D-PRS is the act of converting Icom GPS information generated by Icom D-STAR
radios in GPS mode into TNC2 fomatted APRS strings. It is important to note that
D-PRS is not a protocol but a conversion specification. D-STAR digital voice
mode (DV mode) is a 4800 bps digital data stream with no error detection or
correction. Each transmission consists of a RF header followed by a 4800 bps
stream of bits. 3600 bps of this stream is dedicated to the AMBE encoded voice.
The remaining 1200 bps is used for synchronization and user-defined
capabilities. Icom made use of this user-defined space to pass radio messages
(simple display messages) and to pass serial data.
There is about 900 bps available for the serial data. Icom saw an opportunity to
incorporate GPS information into this serial data. The intent was to maintain
the primary purpose of DV mode, sending voice, while providing a potentially
valuable adjunct data stream, GPS information. I designed D-PRS to take this GPS
information and make it presentable to the APRS world. D-PRS removes the need
for designing special-purpose mapping software just for the unique Icom GPS data
stream. Note that Icom's use of the data portion of the DV signal for GPS is an
Icom implementation, not a D-STAR specification. The D-STAR specification
designates the data "sub-channel" but does not dictate what is done with it.
Icom introduced a new GPS mode called GPS-A mode which is shorter in
format (single line APRS posit) and includes a CRC (CRC-CCITT used by AX.25). I recommend using GPS-A mode on GPS-A capable radios
as a CRC is more reliable than an XOR checksum and the likelihood of an error
disrupting a single GPS-A line is less than the likelihood of interrupting 3
lines in GPS mode. A full description of D-PRS was delivered to the DCC
conference in 2007 and can be found in the
D-PRS white paper.
D-PRS Interface is a Windows GUI application that lets you run a mapping program
locally and watch what is happening on your local frequency.
Click here for more information on D-PRS Interface.
Radio Configuration - GPS Mode
Because there is no error detection or correction on the data sub-channel, D-PRS
mandates a specific message format for radios running in GPS mode. This message
must be the same as calculated on the
D-PRS Calculator page.
Only the RMC and GGA GPS strings are used in GPS mode. Set your radio to only
use those two GPS strings.
Radio Configuration - GPS-A Mode
Radios in GPS-A mode do not need to set their GPS message per the D-PRS
Calculator page. Instead, they should set their UNPROTO to APInnn,DSTAR* Note
that the first part which is commonly called the "unproto" or "destination"
field is comprised of the APRS standard for Icom, API, followed by the first 3
digits of the radio model number. In the case of the handhelds (only 2 digits),
you may optionally use the first character following the model number (92AD
would be API92,DSTAR* or API92A,DSTAR*).
NOTE: It is very important that the UNPROTO does not contain any spaces and that it only contains the ",DSTAR*" as the only "digipeater" in the path.
The asterisk (*) following "DSTAR" is mandatory, as well.
CAUTION: Some browsers will append a space to the UNPROTO when selecting the text for copying into your software.
Do NOT include that trailing space (delete it) when copying into your software.
If you want to copy directly from a page, go
to "calculate" the UNPROTO
Radio Configuration - All Modes
Radios should beacon no more often than every 5 minutes. If you are active
on voice, turn beaconing off since everytime you transmit, GPS information is
transmitted if GPS or GPS-A mode is on.
If you are within range a repeater, set your URCALL to CQCQCQ, RPT1 to the
repeater call, and RPT2 to the gateway call (repeater call with "G" in the
eighth position). This will allow your data stream to reach the gateway but
prevent it from going any further. Most D-STAR repeaters now have D-PRS
implemented on the gateway. You do not have to be registered with the gateway
for this to work.