LPF diplexer filter 300W SSB/CW HF power amplifier (low pass filter)
Transistor amps are inherently rich in harmonics. This is because of the non-linear junction that all transistors have. This design passes the lower desired signal to the antenna port using a low-pass filter, and sends the higher frequency by-products via a high-pass filter into a termination.
The diplexer consists of 6 relay-switched units and covers 1.8 to 30 MHz amateur radio bands. It has 1 input port and 6 antenna outputs, so no additional ant-switch is needed. Outputs can be connected in parallel for multiband antenna (say 10-15-20 meters tribander)
The cores are T68 and T50 by Micrometals, relays are 16 Amps HJR1-2CL 12 VDC, capacitors are MuRata GRM42A SMD high voltage 3.15 KV and several mica units on 160 meters HPF, connected in parallel to meet the hi-power requirements. The load is 12pcs 2W each resistors. FR4 double-sided PCB size 160 x 132 mm.
The filters are carefully tuned on each band to get the SWR as low as 1.2:1 .