[G0HZU_JMR]

Yes, second and third order distortion terms tend to dominate real-world performance.

Most lab spectrum analysers will manage a mixer input IP3 of about +20dBm with 10dB input attenuation. A really good one might manage +30dBm. The noise floor might be -100dBm with a 10kHz RBW and 10dB front end attenuation.

The SFDR would then be 0.666*(20 - -100) = 80dB.

The second harmonic intercept might be +60dBm with 10dB input attenuation. The SFDR here would therefore be about 0.5*(60 - -100) = 80dB.

These were the classic benchmark numbers used at work for a decent spectrum analyser. The 1500MHz HP 8568B analyser has similar specs to this.