Hi Daniel,
Well, the situation now is that Peter -who is also on this list- has
started to work on a proposal for a bitstream format.
Hardware-wize, the most easy thing to do now, is just use a "soundcard"
modem on a PC or some kind of development board.
One interesting way to do this is as done by the "freestar" project
which use a PC and an external USB audiofob which is known to work well.
" http://www.va3uv.com/freestar.htm
That's also the approach I use for my gmsk modem (which is actually
largely based on the gmsk encoder/decoder software part of the
"pcrepeatercontroller" project of Jonathan G4KLX); but -in my case- it
runs on a ARM development board.
See http://villazeebries.krbonne.net/hamstuff/?p=106 for some info on it.
The advantage of using an external USB audiodevice is you do not have to
deal with different behaviour of the PC-based audio devices. (e.g. the
audio device on my laptop actually inverts the audio it receives and
sends). I also tested a griphin iMic with mixed result.
Of course, this is only one approach. One other way would be to use some
kind of chip with embedded ADC and with sufficiant CPU power as the
standalone gmsk modems do.
As I focus myself on "modem" part in this, my goal now it to get
something ready so we can start experimenting. As everybody has a
computer anyway, I think it makes sence to make that the main
development platform at this stage.
Porting it to other platforms can be done latter.
We'll start with something very simple: 4800 bps -what we already have-
and minimal processing in the modem: only deal with syncronisation and
-for the rest- just pass everything transparent.
This would enable other people to experiment with things like FEC,
interleaving, scrambling, ... etc. without having to change the modem
part. The goal is gather some knowledge and experience so what modes
make sence and what do not,
In the mean time, we can look into a version of the modem at other
speeds (2400 bps, 2000 bps, 1600 bps, ...).
73
Kristoff - ON1ARF
On 20-05-12 22:19, Daniel Mundall wrote:
We've designed a digital 10w 2m radio that we're just testing at the moment.
Any input would be great.
Have a look at hamcell.com
73's
Daniel VA7DRM
Sent from my iPad
On 2012-05-20, at 1:00 PM, Kristoff Bonne <[email protected]> wrote:
Hi Matthew,
Well, I try not to look to much at that radio or else I might have to
find yet another excuse if my wife asks me why I need "yet another radio".
(I just bought a 2m/4m portable and a "modified CB" station to monitor
our new local 10 meter repeater one week ago).
:-)
Anycase, the goal is to have a something so that people can experiment
with it with as less hardware requirements as possible.
My preference would be just a basic radio interface board and a couple
of USB audio-fobs that are known to work well.
We first need to gain some experience with this. What modes or speeds
work best, etc.
I also had a request of somebody to think of possible issues to use this
over satellite links. That's also an interesting thing to look at.
73
Kristoff - ON1ARF
On 20-05-12 16:38, Matthew Pitts wrote:
Kristoff,
Sounds good, and I knpw of a transceiver that we could use this with that will
be available later this year. In fact, we could do something a bit more
complex, as far as coding and it should easily handle it.
http://www.nwdigitalradio.com
Matthew Pitts
N8OHU
------------------------------
On Sun, May 20, 2012 10:24 AM EDT Kristoff Bonne wrote:
Hi,
We are looking into the possibility to create an additional modem for
codec2, but for VHF/UHF frequencies.
As a first "proof-of-concept", this would be to convert my gmsk modem to
a new format to carry codec2 voice. This would have the advantage that
the hardware requirement to run this would be minimal.
Sofar, I see two options:
- A 2400 bps modem:
This would be quite sufficient to contain codec2 voice (at 1400 bps),
additional syncronication patterns + some additional data and even an
options 2/3 FEC for the voice part.
- A 4800 bps modem:
This would then give even more headroom, e.g. tu use a 1/3 FEC for voice
(which would make it much more robust) and still have headroom for
syncronisation patterns and some additional data
The 2400 bps modem would have the advantage of the lower bandwidth
(better S/N ratio, better suited for e.g. bands with limited bandwidth:
10 meter, 4 meter).
The 4800 bps modem would have the advantage of the better FEC.
Does anybody have a comments on this?
73
Kristoff - ON1ARF
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