[CW] Learning hints

[Fabian Kurz]

On Thu, Jan 14, 2010 at 02:43:34PM -0500, John Seney wrote:
> What is the best pitch to listen to CW?

As usual, it depends on many things.

The ear's best performance at copying Morse code at low SNRs is
somewhere around 500Hz. There are some interesting papers on this by
Peter Montnemery (SM7CMY) from the early 1990s in which this was
tested with a number of CW operators. This is mainly due to anatomic
reasons: The ear works like a filter bank; at lower frequencies these
filters have a bandwidth of about 100Hz and get wider towards higher
frequencies. Thus the effective SNR increases for a lower pitch with
the same signal energy because the noise energy over the narrower
bandwidth is lower. This is also the reason why very narrow CW filters
are rarely useful.

Using a low pitch on the radio also increases the _relative_
frequency offset between a wanted signal and a close interferrer.

The higher the speed, the closer a part of the spectrum of the keyed
CW signal comes towards very low frequencies, which creates a bumping
sound. Increasing the pitch helps to avoid this. This can also be
improved by making the keying softer, but at very high speeds the
rise- and fall-times can only be so long because the length of a dit
is only so long. A possible solution: Add harmonics to the CW signal,
e.g. by an amplifier with strong distortion. I actually prefer to hear
CW signals with a sawtooth waveform over sinus when I practice with
RufzXP or 'qrq' at very high speeds.

My radios are usually set to 600Hz pitch, fwiw.

73,
-- 
Fabian Kurz, DJ1YFK * Munich, Germany * http://fkurz.net/      .---.
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