(tr)uSDX uses less common techniques for generation of an SSB telephony signal at modest power (a few watts).
There are aspects of the techniques that might raise questions as to how well they work, questions that do not seem to be addressed by the developers.
Wide signal / distortion reports
Whilst there are lots of videos where users demonstrate making QSOs with the (tr)uSDX, credible evaluation of common reports of wide transmit bandwidth is scarce, though spectrum displays of excessively wide (tr)uSDX signals on air are not so rare.
One simple objective measure of IMD is that of a two tone test with spectrum analysis.
Two tone test with spectrum analysis
A two tone test calls for combining two equal amplitude non-harmonically related pure sine waves and feeding that to the transmitter input, and observing the spectral distribution on a Spectrum Analyser.
Ideally, the output should be just the two input components frequency shifted by the virtual carrier frequency (in the case of USB). Practical transmitters are not perfect, so there will also distortion products, and a common measure is that of the 3rd order mix at If F1 and F2 are the frequencies of the two tones (at RF), the third-order distortion products occur on both sides of these tones at 2F2 – F1 and 2F1 – F2.
Above is a figure from an Anritsu application note showing a wider scope of IMD. Distortion products are measured wrt to each of the desired signals or ‘carriers’, and this value is often given relative to those signals as dBc. (The ARRL uses a different method, referenced to two tone PEP.) Continue reading (tr)uSDX IMD performance