I am looking for a output filter to use with a HF linear amplifier called miniPA70 which is available through several online auction sites. The circuit is available here : http://iu3idf.blogspot.com/2017/04/a-small-power-amplifier.html
I am intending to use this amplifier in 80m, 40m and 20m bands. So i need filters for these bands. Most of the filters i saw online were LPF pi-section LC filters. LC filters make sense as they don't dissipate energy. Having a LPF also makes sense as the harmonics will be having frequency as multiples of the useful amplified signal( for 40m band, i can have a LPF of 7.3MHz cutoff; and harmonics will be 14MHz, 21Mhz etc which are filtered out by LPF).
I have the following questions regarding selection of LPF -
The LPF filters out the harmonics whereas it allows the fundamental to pass unattenuated into the antenna. Where is the energy from these harmonics dissipated? (if i use a good quality inductors and capacitors, these components wont be able to dissipate much energy)
Does the energy of harmonics get reflected back to the final MOSFETs and damage them? (If it is so, i should be able to see a high VSWR between PA output and LPF input)
In practice, how much percentage of the energy contained in the harmonics with respect to the fundamental? (I think this depends on what device is used in final. But for a MOSFET, how much should i expect)
Is it a good idea to create a Band Pass filter rather than Low Pass Filter. This filter should be such that all the harmonics will be terminated at a dummy load and filtered output will go to the antenna. (Does this make the MOSFET see less reflections from filter?)