[Elecraft] HRD cw copy

[Sverre Holm]

It is interesting to see the responses to my statement on the difficulty 
of machines copying CW better than humans. Although this is a little 
off-topic here, I hope we can have a short discussion of it anyway.

First, the success of negative SNR communications methods such as 
Olivia,JT65, and PSK31, are evidence that a well-designed computer 
algorithm should perform better than a human. But it is on codes that 
have been designed for machine decoding.

Second, 'better' may mean many things: faster, many QSOs in parallel, or 
- what I imply - at lower SNR and under difficult conditions with fading 
and interference. There is no doubt that a computer has much more 
capacity for speed and parallel decoding than a human.

The steps that a good algorithm needs to do are something like this:
- real-time frequency analysis and filtering
- detect morse signal and lock on to a particular frequency
- adaptive estimation of datarate and adaptive matched filtering for 
optimal detection
- decoding of dashes/dots/spaces into letters
- decoding into words

The first steps are signal processing such as filtering, detection and 
adaptivity. See e.g. 
http://www.journal.au.edu/ijcim/jan99/ijcim_ar1.html for some ideas on 
the adaptive estimation. As a side remark, Coherent CW, was a way of 
avoiding the adaptation to variable rate and ease machine decoding, but 
it does not seem to be a success.

I believe that it takes an extraordinary algorithm to lock onto a very 
weak signal reliably, but even more so to do the last and maybe even the 
second last step, and that this is where the similarity with speech 
recognition is largest. As an example, say that my call is a weak 
DX-call and I'm sending CQ de LA3ZA LA3ZA LA3ZA. On the receiver end you 
hear DA---, LA3-T, L-3ZA due to fading and interference. This is where a 
good operator is able to use a priori information on the syntax of a 
callsign, similarities between morse codes for various letters, and the 
three partial calls to piece this together to LA3ZA.

I'm not saying this is not doable, only that it may take more than a 
month for a good programmer to do this, and maybe much more also.

-- 
Sverre
2008/2009: F/LA3ZA