I'm in the pencil-and-paper stage of building a radio receiver that has the following characteristics:
- AM shortwave/HF
- three fixed frequencies - 3.33, 7.85 and 14.67 MHz
- single upper sideband with full carrier
- BFSK modulation, varying between 2025 and 2225 Hz at 300 baud
- The bands are allocated between 170 and 700kHz of BW, which I think includes guard band
Keeping the focus of this question narrow, to only the frontend - between the antenna and the preselectors -
If feasible, it would be nice to receive all three channels at once, though I understand that that would increase cost and complexity, and the bands might interfere with each other on the board. Failing that, it would be nice to have digital switching between the above frequencies, or mechanical if that's not at all possible.
If I have an antenna tuning varicap, perhaps I could have fixed capacitors across the first and second antenna selection circuits so that it's possible for all three stations to be tuned at the same time.
If I were to build simultaneous receive sections after one wideband antenna, each with their own preselector, what would a power splitter circuit look like? How would this affect impedance matching?