Signal Processing Stack Exchange is a question and answer site for practitioners of the art and science of signal, image and video processing. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have some digital recordings of some received over-the-air CW broadcasts of known plain-text (W1AW code practice) at known WPM code speeds, but in moderate to heavy RF noise and fading.

Can I describe a S/N ratio for the Morse Code in these recordings? If so, how would I calculate this S/N ratio? What bandwidths should I use for the signal and for the noise? Should I use recordings with or without the radio receivers narrow-band CW filter enabled?

If possible, I would like to use these S/N numbers to try and plot the decoding error rates versus the S/N ratios for various "demodulators" (including both software decoders, as well as humans at different experience levels).

share|improve this question
up vote 1 down vote accepted

Personally, I'd use whatever filtering scheme the actual receiver uses. If the narrow-band CW filter is exactly this, or even close, I'd use that. Then try to automatically (or manually) determine the regions where the signal is present. Measure the average power in the "off" regions, and that will be N. Measure the average power in the "on" regions, and that will be S+N. S = S+N - N, and then take 10*log10( S / N ). This will give you S/N ratio for the bandwidth of the narrow-band filter.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.