Hi Peter, yes the non linearity of the diodes makes this VSWR
value approximate.? But for the purpose of tuning an antenna the
minimum value will be at the same tune point.? And for protecting
the finals the voltages calculated will be close enough.
And I think it's worth pointing out that the equation you give, y = ax2 +
bx? gives the power, not a voltage.? This means that the
Vswr calculation will need changing.
AIUI the mode by which the BS170s fail if the VSWR is high is by
exceeding the voltage limit; is the relevant voltage a function of
the sum of the forward and reflected voltages?? Could VFWD + VREF
be used to limit the maximum PA voltage to something that's safe??
It may need to be different for the 9V and 12V versions.
Chris, G5CTH
