Satellites have fascinated radio amateurs since the early days of OSCAR 1 in 1961. Today, getting started with satellite reception and even satellite communication is easier than ever before. With affordable SDR receivers, powerful tracking apps, and simple homebrew antennas, any radio amateur or interested person can receive signals from orbit. This article provides a step-by-step guide through the world of satellite tracking and reception – from theory through software to the right antenna.
Fundamentals: How Does Satellite Tracking Work?
To receive a satellite, you need to know when it flies over your location. Satellites in low Earth orbit (LEO) circle the Earth in approximately 90 to 100 minutes at a typical altitude of 400 to 1200 kilometres. From a given location, they are only visible for a few minutes – a so-called “pass” or “flyover”.
TLE Data and Keplerian Elements
The foundation of every orbit calculation is the so-called Two-Line Elements (TLE), also known as Keplerian elements. These standardised data sets describe a satellite’s orbit with parameters such as inclination, eccentricity, right ascension of the ascending node, argument of perigee, mean anomaly, and mean motion. TLE data is provided by NORAD (North American Aerospace Defense Command) and can be obtained from websites such as CelesTrak or Space-Track.org. Since satellite orbits constantly change due to atmospheric drag and gravitational effects, TLE data must be updated regularly – ideally every one to three days.
Pass Geometry: Elevation, AOS and LOS
For practical use, three terms are central: AOS (Acquisition of Signal) refers to the moment when the satellite appears above the horizon and becomes receivable. LOS (Loss of Signal) marks the moment when the satellite sinks below the horizon again. The maximum elevation indicates how high the satellite stands above the horizon during the pass – measured in degrees from 0 (horizon) to 90 (zenith, directly above the observer). Passes with high maximum elevation (above 45 degrees) are particularly favourable, as the signal is stronger and the satellite remains visible longer. A typical good pass lasts 8 to 15 minutes.
Tracking Software and Apps
There is a wide variety of programmes and apps that enable satellite tracking. Here we present the most important ones.
ISS Detector (Android/iOS)
ISS Detector is one of the most popular apps for beginners. It shows flyover times for the International Space Station (ISS) and many other satellites. The app provides timely warnings before a pass, shows the trajectory in the sky as an augmented reality view, and delivers all important data such as AOS direction, maximum elevation, and LOS direction. With the amateur radio extension, amateur radio satellites are also displayed. The app is free to use, with optional extensions available.
Heavens-Above (Web/Android)
Heavens-Above is a classic among tracking services and is available both as a website and as an Android app. The platform offers detailed pass predictions for thousands of satellites, including visual star charts showing where in the sky the satellite will be visible. Particularly useful is the brightness information for visual observation and the extensive database that also includes smaller satellites.
SatPC32 (Windows)
SatPC32 by DK1TB is a professional tracking programme for Windows, specifically developed for radio amateurs. It can directly control transceivers and rotators and automatically perform Doppler correction. SatPC32 supports virtually all common transceivers via CAT control and rotator controllers via various interfaces. For radio amateurs who want to actively work via satellites, SatPC32 is virtually indispensable. The programme is offered as freeware.
GPredict (Windows/Linux/macOS)
GPredict is a free open-source software for all common operating systems. It offers a clear graphical interface with world map, radar map, and tabular pass predictions. GPredict can also control transceivers and rotators and automatically perform Doppler correction. The software automatically updates TLE data from various sources and is particularly popular among Linux users. The modular interface allows multiple views to be displayed simultaneously.
Look4Sat (Android)
Look4Sat is a modern, open-source Android app specifically developed for radio amateurs. It shows flyover times with detailed information such as frequencies and operating modes and can automatically update TLE data. The app offers a clear display of passes with a polar diagram and is completely free and ad-free. Look4Sat uses the SatNOGS database for frequency information, making it particularly practical for amateur satellite operations.
Receiving Weather Satellites: NOAA and Meteor
Receiving weather satellites is one of the easiest and most rewarding entries into satellite reception. With minimal effort, impressive images of the Earth can be received.
