[TenTec] OT SWR VS Power Loss

[Ken Brown]

>> As Jerry points out, there are some amongst us who believe that a tuner at 
>> the antenna feed point  tunes the antenna wire to resonance. It does not. 
>>     
>
> Why not? The tuner can supply the needed series capacitive reactance to
> bring the feed impedance resistive.
No. The feed point of the antenna still has the same impedance.
>  Isn't a resistive feed impedance (no
> matter what the magnitude) the definition of resonance?
If it is resistive due to equal and opposite reactances at that that 
frequency. If it is just resistive everywhere, I wouldn't call it 
resonance.
> And when that
> antenna is resonant, isn't the current in the wire maximized? Isn't
> there a possibility of greater circulating current than feedline
> current, if the antenna Q is higher.
>   
I don't know, but adding a tuner (that is not a part of the antenna) 
does not change the impedance of the antenna or the resonance of the 
antenna, even if it does change the impedance and resonance of the whole 
system.

The antenna still has the same length of wire, with the same wire 
inductance and capacitance to ground and to other parts of the antenna 
as without the tuner connected, so it still has the same feed point 
impedance. The tuner has not changed the antenna. The tuner may increase 
power delivered to the antenna, by increasing the efficiency of the 
power transfer from the feedline to the antenna. Once the power gets to 
the antenna, the antenna does exactly the same with that power (radiates 
some, reflects some at a particular phase angle, turns some into heat) 
as it did without the tuner there. The antenna has not been tuned. It 
still has the same feed point impedance.
>> Consider a wire longer than a halfwave length with, say, a feedpoint 
>> impedance of 120 ohms instead of the 70 ohms exhibited by a resonant dipole. 
>> The tuner does not change the impedance of 120 ohms to 70 ohms which it 
>> would have to do in order bring the wire to resonance. What the tuner does 
>> do is transform the 120 ohm antenna impedance to the characteristic 
>> impedance of the feedline.
>>     
>
> Then the second duty of the tuner is to transform the resistive feed
> point impedance to that desired by the transmitter and feed line.
>   
Unless you are hoping for some harmonic rejection or other bandpass 
filtering action from the tuner, transforming the impedance is the first 
and only duty of the tuner.
>   
> Because the tuner supplies the reactance needed to make the antenna
> resistive and therefore resonant.
>   
No! The antenna still has the same physical dimensions, and RF applied 
to the feed point of the antenna still travels through the conductors in 
the antenna, affected by capacitance of nearby objects, the inductance 
of the antenna conductors, and reflected from the ends of the conductors 
the same way it does without the tuner in the line. The antenna is not 
resonated by the tuner, although the system as a whole may be.

N6KB