I built the mixer in figure A in 1992 and put it away. I blew the dust off it and tested it today. It seems to work just fine. I set it up for experimenting as in figure B and took measurements.
For the rf voltage I used a signal generator with a sine wave at 0.8 Vpp.
For the lo voltage I used a function generator with sine wave at 0.8 Vpp.
I watched the voltage at the output of the IF strip, which was tuned to 455kHz.
Holding rf at 150 kHz I got good strong 455 kHz sine waves at the output with the LO at 305 kHz and at 605 kHz, as expected. So I know the mixer is good.
But, I tried to modulate a 455 kHz sine wave with a 1 kHz sine wave, expecting output as per figure C. What I got was a nondescript mess. I tried varying the amplitudes of the rf and LO signals, but just got more garbage.
Question: Is this the wrong kind of mixer for modulating audio onto rf?
For the rf voltage I used a signal generator with a sine wave at 0.8 Vpp.
For the lo voltage I used a function generator with sine wave at 0.8 Vpp.
I watched the voltage at the output of the IF strip, which was tuned to 455kHz.
Holding rf at 150 kHz I got good strong 455 kHz sine waves at the output with the LO at 305 kHz and at 605 kHz, as expected. So I know the mixer is good.
But, I tried to modulate a 455 kHz sine wave with a 1 kHz sine wave, expecting output as per figure C. What I got was a nondescript mess. I tried varying the amplitudes of the rf and LO signals, but just got more garbage.
Question: Is this the wrong kind of mixer for modulating audio onto rf?
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