Re: Trial to control CW power (and reduce harmonics as a result) by unbalancing the 2nd mixer #ubitx



Try a higher value for R104 like 100K preset or pot. The current the diodes need to conduct is very small IMHO.


At 09/04/2019, you wrote:
Thank you for the reply Dexter.

The strange thing is that the control voltage at the mixer swings from a virtually zero value (0.2mV DC on key up) and a full conduction value at 245mV DC on key down.

The 245mV value did not change significantly when I reduced the R105/R104 values so it seems to indicate that the mixer diodes are fully conducting on Key down as expected.

Also something I didn't mentioned before: when I disconnect the wire between T4(3,5), that is the clock #1 mixer, and R105 I get no unbalancing of the mixer and a very weak transmitted signal as expected on key-up (or key-down for that matter as it is disconnected).

So it is as if the clock #1 mixer would be much more sensitive to unbalancing than the clock #2 mixer.

Scratching my head on this one.

73, John

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