[TenTec] TUNING, MATCHING, TUNERS

[Stuart Rohre]

As much as our pure outlook cries out for something other than the term 
"your tuner TUNES your antenna", useage of that in the ARRL Handbook, 
Antenna Book and many other sources, by convention, has caused adoption of 
that useage.
Walt Maxwell uses that expression in his classic treatise:  "Reflections".

To tune something means to vary the frequency to most of us; but also 'to 
tune', has come to mean "to bring into resonance".  As Maxwell points out, 
tuning the tuner for a conjugate match at the tuner end of the transmission 
line, means the reactance of the tuner, line, and the antenna as a system; 
is brought to Zero, (or the inductive reactance and capacitive reactance at 
the tuner end is canceled), such that the circuit made by the antenna and 
its components as a system is "tuned" and thus is at resonance.  Resonance 
is the condition of zero reactance, or opposite kinds of reactance being 
equal and  thus canceling.

You have not varied the physical resonant frequency of the antenna wires, 
but the effect is as if you had when you use the tuner re the rig.

You have not changed the SWR between the antenna and the transmission line 
at the antenna end.
Dipoles at the center, in free space, or conditions simulating free space, 
will be closer to 72 ohms than 50 ohms of a coax feed, or higher Z of 
balanced wide spaced feeders.
You have brought the SWR at the rig end to 1:1 by use of the tuner.

Kurt Sterba has discussed this many times and as recently as the December 
"World Radio".

The tuner cancels the reactance that otherwise would be seen by the rig, at 
the rig end of the transmission line plus antenna 'system'.

If the antenna happens to have no reactance re the transmission line, it is 
"tuned" but that is to only one frequency and most hams like to move around 
the bands.  To easily and efficiently do the moving, without high SWR at the 
transmitter, it becomes necessary to employ the tuner which gives you the 
adjustments to cover the range of frequencies desired.  Extremes of SWR may 
cause the rig to lower its power, or create excess loss when high SWR is 
experienced in some types of transmission line such as coax.  Most balanced 
lines have much less SWR loss, thus can and do operate over a wide range of 
SWR with less loss of power due to the SWR condition being other than 1:1.

I am afraid the term "tuner tunes the antenna" is well entrenched in the 
literature and texts.

Stuart
K5KVH