Further to my observation about the Pluto spurious, and in the light of the ongoing discussion, here is the output from the spectrum analyser. These were made at 2.2GHz but I had the same results at 144MHz. There are two taken with SDRC driving the Pluto, one at about 0dBm output and the other at -20dBm output using the tune facility. I checked in all other transmission modes, and with the mic input with the same results. The other two were taken with Pluto driven by SDRAngel at 0dBm and -20dBm. I changed the ref level of the analyser between the different levels. The Pluto was connected directly to the analyser input. The highest level spurs are at around +-1.08MHz.
The Pluto is unmodified, rev B with 0.31 firmware installed. I bought it about a year ago to use with Satsagen to give me a spectrum analyser above the 2.2GHz of my Anritsu.
These measurements are very similar to those made by Rolf DJ7TH, but obviously rather different to those made by others. I cannot reproduce the effect described by Sigi where at lower output the spurs reduce to about -60dBc. I don’t doubt what others are seeing but this is what I see. It is hard to see that this effect is an intrinsic Pluto hardware problem as with SDRAngel and Satsagen the transmission output seem clean. All a bit mysterious really.
