There seems to be some confusion and conflation of these two RX performance
measurement parameters in recent threads. They are NOT the same thing at all.
I'm seeing people write "IP3" (Third Order Intercept Point) when I think they
mean IMD DR3 (3rd order Intermodulation Distortion Dynamic Range - particularly
"close-spaced"), or they are not understanding the difference between between
them. For example saying that Rob's chart is sorted by "IP3", it is not,
actually Rob doesn't even list IP3!
IP3 is a USELESS measurement metric for direct sampling RX designs, and I'd
argue not a particularly useful performance metric for any RX design. Though it
is a number that the JA brands make a big deal about in their advertising, and
have for years now.
IMD DR3 - is arguably the most important RX performance metric, if not the most
important, that is why Rob sorts his chart based on that number. But also
notice that you will never see a radio with poor phase noise ("LO Noise
dBc/Hz") near the top of that ranking, because in those poor phase noise
radios, the phase noise is the key limiting factor for its performance. Direct
sampling designs excel at having low phase noise - as long as the designers
didn't botch the A to D's clock oscillator design.
Duane
N9DG
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