How to measure the performance of the HF receiver?

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.

Mirek SP5GNI

One Comment

  • If the radios were to be compared according to one parameter, the “3rd order dynamic range” seems to be the most appropriate. However, if we expand by other parameters with correspondingly smaller weights to the ranking, it is also important to have a “3rd order dynamic range” for the signal not by 2 kHz, but closer, i.e. in the filter band. Here the impact on the measured parameter will have further parts of the signal path also affecting the listening comfort, not only the “front end”. It also seems sensible to return to the receiver’s sensitivity measurement but not for the signal+noise/noise ratio of 10 dB as it is usually done. Already in the seventies Racal, then the leader in the quality of professional receivers, measured the ratio s+n/n for the signal received 1 microvolt. Such a measurement spoke very much as comfortably, without noise, listens in normal conditions (not in contests), for example in distant seas on ships. Such a measurement pushed down the ranking of the so-called “noise-dynes”. Radio Racal RA 17 from the 1960s had an incredible value for CW – 21 dB.
    SP4FR

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