[Elecraft] [P3] Ability to copy very weak signals

[Al Lorona]

How are your 'ears'-- your ability to copy very weak CW signals?

Here's a way to "measure" your ears. You'll need your panadapter set to a narrow span such as 2 kHz. Turn on averaging so that the noise flattens out to allow you to estimate the true level of the noise. Use a full-screen vertical scale of just a few dB to make it easy to measure small signals just above the noise. 

Whatever your noise floor is, when a signal creates a 3 dB "bump" above the noise floor, that means the signal and noise are equal (because if you add two equal powers you get twice the power, which is a 3 dB bump). We call this condition a "signal-to-noise ratio of 0 dB".

Now tune around the band to find very weak signals and see how much of a bump they make. Here are some rough rules of thumb, rounded off for simplicity:

Height of bump above noise        S/N ratio

6 dB                                 5 dB
5                                    3 dB
4 dB                                                        2 dB
3.5 dB                               1 dB
3 dB                                                        0 dB
2.5 dB                                                 -1 dB
2 dB                                                     -2 dB
1.8 dB                                                 -3 dB


I listed some negative S/N ratios because I've heard of folks who can copy signals below the noise floor! That's crazy!

In any case, this is a very approximate measurement, but it's fun having some idea how well you can actually copy CW at phenomenally low levels.



Al  W6LX