We hear often to speak on the air of VSWR  (report stationary waves voltage), but unfortunately, it seems that there is an ignorance enough great of the real meaning of its importance and what can be made to improve it. Also is  it often timely to remind some definitions and verifications of this subject.
VSWR is by definition the report of the tension maximum HF with the minimum tension the long of a line of transmission; normally this report is valid only if it is measured between a  maximum and an adjacent minimum because the most often we have affair with lines presenting losses. With these losses VSWR  changes value. When the distance from the point where the line of transmission attacks the cost (in general the antenna)  increases; the variation is always such that VSWR seems to become better (more neighbor the unit) when the point measure distances the cost.
For a line of  transmission and a cost given, nothing can be  made, have the extremity of the line leaving from the transmitter, to modify VSWR on the line; this is only by changes of the coast of the cost  (that is to say, in general of the antenna) that we can change the SWR measured to the start of the line. A fort VSWR of this departure is undesirable, mainly because it does not allow to load the transmitter correctly; more, loss HF in the line are increased notably if the former  is long and presents a substantial loss coefficient.
    A line perfectly adapted, functioning with VSWR  1/1 can be obtained only if its impedance characteristic is identical to  the impedance of the cost; most of maid lines quality have an impedance characteristic that is almost entirely resistancing to the  frequency of utilization.
A such line of impedance Zo ended by a pure resistance R will present a VSWR of  Zo/R or R/ Zo, the report ahead to be always equal or superior 1.
Most of errors commit by speaking VSWR comes from what we believe be able to realize the impossible or due to the fact that we interpret  badly the result of measures undertaken.
    For example, an antenna half - horizontal wave presents in principle an impedance of approximately 73 ohms in its center; if we attack it by a feeder 50 ohms flawless, we have inevitably to find VSWR  1,46/1, that is all simply the report 73/50.
This can drive some amateurs to try, without success, to act  on  the antenna to obtain a better  VSWR,  while  the same  antenna  attacked by a  feeder  73  ohms  will give  obviously  VSWR   1/1.  Similarly,  a VSXR  expected meter  for  50  ohms and  used  on  a  feeder  73  ohms,  perfectly adapted to its cost, will show VSWR 1,46/1 although VSWR  is really 1/1.
A lot amateurs use a "limps adaptation" or "coupler  of antenna" between the transmitter and the feeder of antenna. It is an excellent  precaution and that allows in general to obtain VSWR 1/1 measured between ltransmitter and limps it coupling. That is a good thing for the transmitter. But that does not mean that VSWR it the feeder between the coupler of antenna and the antenna itself is 1/1 : VSWR the feeder  can be modified only by an adjustment of the properly told antenna. 
     In summary, a weak VSWR is not a certain guarantee of a good radiation of the antenna and VSWR  1/1 does not entail automatically magical results ; when it is suitably interpreted, VSWR gives precious indications to the amateur, otherwise it will drive to losses of time and to vain discussions.
 
                  Bibliography : QST nov. 1971, p. 44.


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