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A small experimental satellite will bring a crossover transponder from 29 MHz USB to 435 MHz FM
Amateur satellite operations will soon expand with another interesting experimental satellite. HADES-L, developed by the Spanish organization AMSAT-EA, is a small satellite measuring approximately 10 × 5 × 5 cm, yet despite its size, it carries several interesting experiments.
The communication transponder will likely attract the most attention from amateur radio operators. It uses an unusual combination of frequencies – uplink in the 29 MHz band in USB mode and downlink in the 435 MHz band in FM.
Crossover Transponder 29 MHz → 436 MHz
The main communication experimental task of HADES-L is the transponder, which will allow amateur radio operators to transmit on 28.472 MHz USB and listen to their own or another signal on 436.665 MHz FM.
The transponder has a bandwidth of approximately 3 kHz and does not use any access tone. This makes it an interesting combination of two distinctly different amateur radio bands and modes.
The use of the band around 29 MHz for uplink is one of the most interesting features of HADES-L. In satellite operations, uplinks are more commonly found in the 2 m or 70 cm bands, while using the 10-meter band brings a completely different ground station configuration.
At reception, it will be necessary to monitor the Doppler shift, which is significantly more pronounced on the 70 cm downlink than on 29 MHz.
What power will be needed?
AMSAT-EA uvádza odporúčaný výkon uplinku približne 25 W. However, this figure is related to the experimental nature of the system and the characteristics of the receiving antenna used on the satellite. The transponder also has implemented AGC reguláciu, preto je dôležité vyhnúť sa jeho prebudeniu príliš vysokým signálom.
For the amateur radio operator, this means that during the first attempts, it will not be advisable to automatically set the maximum available power. It will be much more interesting to find the optimal combination of power, antenna, and conditions for a reliable connection without unnecessarily stressing the transponder.
Voice and digital modes
HADES-L is not intended solely for classic voice operation. The experiment also allows operation with multiple simultaneous digital signals.
The satellite can work with signals such as:
- CW
- FT4
- FT8
- voice operation.
The first Wednesday of the month is to be reserved for digital modes.
An interesting part of the experiments is also a digital voice beacon. It uses the CODEC2 codec and a convolutional forward error correction (FEC) with parameters K = 7 and R = 1/2.
Telemetry and experimental data are transmitted at a speed of 800 bit/s.
What will HADES-L measure?
The communication transponder is just one part of the mission. The satellite will also collect a number of technical data during its operation.
The experiments include, for example:
- measuring signal and noise levels,
- measuring noise power around 30 MHz,
- monitoring battery voltage,
- measuring internal and external temperatures,
- recording time since the last reset,
- testing energy management,
- experiments with the receiving antenna.
These data will also allow verification of link budget calculations and monitoring the behavior of individual systems during flight.
The satellite also carries a radiation experiment that will monitor electrons, photons, and X-rays. The aim is not only to measure but also to compare the properties of the materials used under conditions of the space environment.
The transponder will not be active continuously.
HADES-L has a relatively small power budget. The average electrical power available for the satellite is only about 175 mW. For this reason, the transponder will not be on throughout the entire orbital period. Its operation is organized in a cycle:
12-minute cycle → 4 minutes active transponder
Amateur radio operators will need to monitor the current pass and the precise timing of its activation while working with the satellite.
The UHF transmitter power also automatically adjusts to the battery status. Depending on its charge, it can operate at +13 dBm or +20 dBm, which corresponds to approximately 20 mW or 100 mW.
For reception on Earth, it will not be a classic 'strong' satellite. A good antenna, low losses in coaxial cable, and a quality receiver can be very important when tracking it.
An interesting task for SDR
HADES-L can also be an interesting target for amateur radio operators using SDR receivers.
On the receiving side, it will be possible to monitor the downlink at 436.665 MHz FM while simultaneously analyzing its level, noise, and Doppler shift. In digital experiments, it may be interesting to observe multiple signals in an approximately 3 kHz wide channel.
For SDR experimenters, HADES-L can represent a good opportunity for comparison:
- various types of antennas
- LNA and filters
- various SDR receivers
- automatic Doppler correction
- quality of FM demodulation
- processing weak signals.
Launch on Falcon 9
HADES-L is set to be launched as part of SpaceX's Transporter-18 mission, as part of a rideshare flight that will carry multiple small satellites into space.
The launch is currently scheduled for October 1, 2026, from Vandenberg Space Force Base in California.
After launch, HADES-L is to head for an orbit at an altitude of approximately 500 × 600 km with an inclination of 97°. The orbit designation is UNNE-1B.
Transporter-18 is also expected to include other small satellites utilizing amateur radio frequencies coordinated through IARU.
Small satellite, interesting experiment
HADES-L is a good example of how even a very small satellite can offer numerous experimental opportunities. Its dimensions are only 10 × 5 × 5 cm, yet it combines a communication transponder, digital voice beacon, telemetry, noise measurement, an antenna experiment, power system, and radiation measurements.
For amateur radio operators, the biggest attraction is undoubtedly the crossover transponder 28.472 MHz USB → 436.665 MHz FM.
The combination of a 10-meter uplink and a 70-centimeter downlink will be interesting not only from the connection perspective but also in terms of experimenting with antennas, link budget, Doppler correction, and SDR techniques.
If the launch and commissioning of the satellite proceed as planned, HADES-L could soon become another interesting object in the sky for amateur radio operators who enjoy trying new methods of satellite communication.
Note: HADES-L is an experimental mission, and parameters, launch schedule, operational modes, and transponder availability may change after launch based on the current state of the satellite and operator decisions.