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Checking old CQ-magazines a while ago I found an article from Bill Orr W6SAI in the June 1993 issue which described results of experiments which I myself had stumbled on by accident, rigging antennas for HF while away from home.
'A casual listener to the amateur bands hears a lot of talk about SWR measurements, and there are plenty of SWR graphs in magazine antenna articles extolling the SWR performance of a particular antenna. In addition, many modern rigs have a built-in SWR meter. And if you read the adds in the amateur magazines, you will see a plentiful supply of SWR meters on which to spend your money. You might get the idea that the SWR meter is an indispensable piece of gear and a vital addition to the shack.
The SWR meter environment
As we have learned in earlier days the SWR meter actually measures the SWR of the antenna system as a whole, not just the antenna itself. That is to say, and SWR reading in the shack is revealing the SWR on the feedline at the end of the line. The reading is a function of the feedpoint impedance of the antenna, the line loss, impedance 'bumps' in the line caused by mechanical joints, and any spurious RF coupling between the field of the antenna and the shield oif the coax line. Thus, the SWR reading at the shack may or may not bear a resemblance to the actual SWR measuremed at the antenna feedpoint.
So what? Why should a high value of SWR upset the experimenter? Many amateurs spend hours diddling with their antennas to reduce the SWR from say 1:7 down to 1:2 and then work harder to get the SWR down to 1:1 or less. Does all this effort make their signal louder, or does it make them more capable of hearing weaker signals? Hardly. In most cases, such an exercise is a waste of time!
(cont. page 5)
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