[aprssig] 1200 vs 9600 baud (was: Tracker3 9600 baud balloon tracker beta offer)

Derek Love DLove at app-tech.co.uk
Fri Dec 20 03:56:24 CST 2013


Have you looked at the "self-organising" TDMA scheme used in AIS? Something like that may be suitable for your needs, especially as it is no longer patented.

I looked into 9600 operation a few years back, and had a number of issues, the principle one being that the preamble and frame synch were poorly defined and then were further confused by the addition of the "data scrambler" which appeared to be applied to both preamble and frame synch as well as the data payload (which made no sense to me). At higher symbol rates, it is imperative that the receiver have a good solid, reliable and tightly defined frame synch to lock onto, otherwise all the following data is lost. 

Even AIS didn't get it quite right and I have to look for 4 different versions of preamble and frame synch to cope with the vagueness of the standard. 

And FEC is essential..... ARQ mechanisms are a pain in the a*** and just chew up bandwidth.

Derek Love, Applied Technology UK
+44 1749 881130

-----Original Message-----
From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf Of Scott Miller
Sent: 20 December 2013 06:13
To: TAPR APRS Mailing List
Subject: Re: [aprssig] 1200 vs 9600 baud (was: Tracker3 9600 baud balloon tracker beta offer)

I want to see more 9600 baud APRS on 70cm - we don't get a lot of consumer RF stuff down in the VHF bands and it's never going to be as cheap as the low-power UHF stuff that's churned out in massive quantities for consumer electronics.

But it shouldn't be just a faster APRS network.  It needs to be a lot smarter - self-organizing and adaptive, not relying on centralized control but also not every man for himself ALOHA networking.

I'm hoping to play around with that some myself, but right now I've got two more pallets of weather stations to finish packing... somehow running a full-time APRS business is leaving me less time to play with APRS.

Scott
N1VG

On 12/19/2013 4:12 PM, Ted11 wrote:
> Scott's balloon tracker has gotten me thinking again about a lingering 
> question, 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.
>
> Beyond those rather rudimentary constraints, I'm not sure how to 
> decide to use 1200 or 9600.  All my APRS stuff so far is done at 1200, 
> but I'm interested in what advantages 9600 might have.  So how would 
> you answer the question, "When should I use 9600 baud for APRS and 
> when should I use 1200 baud?"
>
> Thanks.
>
> Ted
> K5KZ
>
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> http://www.tapr.org/mailman/listinfo/aprssig

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