Here's a question and a comment for Phil, Alex, Tony, et al--
In the SoftRock40 the transformer provides both non-inverted and inverted RF to the switches. The outputs of the FFs are gated so that the switches are operated only over one quarter cycle each (90 degrees). /Why not operate the four switches as two SPDT switches and eliminate the gating of the two FF outputs?/ This would provide two "full wave rectified" outputs, instead of two "half wave rectified" outputs, and therefore a 6dB gain improvement. I use such an arrangement in my "PC-Less" PSK31 interface to generate my I and Q outputs.
I'm also puzzled at the use of the inverting inputs of the audio amplifiers. Since these are very low impedance points in the circuit, the drive to the amplifiers is essentially a current. However, the level of the current is very dependent on the total resistance/impedance in the circuit. In this case, it is the sum of the two 10 ohm resistors, plus the on-resistance of the switch, plus the transformed source impedance. I haven't looked at the specs for the switch, but if there is much variation in on-resistance between the individual switches, it could contribute to gain inbalance between the channels. Is the intention of this to give a good impedance match to the 50 ohm source?
Regards,
Milt, W8NUE
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