@ blackberryer
I cannot see the image unfortunately.? 30MHz is likely to come from the oscillator traces.? Any oscillator tracks routed near the modules or RF signal lines?? Maybe some decoupling caps or series resistor could reduce the harmonics from the clock.? Another possibility could be to add a simple High Pass filter to the high range input.
I am struggling a little to understand what you have written.? I think you are suggesting a method to see 800Mhz signals using the mixer and IF filters.
The IF SAW filter frequencies are fixed and quite narrow, so the signal into the detecting SI4432 needs to be in the range of the IF filter passband, around 433.9MHz.? Of course different SAW filters could be used with different passband frequency.? SAW filters are bandpass filters.
A 130MHz SAW filter is of no use as the SI4432 only receives in the range 240-930MHz.
If the LPF is bypassed then you could mix a LO of (800-433.9 = 366.1MHz) with the 800MHz, however then a signal at 433.9-366.1 = 67.8MHz would be detected and possibly give odd results.? This might be OK so long as the user understood that this could happen.
You could possibly switch in a high pass filter (or bandpass filter) when looking at frequencies above the IF frequency, but there would be a range of frequencies around the IF frequency that would not be usable (say 350-500MHz).? The low pass filter or high pass filters could be external to keep things simple.
For most amateur radio applications having reasonable results in the 1-350MHz region is more useful than 500-800MHz, also the gap between ranges is not helpful, hence the design is optimised for the lower frequencies.
Good luck
Dave
