The ARS Lab Introduces the Receiver Factor
Those of you with sharp eyes may have noticed something interesting in our past reviews. There is a trade off between a receiver's sensitivity and its susceptibility to intermodulation distortion. Raise a receiver's sensitivity, and its IMD performance tends to get worse. Lower the receiver's sensitivity, and its IMD performance tends to improve.

Managing this trade off is one of the more important goals of RF design. Yet, until now, none of the testing done by ARRL or ARS has focussed on the issue.

In our review of the Elecraft K-1, we are introducing a new figure of merit, called the "Receiver Factor." This concept has been tucked away in Introduction To Radio Frequency Design, by Wes Hayward, W7ZOI, but , until now, no one has been using it.

The Receiver Factor is defined as a receiver's third order IMD intercept point, minus its noise figure. Thus, it neatly deals with the sensitivity/IMD tradeoff. Furthermore, both parts of the equation are "bandwidth invariant," so we don't have the bandwidth problems that plague so many other measurements. The shorter the bar, the better the tradeoff has been managed.

Here is the table that appears in the K-1 review.

A glance at the table tells you some intriguing things. Yaesu and Elecraft have managed the tradeoff very well. The receivers using Gilbert Cell mixers (like the K-1, DSW-20, SST, and K-1), receive awful scores.

Mixed in the swarm of Gilbert Cell receivers are several that shouldn't be in the same crowd; namely, the QRP Plus, Argonaut II, and Norcal 20. In spite of using superior mixers, they have received poor scores. A strong hint of flaws in the design.