In the comment to “HF5L Radio Club in SSB Fieldday 2018” Marek SP5IXS rightly pointed out that “third order dynamic range is a key parameter”. He also asked good questions: What is the difference between IP3 and “3rd order dynamic range”? What is the relationship between RX sensitivity and “3rd order dynamic range”?
As for the “3rd order dynamic range” I found a good definition: it is the difference in decibels between the minimum discernable signal and a signal that is off frequency that causes 1 dB of gain compression in the receiver. That is, it is conventionally assumed that decreasing the gain by 1dB is a noticeable degradation of the receiver’s properties, causing the receiver to be less sensitive to weak signals.
IP3 (hird-order intercept point) is another measure of the same feature, i.e. the receiver’s sensitivity to overdrive as a result of its non-linearity. This is defined even in Wikipedia.
But – as Sławek SP5ICS quoted – from May 2016 you may notice ARRL is no longer publishing third-order intercept point data for receivers. Technology has changed, and most modern receivers do not have a 3:1 ratio between the IMD signal level and the IMD input level. This ratio can be significantly higher or lower than 3:1. Since the IP3 figure is mathematically based on a 3:1 ratio, publication of this data would be meaningless. Instead, pay attention to the three dynamic ranges — IMD, blocking, and reciprocal mixing. The quote comes from the newest (August 22, 2018) review of receivers in QST Magazine.
Like the Sherwood Engineering ranking, the QST Magazine table is based on the value of “2 kHz 3rd-order dynamic range”, which in my opinion is a sufficient argument to consider this parameter as the main measure of the ability to receive weak stations in the presence of interferences. So let’s forget about IP3!
BTW it is curious that the differences in position and numerical values between the two rankings are significant. For QST Magazine No. 1 is FTdx5000D, No. 5 is Elecraft K3S, No. 8 is FlexRadio-6700, No. 12 is (new SDR Icom) IC-7610, No. 22 is TS-590S, No. 23 is Perseus, No. 28 is IC- 7300, and No. 40 is FT-991.