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[aprssig] Help for course/speed/altitude etc HF APRS

Jack Chomley radio at dodo.com.au
Sun Apr 29 00:57:41 UTC 2007


I should have looked in the manual further :-) Looks like I can run the 
TM1+ in NMEA mode and simply select a transmit timer value, so it does not 
continue to broadcast EVERY sentence the TM1+ gets from the GPS.
In my case, the TM1+ can look for the header ($GPRMC) and I then either set 
the sentence length or termination character and it will be sent out the 
radio port at intervals set by my Tx timer value.
73s Jack VK4JRC

 From the Tigertronics TM1+ Manual:

NMEA Mode
This mode was designed primarily for GPS
tracking applications, where entire NMEA sentences need to
be sent. However, this mode can also be used in any
application where the desired data is identified by a known
preamble (header). In operation the incoming data is
searched for a predefined string (Data Header). When the
string is received, the unit starts storing data in its buffer. It
continues to store data until a user specified termination
character is received or until the buffer overflows. The
buffer length is 105 characters. This is sufficiently long to
store any NMEA string. The user can program up to three
Data Headers to search for. A header can be up to six
characters long. The unit searches for and transmits each
header in sequence. A transmit timer is provided in this
mode so that data can be transmitted at any user-defined
interval between 1 second and 68 minutes. NMEA Mode
allows the user to configure up to ten different "Profiles",
each with it's own SSID, Digi Path, Transmit Timer Interval,
TX Delay and Tail Delay.
Delay and Tail Delay. The other information used by these
modes (MyCall, ToCall, etc.) is shared among all of the
profiles. Each profile can be selected by the user in the field,
without the need for a computer. This is useful in situations
where the operator is driving from one area to another, and
needs to switch the Digi path from a local path to a more
generic one. It is also a convenient way to change timer
intervals for changing situations, like when you are no longer
moving.

>I would think that for HF you'd want the shortest packet possible,
>so make sure you're not sending GPRMC strings over the air.  Try for
>Base-91 or Mic-E format packets instead  if the TNC's will do that.
>
>That said, the TNC needs to receive GPRMC sentences from the GPS in
>order to get course/speed, and GPGGA sentences to get the altitude.
>
>I don't know whether that info will help you, but each little  bit
>of knowledge might get you closer to a solution.
>
>--
>Curt, WE7U.                             archer at eskimo dot com
>http://www.eskimo.com/~archer
>   Lotto:  A tax on people who are bad at math. - unknown
>Windows:  Microsoft's tax on computer illiterates. - WE7U.
>The world DOES revolve around me:  I picked the coordinate system!"
>
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