The existing filter can be used to make one for either 40/30m or 30/20m.? You cannot cover
40 and 20m with the same filter as the 40M harmonics fall in or near 20M.? ?Of course
external switched filter is easy to do.
The 13.56mhz is generally used for heating and other processes allowed in the ISM band.
Those less than 100W amps are likely used as drivers for KW sized (induction heating
and sputtering).? As a result linearity is not a factor and class B or C is often the case.
Allison
