[TowerTalk] SWR is what SWR meter measures

[Bill Coleman]

On May 12, 2005, at 7:00 PM, Jim Lux wrote:

> With a 2:1 mismatch at the far end the return loss is 10 dB. This is
> another way of saying that for every 1000 watts you send to the  
> antenna,
> 100 watts is reflected back towards the transmitter.  The radiated  
> power is
> reduced from 1000W to 900W (about 0.5 dB decrease)

But what happens to that 100W? It isn't dissipated at transmitter.  
Most of it is reflected back down the transmission line. And then 10%  
is reflected back. And so, back and forth it goes until all the  
energy ends up in the antenna.

It isn't the SWR can reduces the energy feeding the antenna. If we  
assume a lossless transmission line as above (you indicated that all  
1000 watts from the transmitter reached the antenna), then SWR  
doesn't matter.

Of course, transmission lines are anything but lossless. The initial  
trip to the antenna incurs some loss, each reflective trip incurs more.

The key to efficient antenna operation is eliminating loss, not  
lowering SWR. (Although, in some cases, lowering SWR can eliminate loss)

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901