[aprssig] 9600? Faster?
Tim Cailloux
tim at cailloux.com
Thu Jul 7 10:37:55 EDT 2005
Earl Needham wrote:
> Well -- are we stuck at 1200? Or should we try something even
> faster than 9600?
I work on mobile data for a career, and 19200bps is about the limit of
what you can do with one receiver and still get decent range in a land
mobile environment, with a FEC optimized for mobile data. Faster speeds
require some sort of diversity receive. It comes down to a decision
between capacity and coverage, and it is always a trade-off. 9600bps
buys you more users than 1200bps, but the radios have to be set up to do
it to gain any advantage.
I think someone on the list posted that the D700s run a 250ms TX on
delay (or some large number N, where N >>> time to transmit the data at
1200bps). Why run 9600bps when the speed increase on a per-transmission
basis is negligible compared to the overall packet transmission time?
Running faster data speeds will require some optimization of the
radio-modem interface and careful selection of the radios used in the
environment. Even among the land mobile voice radios, the fastest a lot
of radios could reasonably go is less than 9600bps. If amateur
transceivers are designed around voice and 1200/2400bps packet, I
wouldn't say it's reasonable to expect all that many to do 9600bps out
of the box, regardless of the presence of a 9600bps pin on the accessory
jack of the radio.
On a smaller scale, I certainly think that users can build a 9600bps or
faster setup (and I enjoy seeing it done), but large scale the chances
of higher speed seem limited.
(I only wish I could retrofit my company's 43.2Kbps stuff for APRS and
amateur data!)
tim
--
Tim Cailloux
tim at cailloux.com
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