[aprssig] APRS SDR

Matti Aarnio oh2mqk at sral.fi
Sun Dec 12 10:05:47 CST 2010

On Sun, Dec 12, 2010 at 10:03:16AM +1000, Andrew Rich wrote:
> Hello
> I wonder if any work has been done in making a software defined APRS device ?
> In that the hardware is common but the features and TX and RX are very much software derived ?
> - Andrew VK4TEC - 

Lets see...

Old TAPR TNC2 did following in hardware:

 1)  (AX.25) HDLC processing
 2)  Bell202 AFSK
 3)  DCD

Radios were pretty much hardware too, even single frequency xtal rigs.

The AX.25 and above it (alike APRS) have always been entirely software.

The HDLC processing hardware is rather rare in modern microprocessors,
thus it is often done in software.  SDR you might say.

Bell-202 modems used to be "hardware", these days they are often software.
If Bell-202 is software, then DCD is trivial addition on that software.

There are several "DSP TNCs" around.

Having a special SDR hardware that takes application bits in on one end,
and puts IF/RF waveforms out on other is usually seriously more expensive
approach.  A mid-scale Xilinx Virtex-IV, and 100 Msps ADCs/DACs does cost
several kilo-dollars, or more commonly tens of kilo-dollars.

Long ago there were 56kbps modems with early Xilinx FPGAs for waveform
generation and detection. One could say that WA4DSY was "software defined",
as the used hardware is software reconfigurable.

73 de Matti, OH2MQK

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