[aprssig] RFM22B UHF Transceiver Module

John Gorkos jgorkos at gmail.com
Wed Dec 12 14:30:27 EST 2012

I recall that project, I read several messages between you and another guy
about the Hamming code.  I think Andrew Pavlin hit on the answer, though:
I have 3 other radios that speak GMSK 9600 AX.25 (Kenwood D72, D710, D7).
It would be cool to have a ammo can full of 5 or 6 micro-trackers that I
could build for $50 each that do 100mw with a GPS module built in that can
interface with the several thousand dollar investment I already have.
  They'd be great at public service events, heck, they'd even be great to
go camping with ("sure, you can go explore the woods, take your tracker").
 Pull out my D72 and find out where everyone is within 2 or 3 minutes.
Can't get a signal from one of the trackers?  Hook up a bigger antenna to
the D72 (omni) or a yagi.  Put them in some sort of digi mode, and you've
got a nearly disposable mesh network.  The key is that we really only need
to crack this nut once:  we have a dirt-cheap 100mW radio module that is
capable of sending raw bytes in ALMOST the right modulation scheme. Once
we come up with the C library that says "Take this string and send it over
this SPI channel, configured with these parameters" and it makes the
RFM-22B transmit a digital signal we can receive and decode with our
Off-The-Shelf APRS gear, ANYONE can spend $50 and build a microtracker.
Heck, Scott can probably churn these things out in batches of 100 with a
manufacturing cost of $30 and sell them for $60.
I'm not opposed to Gregg's suggestion of reviving the OpenTrac model.  I'm
less concerned about WHAT data we send over these radios than I am with
HOW we send it, in terms of modulation.

John Gorkos

On 12/12/12 2:09 PM, "Scott Miller" <scott at opentrac.org> wrote:

>I've mentioned it before, but I built an OpenTracker USB / Tracker3
>board some months ago that takes the RFM12BP 500mW module.  Presently it
>runs at 4800 baud with Hamming(7,4) error correction.  I had two sample
>units out in the Black Rock desert last July for testing, but I think I
>blew the PA transistors - maybe a bad antenna connection.  If there's
>sufficient interest, I could probably make a few more.
>On 12/12/2012 11:01 AM, Jason KG4WSV wrote:
>> On Wed, Dec 12, 2012 at 11:59 AM, Andrew P. <andrewemt at hotmail.com>
>>> Ah, but wouldn't it also be nice to have the modules compatible with
>>>the thousands of already-deployed 9600 TNC's built into every Kenwood
>> That was pretty much my thought.
>> If I want to build something that isn't compatible, I can use Xbee Pro
>> (100mW, 900MHz or 2.4GHz) or 9XTend (1W, 900MHz) and have a complete
>> radio module with a serial interface.  No radio management required
>> after initial configuration, power it up and feed bytes into the
>> serial port.  Oh yeah, and I can have on-air data rates of up to 115k
>> baud.
>> If these chinese modules work out, maybe they'll be so cheap and
>> convenient and useful that we (hams) won't mind building a separate
>> incompatible network; it wouldn't bother me at all to be proven wrong.
>>   I applaud John for doing the work to try and figure these things out.
>> -Jason
>> kg4wsv
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