The DC receiver project is progressing slowly. Yesterday I lashed up another band pass filter,BPF,using 10mm coils from Spectrum Communications. With a bit of fiddling it worked well. The PCB design is almost done and for the first time for me the BPFs will use all SMD components to keep the size and weight down.
Looking back to the last project convinced me that there had to be a better way of band switching than using relays. A trawl of the Internet brought up a relatively simple diode switched circuit which works well. The measured isolation between on/off states is 44db on 14 MHz which corresponds to predicted results,even with such a very crude lashup on the bench. That was with 0 dbm input so I am hoping it will be a few dbs better at normal signal levels and with better layout.
The switch uses 1N4148 diodes as they are cheap,usually 1p each when you buy 100,and readily available. What was slightly disappointing was the 33mA current draw,I had expected less and need to check the Iss (saturation) current for these diodes and see if it can be reduced. But 33ma is still better than the 2 relays used before.
Next is the RF stage which needs to be as linear as possible with about 15db gain.
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