[aprssig] 1200 vs 9600 baud
aprs at pe1rdw.demon.nl
Fri Dec 20 10:53:37 CST 2013
On 20-12-13 15:33, Robert Bruninga wrote:
>> 1200 vs 9600 baud for APRS. I think I understand this:
>> 1. 9600 lets you send more data per time interval.
>> 2. 9600 requires tighter radio integration (can't just plug into the
> microphone jack).
>> 3. 9600 seems to work best (only?) on UHF.
> As implemented, with typical TX delays, 9600 is only about twice as fast
> as 1200
> Fortunately 1200/9600 are fully factory integrated in all commercial APRS
> radios so it is trivial to compare.
> 9600 baud is 7 dB or so worse than 1200 as measured with fully integrated
> factory adjusted radios. UHF is worse for 9600 baud due to 3 times more
> rapid mobile flutter. UHF has almost ten times more path loss than VHF
> but usually pick up about 3 dB in easier to achieve antenna gain.
>> So how would you answer the question, "When should I use 9600 baud for
> APRS and when should I use 1200 baud?"
> Use 9600 when you have dedicated built hardware with extremely short TXD
> and no transceiver T/R switching delays between fixed stations (no mobile
> flutter). . All modern antenna switghing is electronic and instantaneous
> so the biggest delay is the transceivers PLL synthesizer T/R switching.
> This is why off the shelf Amateur Transceivers simply are too slow for any
> benefit for bursty 9600.
> Amateur 9600 wins when doing bulk file transfer with long packets and
> continuous data, not short bursty data where the delays are longer than
> the data burst.
> That said, the best way to improve 1200 baud VHF performance is to shorten
> the packet and get rid of all the redundant text. Classic wasteful
> packets are digipeaters with Beacons like "Green Mountain digipeater -
> Green Mountain Radio Club, GMRC"
> Bob, WB4aPR
> aprssig mailing list
> aprssig at tapr.org
that offcourse does not mean 9600 is useless for aprs, it can be
perfectly used for backbone trafic where 1k2 trafic is collected from
more then one source, probably a number of alt inputs for short period
trackers and maybe even a stream from aprs-is covering several hunderd
kilometer and unlike 1k2 dwait does not have to be 0 because there is
more then enough bandwith for these types of digipeaters to wait for
eachother and still have relevant data in fact putting dwait to a
resonable level will reduce the poor txd problem.
Personaly I do not see the poor preformance of 9k6 for mobiles as a
problem because aprs is not just for mobile use, it is a 2 way medium of
local assets, not just trackers.
73 Andre PE1RDW
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