[Elecraft] resitance vs impedence

[Vic Rosenthal]

Ken H wrote:

> While setting up a dipole antenna tonight a question come up while discussing
> the tuning with myself:  Which is the "most effective" antenna -
> understanding it will be matched with a antenna tuner, either the internal
> autotuner or an external manual tuner - a dipole type antenna with a
> resistance of R=6 ohms and impedance of X=16, or the same dipole type antenna
> with R=48 and X=146?  Both of these settings have the same SWR=6.5
> 
> I guess that same question would apply to a short vertical, or end fed zepp
> type antenna.

The efficiency of the antenna is defined as 100 * Rr / Rl where Rr is the 
radiation resistance and Rl is the resistance (at RF) of the conductors making 
up the antenna.  Assuming the antennas you describe have the same or similar 
conductor resistance, then, the one with the higher radiation resistance will be 
more efficient.  Of course, tuner losses also come into the picture.  In your 
example the reactance is inductive, and that is easy to cancel out with a 
capacitor.  If there was a lot of capacitive reactance that had to be canceled 
by an inductance, you might have more tuner losses.

In the case of a non-ground-independent vertical, the equivalent resistance of 
the ground path is also in the circuit, and this can make a big difference in 
efficiency.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco