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[aprssig] Help with Interfacing a GPSto Kantronics KPC-3

Jason Winningham jdw at eng.uah.edu
Thu Jan 4 13:05:15 UTC 2007


On Jan 3, 2007, at 9:44 PM, Joel Maslak wrote:

> And still *MUCH* shorter with a decent radio than the smallest  
> possible D700 packet - no half second TX Delay!!!  (at least until  
> the first digi)

Well, digis are not only responsible for the majority of on-air  
copies of the packet, they also cover vastly more _area_ due to the  
fact they typically have much larger antenna height _and_ higher  
gain.  Therefore they use far more available bandwidth over the life  
of the packet than a D700 operating mobile, even accounting for the  
abominable 500ms txdelay.

NMEA strings are bandwidth hogs, pure and simple.   They are over  
twice as long, including AX.25 headers, and they convey less  
information.

Drop $30 on an opentracker.  No, it doesn't decode, but if you are  
transmitting NMEA sentences with a TNC you're not actually looking at  
any received data anyway.  OK, maybe a couple of hardcore APRS folks  
may look at raw APRS packets and get something out of it, but if  
you've got a GPS tied to the TNC serial port then you are not using  
an application to decode packets - e.g., you're operating just like a  
dumb tracker and you're wasting more bandwidth and using more  
expensive (and bulky) equipment to do it.

If you're not going to decode anyway then get an OT, set the RX  
sensitivity to avoid collisions, and save some bandwidth.

-Jason
kg4wsv







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