Globalstar STX3 User manual

8545-0198-01 Revision 1.9 STX3 Users Manual
9/24/2020 Globalstar, Inc. Confidential and Proprietary
STX3 Users Manual
Globalstar Satellite Transmitter Module - Third Generation

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Printed in the United States of America

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Table of Contents
1Introduction ......................................................................................................................................................................................1
1.1 Purpose.....................................................................................................................................................................................1
1.2 Applicable Documents.............................................................................................................................................................. 1
1.3 Description ............................................................................................................................................................................... 1
2Application ........................................................................................................................................................................................2
2.1 Theory of Operation .................................................................................................................................................................2
2.2 Block Diagram...........................................................................................................................................................................4
3Physical Characteristics .....................................................................................................................................................................5
4Reference Design ..............................................................................................................................................................................9
4.1 Antenna Requirements ..........................................................................................................................................................10
1.1. Trace and Cable Losses........................................................................................................................................................... 10
4.2 Effect of Plastic on Radiation.................................................................................................................................................. 11
4.3 Power Supply Design ..............................................................................................................................................................11
4.4 Bill of Materials.......................................................................................................................................................................12
4.5 PCB Layout..............................................................................................................................................................................13
5Application Programming Interface ................................................................................................................................................ 15
5.1 Serial Port ............................................................................................................................................................................... 15
5.2 Serial Packet Mode................................................................................................................................................................. 15
5.2.1 Serial Packet Format .......................................................................................................................................................... 16
5.2.2 Serial Packet Commands....................................................................................................................................................16
5.2.2.1 Send Data (0x00) .......................................................................................................................................................16
5.2.2.2 Query Electronic Serial Number (ESN) (0x01) ........................................................................................................... 17
5.2.2.3 Abort Transmission (0x03) ........................................................................................................................................17
5.2.2.4 Query Bursts Remaining (0x04)................................................................................................................................. 17
5.2.2.5 Query Firmware Version (0x05) ................................................................................................................................18
5.2.2.6 Setup (0x06) .............................................................................................................................................................. 18
5.2.2.7 Query Setup (0x07)....................................................................................................................................................19
5.2.2.8 Query Hardware Version (0x09)................................................................................................................................19
5.2.2.9 CW Test Mode (0xFC 0x01) ....................................................................................................................................... 20
5.2.2.10 Send Test Packet (0xFC 0x02).................................................................................................................................... 20
5.2.2.11 Modulation Test Mode (0xFC 0x03) .......................................................................................................................... 21
5.3 Example CRC calculation routines for serial packets..............................................................................................................22
5.4 AT commands.........................................................................................................................................................................24
6Test Modes......................................................................................................................................................................................27

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7REGULATORY APPROVAL ................................................................................................................................................................28
7.1 Radio Astronomy Site Avoidance ...........................................................................................................................................28
7.2 Regulatory Notices .................................................................................................................................................................28
8Appendix A – Antenna Manufacturers............................................................................................................................................31

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1Introduction
1.1 Purpose
This document describes the physical, electrical, and functional characteristics of the STX3 satellite transmitter module. The
information contained in this document is intended to provide the end user with the necessary technical information required
to use the module in a custom application.
This document is intended to be used by engineers and technical management and assumes a general knowledge of basic
engineering practices by the user.
Please note that Globalstar is only responsible for ensuring that the STX3 meets the published manufacturing specifications
described herein.
1.2 Applicable Documents
STX-3 Reference Design
1.3 Description
The STX 3 is a simplex Satellite transmitter designed to send small packets of user defined data to a network of low earth
orbiting (LEO) satellites using the Globalstar simplex satellite network. The received data is then forwarded to a user defined
network interface that may be in the form of an FTP host or HTTP host where the user will interpret the data for further
processing.
The STX3 is a surface mount module designed to attach to a user defined host PCB which must provide power, an RF
connection to the transmit antenna, and communications with a host processor which will control the operation of the STX3.
All electrical connections are provided via the castellated pads on the perimeter of the PCB.
The STX3 is a small, low-profile device with the dimensions shown below.
Figure 1 (dimensions in inches)

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2Application
2.1 Theory of Operation
The STX3 operates on the Globalstar LEO satellite network. LEO (Low Earth Orbit) means that there are a number of satellites in low
earth orbit that constantly orbit the planet and can communicate with Globalstar devices that are within range of its current
position.
Figure 2 LEO Constellation
Since the satellite position is constantly changing, simplex devices on the ground will transmit (with no knowledge of any of the
satellites locations) and the transmission may be received by one or more satellites. These satellites will then relay the message to
the nearest satellite gateway as shown below. Once received by the satellite gateway, the simplex message will be delivered to the
simplex gateway where redundant messages are discarded and the data from the message is sent to the OEM via the Internet.
Figure 3 Simplex Messaging

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Messages are composed of 1 or more 9-byte payloads. The STX3 can only transmit 9-byte on-air messages, so user payloads greater
than 9 bytes will require multiple on-air packets to be transmitted for each user payload.
There are brief periods of time where there is no satellite in range of the simplex transmitters due to obstructions and/or satellite
coverage geometry. Since a simplex device has no way of knowing if a transmitted message has been successfully received, the STX3
device is designed to send multiple (redundant) transmissions for each message being sent over the Globalstar network. The default
value for the number of redundant transmissions per message is 3. This means that each message sent to the STX3 will be
transmitted 3 times. Each transmission will contain the exact same data payload. The redundant transmissions of each message will
be sent on a randomized 5-minute nominal interval.
The transmission sequence for a single-packet message using the default setting of 3 redundant transmissions is shown below.
The transmission sequence for a two-packet message using the default setting of 3 redundant transmissions is shown below.
For normal conditions where the transmitter has an open view of the sky, this will result in a better than 99% chance that the
message will be received.

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2.2 Block Diagram
The basic elements of a design utilizing the STX3 simplex transmitter are shown below.
Figure 4
The STX3 provides separate power supply inputs. The digital power supply input (VDIG) is a low power input which powers the
digital portion of the STX3. This provides the capability to leave the STX3 in a low power consumption state when the transmitter RF
section is idle. The RF power supply input is a high power input which is only required while the STX3 is transmitting a data packet.
Since the transmission duty cycle is very low, this supply may be turned off the majority of the time and only active during the
transmission of a packet. Due to the random nature of the burst transmissions, and open collector output (PWR_EN) is provided by
the STX3 which can directly control the high current supply for VRF. This will ensure that the RF power supply is enabled for the
minimum amount of time to complete each transmission. It may also be monitored by the host to determine when each burst has
been completed without the need to query the STX3 via the serial host interface.

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3Physical Characteristics
Figure 5 Top View

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Figure 6 Recommended PCB footprint layout (dimensions in inches)