Advanced-Rocket Tracking Using Onboard Radio Transmitters

I. General Considerations

There are two main types of radio tracking. These are GPS based and direction finding. In each of these categories there is equipment that requires an Amateur (Ham) Radio license, and other equipment which does not. I will try to present an overview of these types of equipment and the associated methods. I will append web page links for companies that make or sell relevant equipment at the end of the article.

II. GPS BASED SYSTEMS
GPS based systems have the advantage of telling you where your rocket is, with good precision. It provides a specific position to go towards and can be used with mapping software to plot an approach path. There are some very good apps, that are free or inexpensive, to track GPS coordinates on smart phones.

Amateur (Ham) Radio “APRS” allows use of better antennas on the rocket, and use of digital repeater stations, “digi-peating” or simply “digi” to extend range. There are apps available, and simple interfaces, to allow receiving APRS data and plotting on maps using smartphones and similar devices, such as tablets and even iPods. Amateur Radio systems allow for more flexibility in settings and frequencies. They are available on different bands, and if built up from components can even have multi-band capability in the same unit. If a digi-peater is being used, it makes sense to keep all units on the digi’s frequency, and this also allows for cooperation when looking for a rocket.

Non-licensed bands are limited in power and transmitting antenna. Very useful for “average” high power rockets. They may not have the range for very high altitude or long range flights. In most cases at Lucerne Valley, with waivers available at ROC launches, they should be more than adequate. Almost all non-licensed systems are set up to be “turn-key”, and work out of the box with no configuration required. Some non-licensed systems have Bluetooth interfaces that can send position data directly to a smart phone, but most require the user to read the coordinates from the receiver and manually enter them into the phone.

The advantage to GPS based systems is the search is much simpler, since your rocket essentially tells you where it is. There is also the possibility, depending on specific systems, to have telemetry data for things like system voltage, temperature, etc. Some units will take analog or digital data points, and send them as telemetry data also; so you could set up a barometric pressure sensor, accelerometers, even switches to detect parachute deployment.

Amateur Radio GPS Systems
There are two main ways to get GPS data using the Amateur Packet Reporting System (APRS) protocol. You can purchase an all-in-one tracker, which includes GPS, all APRS circuitry, and a transmitter in a single assembly. You can also assemble your own system using separate GPS, APRS module, and a transmitter or transceiver.

There are trackers made specifically for rocketry. Among the most popular are the units made by Big Red Bee. They are available for both the 2 meter and 70 centimeter ham bands. They can be ordered with default settings including the callsign of the purchaser, so only the receiving station need to be configured. You can also purchase a programming cable to allow various parameters to be customized, such as how often it transmits position data, whether the signal should be digi-peated, a short text message, etc. These trackers provide a very simple option for a beginner, with the possibility of more control over configuration as the need arises.

The second option, assembling your own tracker from modules, allows a wider range of choices of band and frequency, GPS type, and APRS module capabilities. In many cases, an APRS module and GPS can be fitted to an inexpensive hand-held transceiver and antenna. Assembling your own system provides the most flexibility, but also means that you have to do all configuration and integration yourself. These systems are quite the opposite of a “turn-key” system that will work out of the box.

You can select a more standard GPS, or one capable of high altitude operation. A “standard” GPS will usually stop working at about 60,000 feet. This is not usually a significant limitation, but if you are flying a rocket above that level you would need a specialized GPS. GPS modules can be purchased from various sources (Ebay, Fry’s Electronics, Adafruit, Argent Data, etc.) for prices ranging from under $20 to around $100 dollars. Note that this is a GPS receiver module only—no display, bells, or whistles.

APRS tracker modules vary in capabilities; such are types of telemetry, ability to decode APRS packet, and even the ability to work as a digi-peater. Prices range from about $40 to about $80 and up. You may be able to find kits for a bit less. These modules are available from Byonics, Argent Data Systems, and RPC-Electronics.

Transmitters or transceivers can either be simple modules or complete hand-held units. Byonics and Argent Data sell modules of varying capability. Many hams prefer to use an inexpensive hand-held. There are imported hand-held radios from companies like Bao Feng (aka Po Fung), Wouxan, and TYT which are very small, lightweight, and inexpensive. Many are available for under $40 from Amazon andother online retailers . These are generally capable of operating on more than one band, and can be used on a number of frequencies within each band. The most common combination is 2-meters and 70 centimeters in a dual-band radio.

Non-Licensed GPS Systems
There are some GPS based systems available that are specifically designed for rocket tracking. They operate on a 900 MHz UHF band, and have ranges sufficient for any flights likely to happen at ROC events. In my opinion, the two best options are from Big Red Bee and Egg Timer Rocketry.

The Big Red Bee system is ready to go out of the box and is a completely turn-key system. The 900 MHz, non-licensed, version is used with a receiver that connects to a computer, or can have an optional LCD display added to eliminate the need for a computer.

The Egg Timer Rocketry system is only available in kit form, so it must be built by the user. I haven’t built one, but it looks like anyone with electronics or kit building experience should be able to complete one with no problem. This is also a 900 MHz system with a computer-dongle receiver. There is an optional stand-alone receiver with LCD display, that can be used with an optional Bluetooth adapter to allow navigation to the rocket using a smart phone. Egg Timer products require assembly, but are also priced lower than other options.

III. Direction Finding Systems
Direction Finding provides a signal to follow to your rocket. It can have issues with reflections and other propagation phenomena, and require more skill for success.

Amateur Radio Direction Finding (ARDF) allows use of various frequencies and higher power level. Also better antennas can be used in the rocket. In most cases it does not require much power to track a rocket using ARDF gear, but the options are there. Since most tracking is done on VHF or UHF bands that the average ham already has equipment for, the cost is less. If you do not have equipment for these bands there are a number of low cost hand-held units, and in many cases a scanner works very well. A directional antenna makes things easier, as does a good attenuator. These can be purchased or built yourself pretty cheaply.

Non-licensed direction finding equipment is more limited in frequencies, power, and transmitter antennas available. Again, power is not the only factor for range—the receiving equipment is much more flexible. The commercially available systems are quite adequate for most launches at Lucerne Valley.

With direction finding systems a beacon transmitter in the rocket sends out a signal that can be tracked with a suitable receiver using a directional antenna. Unlike GPS based systems, direction finding does not give you the specific location of the rocket. It provides a direction that you can go to find the rocket. There are a number of factors that can complicate this process. The main issue is that when the rocket reaches the ground it is common to lose the signal until you are very close. If a rocket flies several miles downrange, you have to keep track of the direction it was in from your position and head towards it until you can find the rocket or pick up the signal again. There can also be issues with “multi-path” images, which means that the signal from the rocket may reflect off of a building or other structure, and you can wind up following the wrong signal. Direction finding requires some skill and practice, and there are local, national, and international clubs and competitions for Amateur Radio Direction Finding (ARDF). This commonly called T-Hunting (transmitter hunting) or Fox Hunting. This is very different from GPS tracking—instead of your rocket telling you where it is, you get a direction to head while looking for it, with little or no information on how far away it is. This can be very effective, but not as easy as going to a specific location.

There are a number of sources for direction finding beacons that transmit on ham frequencies. Big Red Bee and Adept market beacons for rockets. There are several manufacturers who make small beacons for ARDF use that are suitable for rocket use, including Byonics, Communications Specialists, and Doppler DF Instruments. Most can be used with the beacon transmitter in the rocket and almost any hand-held ham radio or scanner. Some have specialized receivers available that are designed for finding their matching transmitter. Amateur radio allows a lot more flexibility in bands, frequencies, transmitter antennas, and power output than non-licensed options. You can also buy or build a fairly simple controller that transmits with a hand-held radio or modular transmitter. Only an entry level “Technician Class” amateur radio license is required to operate the transmitters typically used in rockets. Note that no license is required to use a receiver to search for them.

Direction finding beacons that do not require a license are bit more limited. They are marketed by Walston Retrieval and Communication Specialists; although the Comm-Spec are market as “cat locators” they are sometimes used for rocket tracking. Note that Communication Specialists used to sell a similar system under the “Rocket Hunter” brand, which are not legal to use due to the frequencies they operate on, and they were ordered by the FCC to “cease and desist”—so they moved their product to ham radio frequencies that require a license, and also came out with their “cat locator” that actually operates on frequencies intended for wildlife tracking, but so far no issues from the FCC with that use.

IV. In Summation

The main options for rocket tracking are GPS based and Direction Finding equipment. The GPS based systems may also provide live, in-flight telemetry, and will provide a specific, three-dimensional, location for your rocket in real time. The direction finding systems provide the heading to your rocket. The GPS systems are more complicated in the rocket and on the ground, and generally more expensive.
So the basic choice is do you want to know what direction to look for your rocket, or do you want the rocket to tell you where it is?
Amateur Radio systems require a license, but allow more flexibility than non-licensed systems—including the ability to build your own system from scratch.
There are undoubtedly manufacturers and systems out there that I am not familiar with, so if you are using one of them please email and let me know how it is working for you.

David Smith, W6DPS

Email: DaveW6DPS (at) gmail dot com

Where to find equipment:

BIG RED BEE; ARDF beacons and all-in-one trackers designed for rocketry, both ham and non-licensed
http://www.bigredbee.com

EGG TIMER ROCKETRY; non-licensed GPS trackers and electronics for rocketry
http://eggtimerrocketry.com

BYONICS: APRS, GPS, and transmitter modules, all-in-one trackers, and direction finding transmitters
http://www.byonics.com

ARGENT DATA SYSTEMS; APRS, GPS, and transmitter modules
http://www.argentdata.com

RPC ELECTRONICS; APRS modules
http://www.rpc-electronics.com

DOPPLER DF INSTRUMENTS; Amateur Radio direction finding equipment
http://www.silcom.com/~pelican2/PicoDopp/MICROHUNT.htm

COMMUNICATION SPECIALISTS; Amateur Radio and non-licensed direction finding equipment
http://www.com-spec.com/rocket/index.html

WALSTON RETRIEVAL; non-licensed direction finding equipment
http://www.walstonretrieval.com/

MULTRONIX, Very full featured , non-licensed, GPS tracking system for high power rockets
http://www.multronix.com

REAL FLIGHT SYSTEMS, Non-licensed GPS Tracking, telemetry and data logging equipment designed for rocketry
http://www.realflightsystems.com/