[Lowfer] GMSK discussion...interesting !!

[Neil Klagge]

JL, JD, JA, and others....

This has been an interesting discussion for me to follow. I did a wikipedia
search and found the following paragraph. I noted with special interest the
last sentence below about QPSK vs GMSK.
-------------------------------------------------------------
In digital communication<http://en.wikipedia.org/wiki/Digital_communication>
, *Gaussian minimum shift keying* or *GMSK* is a continuous-phase (unlike
PSK that shifts its phase with the modulation) frequency-shift
keying<http://en.wikipedia.org/wiki/Frequency-shift_keying>
 modulation scheme <http://en.wikipedia.org/wiki/Modulation>. It is similar
to standard minimum-shift keying (MSK); however the digital data stream is
first shaped with a Gaussian
filter<http://en.wikipedia.org/wiki/Gaussian_filter> before
being applied to a frequency modulator. This has the advantage of reducing
sideband <http://en.wikipedia.org/wiki/Sideband> power, which in turn
reduces out-of-band interference between signal carriers in adjacent
frequency channels. However, the Gaussian filter increases the modulation
memory <http://en.wikipedia.org/wiki/Modulation_memory> in the system and
causes intersymbol
interference<http://en.wikipedia.org/wiki/Intersymbol_interference>,
making it more difficult to differentiate between different transmitted
data values and requiring more complex channel equalization algorithms such
as an adaptive equalizer <http://en.wikipedia.org/wiki/Adaptive_equalizer> at
the receiver. GMSK has high spectral
efficiency<http://en.wikipedia.org/wiki/Spectral_efficiency> (i.e.
narrower), *but it needs a higher power
<http://en.wikipedia.org/wiki/Electrical_power> level than QPSK
<http://en.wikipedia.org/wiki/QPSK>, for instance, in order to reliably
transmit the same amount of data <http://en.wikipedia.org/wiki/Data>.*
* -----------------------------------------------------------------------*
*So, *now I am thinking I should experiment with QPSK on this band. I have
used it on other bands during qso's and found that it decodes at a higher %
of characters than BPSK, so maybe that is the way to go....

More on-air experimentation is needed....
My $2 worth..... (inflation, you know...)
Neil