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ADS-B-Synthesizer.php    7585 Bytes    03-06-2024 17:49:15


ADS-B Synthesizer • Signal Generator


UHF Synthesizer with a Teensy® 4.0







Achtung
This Synthesizer is a tool for developping ADS-B Receivers, when you are in a place with absolutely no real-world air traffic. Use it with a power splitter and a Noise Source to make Bit Error Measurements of your DIY receiver. Your flight-simulator does not need such thing. And yes, broadcasting the presence of Air Force One mayst cause confusion. For a first iteration, consider it as illegal !




✈ Modulation • Dataframe




ADS-B uses Pulse-Pause-Modulation (PPM), the Bandwidth is 1 MBit/s and the length of the frame is 56 or 112 Bit, lasting 56 µs or 112 µs. To make things easier, we double the Bandwidth to 2 MBit/s and use ASK.

As we can set the Baudrate of the Serial Ports very precise, we used Pin 11 (SPI, MOSI) for that. With 1 Bit / 0.5 µs, we can reproduce the preamble, which takes 8 µs or 16 Bits, very precise. To represent the payload, we use 2 Bits to depict a LOW = 01 and a HIGH = 10. In order to avoid confusion, we use the word Dits to represent 2 Bits. (2 Dits = 1 Nibble).

A complete Packet




✈ Principle of Operation • Proof Of Principle





Block Diagram of our Modulator

The Teensy 4.0 is mounted on the bottom side. The complete circuit is powered via the usb port. It draws about 150 mA at 5.0 V.

The Synthesizer consists mainly of the following components (Minimum Equipment List) :

DEVICEREMARKS
XLL535A90.000000IStandard Clock Oscillator 1090.000000 MHz LVDS 3.3V, 50 ppm
ETC1-1-13TRSignal Transformer 4.5-3000 MHz, IL 2 dB, Impedance Ratio 1:1
ADE-5+RF Mixer, Level 7, 5 to 1500 MHz, used for the ASK
SF2321DLow-loss SAW Filter, CENTER = 1090 MHz, BW = 30 MHz
TEENSY® 4.0Teensy® 4.0 Development Board by PJRC
PCBADS-B-TX-2.zip from this website


Setting the Function Generator (DS345) to 2 MHz Squarewave, 0.2 Vpp with 0.1 V Offset and injecting this baseband into the IF-port of the Mixer, we can see the following Spectrum :



Resulting Spectrum of the Modulator



✈ Downloads








✈ Share your thoughts



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t1 = 6584 d

t2 = 200 ms

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