[Lowfer] GMSK discussion...interesting !!

[Neil]

You're welcome, John. This has been interesting for me.

Sent from Neil's iPhone

> On Apr 30, 2014, at 10:35, John Langridge <jlangridge at sbcglobal.net> wrote:
> 
> Great info Neil, Thank you.  I will study this further. You have dug a whole lot deeper on this topic  than I ever have in the past.
> 
> 73!
> 
> John XIQ
> 
> 
> 
> 
> ________________________________
> From: Neil Klagge <lowfer.nklagge at gmail.com>
> To: Lowfer List <lowfer at mailman.qth.net> 
> Sent: Wednesday, April 30, 2014 10:36 AM
> Subject: [Lowfer] GMSK discussion...interesting !!
> 
> 
> 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
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
> Post must be less than 50KB total for message plus attachment!
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
> Post must be less than 50KB total for message plus attachment!
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html