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[aprssig] RFM22B UHF Transceiver Module

Derek Love DLove at app-tech.co.uk
Thu Dec 13 10:12:09 UTC 2012


Just to add my 2p's worth...

I've implemented APRS 9600 GMSK, Marine AIS at 9600 GMSK, Mobitex at 8000
GMSK as well as "conventional" FFSK at both 1200 and 2400 bps (mainly for
MPT1327).  I've also implemented a wide variety of PMR modes, and at the
moment 4-level FSK is my favourite (as used in dPMR and DMR -this could give
you 19k2 bps in a 25k channel, but the symbol rate of 9600 makes the
filtering etc. much easier to implement in a cost-effective manner). Any
modulation scheme much higher than this takes you into the realm of linear
PA architectures (which my employer would be very happy to sell you
solutions for, but...) 

Of all of them, APRS was the worst to implement at the air-interface level.
If there is a move to goto a new modulation/protocol scheme, please, please,
please may it include:
	A properly defined, unambiguous preamble (24symbols would enough)
	A properly defined, unambiguous Synch pattern that doesn't false too
often (ie: at least 24bits)
	A half decent FEC

I've had a VX-8 sitting on my desk for the past week here in the west of
England, and, although I can hear a number of stations, there isn't a digi I
can get into.....

Derek Love, G7ORK, UK



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