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Old December 24th 05, 12:38 AM posted to rec.radio.amateur.antenna
Roy Lewallen
 
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Default Standing Waves (and Impedance)

Reg Edwards wrote:
. . .
But the meter does not indicate SWR on any line. It merely indicates
whether or not the load on the transmitter is 50 ohms. Which is nice
to know. But, nevertheless, you have been fooled!
. . .

Let's not be fooled by these contrived misstatements.

An SWR meter tells us the SWR on a transmission line to which it's
connected, providing that the line and meter impedances are the same.
This can easily be verified with a couple of simple experiments. So it
does indeed indicate the SWR on a line. It will, of course, still give a
reading under other conditions, such as when the line and meter Z0 are
different or when there's no line at all, in which cases it means only
what Reg says(*). But I'm afraid that the effort to leave a legacy of a
new TLA (three letter acronym) for SWR meters is causing Reg to adopt an
increasingly distorted view of what SWR meters can and can't indicate.

(*) Any kind of test equipment can be misused or the results
misinterpreted. For example, anyone using a 1000 ohm/volt voltmeter to
read voltage in a high-impedance circuit will not see the voltage which
is there when the meter is disconnected. Likewise, measuring high
frequency waveforms with a 10 pF scope probe, even at moderate
impedances. The list is endless. But this doesn't justify renaming each
of those pieces of test equipment to accommodate the most naive user.

Roy Lewallen, W7EL


 
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