I speculated in a recent Reddit post that some 48kHz spurs that I saw in the T41 output spectrum when using T41EEE-9 were “LO frequency related and may be addressed with calibration”. The first part of that is likely true, the second probably isn’t though I haven’t confirmed it because of the process involved with calibrating the T41 with v11.
I switched back to my T41-Vxx software where I have more control to examine things closely. I made a number of observations. First, the output spectrum with my software didn’t have the 48kHz spurs. Here is the spectrum with T41EEE-9:
The 48kHz spurs are the second most prominent component of the spectrum. Here is the spectrum with my T41_Vxx without transmit IQ calibration applied (note span difference):
The 48kHz spurs are not present or at least are driven below -75dBm.
Here it is with my T41_Vxx with transmit IQ calibration applied:
Again, no 48kHz spurs, but it has picked up 10kHz spurs. Interesting. These were the result of applying the transmit IQ calibration factors. The factors were determined before I added the BPF board but I don’t think adding the board affected the calibration (verify).
Both of the T41_Vxx versions have smaller spurs related to the T41 sample rate of 192kHz. But applying the calibration factors did not change these. I don’t have a 500kHz span image for T41EEE-9, but I assume it has 192kHz related spurs of some magnitude as well (verify).
Looking at a wider span you can see 514kHz related spurs from the power supply board 3.3V regulator switching frequency. It’s down over 60dBc but it would be nice if it wasn’t there at all.
It’s clear that we have to zoom in to see the effects of calibration. I need to use my oscilloscope for that. I’ll do that next.