Topband: Flooded CATV cables for TX

[Jim Brown]

On Tue, 24 Feb 2009 09:24:58 +0100, Lennart M wrote:

>Like many of you I have been using "outdoor drop cable" for RX 
>antennas without any problems.

I have no experience with using cable like this for transmitting, 
however I'll offer some thoughts. 

1) You didn't say what frequency or transmit power you are 
thinking about.  Let's assume 160M, since that's the reflector 
we're using.

2) Look at the resistance (at RF) of the two conductors, and 
compare it with coax that IS commonly used for transmission. The 
drop cable I see here in the US has copper clad steel (CCS) as a 
center conductor and aluminum foil with braid for shield. 

3) To get a handle on resistance, look at DC resistance, AND look 
at graphs of attenuation versus frequency. If you can't find those 
data for the cable you have, look at that data for cables of 
similar construction. CCS is used in some Belden RG59s, and their 
data shows that skin effect hasn't really kicked in much below 5 
MHz, so much of the current at 1.8 MHz will be in the steel. 

4) Try putting connectors on it and running some power into a 
dummy load. Measure power at both ends. Feel the cable after 
you've been heating it for a while.  

My guess is that the cable will work just fine at moderable power 
(100 watts) but may not work at 1kW. On the other hand, I've used 
Belden RG59 at 1.4 kW on 1.8 - 7 MHz with dipoles under contest 
conditions (lots of transmitting) with no problems. I had good 
Amphenol PL259s on it, but SWR was far from flat over the entire 
band.

73,

Jim K9YC