Design of a TV Tuner based radio scanner

in Electronics, Electronics - Radio, TV Tuner

Building radio frequency devices becomes difficult starting from VHF band. Moreover, tuning various stages is difficult without expensive electronics equipment. But a ready made unit can be used as the frontend of any radio receiver operating in the VHF – UHF band. That unit is the tuner coming from a TV, from a STB or from a PC card. It has the advantage of covering a wide spectrum of frequencies at a reasonable reception quality well above homemade radio receivers.
In order to build a TV tuner radio scanner you need, of course, a tuner. Also you must be able to build some detectors (demodulators) for the common analog modulation schemes. Some frequency mixers need to be built too. Although designed for analog modulation, the scanner is able to demodulate digital signals using the PC sound card as input. The whole constructional project is not difficult because it is modular and you don’t have to build all modules to get it working with a specific RF signal. Let’s take a simple example: if you are interested in receiving broadcast FM radio stations, you only need a simple FM detector that can take as input the tuner’s intermediary frequency. Of course, if you want to improve it you can add a stereo and RDS decoder. On the other hand, if you are interested in digital aviation signals, you’ll need a detector with a tunable local oscillator to overcome tuner large frequency step and a tunable IF filter. To maintain the modular design of the project, you could make this from two modules: a frequency downconverter with the tunable oscillator and filter followed by a fixed frequency detector. In the end, the main point of building this is obtaining the same results as with Realtek SDR devices and SDR#. The functional schematic of the scanner is shown in the figure below.