You are going to want to track your HAB during its flight, to keep tabs on it, see how high it goes, and stand some chance at recovering it. On most flights, especially those with expensive gear on-board, you may want a backup tracker – just in case. It is possible to try to locate your HAB using some sort of radio direction finding gear, but this can get complicated quickly. For most flights, you will simply want employ some sort of GPS system that can report back to you with location. Care must be taken in the design and placement of this gear to make sure that your GPS can receive the needed radio signals from the GPS satellites. The system would also need to somehow report back with another radio signal. Also be aware that not all GPS chipsets will work at high altitudes.
Common options today:
-HAM radio APRS system
-RTTY or LoRa based tracker
-Cellular based tracker
-Satellite based tracker
Design considerations:
-If you value your payload, consider multiple trackers
-Not all GPS chipsets work at high altitudes.
-GPS is a radio receiver. It can be jammed by nearby noisy electronics like cameras.
-A GPS receiver must be able to clearly ‘see’ the sky to get a position fix.
-A tracker needs to also transmit its location to you. Obstructions close to the ground may interfere.
-The higher a transmitter travels, the larger the area that can hear it.
APRS (Amateur Position Reporting System) is a packet radio protocol developed for Amateur Radio (HAM) that can handle position information and some basic telemetry data. HAM operators (and their clubs) operate radio repeater systems that can receive and boost APRS signals. There are also Internet Gateways (iGates) that receive these signals and direct the information on to the Internet. So by using this wonderful existing HAM infrastructure, you can ‘hear’ and follow the positions of your payload and your chase cars. The radio frequencies and rules for operation differ between countries [In North America, APRS can be readily used for HAB and is generally on 144.390MHz]. The APRS device must be turned-on by a licensed HAM. A license is not hard to get – pass a test, pay a small fee – and doing so would open up opportunities for other interesting radio projects.
Over in England, where the APRS protocol is prohibited above the ground, there has been great success in using a low-power radio signals based upon RTTY. There, specific frequencies and protocols have been agreed upon so that a network of receiving stations could be constructed. The data rate for RTTY is very low, but is enough to carry position data. If you are patient, small images can be sent.
Over the past decade, a proprietary protocol called LoRa is seeing increased use. LoRa is designed to support the Internet-of-Things revolution by providing a consistent platform for the bi-directional transmission of data over a rather long range. A LoRa transceiver is purchased pre-built and is the size of a postage stamp. For communication, an identically programmed LoRa system must also exist at a ground station. The data rate is better than RTTY and each end can transmit and receive. Dave Akerman’s Pi-in-the-Sky LoRa system is my favorite application of this. We have worked together on a TTGO T-Beam version of this as well.
The cellphone network is designed for ground use only. Attempting to use a cellular device above a few thousand feet can be difficult and can cause issues for the cell provider. On or near the ground though, cellular can be used to for simple position data as well as high bandwidth services like live video. Small SMS based tracking devices can be purchased cheaply to provide basic backup tracking. [Application works as advertised but it is illegal to transmit from a cellphone while airborne. Title 47 § 22.925 : “Cellular telephones installed in or carried aboard airplanes, balloons or any other type of aircraft must not be operated while such aircraft are airborne.”]
With the advent of the satellite constellations, it is now possible to bi-directionally relay standard voice and data network anywhere in the world. These systems require a subscription service and charges are based upon the amount of data relayed. The tracker unit must be able to communicate clearly with the satellites as they pass overhead.
-Paul Lowell, KD4BFP