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M7 GX Technical Manual 49 Raveon Technologies Corp.

9600 baud as at 4800 baud. Its performance is optimized for 4800 baud 2-level

modulation and 8000 baud 4-level modulation.

If 4-level modulation is used (8000 and 9600 baud over-the-air), the “Modulation

Balance” procedure must be re-done anytime the radio frequency is changed. This

procedure must be done by a qualified radio technician. See section 10.7 for

details on how to do this procedure.

The maximum over-the-air baud-rate for a wide-band model (25kHz channel

spacing) is 19200bps. Due to IF filter limitations, it does not work as well at 19200

baud as lower data rates. Its performance is optimized for 9600 baud 2-level

modulation.

10.4. TDMA Overview

TDMA, or Time-Division-Multiple-Access is a very effective way of allowing a lot of

radios to share one radio channel. Used extensively in GSM cellular and APCO

public-safety systems, TDMA excels at allowing quick and reliable access to radio

channels. It allows 2-10 times more radios to share a radio channel than

conventional carrier-sense methods. This allows 2-10 times more tracking radios

on one channel, as compared to radios that do not have TDMA capability.

The following diagram illustrates how it works.

When a RV-M7 GX wants to report its position and status, it waits until its assigned

time-slot, and then transmits its data. By default, TDMA time slot positions are

assigned by unit-ID, so RV-M7 GX with ID 1 uses the first slot, and ID 2 uses the

second slot, and so on.

A TDMA “Frame” time is the time it takes all units to transmit once. This is

configured with the TDMATIME xx command. The factory default is 10 seconds,

so every 10 seconds, each RV-M7 GX may transmit. The TDMA frame must be

set long enough for all units to transmit. For example, if you have 50 RV-M7s, and

use 200mS TDMA slots, then the TDMATIME should be set to 10 seconds. The

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.

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Raveon RV-M7 Spezifikationen Seite 49