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[aprssig] APRS digi performance and TONES!

Chris Howard w0ep at frii.com
Thu Sep 6 19:49:53 UTC 2007


Sounds like this would make a great topic for the APRS wiki!
   -- what are the specs
   -- what tools to use to tune (receiver, laptop and a
       soundcard audio spectrum program?)
   -- how to adjust various tnc's and other devices

Chris
w0ep


On Thu, 2007-09-06 at 10:14, Robert Bruninga wrote:
> > Something else I've noticed, is that your mobile 
> > will work just fine at home, but when you get 
> > 1000+ miles away, something about the digis is 
> > different, and your mobile might not "see" any APRS 
> > activity.  
> 
> STUMP ON:  This is because sometimes packet is treated as
> plug-n-play.  Just plug in a TNC and "it works", ignoring the
> fact that there can be 60 dB differnce between "it works" for a
> 50W rig 2 miles away, versus, a 1 W signal at 30 miles away...
> 
> The tones have to be set for:
> 1) Proper modulation
> 2) Proper "skew" High tone versus low tone
> 3) Emphasis. De-emphasis, or none
> 
> There are LOTS of bad signals on the air (in fact the majority
> are not properly set and sound bad!).  They "work" sometimes
> with some rigs, but because they are so far from being optimum,
> they don't work with some others.
> 
> The internal TNC in the kenwoods are connected directly to the
> discriminator and give a flat rsesponse.  They can decode other
> flat packet signals with as little as 3 tiny LCD marks showing.
> The kenwoods will also work OK with a digi that has proper
> emphasis and de-emphasis, but they and most other decoders will
> fail even on a full scale signal if the tones are too skewed.
> Most TNC's will choke if the low tone is more than a few dB
> higher than the high tone. 
> 
> Listen to the signals on 144.39 and the wide variety in tone
> levels, skew, and deviation tell you why performance varries so
> greatly.
> 
> PACKET is not plug-and-play.  Like anything else, it requires
> proper settings for optimum performance.
> 
> 
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