Tactical Tracking System

This page describes a Tactical Tracking System for high altitude balloons – or any other object – based on the Automatic Position Reporting System (APRS). The term Tactical Tracking here refers to real-time tracking and chasing, where the coordinates of the tracked object are received in real time and sent to a car navigation unit that is able to dynamically update the target coordinates.

The tracking system is based on APRS. Therefore it has many years of heritage and can take advantage of an existing global APRS network. It does not require any R&D since all components are available off-the shelf and even complete turn-key solutions are available.

In addition to position reporting, the system can also transmit telemetry read via analog and/or digital inputs.

Functional Overview

The tracking system consists of the following subsystems:

1. The transmitter placed on-board the balloon. It transmits GPS coordinates and other telemetry at regular intervals.
2. The global APRS network that receives the APRS packets from the balloon via digipeaters and publishes them on the global APRS network, see http://aprs.fi/
3. A mobile APRS receiver station that is used for real time tactical navigation in the field where no Internet is available. This station also receives the APRS packets directly from the balloon.

Diagram

On-Board Transmitter

GPS Receiver

• Garmin GPS 18x LVC: https://www.argentdata.com/catalog/product_info.php?cPath=23&products_id=37
• Trimble Copernicus GPS Receiver: https://www.argentdata.com/catalog/product_info.php?cPath=23&products_id=95

OpenTracker+ SMT

The OpenTracker+ is an open source APRS tracker that receives NMEA data from a GPS receiver, encodes it into APRS packets and generates AFSK signal suitable for audio input to an FM transmitter. It can also transmit telemetry data that is read from the built-in temperature sensor (non-SMT version) as well as the available ADC channels.

OpenTracker+ can be purchased assembled and tested or as a kit. Additionally, there is an SMT version, which is the one we are using. The SMT version does not include a built-in temperature sensor or LEDs.

Specifications for SMT version
Operating modes	1200 bps AFSK (RX and TX) 300 bps AFSK, PSK31 (TX only)
Supply voltage	DC 6.5 to 28V unregulated or 5V DC regulated
Current consumption	8 mA idle, 20 mA transmitting
Size	31x18x5 mm (24-pin DIP footprint)
Weight
Operating temperature
GPS interface	NMEA in/out
Mechanical interfaces	Pin-header or wire
Special features	Max 200 mA @ 5 V available for GPS Source code released under Modified BSD license 8-bit analog TM from ADC1-5 digital TM for T1CH1 and ADC6-9

Pinout
Pin	Name	Function	Utilisation
1	5VIN	Regulated 5-volt input
2	RXD	RS-232 data in (from GPS or computer)
3	1WIRE	Dallas 1-wire bus for external sensors
4	AOUT	Audio out to radio
5	ADC5	Analog input
6	T1CH1	Timer channel
7	ADC6	Analog input
8	RST	Reset (active low)
9	ADC7	Analog input
10	IRQ	Transmit-now, profile select, or counter
11	ADC8	Analog input
12	ADC9	Analog input
13	AIN	Audio input from radio
14	ADC4	Analog input
15	ADC3	Analog input
16	TXD	RS-232 data out
17	RED	Red LED output
18	GREEN	Green LED output
19	ADC2	Analog input
20	ADC1	Analog input
21	PTT	Push-to-talk signal to radio
22	REGOUT	Regulator output - 5 volts
23	GND	Ground
24	REGIN	Regulator input - 6.5 to 28 volts

Resources

• Website
• OpenTracker+ Support page (firmware, schematics, source code, etc.)
• OpenTracker+ Manual

SRB MX146 FM Transmitter

TBC whether we use 5V or 8V version

The MX146 is an embeddable VHF transmitter module from SRB Electronics. It's programmable for any frequency from 144-148 MHz in 2.5 kHz steps, or it can be used on one of 16 pre-programmed frequencies.

Power output is 500 mW minimum, and typically closer to 850 mW. It draws under 1 mA in standby, has a fast wake-up time (< 25 ms) and is suitable for voice or data with bitrates up to 10 kbps or more.

Specifications
Frequency range	144MHz to 148MHz
Channel spacing	2.5kHz
Modulation	Digital injection modulation
Modulation Bandwidth	>20kHz
Modulation Sensitivity	23kHz/V (typ)
Input Impedance	~600Ω
Spurious suppression	> 80dB (channel spacing > 10kHz, typ)
Harmonic suppression	45dB
Frequency stability	+/5ppm (typ)
Turn On delay (after PTT)	25msec (typ)
Output power	> 500mW (nominal) into 50Ω
Programming	SPI® and I2C® interface or 16 preprogrammed frequencies, pin selectable. 3.3V CMOS level
Supply voltage	+8VDC (7.5V to 8.5V) or 5VDC
Current consumption	< 5mA RX < 400mA TX
Size	50x25x2.5mm
Weight
Operating temperature	-40°C to +85°C
Mechanical interfaces	Pin-header or wire
Special features

Resources

• Website
• SRB Yahoo Group
• User's Manual