NOAA Weather Satellites (APT on 137 MHz)
The NOAA satellites (NOAA-15, NOAA-18, NOAA-19) transmit in APT format (Automatic Picture Transmission) on frequencies around 137 MHz. APT is an analogue transmission method that has been used since the 1960s and is characterised by its simplicity. The signal can be received with a simple receiver and a basic antenna.
- NOAA-15: 137.6200 MHz
- NOAA-18: 137.9125 MHz
- NOAA-19: 137.1000 MHz
For reception, all you need is a receiver covering the frequency range around 137 MHz (for example, an RTL-SDR dongle), a suitable antenna, and decoding software. On the PC, programmes such as WXtoImg (a classic, no longer actively developed), SatDump, or noaa-apt are suitable. On Android, the app “Satellite Tracker” by Luigi Calisi can record the signal directly via the headphone jack and decode it. The received images show cloud formations, coastlines, and with infrared channels, temperature distributions – directly from space to your own screen.
Meteor M2-3 and M2-4 (LRPT on 137 MHz)
The Russian Meteor satellites transmit in LRPT format (Low Rate Picture Transmission), a digital method that delivers higher image quality than analogue APT. Meteor M2-3 and M2-4 also transmit in the 137 MHz band and can be received with the same equipment as the NOAA satellites. However, the decoding is somewhat more demanding, as a digital signal must be processed.
The software SatDump has established itself as the standard tool for Meteor reception. It supports both real-time decoding and post-processing of recorded IQ files. The resulting images are noticeably sharper and more detailed than APT images and can be displayed in various colour composites. Meteor satellites also transmit usable infrared images at night.
Amateur Radio Satellites
Amateur radio satellites offer the fascinating possibility of establishing radio connections via space. No licence is required for reception only; for transmitting, a valid amateur radio licence is needed.
Popular Amateur Radio Satellites
- SO-50 (SaudiSat-1C): One of the longest-active FM satellites. Uplink on 145.850 MHz (67 Hz CTCSS tone required), downlink on 436.795 MHz. SO-50 is relatively easy to work and a good entry satellite for FM satellite communication.
- RS-44 (DOSAAF-85): A Russian linear transponder satellite with uplink in the 70 cm band (435.610–435.680 MHz) and downlink in the 2 m band (145.935–145.995 MHz). RS-44 has a comparatively strong transponder and is well suited for SSB and CW operation.
- ISS (International Space Station): The ISS has a crossband repeater (uplink 145.990 MHz, downlink 437.800 MHz) and occasionally transmits SSTV images on 145.800 MHz. The repeater is FM-based and allows contacts with handheld radios and simple antennas, as the ISS has a very strong signal.
- AO-91 (RadFxSat/Fox-1B): An AMSAT FM satellite with uplink on 435.250 MHz (67 Hz CTCSS) and downlink on 145.960 MHz. AO-91 is only active during solar illumination and also offers a good entry opportunity. Note: The lifespan of Fox satellites is limited – check whether the satellite is still active before operation.
Doppler Correction
An important topic in satellite communication is the Doppler effect. Due to the high speed of satellites (approximately 7.5 km/s in LEO), the received frequency shifts: as the satellite approaches, the frequency is higher than the nominal frequency; as it moves away, it is lower. At 70 cm, the Doppler shift can be up to plus/minus 10 kHz; at 2 m, approximately plus/minus 3.5 kHz. For FM satellites, this is usually still tolerable; for SSB and CW operation, however, the frequency must be continuously tracked. Software such as SatPC32 or GPredict can do this automatically when the transceiver is connected via CAT control.
Antennas for Satellite Reception
The choice of antenna depends on the intended use. For pure weather satellite reception, simple constructions are sufficient; for active satellite communication, more capable antennas are needed.
V-Dipole
The V-dipole is the simplest antenna for satellite reception at 137 MHz. It consists of two metal rods or wires arranged at an angle of approximately 120 degrees to each other. The total length corresponds to approximately half a wavelength (about 1 metre). Despite its simplicity, a V-dipole delivers surprisingly good results for NOAA and Meteor reception. Construction takes less than an hour and costs only a few euros.
