From: Eric Lemmon WB6FLY 
Date: Fri, 07 Nov 2003
Subject: [Repeater‑Builder] Double-Shielded Coax

In recent postings to the list there have been several references to the 
need for double-shielded coaxial cable when hooking up components within 
a repeater cabinet.  Although RG‑142/U is widely used by repeater 
builders, perhaps a better choice for some applications is RG‑400/U (note 
that RG‑400 is NOT the "LMR‑400" cable).  At first glance, RG‑142/U and 
RG‑400/U appear identical, with see-through brown jackets, but there is 
a significant difference between the two:

   RG‑142/U has a solid steel center conductor that is silver plated.

   RG‑400/U has a stranded copper center conductor, with each strand 
   silver plated before twisting into the center conductor.

Both types of cable have double, silver-plated copper braided shields,
and a Teflon dielectric.  Both types have similar RF characteristics. 
Because of its flexibility, RG‑400/U is better suited for bench test
leads or to connect any repeater component that is mounted on a movable
panel or on the inside of the cabinet door.  When flexed repeatedly, 
the steel center conductor of RG‑142/U can fracture and become a noise
generator. 

I personally have settled exclusively on crimp-type connectors 
made by RF Industries, and I swear by them.  Whether N or BNC, I use 
only the silver-plated connectors with gold-plated center pins and Teflon
dielectric.  It helps to have the proper tools to strip and crimp each
connection, and I am very pleased with the quality.

73, Eric Lemmon WB6FLY