[amsat-bb] Re: BeeSat at 4800 GMSK
Nathaniel S. Parsons
nsp25 at cornell.edu
Sat Apr 10 22:31:30 PDT 2010
Thanks for the reply while we still have time to fix things and stay on
Do you think it would be feasible to implement Mobitex in software on a µC,
given a transceiver in transparent mode (will modulate and send any bits it
receives on serial, and demodulate/receive any RF it receives)? We already
have one dedicated to comms, and all other algorithms take place on a
separate processor. I ask because at this point, it would be easier to
change the software than the hardware (software has no mass or volume).
I'd say Block formatting, CRC and bit & Frame Sync would be easy enough
(everything's a multiple of a byte) because they're completely described,
but the interleaving and scrambling aren't which makes things much harder.
On Fri, Apr 9, 2010 at 4:03 AM, Mike Rupprecht <mail at mike-rupprecht.de>wrote:
> Hi Nate,
> Sorry for the long delay....
> MixW doesn't support GMSK. You mix that with MFSK.
> BeeSat has two CMX909B modems (CML) onboard. The data is sent in the
> format, not AX.25 !
> See here for more information about Mobitex:
> The CMX909B is a half-duplex Gaussian Minimum Shift Keyed (GMSK) BT = 0.3
> modem data pump with on-chip packet data handling. GMSK modulation
> the data throughput for a given bandwidth RF channel and the on-chip packet
> data handling relieves the host µC of regular processing tasks, such as
> maintaining Bit and Frame Synchronisation, Block Formatting, CRC and FEC
> Error Processing, Data Interleaving and Scrambling.
> 73, Mike
> -----Ursprüngliche Nachricht-----
> Von: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] Im
> Auftrag von Tom Azlin N4ZPT
> Gesendet: Freitag, 9. April 2010 00:28
> An: AMSAT-BB
> Betreff: [amsat-bb] Re: BeeSat at 4800 GMSK
> Hi Nate,
> I was not aware MixW had MSK in it but still identical to GMSK. Perhaps
> you are thinking of MFSK? In the MixW program there is MSFK16, a
> multitone frequency shift signal, is supported, but not Minimum Shift
> Keying or Gaussian Minimum Shift Keying signals. And also FSK, aka RTTY.
> There is work going on to make a sound card 4800 bps 0.5 time-bandwidth
> product GMSK soundcard modems for use in GMSK DV adapters to use with
> D-STAR radios. Perhaps that could be adapted for your purpose?
> http://www.qsl.net/kb9mwr/projects/voip/dstar/G4KLX.html seems to
> describe some of the work.
> http://groups.yahoo.com/group/dstar_development/ and
> ttp://groups.yahoo.com/group/pcrepeatercontroller/ are where I see the
> discussion underway.
> Separate discussion is using an external sound card interface like the
> Rigblaster, to connect a computer and radio.
> 73, Tom n4zpt
> Nathaniel S. Parsons wrote:
> > Can I assume MSK=GMSK? I thought they were different, but they are the
> > and since MixW has MSK, and I could use that with a Rigblaster, etc,
> > -Nate
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