[TowerTalk] Mystery hardline

[Jim Brown]

On 11/2/2010 7:37 PM, Robert Chudek - K0RC wrote:
> Any idea of what this stuff is?   Specs?

Nope. BUT -- loss in ANY transmission line is primarily due to I squared 
R losses in the copper, both center and shield.  Dielectric loss doesn't 
begin to show up until at least UHF, and even then, R still dominates.  
SO -- measure the DC resistance of center conductor and shield, and 
compare that with DC R of other coax of similar size (see the data 
sheets).  Yes, R is increased by skin effect, but the STARTING point for 
the equation that tells you how much loss is the DCR.  The loss in your 
cable will be pretty close to the loss in cable of equivalent DCR.

There is a second factor here -- the impedance of the cable. The matched 
loss of 75 ohm cables are inherently about half that of 50 ohm cables 
for equal copper because the current is 67% of the current in 50 ohm 
cable, and power is I squared R.  THAT'S why parallel wire lines have so 
much less loss -- they have a much higher impedance, so the current is 
far less to carry the same power.

73, Jim K9YC