So What is Happening?

You smell a burnt resistor, you see a discolored resistor and you see no voltage on the other side of the resistor. You conclude it is a defective (smoked) resistor. But that is just one part of the issue and next question follows the "WHY" is it toast.

Our burnt resistor is an easy problem to define as we have sensory tests to tell us exactly its condition: smelly, discolored and open. The Transmit issue with the MHST is similar but different in that it appears only on transmit, can be heard 300 miles away and is consistently linked to the actual desired transmit signal. 

I think back to the early 1960's SBE-33 SSB Transceiver that had a receive "birdie" just above the high end of the 40M Band. The SBE Engineers never did fix it but instead highlighted its usefulness in determining the dial calibration. Quote: "If you hear this signal at the specified location, then your dial calibration was right on." We can't use that logic or excuse with the MHST.

Yesterday I diddled with the VWS code for the Arduino Sketch so that the Quadrature Outputs are on CLK0 and CLK2 versus CLK0 and CLK1. Long ago there were issues with using CLK0 and CLK1. There seemed to be a shift to using CLK0 and CLK2 for LO and BFO. Here is a link to a quadrature application issue using CLK0 and CLK1 -- you decide, but I decided to change to CLK0 and CLK2. See below.

CLK0 and CLK2 ~ 90 Degree Phase Shift

The change improved the situation but did not resolve the problem. I do consider this a positive change. The photo was taken at the output side of the Si5351 while connected to 10K trim pots which are in line before application to the ADE-1's using the center wiper as the feed point. This lets you fine tune the LO signal inputs to the ADE-1's so that they are balanced.

If I were smart enough and had extensive software skills, my next step would be to use a different code approach so that the Pi Pico would follow the QUISK directives but generate a single LO at 4X and then rely on a 74AC4 to provide the quadrature output at 1X. That works with the Soft Rock Transceivers and works on my other SDR without having the funky signal to ride along.

We must be thankful for such problems as it keeps us out of the bars and from getting into all sorts of other trouble.

Them that know can make it go.

73's

Pete N6QW