HackRF - Spectral purity

An important thing to be aware of when using a wideband SDR like the HackRF or something like the Ettus E100 is RF spectral purity. How clean or dirty is the signal coming out of the SDR?

If you are running 30mW into an inefficient radiator or a dummy load for tests around the shack it probably doesn't matter a lot but as soon as you attach a decent antenna or amplifiers you'd better be sure you aren't stomping on parts of the spectrum you should'nt be.

Ettus E100 TX on 250MHz

I ran some basic tests on my HackRf recently using VK1XT's Rigol spectrum analyser, even out of the box it is pretty clean, I'd suggest it's probably better than the typical Baofeng (or similar) cheap eBay handheld and it is certainly cleaner than the much more expensive E100 I have used before. You can see the 1st harmonic at 500MHz is about -10dBc and the 3rd perhaps -22dBc on the E100.

HackRF on 2M

Transmitting on 144MHz on the HackRF you can see from the image that the 1st harmonic is about -35dBc and the 3rd is at -32dBc. (more to come).....