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[aprssig] Rant - Cross platform portability

Dave Baxter dave at emv.co.uk
Wed Sep 20 08:52:57 UTC 2006


Hi...

I'm more than aware of what can and does get done in a PC (or anything
else) that does audio/soundcard based DSP, yes, the A/D conversion needs
to be done on a timely basis, and yes the "processing" can be batched
behind the scenes.

However.....   Of the Ham population, who actually program anything
significant, what percentage of them have the skill's to do that on any
platform/language combination.  Of them, who has the spare time and
inclination to learn something totally different, if they don't "need
to"...  I suspect a small fraction of 0.1%  Good on them though, go roll
with it...

As to Java's IO control, well, it's already been said.  Sun's dropping
of native java support for COM port, at about the time of the rise of
USB strangely is a pain.  Utilities like RXTX work, but again, there
seem to be several versions skulking about, and not all the new ones
work with newer Java app's.  Then you're back in the usual mess, of how
to get right down to the metal as it were, across multiple platforms, so
you can never have true cross platform portability if you are going to
use external IO.

As others have said, the main problem for the users, is getting it all
installed up and running, citing LimeWire as a good example of how it
should be done (regardless of what I think of the app itself, and some
of it's users!)  It is certainly a "hands off" approach, and sorts out
what it needs, and goes and does it.   Sadly, much ham (and an awful lot
of commercial stuff sadly) does not do that.

True SDR however, that's in truth (for a HF RX typically) a multi
hundred MHz A/D with a roofing filter (sometimes not even that, then
aliasing effects can be used to get VHF coverage too!) then ALL IF
processing, filter synthesis and demod etc, right down to baseband is
done with DSP.  "True" SDR systems can therefore handle multiple signals
and modulation schemes simultaneously, within the capabilities of the
number crunching hardware involved.

The closest common ham application that can do something similar to
that, are some PSK31 systems, where you can demodulate more than one
signal simultaneously.  But, that is done from a low frequency IF, audio
in this case.

The majority of the so ham so called SDR stuff currently about, is
computer controlled analogue RF/IF, down to for example 12kHz, then
soundcard DSP.  That is not true SDR.   Go look at what Amsat among
others are doing in respect of true SDR.   I doubt much will be done in
Java, but I could be wrong.  It would certainly be a good way to go for
the User Interface part, but I doubt for the embedded code.

It's not beyond imagination, to have one box that could do just about
everything.  PSK31, WJST, CW, APRS as well as "normal" voice comm's, all
running together on the same hardware.  Transmitting on one HF band,
while doing that Receiving on another though, is still as much a
challenge as it always was, but numerically not impossible.  I guess the
closest we have to that at the moment, on VHF at least is DSTAR, but at
a cost.

I'm sure Java will improve over time, but it has a way long way to go
yet, for true "all hardware platform" portability that some may claim it
has now..

Cheers All..

Dave G0WBX

> -----Original Message-----
> From: Gregg Wonderly [mailto:gregg at wonderly.org] 
> Sent: Tuesday, September 19, 2006 3:53 PM
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] Rant - Cross platform portability
> 
> Dave Baxter wrote:
> > It also is not "real time" critical as DSP code would be, 
> and does not 
> > need any specific hardware IO, like to control a rig etc.  
> It's purely 
> > web based.
> 
> DSP processing of an AUDIO stream does not have to be done in 
> real time.  The audio stream needs to be collected without 
> loss, and the audio hardware, buffers and OS drivers do this 
> for you on PC class computers.  You can then just process 
> that stream using time sharing software systems.  Look at the 
> SDR-1000.  It is software defined radio which is using 
> windows for control of the RF deck.  The RF deck converts the 
> RF that you are tuned to, into a 44khz wide audio stream 
> through frequency conversion.  That goes into a high quality 
> audio card to miminize loss and maximize performance.  But, 
> then everything you hear and everything you transmit is 
> processed by a non-real time OS environment.
> 
> > Of course, if we start to see 10/100 network ports on 
> radio's (as much 
> > "High End" test RF equipment from the likes of Agilent and R&S is 
> > beginning to sport) that would make things a lot easier to do with 
> > Java.
> 
> Java is not just restricted to network communications.  There 
> are various APIs for doing serial and parallel port 
> communications as has already been brought up in this 
> discussion.  What was at issue in the previous discussion, 
> was the the "free" version for windows that Sun had on their 
> web site disappeared.  It can still be distributed by those 
> who have it.  Or, the RXTX project can be used, as can the 
> commercial packages.
> 
> Gregg Wonderly
> 
> 
> 




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