Mike's comments still seem to make the assumption that a human brain can
do better than software. Why ?
It doesn't matter how good your eyes are at perceiving subtle
differences of tone or colour interspersed with static crashes, or ears
at hearing minute changes in a single tone, they can only see / hear
amplitude changes and are throwing away all the information contained in
the phase of the signal - 3dB worth if your interpretation is perfect
and probably a lot more.
Why assume a machine cannot do better - the world is now full of
communication signals travelling over links that would be impossible for
analogue information. We just need to choose a scheme optimised to the
type of signalling we want to do and write software to implement it in
such a way that the average amateur (who won't build anything of course)
can just plug in and go.
It is very arrogant to assume the human brain can always do better than
a machine just because we feel it ought to.
PSK will do better on LF than SLOWCW DFCW etc. in similar bandwidths,
but we need to implement it properly. The US Lowfers are there, and
showed this years ago. All we need is decent frequency stability in
receiver and transmitter and a preparedness to not insist on relying
blindly on Soundcards to meet all our data comms needs.
If the link won't support lower and lower bandwidths - the simplest
route to weak signal working - then use coding to achieve this with
wider signals. And here only machines can do the job. I can't somehow
visualise a human brain doing the Viterbi error correction algorithm in
real time from a Spectrogram
--------
I understand there was a quote published in QST (or QEX ?) some time ago
from the FCC to the ARRL that "If amateurs did not improve their
technology they would lose spectrum". Can anyone in the US confirm
(or deny) this and point me at the reference.
Andy G4JNT
-----Original Message-----
From: Mike Dennison [mailto:[email protected]]
Sent: 2001-02-19 16:37
To: [email protected]
Subject: LF: Where next?
> ..................... 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
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