Turnstile Antenna
The turnstile antenna (also known as crossed dipole antenna) consists of two crossed dipoles fed with a 90-degree phase shift. This creates circular polarisation, which is ideal for satellite reception, as the polarisation of the signal constantly changes due to the rotation and tumbling movements of satellites. A turnstile antenna for 137 MHz is easy to build yourself and offers a much more uniform reception pattern compared to a simple dipole.
QFH Antenna (Quadrifilar Helix)
The QFH antenna is considered the queen of satellite reception antennas for omnidirectional reception. It produces nearly perfect circular polarisation with a hemispherical radiation pattern covering the entire sky. Construction is somewhat more demanding than a dipole, but numerous building instructions are available on the internet. A well-built QFH for 137 MHz delivers excellent results for weather satellite reception and requires no rotator.
Yagi Antenna
For active satellite communication and receiving weaker signals, Yagi antennas are the first choice. They focus the signal in one direction and thus offer higher gain than omnidirectional antennas. For satellite communication, crossed Yagis are frequently used, which produce circular polarisation. Yagi antennas must be tracked to follow the satellite – either manually by hand or automatically with an antenna rotator.
Arrow Antenna
The Arrow antenna (Arrow II Satellite Antenna) is a portable, handheld dual-band Yagi antenna specifically developed for portable satellite communication. It combines a 3-element Yagi for 2 m and a 7-element Yagi for 70 cm on a common boom with a handle. The Arrow antenna has established itself as the standard for portable FM satellite communication and makes it possible to work satellites with a handheld radio. Manual tracking by hand is easily achievable.
RTL-SDR: The Affordable Entry Point
An RTL-SDR dongle (Software Defined Radio based on the RTL2832U chip) is the most cost-effective entry into satellite reception. For approximately 25 to 35 euros, you get a wideband receiver covering the frequency range from about 24 MHz to 1766 MHz. This allows receiving virtually all satellite signals in the VHF and UHF range.
Recommended is the RTL-SDR Blog V3 or V4, which offers better reception performance, a more stable housing, and a TCXO (Temperature Compensated Crystal Oscillator) for less frequency drift compared to the cheapest no-name dongles. As software, SDR# (Windows), SDR++ (cross-platform), or CubicSDR (cross-platform) are suitable for reception, while SatDump handles the decoding of satellite signals.
Practical Tips for Getting Started
- Start small: Begin with receiving NOAA weather satellites. They transmit strong signals and can be received with minimal equipment. An RTL-SDR dongle and a V-dipole are sufficient for the beginning.
- Choose your location: For satellite reception, a location with the clearest possible view of the sky is ideal. Buildings, trees, and hills can impair reception at low elevation angles.
- Keep TLE data current: Outdated TLE data leads to inaccurate pass predictions. Update orbital data at least weekly, for important passes even daily.
- Make recordings: Record the baseband signal (IQ data). This way, you can repeat the decoding later at your leisure and try different settings without having to wait for the next pass.
- Be patient: Not every pass is equally good. Passes with low elevation yield weak signals, and atmospheric conditions can affect reception. The best results come from passes with a maximum elevation above 30 degrees.
- Use the community: Online forums, Reddit groups (r/amateursatellites, r/RTLSDR), and local amateur radio clubs are excellent sources for help and inspiration.
- Explore SatNOGS: The SatNOGS network is a worldwide network of satellite ground stations. Even without your own receiving equipment, you can view satellite data there – or contribute your own station to the network.
Conclusion
Satellite tracking and reception is a fascinating field that extends amateur radio by a literally new dimension. Getting started is surprisingly simple and affordable: with an RTL-SDR dongle for around 30 euros, a homebrew V-dipole antenna, and free software, you can already receive your first weather satellite images. From there, you can work your way up step by step – to better antennas, to active satellite communication with your own licence, or even to building an automated ground station. The combination of technology, natural science, and the magic of receiving signals from space makes satellite reception one of the most exciting areas in amateur radio.
73 – your oeradio.at editorial team
Transparency Notice
This article was researched and written with the support of AI (Claude, Anthropic). All content has been reviewed by the oeradio.at editorial team.
