[TowerTalk] Dipole fed with balanced line?

[Ken]

Steve,

The issue is not about I^2R losses and feedline cannot compensate for missing antenna wire.   It's the antenna wire that radiates, not a properly balanced feedline.

How do you "increase the feedpoint current...by 19%" other than by increasing power?   BTW, increasing the feedpoint current by 19% is a 40+% increase in power (P=I^2*R).  That's a significant increase, not "only a fraction of a db". 

If the solution was that simple, we could have efficient "limited space" antennas by putting a 600 ohm resistor at the end of an open wire feedline and not need the antenna at all!   ;-)

73, Ken
WA8JXM

On Jan 17, 2012, at 7:07 AM, Steve Hunt wrote:

> Ken,
> 
> EZNEC predicts that a 100ft dipole used on 80m is only a fraction of a 
> dB less efficient than a full half-wave; the feedpoint current only has 
> to increase by about 19% to "compensate for the missing 32ft", so the 
> I^2R losses don't increase much. Its feedpoint impedance is of course 
> quite reactive, but not enough to cause significant further losses in 
> the feed and matching systems.
> 
> A good "rule of thumb" is not to go shorter than 3/8 wavelength - much 
> shorter and losses in the feed/matching systems begin to rise quickly. 
> That equates to 100ft on 80m, 50ft on 40m, 25ft on 20m etc.
> 
> 73,
> Steve G3TXQ