Since the modified Spectra exciter has some spurs at 463 and 1390 MHz at -40 to -50 dbc it was decided to fabricate a 5 pole combline band pass filter. The design goal was -70 db at 463 and 1390 MHz. A five pole filter was designed to give -77 at 463 and -104 at 1390 MHz. Performance plots from the network analyzer show -79 and -102 db, pretty good prediction. This filter should put all spurs from the exciter at >-120 dbc before going into the 90watt power amplifier.
Network analyzer plot
Finished band pass filter
SMA female connectors were used since the entire repeater will have them on all low level transmit and all receiver connections.
Disassembled filter. I shouldn't have used brass tubing, Copper would have been better and lower loss. Computer said 0.35 loss, actual loss was 0.46 db. Pretty close me thinks!
Another shot of the resonators
The housing was machined out of a block of Aluminum, 1 X 2 X 3.3 inches.
Tuning screws are (5) #8-32 X 1 1/4 inches. Housing screws are all #2-56 stainless pan head phillips.