[aprssig] APRS SDR

Dave dave at g8kbv.demon.co.uk
Mon Dec 13 13:30:38 CST 2010

Take a look at MultiPSK.  That (AFIK) has some APRS functionality, and 
also I/Q audio interface to/from SDR.  (Shame about the user interface, 
but lots of people seem to like it all in one dialogue!)

Also, FlDigi, with Jpskmail.  All software, and can produce the audio 
stream you then translate to RF, and the other way round.  jpskmail also 
has some APRS functionality.   (And a truly beautiful UI!)

You don't need mega DSP systems, or GHz clocked A/D-D/A's etc, take a 
look at what can be done with simple I/Q mixers and SDR software.  Just 
look at WinRad, PowerSDR and all the others, right down to Rocky, all 
work with simple hardware such as a Softrock, so long as you already have 
a half decent PC to play with.

With modern multi core CPU's and OS's to suit, it's only going to get 
much easier as more and more people get their head's around the 
principles, while other people engineer better ways to use the multi core 
CPU's for jobs like this.

The single biggest problem, is getting a decent true stereo soundcard, 
that doesn't do odd things, or have drivers that mess with other aspects.

SDR is at the beginning of it's life in the Amateur world.  It's been a 
major player in some professional/secure comm's systems for a while, 
there is  l o t s  of opertunity for the amateur to experiment with this.

Lets not just stick with 1200bd AFSK, though it works reasonably well.  
There are many other schemes to play with.  Or even improve on AFSK while 
still using it.



Dave G0WBX.

On 12 Dec 2010 at 18:05, Matti Aarnio wrote:

> 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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