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On Sun, Jun 27, 2021 at 01:59 PM, Evan Hand wrote:

If this is the case, then working out a way to get a better square wave out of the Si5351 would help.

When people were trying to figure out the original uBITX spur issues the idea of adding buffers, like digital hex inverters was suggested. As both the absolute level of drive as well as the asymmetry of the output impedance of the Si5351 were discussed as possible issues. The final answer to those spurs turned out to be other issues.?Still buffers may be worth trying.

Although it would not individually match each of the four diodes, could a simple center tapped pot between the legs of one of the ports, to allow a simple null adjustment be good enough to get the carrier suppression down to a acceptable level.?

As a hack, could a small adjustable DC offset voltage to the diodes possibility be able to counter the unbalance?

As the mixers are reasonably matched already by using the matched diode pairs, the amount of tweaking of the mixers needed, may be small enough that something simple like these could work.?

Tom, wb6b