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[aprssig] RFM22B UHF Transceiver Module

John Gorkos jgorkos at gmail.com
Wed Dec 12 17:43:49 UTC 2012


I think this is a "Holy Grail" kind of quest (no, not the ones with
African or European Swallows).  The quest to get working GMSK 9600 APRS on
a RFM-22B is one worthy of the attention of some of the really smart folks
around here.  RFM-22-equipped trackers with $30 GPS modules, powered by 4
AA batteries with a $5 Atmega chip driving the whole thing, would be a
huge win for race tracking, parade management, scout management, etc.  I'm
using the RFM22 for another (semi-commercial) project, but I'll be happy
to contribute anything I learn.  If someone is really willing to take on
figuring out a two-way 9600bps APRS Tracker for 430MHz, I'd be willing to
front a couple of modules and an arduino.

John Gorkos
AB0OO

On 12/12/12 12:07 PM, "Jason KG4WSV" <kg4wsv at gmail.com> wrote:

>On Wed, Dec 12, 2012 at 11:00 AM, Thomas Krahn <thomas at tkrahn.com> wrote:
>> I'd be interested in doing exactly this. Do you have any pointers how
>>this
>> could be done? How do the modules do the scrambling? Or do I need to do
>>this
>> by myself in software?
>
>You must do it in software.  You also have to provide the AX.25 frame
>delimiters, etc.
>
>> Also my understanding is that the RF modules only accept input data in
>>byte
>> format, not bitwise. Therefore in my understanding we'd need some non
>> trivial conversion with overflow bits to implement AX25.
>
>Correct - you have to generate the bit-stuffed bitstream and present
>it to the radio as bytes - it's not terribly difficult, but not as
>trivial as just shoving bytes into the radio, either.
>
>
>Theirs is a work in progress - I think they're currently using matlab
>to generate bistreams while they figure out the radio operation.
>
>-Jason
>kg4wsv
>
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