[aprssig] Receive Only APRS

Jason Winningham jdw at eng.uah.edu
Sun Dec 10 08:37:49 CST 2006

On Dec 10, 2006, at 7:51 AM, M J wrote:

> Any opinions about choices available?

Once choice is to get the TNC of your choice and only hook up your  
scanner's speaker output.

Here is one example of a decode-only circuit:


I have one of these in front of me right now decoding packets from an  
old uniden police scanner found in my parents' basement.  The down  
side to it is that, unless you've got components and a programmer on  
hand, it's far simpler and not much more expensive to go and get  
yourself a TNC-X kit http://www.tnc-x.com/ or wait a bit until more  
kits are available and get a Tracker2  (now in beta; I have one and  
it's great for APRS).  If you're not familiar with packet and  
hardware tinkering, you should probably wait a while on the T2.

There are various decoder circuits out there; some use the MX614  
modem chip (Scott stocks 'em at http://www.argentdata.com/catalog/).   
Some use an XR2211, and some use a simple zero crossing detector  
circuit.  Most are based on a PIC microcontroller of some variety.

The absolute cheapest way to go is with a software decoder like AGWPE  
(this method in generally called sound card packet), but I found that  
to be the most frustrating to get working, too.  You may be able to  
get by as simply as plugging an audio patch cable between the scanner  
and computer, but in my experience you're not going to get far  
without including an audio transformer and some attenuation.


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