[Elecraft] OCF antennas

[Jim Brown]

On 3/10/2012 5:14 PM, Hisashi T Fujinaka wrote:
> I think the advantage (not magic) is that you get less loss in ladder
> line than you do through the dielectric of coax.

FALSE!  For all practical purposes, there is NO dielectric loss in coax 
below about 500 MHz, where it just BEGINS to show up. Virtually all the 
loss in any dry transmission line at HF and VHF is due to simple Ohm's 
Law in the copper (including the increase in resistance due to skin 
effect). It's all I squared R loss.

The advantage of open wire line is solely the result of their higher 
IMPEDANCE, which means that for a given power level, the CURRENT is much 
less.  For the same reason, 75 ohm coax has a bit less loss than 50 ohm 
coax for the same conductor size.  So-called WINDOW line loses this 
advantage when it gets wet, because then it DOES have dielectric loss.

BTW -- when you're analyzing these things, you must consider the heat 
produced in a common mode choke when the antenna has a lot of imbalance. 
An off-center fed antenna has a LOT of imbalance.

73, Jim Brown K9YC