[aprssig] RFM22B UHF Transceiver Module

Jason KG4WSV kg4wsv at gmail.com
Wed Dec 12 12:07:15 EST 2012

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.


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