Amateur Extra: Minimum Discernable Signal

The Amateur Extra torture question of the week is taken from sub-element 4 (amateur practices) section C (receiver performance) [E4C07]

What does the MDS of a receiver represent?

A. The meter display sensitivity
B. The minimum discernible signal
C. The multiplex distortion stability
D. The maximum detectable spectrum

If you stop to think about the possible answers, as they relate to radio receivers, options C and D don’t look very good.  They actually look sort of like gibberish.  Let’s get rid of those.

Option A, Meter Display Sensitivity, sounds like a plausible answer.  But its wrong.  The correct answer is B. The minimum discernible signal, or minimum detectable signal

But what is MDS, anyway?

It’s the lowest power signal your receiver can be received by the input, and then turned into any sort of useful information.  Basically the smallest signal that would be audible (or visible) over background noise.

The actual value of MDS is dependent on a few factors, including bandwidth and temperature.  Theoretically, the lower you can get the temperature of your receiver, the weaker the signal you should be able to detect.

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