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[aprssig] More efficient use of channel capicity through shorterpackets

scott at opentrac.org scott at opentrac.org
Thu Oct 12 21:21:35 UTC 2006


> For my calculations I am going to pull a TXD of 100 
> milliseconds out of 
> my hat.

That's fairly reasonable.  I usually assume around 120.

> I believe is commonly used, a TXTail = 100 milliseconds.  20 

Is that common?  I know none of my trackers do that.  Their tail is about 13
msec.

> using Mic-E, mostly without extraneous comments, and the rest are 
> sending uncompressed data in the 40 character range.

APRSworld says the average comment text length is 29.5 characters, if you're
wondering.

> numbers would be 150 msec (TXD+TXT) and 308 msec (data packet) for a 
> total of 458 msec.

I think this is close to what I'm seeing in real life.  I'm working on
improving my timeslotting support to use the 1pps signal from the GPS
receiver - I'm trying to get at least 2 slots per second for a commercial
customer.

> As things stand now, with 1200 baud on 144.39, reducing 
> TXD+TXT to the 
> bare minimum nearly cuts the typical on air time in half, perhaps 
> efforts should be expended in that direction first? 

Absolutely.

Scott
N1VG







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