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Satellite Uplink and Downlink: How Does it Work?

To transmit data back and forth or to act as a receiver for other signals or commands, a satellite may need to link with ground stations. These connections, called uplinks or downlinks depending on the signal’s source, are a common method of interacting with satellites once they’ve left the planet’s surface.

But what are the specifics of satellites uplinks and downlinks?

Why might we use them, and how do they work?

How does a satellite uplink work?

A satellite uplink is defined as when a signal is sent from a ground-based station or receiver up to a satellite in orbit.

Satellite uplinks are useful for when a ‘lesser’ station needs to send its signals to a larger network. The vantage point of a satellite is the ideal place to propagate such signals farther and wider, which is why satellite uplinks are useful in telecommunications.

From the user perspective, an uplink begins with a signal that needs to go elsewhere with the help of the satellite. It’s the opposite of a downlink.

An uplink begins with the data from the source, which travels to a modulator. The modulator takes the data and turns it into a modulated signal to be transmitted, where it then goes to an upconverter that turns it into a very high-frequency signal. Once passed through a power amplifier, the signal goes to a satellite dish and is transmitted to the satellite.

Satellite uplinks can be used to issue commands that affect the satellite’s operations in space. These can be to perform a taks, reset a satellite’s onboard systems or even a ‘kill command’, shutting the satellite down and ceasing all activity.

How does a satellite downlink work?

The inverse of uplinking, a satellite downlink occurs when a signal travels from a satellite to a ground-based station or receiver. Information taken in this way is accordingly a download, with an upload being the respective result of a satellite uplink.

Downlinks are useful for satellites taking photographs, video, or other information that needs to be beamed back to Earth for processing and study. With modern technology, this can be handled through purely digital means, unlike the earliest spy satellites which dropped physical film to Earth that needed to be developed.

From the user perspective, a downlink originates from elsewhere and comes to the user with a signal to be received.

A satellite downlink begins with the signal from the satellite being sent to, and received by, a satellite dish. It then passes to a power amplifier, which filters out noise and clarifies the total strength of the signal. It then passes to a down converter, which works counter to an upconverter and reduces the frequency of the signal.

Finally, the signal moves to a demodulator, where the original information is filtered out from the carrier signal and sent to a router to be sent to the appropriate network components.

What is an uplink station?

A ground station is a radio station that, among other roles, can be used to establish satellite uplinks. The classic ground station that comes to mind features a parabolic antenna using a large concave dish.

Some ground stations are not used for the purposes of uplinking with satellites and instead exist to communicate with manned spaceflight crews or to download telemetry data from satellites.

Some stations are dubbed telecommunications ports, or simply ‘teleports’. These serve as hubs that connect satellites to terrestrial networks for the purpose of networking and telecommunications. These teleports are also sometimes used as uplink stations.

Some major ground stations and Earth terminal complexes include:

  • Goonhilly Satellite Earth Station, located on Goonhilly Downs near Cornwall, UK. It was once the largest satellite station in the world, but was shut down in 2008. It played a key role in events like the Apollo 11 moon landing and the Olympic Games.
  • Kaena Point Space Force Station, located on the island of Oahu in Hawaii. Among its many roles working alongside the US Department of Defense, it aids in the control of satellites by relaying commands via uplink.
  • Goldstone Deep Space Communications Complex, located in the Mojave Desert in California. One of its main purposes is to communicate with interplanetary space missions, providing two-way links that help to control spacecraft from Earth.

What are the frequencies for uplink and downlink communications?

Uplink frequency and downlink frequency should not be the same for satellite communications. This is because, for instance, an amplified uplink signal (which will be in similar frequencies to a downlink signal) will jam the weak uplink signal.

For this reason, uplink frequency should always be kept at more than downlink frequency.

In an uplink process, the post-modulator signal lies at around 70-140 MHz, which is then upconverted to above 1,000 MHz in the L-band of radio frequencies.

For the downlink process, these numbers apply in the reverse for their respective stages. This complex frequency conversion work is, fortunately, handled automatically through electronics.

How can I uplink/downlink with my satellite?

Bright Ascension’s Mission Control Software is a flexible, easy-to-use solution for the monitoring and control of satellite missions and operations. It integrates seamlessly with flight software with almost zero manual effort, simplifying satellite uplinks and downlinks and making them as effortless as possible.

Learn more: Book a demo

We run regular demo sessions for our Flight Software Development Kit and Mission Control Software that you can book at any time. These are group sessions but you can join anonymously and participate as much or as little as you like. Book demo today.