a very low loss coaxial cable, 

> twin runs as you
> noted, only I'd get something like hard line or fairly large diameter 
> rubber coated TV
> cable trunk line. 
> If you're sure to have water enter the conduit, and I'm convinced it 
> will, then installing
> twin lead as you describe will prove to be an exercise in futility.
>> Dick W0EX
>> >Message: 2
> >Reply-To: <[email protected]>
> >From: "Tom Scott" <[email protected]>
> >To: "Antennas Reflector List" <[email protected]>
> >Date: 2003年10月13日 15:08:57 -0700
> >Subject: [Antennas] Buried ladder line?
> >
...
> >Has anyone ever considered running ladder line underground through 
large
> >diameter ABS tubing?...
> > 
> >I'm not interested in proposals that involve burying pairs of coax; yes
> >that can maintain balance, but is lossier with a mis-match than ladder
> >line.
> > 
> >Thanks!
> >