What Does It Take to Talk to a Satellite?
Topics: #Tejtronics, #SatelliteGroundStation, #RFEngineering, #SatelliteCommunication, #SatCom, #SpaceTech, #AntennaEngineering, #VHF, #UHF, #MadeInIndia, #AtmanirbharBharat, #DeepTech, #IndianEngineering
Satellite Ground Station - From Design to Deployment
A satellite ground station is easy to recognise A mast. A pair of antennas pointing towards the sky. a set of VHF and UHF cross polarised yagis mounted on Tejtronics custom built Azimuth and ELevation Antenna positioners. Set of UHF and VHF cross polarised yagi antennas on test along with Tejtronics Azimuth and Elevation antenna positioners, mast head preamp and digitally controlled polarisers A few racks of electronics. Article content 2U mountable rack units of Tejtronics satellite ground staion complete with power supply, antenna positioner controller, VHF power amplifer and UHF LNA What is harder to see is the engineering behind it. Because a ground station isn't really an antenna connected to a radio. It is a carefully engineered chain in which antenna gain, polarization, link budget, feeder loss, noise figure, RF power, impedance matching, tracking accuracy, structural loading, protection and control all have to work together. And when we started building this satellite ground station at Tejtronics, we made a deliberate decision: We didn't want to simply integrate a collection of imported boxes. We wanted to understand, calculate, design and build the system ourselves. That decision meant going back to first principles. Calculating the RF link. Designing the antennas. Working through the receive noise budget and feeder losses. Determining the transmit power requirements. Engineering the polarization network. Designing the RF switching and protection. Calculating the mechanical loads and positioning requirements. And then turning those calculations into hardware that could operate together as one ground station, designed as a system from the beginning. The result is something we are immensely proud of. It starts at the antenna. We designed and built our own cross polarised VHF and UHF Yagi antenna systems, providing independent horizontal and vertical RF paths. That gives the ground station something particularly important for satellite communication: Control over polarization. For VHF, we designed the TT RF PL 001 software controlled polarizer. It operates across 135–155 MHz, with specified insertion loss below 0.5 dB, and allows the station to electronically select Horizontal, Vertical, RHCP or LHCP polarization. And it isn't a standalone box added afterwards. The system was designed so the polarizer works together with the dual polarized antenna and antenna positioner — combining electronic polarization selection with mechanical antenna positioning. Then came getting RF power to — and from — those antennas efficiently. We designed our own VHF and UHF power divider/combiners. The VHF TT VPD 001, for example, is a 50 Ω passive RF network designed for 135–155 MHz, with specified insertion loss below 0.5 dB. It can divide an RF signal into equal amplitude( 3dB) paths or combine two RF paths while maintaining isolation between ports. The UHF version performs the corresponding function in the 400–500 MHz range. And because this equipment lives outside, RF performance was only part of the problem.The outdoor RF chain was designed around machined aluminium enclosures, mast mounting, grounding and surge protection rather than treating environmental protection as an afterthought. Thanks to our experience of building low insertion loss GDT based surge arrestors Receiving a weak satellite signal created a very different challenge. Every fraction of a dB lost between the antenna and receiver matters. So rather than compensate for feeder loss later in the rack, we developed the TT RF MHB 01500 UHF masthead preamplifier to put gain where it matters most: at the antenna, before the long coaxial feeder. It covers 300–500 MHz and provides 12 dB gain. But there was a harder problem. The same antenna system also has to transmit. Putting a sensitive LNA close to an antenna that can suddenly see high transmit power requires considerably more than simply adding an amplifier. So we engineered a TX bypass and protection system into the masthead preamp. It can sense transmit RF at approximately 0 dBm, bypass the LNA and connect the radio directly to the antenna path, while supporting up to 100 W RF during transmit. Why 0dBm you ask? Most SDRs can ouput about 6 dBm, we want to make sure we sensed even lowere hence 0dBm. The LNA therefore sits exactly where we want it during receive... …and gets safely out of the RF path when we transmit. The complete architecture even allows DC power for the masthead electronics to be delivered through the RF feeder using a bias tee, avoiding another long cable run up the mast. The bias tee for the system also now sits safely with in the 2U rackmountable RF amplifier unit. At the other end of that transmit chain, we needed power. So we built that too. A 2U rack mountable 100 W VHF RF power amplifier, designed to take approximately 0 dBm input and produce 100 W RF output. But producing 100 W was only part of the design requirement. The amplifier incorporates SWR measurement and protection mechanisms, because a field RF amplifier also needs to know when something is wrong at its output — and protect itself and the rest of the RF chain when that happens. Alongside it, we developed our own 2U rack mountable power supply, giving the station a purpose built rack level power architecture rather than another collection of adapters and bench supplies. And then there is the part everyone notices in the videos. The antennas move. A LEO satellite doesn't politely stay in one place in the sky while you communicate with it. The station has to continuously follow its trajectory in azimuth and elevation during the usable pass. So we developed our own antenna positioners and control system, engineered around the mechanical loads, antenna structure and tracking requirements of the station with 0 backlash and less than 0.5 degree pointing accuracy and built in trust bearing and torque which can outperform many of the established products in the market. Since these antenna postioners where built from day one to talk to computers, digital interface like interface to SatPC32 has been built into the firm ware. The control unit comes with a native USB c interface too. And supporting all of this is something decidedly less glamorous, but absolutely fundamental: The crank up mast. The mast, antenna structure, positioners, cabling and RF hardware cannot be designed independently of each other. Wind loading, torque, structural rigidity, cable routing, installation, servicing and the ability to safely raise and lower the antenna system all become part of the same engineering problem. Article content Picture of the crankup mast's first test. The Mast can be be erected to a height of 27 feet and can be compressed to a height of 15 feet. We are working on a more compact version of a mast that is man portable and will be revvealed very soon. So the mast was part of the ground station design too. None of this happened by accident. It was not: "We couldn't find a component, so let's make one." It was months of calculations, simulations, prototypes, machining, PCB design, RF measurements, mechanical design, testing, failures, corrections and testing again. Every subsystem had a purpose. Every interface had to be understood. Every dB mattered. Every degree mattered. And eventually all those calculations became aluminium, PCBs, coaxial cables, gears, motors, antennas and racks of electronics. Then came the moment when we could stand back and look at the complete station. Cross polarised Yagi antennas. Polarizers. VHF and UHF power divider/combiners. RF surge protection. UHF masthead preamplifiers. Bias tee power delivery. Antenna positioners. Crank up mast. Rack mount power systems. 100 W VHF power amplifier. Control electronics.All neatly kept in a 24U rack enclosure. Designed to work together. Designed and engineered under one roof. And, most importantly, designed and built in India with a single purpose. To build the capability to engineer sophisticated RF and satellite communication systems here — from first principles. There is something deeply satisfying about watching the finished station come alive. The mast goes up. The positioner starts moving. The antennas turn towards a point in an apparently empty sky. And somewhere hundreds of kilometres above us, travelling at several kilometres every second, is the spacecraft all those calculations were meant to find. Then the signal appears. At that moment, the equations are no longer equations. They work. That is the story behind this ground station. And for us at Tejtronics, it is only the beginning. Over the next few weeks, we'll take you behind the engineering of some of these systems — because there are some fascinating stories hidden inside those boxes. Explore what we are building at Tejtronics: www.tejtronics.com Defined by Innovation. Powered by Design. Engineered with Precision. Tejtronics SatelliteGroundStation RFEngineering SatelliteCommunication SatCom SpaceTech AntennaEngineering VHF UHF MadeInIndia AtmanirbharBharat DeepTech IndianEngineering
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