This is pretty strange.

Suppose Reg has a 50 ohm line of some length connected to an antenna
whose impedance is 100 + j0 ohms. After putting away his evening's
bottle of wine, he climbs the tower and inserts a 50 ohm SWR meter at
the antenna. He climbs back down, gets out his vintage brass telescope
and keys the transmitter. Then, steadying himself, he peers through the
telescope and sees that the SWR meter reads 2:1. (Being a clever person,
he mounted the meter upside down so it would be right side up in the
telescope, obviating the need for the added challenge of mental inversion.)

I have an identical antenna, feedline, and SWR meter. I sit in my warm
shack sipping my moonshine, connect the SWR meter to the input end of
the line, hit the key, and note that the meter reads 2:1. Or perhaps
slightly less if the line is noticeably lossy.

Reg says:

Placing the SWR meter at the start of the feed-line terminated by the
antenna, will tell you NOTHING about the SWR on that line.

I guess the 2:1 reading from the meter at the input end of the line is
telling Reg nothing, while the 2:1 reading at the antenna is. Strange.
The fact is that it's the SWR on the line, and it can be measured at any
point along the line. I like my method better, but each to his own.

Roy Lewallen, W7EL

Reg Edwards wrote:
Roy, you surprise me. Try a jug of Moonshine.

Placing the SWR meter at the start of the feed-line terminated by the
antenna, will tell you NOTHING about the SWR on that line.

It is the antenna input impedance which determines the SWR on the
line, and the meter doesn't have the foggiest idea what THAT is.

The unknown antenna impedance is at the other end of a line of unknown
length, unknown impedance and unknown loss. Unknown, that is, to the
meter.

YOU might have that knowledge. But then you can CALCULATE what the SWR
is on the line. Meter readings having been discarded as useless.

I repeat - the meter tells you only whether or not the transmitter is
loaded with a resistive 50 ohms. No more and no less. If it is not
50 ohms the ambiguous meter will not even tell you the actual value of
Z.

Intoxicated or not, if you insist on a meter reading, there is no
alternative to climbing the antenna mast.
----
Reg, G4FGQ.

PS. The use of SWR by American plug and socket manufacturers to
describe unrelated characteristics of their products is a small
indication of the abysmal depths to which engineering has descended.
Technical specifications are reduced to Camm's Comics. But they look
good to the uninitiated.
----
Reg.
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