Good-day Tom & others:
A suggestion has been made: Harmonics found in the LO signal will mix with 'out of band signals' to create spurs. An obvious example would be:
Signal - 3x LO -> IF frequency.
10.000 - 3x 3.2 -> 400kHz
Since the BC-453 has an accurate dial and a 10MHz signal is easily found a test rig can easily demonstrate the proposal above. The desired 80m signal would be at 3600 kHz.
I propose to build this circuit using a 2n3819 + some sort of binary divider. I'm thinking a 4027 JK FF. Alternately, other frequencies might be tested:
1512(kHz) - 3x 400 -> 312(kHz)
This is a conveniently done here at my QTH. ABC Radio National broadcasts on 1512 locally. Other nearby stations (both weak and strong) will provide more test signals.
Once this has been done, I can test Wayne's suggestion of feeding a sine-wave to the mixer at the frequencies listed above.
Leslie