By memory I think you will find the mixer is a CA3028 transistor array or similar. Look in any 1970s? American? radio constructor books for details of these chips, they were used often before the days of LSI.? Three transistors, long tail differential pair in a round case with 7 legs
Basically, the oscillator into the? base of the long tail, signal into one base of the differential pair. The two products are available at the output. The LPF will remove the high product 3.455 +2.455? to? 3.455 + 3.455 = 5910 to 6910, leaving the low product 3.455 - 2.455 to 3.455 - 3.455 = 1 to 0 megs, this product passes to the counter module. This is a very elegant way to do this, as it also automatically reverses the count.....? the FRG7 actually tunes backwards. The second IF is below the first IF, and the first IF is above the signal frequency, that is the basis of drift cancelling...... both first and second signal mixers using? the same VFO....?
