[amsat-bb] Re: Can D-Star work on VO-52?
vk3jed at gmail.com
Sun Feb 25 20:57:54 PST 2007
At 03:22 PM 2/26/2007, Edward Cole wrote:
>Not only will SDR permit legacy modulation modes, but permit
>changing into new modes as they are developed. One of the most
>difficult "growing pains" of new technology is the rapid
>obsolescense of equipment as a new mode matures into a new
>"standard" (e.g. 8-track/cassette/CD/... or Betamax vs VHS). The
>SDR allows all and anything, limits are your imagination!
Indeed, we have already seen this with the "first generation SDRs"
that exist today. You're using yours to read this message! ;) Yes,
I'm talking about the PC/soundcard combination, which is commonly
used as a SDR to run both legacy modes such as CW, RTTY and SSTV (and
Baird style NBTV!), as well as new modes such as PSK-31, JT-44 and
the wide array of PC based digital modes we are using today. Even
digital voice is covered, with DRM being available on the PC (I'm yet
to fire up DRM on the air, need to find some locals on HF).
>Joeseph: this still doesn't answer your question :-)
The answer to that lies in how tolerant D-Star is of frequency errors
(i.e. Doppler shift). Digital modes vary widely in their tolerance
of frequency shift. Most of the ham modes are optimised for narrow
bandwidth, and therefore they can be susceptible to Doppler. Another
issue is whether the clock recovery is capable of dealing with a
slightly non standard bitrate. This effect is also Doppler related,
and was what nearly sunk the Huygens mission on Titan. Fortunately,
one of the engineers insisted on testing the comms system while
Cassini was en route to Saturn and they were able to find a
workaround for that problem. The full write up is available on the
Net and is a good read. Try Google. :)
Still no answer to the original question, I don't know much about
D-Star, and it's unlikely to be commonplace here until the next
generation of SDR hardware is commonplace (assuming D-Star will be
available as a firmware upgrade from Icom or someone else). The
existing hardware based implementations are too expensive for
sufficient uptake with our low population density.
I'm more inclined to spend $1000 on a SDR that can be programmed to
do whatever modes are flavour of the month relatively cheaply (plus
good old AM/FM/SSB/CW/PSK/packet etc) than spend $1000 on a radio
with a new mode that works well but no one else has.
73 de VK3JED
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