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[aprssig] 434 MHz tracking

Scott Miller scott at opentrac.org
Mon Aug 6 00:27:00 UTC 2007


1200 baud @ 50 watts = 0.0417 joules per bit
19200 baud @ 0.01 watts = 0.000000521 joules per bit

That's the Eb part of Eb/N0.  Sometimes it pays to be slow and loud!

What APRS really needs is a decent FEC scheme, and some minimum 
standards on TX delay.  And if it ever goes to baseband FSK, I'd rather 
see it at 2400 or 4800 baud, where equalization isn't as critical and 
it's not pushing the limits of voice band radios so far.  Unless all the 
manufacturers somehow spontaneously get their acts together and give us 
affordable radios that do 9600 baud and above in a reliable and 
interoperable manner, but I'm not going to hold my breath.

Generally, APRS doesn't need to be fast, it needs to be robust and reliable.

Just adding 1 pps GPS timing to APRS stations, and aligning 
transmissions to timeslots based on this reference, would double the 
channel capacity compared to plain old dumb ALOHA like we've got now. 
Remember that APRS doesn't have these things because if the standards 
were set that high and people couldn't reuse old hardware and cobble 
systems together for virtually nothing, APRS never would have caught on 
to the degree it has.

Scott

Andrew Rich wrote:
> You know its a pity that we hams could not use the technology of easy 
> radio on the ham bands.
>  
> I see that a 1200 baud packet takes a seconds to send.
>  
> On the weekend I was sening 20ms databursts @ 19k2 on 434 MHz at 10mW
>  
> I wonder if we are ever going to break the shackles of 1200 baud ?
>  
>  
> 
> 
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