Over on YouTube channel Rate My Radio has uploaded a set of three videos showing how to use an SDRplay RSP2 as a low cost spectrum analyzer to measure the inter modulation distortion (IMD) performance of lower end hardware TX capable radios. The test can only be performed on radios that have IMD performance less than that of the RSP2, so very high end amateur radios cannot be tested.
The process is to use audacity to play two audio tones into the transmitting radio under test, and then the SDRplay is used to receive the output. On the SDRuno software you're then able to see the third order and higher IMD products. Later he also performs white noise IMD tests as well. Below is the video description:
We cover 2 Tone Testing, White Noise Testing, and how the later can be particularly useful in terms of station monitoring. Naturally, we show the effects of 'all knobs to the right' :)
Jarrad also covers how with just an SDR Play and a 'rubber ducky' antenna, station performance can be monitored in real time.
Why would a Ham want to do this? The answer is simple: To defend their station performance against that on air Expert, who got their ticket when you needed to send CW at 50WPN, who served in the military radio unit for 20 years, has 3 engineering degrees and worked as a professor at both MIT and Havard, not to mention the times they lectured at Cambridge & Oxford.
With an SDR Play and a bit of simple math, any OM can put such experts in their place.