Soon after the original tinySA was offered, I made a video showing how to make an MDS measurement of a receiver by using the tinySA in 'Signal Generator' mode. But with the tinySA's minimum output being -76dBm (almost S9), a lot of external attenuation was required to get the signal within range of typical MDS values.
The new tinySA ULTRA has a minimum output of -123dBm, making it much easier and less expensive to make the same test. And with less clutter since less external attenuation is needed - actually, none, other than the step attenuator you'll need anyway.
You can see the original video here.
A former co-worker of mine verified the output level accuracy of my tinySA ULTRA with an HP power meter and found it to be within 1dB of its indicated value on HF down to -100dBm. After that, inaccuracy increases to 3dB at -123dBm.
So, with the output set to -100dBm, and a 0-62dB step attenuator, I did a quick by-ear comparison of my new Index Labs QRP+ to my IC-705.
This is an easy, inexpensive and quick way to verify a receiver's sensitivity as you may wish to do after a kit build, an alignment or an eBay purchase.
A good step attenuator is required - not one of the plasticky toys being offered. I use a HecKits attenuator and highly recommend it as an excellent one to own.