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 navigation unit that is able to dynamically update the target coordinates.
The tracking system is based on APRS and has many years of heritage. When used on standard amateur radio APRS frequencies it can take advantage of the existing global APRS network of digipeaters and IGates, but it can also be used in point-to-point links on any suitable frequency including unlicensed bands.
In addition to position reporting, the system can also transmit telemetry read via analog and/or digital inputs.
The page is intended to present a reliable tracking solution for those not already familiar with APRS. If you are already using APRS, you may find the information on this page trivial.
Contents
Functional Overview
The tracking system consists of the following subsystems:
- The transmitter placed on-board the balloon. It transmits GPS coordinates and other telemetry at regular intervals.
- The global APRS network that receives the APRS packets from the balloon via digipeaters and IGates and publishes them on the Itnernet, see http://aprs.fi/ – this can be used to follow the balloon trajectory from anywhere over the Internet.
- A mobile APRS receiver station that is used for real time tactical navigation in the field where no Internet is available. This station receives the APRS packets directly from the balloon.
A functional diagram of the complete tracking system is shown below followed by a description of each functional block.
- GPS Receiver
- The GPS receiver tracks GPS satellites and calculates the position of the balloon in real time. It sends standard NMEA formatted data to the APRS packet encoder. Besides the obvious low mass and power requirements, it is very important that the GPS receiver works above the 18km limit.
- APRS Encoder (TNC)
- The APRS encoder takes the input digital data (position and telemetry) and converts it into 1200bps AFSK audio signal. In other words, this is where the conversion from digital data to analog signal takes place.
- FM Transmitter
- The FM transmitter converts the audio signal containing the 1200bps AFSK data to VHF or UHF radio signal.
- FM Receiver
- The FM Receiver receives the VHF/UHF radio signals and converts it into audio signal that contains the 1200bps AFSK data.
- APRS Decoder (TNC)
- The APRS decoder decodes the received AFSK data into APRS packets from where the balloon position and telemetry can be extracted. Technically, this is where the conversion from analog signal to digital data occurs.
- Tactical Navigator
- Car navigation unit that supports tactical navigation (chasing). It receives balloon position data from the TNC and plots it on the map. In tactical mode it updates the route from the current location to the target location (balloon position) in real time.
- Telemetry Logger
- This functional unit is used to log the received APRS packets from the balloon, both position report and telemetry packets. This can be a simple laptop or netbook connected to the TNC.
- Digipeaters and IGates
- These are automatically part of the system if using amateur radio APRS frequencies. This is an existing infrastructure and will not be described further here.
Components
This section presents the physical components of the tracking system and provides a mapping for each component to the functions they provide.
Component | Description | Functions |
---|---|---|
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 |
|
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 |
|
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 MX146LV
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.
The MX146 comes in two versions:
- +8VDC version that gives > 500mW RF out
- +5VDC version that gives > 350mW RF out
We chose the 5V version because its lower power consumption and to allow operation of all components from a single 5VDC supply. In addition to the lower power consumption, the 5V version is capable of higher duty cycle than the 8V version.
Specifications (5V version) | |
---|---|
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 | min 350mW into 50Ω (400mW typ) |
Programming |
|
Supply voltage | +5VDC (4.7V to 6V) |
Current consumption | 1mA stdby, TBD mA TX |
Size | 50x25x2.5mm |
Weight | |
Operating temperature | -40°C to +85°C |
Mechanical interfaces | Pin-header or wire |
Special features |
Resources:
Kenwood TM-D710E
AvMap G5
Telemetry Recorder
Budget
Link Budget
Using a roof mounted car antenna as well as MGA