Probably I don't need any SINAD software at all. Recently I bought a two channel analogue voltmeter (see pic) rated up to 1HMHz.
For example, a receiver of sensitivity of 0.25microV at 12dB SINAD. With a 50 ohm system 0.25microV = -119dbm.
The cheap FM walkie talkie signal generator can go down all the way to -132dbm or 0.0563 microV. The following video shows the procedure how it can be done with an analogue voltmeter at 33 minutes:
https://youtu.be/C9ydYR9hlCk
The video is a bit confusing, he was actually calculating:
SINAD = 20log(S+N+D)/(N+D)