M7 GX Technical Manual
52
Raveon Technologies Corp.
simplest way to set it the
TDMATIME
is to make it equal to the
TXRATE
, the rate
you wish to report position
The duration of a TDMA time slot is programmed into the
RV-M7 GX
with the
SLOTTIME
command. If
SLOTTIME
is set to 200 milliseconds (factory default),
then every 10 seconds, the RV-M7 will have a 200mS window to report its position
in.
All TDMA frames are synchronized automatically in all
RV-M7 GX Transponders
to
the top of the minute. Slot 0, frame 0 is at the top of each minute.
A unit may be allocated additional time slots. The SLOTQTY command sets the
number of slots each unit receives. It is normally set to 1.
10.5.
Configuring TDMA Operation
Step 1.
Determine your over-the-air baud rate. See section 11.3 for
information on baud-rate selection. Raveon recommends 4800 baud
for narrow-band and 9600 baud for wide-band radios.
Step 2.
Determine the position transmission time, in milliseconds. Again,
review the table in section 11.3 to determine how long a position
transmission at your selected baud rate will take.
Step 3.
Repeaters. If a repeater will be used in the system, then the
transmission time must be doubled, because each position will be
transmitted twice, once by the originating RV-M7 and once by the
repeater.
Step 4.
Determine TDMA slot time required to send the position. Slot times are
programmed with the
SLOTTIME
command, and are in 10mS
increments. Always add 10mS additional time for some margin. For
example, if your position transmission requires 65mS, then the correct
SLOTTIME
to program would be 80mS. The
SLOTTIME
must be
greater than the duration of the position transmission. If a repeater is
used with a 80mS position report, then the
SLOTTIME
should be set to
at least 160mS. Note, the SLOTTIME may be set longer than required
to transmit a position, it just may not be shorter. If Encryption is
enabled (which it is by default), the slot time must be 20mS longer to
account for the encryption/decryption processing.
Over-the-air rate
Number of
Modulation
Levels
Position
/Status
Transmissio
n Duration
Suggest TDMA Slot time
4800bps
(R2=3)
Default setting
2
70mS
100mS
8000bps
(R2=4)
4
50mS
100mS
9600bps
(R2=5)
2
45mS
50mS (No Encryption)
70mS (if encryption enabled)
14400bps
(R2=10)
4
30mS
50mS
