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[aprssig] D-Star replacement for APRS: [Was: D710 GPS Port]

Stephen H. Smith wa8lmf2 at aol.com
Tue Aug 14 18:17:54 UTC 2007

William McKeehan wrote:
> Has anyone looked at D-Star as a potential replacement for APRS?
> It seems to have a lot of the basic functionality.
There are a LOT of technical, organizational and political obstacles to 
this ever happening.

Partly as a result of the APRS founders shoe-horning and somewhat 
kludging APRS into the protocols, hardware and infrastructure of the 
preceding connected-packet era (do I dare use that over-used buzzword 
"leverage"?), APRS has succeeded because it has allowed us to do a lot 
of "neat stuff" with really cheap existing hardware.    This will *NOT* 
be the case with D-Star.    A migration to D-Star will be a wrenching 
total transition to *ALL NEW* base stations, mobiles, hand-helds and 
repeater infrastructure.  

D-Star is not a short-burst packetized transmission format. It's 
primarily a digitized voice format that can carry a limited amount of 
other data embedded in the main voice data stream.   As a result, the 
simple single-frequency store-and-forward "digipeaters" we use on APRS 
won't work with it.   You would be faced with coordinating a traditional 
full-blown two-frequency "repeater pair", along with using a separate 
receiver, transmitter and duplexer, just like present voice 
repeaters.    Further , getting more than one repeater hop isn't a 
matter of the second repeater hearing the first one, and then 
retransmitting what it hears a moment later. It involves a complex 
land-mobile-style backbone of links on another band, usually 1200 MHz to 
connect repeaters together in real time.

Further, no manufacturer seems to have adopted it, except Icom.  

While the only mfr to officially support APRS is Kenwood, at least you 
*CAN* add APRS hardware (TNCs, TinyTracks, Open Tracks, etc.) to other 
radios.  This is not going to be the case with D-Star which is an 
entirely digital modulation technique totally different from the analog 
FM we use with APRS packet, that is built-into purpose-built radios.  It 
is very unlikely you would be able to add D-Star to any existing radio, 
especially hand-helds. 

Achieving anything remotely like the coverage of  the current 
analog-FM-packet-based APRS network (where just about any FM radio made 
in the last 30 years or so can be pressed into duty as a digipeater by 
adding a $50 TNC). Duplicating this coverage with D-Star would require 
literally tens of millions of dollars of brand-new infrastructure. 

Further, the present network reflects the sum total of a lot of small 
steps made independently by clubs and individuals.  A nationwide D-Star 
"APRS- replacement" infrastructure would require a degree of 
coordination (and financial commitment) by clubs and individuals 
unprecedented in amateur radio.

My guess is that we will get "islands" of D-Star activity in major 
metropolitan areas (where the population density of hams is great enough 
to support the major infrastructure investments required) , surrounded 
by hundreds (or thousands) of miles of non-coverage.   I.E. the 
individual ham or small club in a small mid-western town or rural 
Kentucky that threw up an old hand-me-down 2-meter rig and a TNC to fill 
in  the APRS network at almost no cost, is NOT going to lay out the 
several thousand dollars minimum to put up a D-Star repeater, let alone 
the backbone to link it to other D-Star systems.

Before they make this major investment, users are far more likely to use 
Internet access from their cellphones to send/display GPS position 
reports and send/receive short text messages.  (Envision an APRS-like 
application overlaid on Google Maps running on an iPhone-like device.]


Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

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