Design and Implementation of a 5.8 GHz superheterodyne FM Video Receiver

University essay from Linköpings universitet/Fysik och elektroteknikLinköpings universitet/Tekniska fakulteten

Abstract: This master thesis presents the design and implementation of a super heterodyne 5.8 GHz receiver system for wireless transmission of phase alternating line (PAL) composite video signals. The system is implemented using surface and hole mounted devices on four separate printed circuit board (PCB) stages. These stages include a 5.8 GHz radio front-end, a 480 MHz intermediate frequency (IF) stage, a local oscillator (LO) block and frequency demodulation circuit for frequency modulation (FM) signals. Each receiver stage is interconnected using sub-miniature version A (SMA) connectors. The radio front-end PCB consists of a low-noise amplifier (LNA), a 5.8 GHz distributed element pre-select filter and a passive double-balanced mixer. This mixer uses seven discrete injection frequencies at 5260-5380 MHz that are provided by the LO block using a programmable phase-locked loop (PLL) frequency synthesizer device. The IF stage uses an automatic gain control (AGC) feedback loop with a dynamic range of 60 dB. This AGC loop is implemented using a directional coupler, a detector device, a tuning circuit and a variable gain amplifier/attenuator (VGA). The IF at 480 MHz is selected with a 25 MHz surface acoustic wave (SAW) filter. The IF is demodulated to a PAL composite video format using a PLL FM discriminator device intended for direct-broadcast satellite (DBS) signals. This device is fitted to a separate demodulation stage in conjunction with a picture adjustment circuit and a FM de-emphasis network. The output of the demodulator stage is a 75 Ω PAL composite video signal.

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