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<a class="moz-txt-link-abbreviated" href="mailto:preed@dnaco.net">preed@dnaco.net</a> wrote:
<blockquote cite="mid43B6EFA2.3030500@dnaco.net" type="cite">
<pre wrap="">Does anybody know what NMEA sentences the Kenwood APRS radios use from
the GPS for their various APRS transmissions?
</pre>
</blockquote>
<font face="Arial">In the standalone "APRS" mode, all they require is
$GPRMC which give the radio LAT, LONG and SPEED. If the GPS is also
providing $GPGGA sentences, elevation will also be encoded into the
Kenwoods' Mic-E format transmissions<br>
<br>
<br>
The Kenwood TH-D7 and D700 are operated in the "PACKET" (not "APRS")
mode when used with an external computer attached. In this mode, the
internal firmware will echo data received at the dedicated GPS port out
the main data port along with received packets. This echoing
operation can even convert baud rates -- GPS data arriving at the
radio's GPS port at the NMEA-standard 4800 baud can come out the main
port at 9600 baud. <br>
<br>
The program running on the attached computer needs to know how to
separate received off-air data from GPS data. Most current APRS
applications do this automatically when you select the same COM port
number for the TNC and GPS. <br>
<br>
<br>
However, there is one significant limitation in this mode. GPS
receivers output several different "sentences" (strings of data) which
contain various combinations of lat/long, time, heading and speed and
altitude information. These sentences are normally repeated,with
updated data, once every second. The key fact is that the Kenwood GPS
passthrough function can echo ONLY ONE of these sentences at a time.
The most commonly used GPS data sentences, and the data they contain,
are:<br>
<br>
<br>
=== GPGLL (LAT, LONG, Time)<br>
<br>
=== GPRMC (Time, LAT, LONG, SPEED, MagVar) <br>
<br>
=== GPGGA (Time, LAT, LONG, GPS Valid, Number of Sats Used, Hdop,
ALTITUDE) <br>
<br>
=== GPGSV (Satellite Status)<br>
<br>
=== GPZDA (Time, Date)<br>
<br>
==== GPVTG (Compass Heading, Ground Course Velocity)<br>
<br>
<br>
<br>
Assuming the GPS device actually outputs GPRMC, GPGLL, and GPGGA (in
some GPS units each sentence has to be turned on or off in a setup
menu) the results will vary depending on how the D7 or D700 is set. <br>
<br>
<br>
1) When the US version D7A(G) or any D700 is used in *standalone*
'APRS" mode, the transmitted beacons (always sent in the
highly-compressed Mic-E format) will contain altitude IF the GPS
outputs the GPGGA string. The Euro versions of the THD7 don't encode
altitude, even if altitude IS present in the GPS data stream. Note
that you can shorten the Mic-E burst (useful for posit-after-voice
operation) by turning off the GGA string in the GPS device, so the
comment field doesn't get filled with altitude data.<br>
<br>
<br>
2) When the D7/D700 are used in "PACKET" mode with an external
program, the internal firmware echos ONE (and only one) selected string
of your choice received at the Kenwood GPS input out the main serial
port connected to the PC. The command " GPSTEXT " sent to the
D7/D700 internal TNC determines which one GPS string is captured and
forwarded to the PC. You can see and/or alter this command in the TNC
initialization file THD7.CMD or D700.CMD) in UI-View.<br>
<br>
If you initialize with " GPSTEXT $GPGGA ", the APRS program on the PC
will be able to "see" (and therefore transmit) LAT, LONG, TIME and
ALTITUDE but not speed and heading.<br>
<br>
If you initialize with " GPSTEXT $GPRMC ", the APRS program on the PC
will be able to see LAT, LONG, TIME and SPEED. but not altitude.<br>
<br>
If you initialize with " GPSTEXT $GPGLL " the APRS program on the PC
will be able to see LAT, LONG, and TIME only with no altitude or speed
information.<br>
<br>
<br>
3) If you connect the GPS device directly to the PC through a second
serial port (i.e. not using the Kenwood pass-through feature) --AND--
your PC-based APRS software knows how to parse and extract data from
multiple GPS sentences simultaneously and then format this data into
APRS format (UIview does this), then you can transmit LAT, LONG,
SPEED, and ALTITUDE at the same time. <br>
<br>
<br>
<br>
<br>
<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
EchoLink Node: 14400 [Think bottom of the 2M band]<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.com">http://wa8lmf.com</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://webs.lanset.com/wa8lmf/DigiPaths">http://webs.lanset.com/wa8lmf/DigiPaths</a> <br>
<br>
Updated APRS Symbol Chart <br>
<a class="moz-txt-link-freetext" href="http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf">http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf</a> <br>
<br>
<br>
New/Updated "Rev G" APRS <a class="moz-txt-link-freetext" href="http://webs.lanset.com/wa8lmf/aprs">http://webs.lanset.com/wa8lmf/aprs</a><br>
Symbols Set for UI-View, <br>
UIpoint and APRSplus:<br>
<br>
<br>
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