Discovered a mistake in the active mixer board, one of the inverting input was not AC grounded! It was left opened. That should be a major cause of the weird result of last test. By shunting a 10nF capacitor across the inverting input to ground, the mixer works much better. As the screen showing a 1MHz tone mixed with a 1.1MHz tone, the 100KHz product signal is clearly seen and it's much stronger and spurious products is reduced, compare to the result from last test.
RF:1MHz -20dbm
LO:1.1MHz -20dbm
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