[TowerTalk] CATV Hardline

[Pat Barthelow]

Hello Tom,

That stuff is getting harder to find.  Used to be CATV companies locally  
gave free reign to hams locally to pick through the piles of spool ends; Now 
local CATV Comapnies often say no to hams, and let metals recyclers get the 
ends.  Great, Extremely low loss stuff, the 75 ohms impedance can be dealt 
with in various ways,  (or even ignored iin a lot of cases)

Your thought of splicing probably should be improved, so as to not produce 
large impedance disturbances on the line, especially if using in the VHF/UHF 
or higher frequencies.

I have a collection of old  EME (moonbounce) Engineering newsletters from 
Eimac that shows a lot of examples of large VHF and UHF arrays that were 
homebrewed, and needed  to work well for Moonbounce.  Was surpised to see 
one example using a junction of 75 ohm CATV feeders  simply strapped  all 
the shields togiether with hose clamps,  with the center conductors simply 
extended 3" or so straignt  outside the jackets, and strapped together, 
soldered,  with bare wire.... no impedance matching considerations at all, 
on a VHF EME antenna!

If your cable  is .75" cable, splice connectors are very easy to make, using 
a double female UHF connector, a hack saw, hose clamps, and sealing tape.  
The barrel connector center contacts accept the .750 cable center with a 
snug fit, and the OD of the barrel is a slightly loose internal fit to the 
cable jacket.  You remove (dig out  with Needle nosed pliers)  the foamed 
dielectric about 1.5 inches in on the cable ends and push fit the cable 
into/onto  the barrel after hacksawing several slots parallel to,   and 
symmetrically  around,  the cable jacket  centerline.   The saw kerfs allows 
the ID of the jacket to slightly decrease, and a  snug fit to the barrel 
when clamped.   Use dielectric grease between the barrel, and the inside of 
the aluminum jacket, and tighten the jacket, using small hose clamps.  Seal 
the whole thing really, really,  well with electrical tape, coax seal, 
etc...
As I recall, on middle HF freqs the stuff has less than .1 db per hundred 
feet loss.
The jacket kinks with permanent deformations easily if you or someone before 
you bent the cable
into too small of a radius.  Be careful to avoid this..

73, DX, de Pat AA6EG aa6eg at hotmail.com;
                  Skype:  Sparky599

>From: "Tom Hellem" <tomhellem at czo.net>
>To: "Towertalk submit" <towertalk at contesting.com>
>Subject: [TowerTalk] CATV Hardline
>Date: Thu, 14 Sep 2006 20:41:30 -0500

>
>I have three spool ends of 3/4" CATV hardline, the stuff with the rigid
>aluminum jacket. It was lying in a field for probably upwards of 10 years.
>When you look at the open end, the dielectric appears to be somewhat
>deteriorated, but cutting off 6 inches or so reveals what looks to me like
>it's in good shape. I am contemplating using the stuff for a 300 foot run
>out to my tower, underground. It will need to be spliced a couple times,
>which I would accomplish by briging the cable ends up above ground, 
>twisting
>and soldering the center conductor together and bond the outer jacket, all
>in some sort of weatherproof junction box.
>Does this sound like it could work, or am I just asking for trouble? Is
>there a way to test the stuff? Could it be contaminated and unuseable while
>still appearing to be in good condition?
>Any input would be appreciated.
>
>Tom Hellem K0SN
>Porterfield, WI