From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Mon, 19 Feb 2001 16:37:16 -0000
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Subject: LF: Where next?
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> ..................... One such candidate could be the Steve Onley's FDK.  I
> know that, theoretically, PSK can have an advantage over non-coherent
> FSK, but this doesn't take into account phase distortion over very
> long paths.  But I will leave to others to discuss about the pros and
> cons of the two methods.
> 73  Alberto   I2PHD

A factor that is often ignored when comparing PSK08 (for instance) 
and QRSS is the difference between relying on a machine to 
interpret the results and using the brain. The spectrogram-type 
programs do wonderful work but the final 10dB or so is down to the 
brain deciding what is a valid signal and what is not, then deciding 
whether it makes sense or not.

We really would have a winner if we can combine the obvious 
theoretical advantages of using FM (or phase mod) rather than AM, 
especially when noise is a significant limiting factor, with the 
advantages of a display that allows the brain to add some dBs by 
intelligently interpreting the result. 

For instance, how about produce a display that is the result of 
subtracting the signals and noise in a given audio band, with the 
signals and noise in another band of the same bandwidth. This might 
provide a means of reducing the effect of wideband noise such as 
static (but not random noise) on a conventional mono-frequency 
transmission by subtracting the noise in the 'no-signal' band from 
the band containing the signal. It might also provide a 'comparitor' 
effect so that FSK signals can be better detected - for a given time 
period, if the output of 'channel A' is bigger than the output of 
'channel B' then it is a binary '1'; if the other way round it is a binary 
'0'.The important thing is to resist the temptation to feed this into a 
machine that tries its best to work out whether it is a valid character 
or not - this is the bit that the brain does better.


Mike