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AC coupling discrimination control
I have been working up something like the BandidoII in Eagle, and simulating subcircuits with LTspice. I have noticed that the Tesoro models featured on this site all use direct coupling between the TX oscillator and the discrimination control circuit.
At one extreme of the discrimination pot setting, the DC level of the oscillator output influences the duty cycle of the zero crossing detector. How can this be good?
It seems to me like an isolation cap of say, 10nF should be included in the circuit. For instance, looking at Carl's BandidoII uMAX.PDF, putting a .01 cap between the top of C2 and the left side of C9 allows the duty cycle of the output of IC5b to remain 50%, independent of the discriminate pot's setting.
I know that I'm going to make room for such a cap on my PCB (if and when I ever actually finish it).
Anyone else agree?
At one extreme of the discrimination pot setting, the DC level of the oscillator output influences the duty cycle of the zero crossing detector. How can this be good?
It seems to me like an isolation cap of say, 10nF should be included in the circuit. For instance, looking at Carl's BandidoII uMAX.PDF, putting a .01 cap between the top of C2 and the left side of C9 allows the duty cycle of the output of IC5b to remain 50%, independent of the discriminate pot's setting.
I know that I'm going to make room for such a cap on my PCB (if and when I ever actually finish it).
Anyone else agree?