29-06-2012, 01:18 PM
Hmm. In my idea as published above, I see that I overlooked the obvious requirement to make the L.O. freq. variable! Such is the unwanted by-product of thinking too hard about a given problem and getting too enthusiastic about it! 
Anyway, the fix seems obvious: replace the 1 MHz xtal osc. with a high-stability L/C tuned oscillator.
Having said all that and after much thought, in order to produce the L.O. signals that you require for the received signal freq. range you want and using a minimum of components to do that, I have now reached the conclusion that, in effect, a wide-range signal generator, incorporated into the receiver design, is the only way forward: three tuning controls: L.O. range switch; L.O. freq.; R.F. tuning.
Al.
Anyway, the fix seems obvious: replace the 1 MHz xtal osc. with a high-stability L/C tuned oscillator.Having said all that and after much thought, in order to produce the L.O. signals that you require for the received signal freq. range you want and using a minimum of components to do that, I have now reached the conclusion that, in effect, a wide-range signal generator, incorporated into the receiver design, is the only way forward: three tuning controls: L.O. range switch; L.O. freq.; R.F. tuning.
Al.
