This is all-important. Extremely weak stations require considerable
additional work by the 'computer between the ears' to decipher
what is signal and what is noise on the screen - just like aural
Morse, but visual. This accounts for several extra dB of gain, and
however slow you send the Morse, this advantage is still available.
It would take a very sophisticated computer to be as good.
NO ! With these modes the computer is not doing anything to aid
extraction of the signal that could not be done with conventional
hardware. The 'several extra dB gain' is just there because more
noise has been filtered out. The brain is just looking at amplitude
changes in this narrow bandwidth and integrating over the signalling
period (looking at brightness over the length of a dot).
All Spect.... is, is a bank of narrow filters. There is nothing in
theory to stop you making a crystal filter, or a whole bank of them this
narrow. For a display mechanism, a chart recorder - multiple pen ones
are available. All this technology was available in the 1950s as I'm
sure those who were around in that era will remember.
All the computer does is make this much simpler and cheaper and
available to everyone, it is only a filter and display mechanism so
please can we stop referring to Spect... as computer modes. It can
be done in other ways.
Coherent etc and PSK31 are computer modes, SPECT..... is not, it is
only a filter bank and display.
Real computer / DSP modes mean making use of coherent detection and
error correction - and have nothing to do with the speed of the
signalling.
There seems to be no appreciation on this newsgroup of the real value of
coherent detection - that is, having phase information available when
the signal is decoded and coherently locking to the signal carrier and
bit timing. Simple theory, as I covered in a previous email, shows
mathematically the considerable theoretical advantage of coherent
detection over non coherent, there is no dispute about this.
SO unless your ears / eyes can respond to signal phase, is doesn't
matter how much personal pride says that the brain is a marvelous
computer, is will never compete against PSK :
Given the same TOTAL overall signalling speed and comparing like with
like on the end to end link.
Repeating CW characters time and time again has to be compared with true
error correction and low data rate signalling.
Computer error correction does the same job as the eye interpreting
between the dots on Spect..., and with well chosen codes can do an
awful lot better. These optimum codes are only just beginning to appear
thanks primarily to the huge research effort funded by the mobile phone
industry, but hopefully Coherent etc will soon make use of them - the
equations are public information. The maths is similar, just the
implementation different.
Coherent etc and PSK31 are computer modes, Spect... is not.
Andy G4JNT
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