Re: [IRCA] Cable connectors

[Rick Kunath <k9ao@xxxxxxxxxxx>]

Craig,

I'm curious to know about the construction of the RG-6 cable that you used for 
your test?

Was this just braid shielded? And if so what was the shield coverage? Was 
there any foil over the dielectric, and if so was that foil bonded to the 
dielectric or just folded?

Good quality RG-6 cable will have a polyfoam dielectric. Over that will be a 
foil covering. This foil will be bonded (glued) to the dielectric and 
overlapped along the seam. You can tell this because you can't peel it back if 
you strip away the outer jacket and braided shield. If it's loose or the seam 
opens, it's pure junk. Then over the top of the foil should be a shield of 98% 
coverage. This will be easy to see by eye. If you can see through the braid to 
the foil or the dielectric if there is no foil, i.e. the weaves of the braid 
are open. It's junk. After that, if it's overhead RG-6 there will be a black 
vinyl jacket and generally a single messenger wire. This is designed to 
support the weight of the cable as it hangs in the air. This is generally 
called "figure-8" cable, because of the way a cut cross-section looks. If it's 
designed for underground use, there will be no messenger, but there will be a 
sticky flooding compound between the braid and the jacket. This is designed to 
keep out water should the jacket get nicked. The jacket of direct burial cable 
is generally thicker too.

You'd be surprised at how much junk CATV cable there is out there. I always 
strip back the end of anything I'm going to buy if I don't already know the 
source and examine it visually.

Additionally, I always place a ferrite choke over the outside of the cable at 
the termination end as well as the receiver end, to choke off any common-mode 
currents on the outside of the shield.

As to quad-shield cable, the additional shielding effects of this may be offset 
by the fact that's most of it is not designed for outdoor use. Connectors are 
more difficult to install, though not by much of you have the proper tools and 
connectors.

As to connectors, what did you use on that RG-6 cable you tested with? Was 
this a standard 1/4 inch cable prep (stripped with a calibrated stripper tool) 
and the foil left intact to fit inside of the connector barrel, then the shield 
fanned out symmetrically and crimped using the approved crimping tool for the 
connector used? This varies according to the connector manufacturer.

The problem with any balanced feedline is always line-balance. Since the 
electric and magnetic field of the signals extends outside the physical area of 
the twisted pair, there will always be interaction between pairs within a CAT 
type cable. You would need far more spacing between pairs than is available in 
the CAT cable design to prevent interaction between pairs. Additionally, 
laying the cable on the ground or near to conductive surfaces will also upset 
the line-balance (for UTP cable.) And this prevents the common-mode rejection 
of signals common to both wires of the twisted pair from canceling completely. 
Shielded CAT cable is a different animal, outside effects being much less, but 
the inter-pair coupling is still an issue.

Anyway... I'm just curious about the test setup.

TIA
Rick Kunath



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