TSA5523 Tuner Modules from PC TV Cards

Some of the previous posts show methods of generating analog video with microcontrollers and RF modulation of it using ready made modules. Analog video is no longer in use in most parts of the world. TV tuner cards for analog signals are no longer manufactured and old ones are difficult or impossible to install on newer computers because there are no drivers. Despite this, analog video capture devices are cheap and widely available. Most are USB dongles, with video and audio inputs, no tuner.

Since I had some old TV tuner cards that were no longer compatible with my PC or had poor performance, I decided to take the tuners out of them. To my surprise, different tuners from different manufacturers looked pretty much the same on the inside. All of them used the same integrated circuits. The tuners I found are actually complete receivers, with included demodulator. This means you can get analog audio and video straight from the module pins. There are also modules with FM support, with stereo decoder.

In the photo below, you can see two tuners. The top one has FM radio support. You can see that it's similar to the other, but the rightmost compartment has some additional filters for FM IF.

Tuners from TV cards

How to identify an unknown radio tuner

Radio frequency tuners can be found in a lot of devices, starting with TV sets, set top boxes and PC tuner cards. A tuner is a device that takes a ”chunk” of a frequency carrier of a bandwidth, amplifies it and then shifts it (usually by down-converting) into a fixed frequency that will be fed into a demodulator device. Tuners are difficult to build and a DIY tuner will never have the performance of one from a radio receiving device. The RF signal enters a baseband amplifier. Further, this signal is mixed with a local oscillator with variable frequency. The result exits the tuner as Intermediate Frequency (IF). Sometimes the tuner also contains a filter at the IF output. These functional blocks can be integrated into a superheterodyne receiver with ease (just add a detector). So, what can you do with a tuner? Keep reading.

MxL5007T tuner radio

MxL5007T is a tuner IC designed mostly for digital signals (DVB-T, ATSC), but it can be used for analog reception too. I will show you how I took it out from a receiver so I can use it in my projects. It has a programmable IF output and it can receive anything from 44 to 885 MHz. There is no datasheet for it, but there are Linux drivers.

Looking at the PCB of a SCART DVB-T MPEG2 receiver I found no components I could use. But, a closer look at the tuner which was basically an area of the PCB enclosed in metallic box revealed only a few tracks coming out of the tuner area. Since it's rather easy to interface a tuner to a simple demodulator and build a high quality receiver, I decided to try to cut the original receiver PCB around the tuner and see if I could control and use it in my projects.

Design of a TV Tuner based radio scanner

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.

Functional schematic of the scanner. Don't worry, you don't have to build everything from scratch.