[Amps] High SWR

[Scott McGrath <mcgrath@fas.harvard.edu>]

SWR is an obsession with the CB set and some others CB's could not 
tolerate a high SWR due to the cheap finals used the high RF voltages 
would blow the junction.     This effect created the oral tradition of 
1:1 SWR == Antenna System Goodness (tm).   It's hard to counteract what 
'everybody' knows.

In reality and especially with a tube amplifier and a Pi output tank the 
antenna system can be brought into resonance at a wide range of 
impedances and resonance is what we are looking for and it really is 
Antenna System Goodness in MOST cases.    As the reflected power is 
definitely real but it is best expressed as the reactive power in a 
system which effectively is lost.   With ladder line if long enough will 
re-radiate some of this 'lost' power.

Short answer is the only thing SWR is good for is determining at what 
point the RF voltages induced by the mismatch will damage your 
transmitter system.    This is why modern rigs fold back transmitter 
power when excessive SWR is detected,  This keeps the voltage developed 
at a low enough  level to prevent damaging the finals.

- Scott N1JIN
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