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TV Tuner Radio

TV Tuner Radio

28.02.10



This project was largely inspired by this Swedish guy's TV tuner projects (be sure to see the rest of his site) which caught my attention because a) all the heavy lifting is done by the TV tuner and b) the reception range is massive! Basically what one does is interface with the TV tuner, which is easy for the older analog tuners and more invasive for the newer digital tuners. The TV tuner will provide a constant 38,9MHz intermediate frequency output here in Europe, or 45,75MHz overseas. To hear what the TV tuner is receiving we need to demodulate the IF from the tuner, which can be done using any old FM radio after a little hacking. Quite simply, the FM radio is modified to receive at the intermediate frequency of the TV tuner. Since TV broadcasting went digital last year here in Norway, internal TV tuners have become obsolete so acquiring one is no problem. In fact, the TV you harvest a tuner from can still be used afterward to watch movies and such via the external input (scart, composite, s-video, etc). The tuner itself is the shielded box with an antenna input, which you can see in the above picture. I forgot to take a close up of it, but the Swedish guy has a thorough explanation of tuners if you need more info.

I knew I could harvest a tuner, but I didn't know whether I could modify a radio or not. Prior to this project I had no knowledge of radios, believe it or not, so this was all new to me. I had a cheap radio in my parts bin which was of no interest to me before, but suddenly now became appealing. Inside it had two ICs, one for audio amplification (TDA2822), and one AM/FM reception and demodulation (TA2003). In addition to these two valuable chips there was also a 10,7MHz filter and discriminator which I could use to demodulate the IF signal, and a variable capacitor. Basically everything I needed. By tracing the PCB and making a schematic over the radio I was able to see what needed to be modified.

Schematic

The TDA2822 is just wired up like they show in the datasheet with an AF filter on the input. The TA2003 is fixed so it only receives FM at 38,9MHz. The IF at 38,9MHz goes through the SAW filter which removes the frequency components far above this which result from frequency mixing. The now much cleaner IF signal goes into the TA2003 chip and is mixed with the frequency determined by the LC circuit on pin 13, which should be 38,9 - 10,7 = 28,2MHz. The resulting 10,7MHz signal is then sent through a filter, and finally to the demodulator. The discriminator on pin 10 is used to extract the audio signal. The final demodulated signal exits the chip at pin 11 and is sent through some audio filters before being amplified. There's a lot of complicated theory behind all of this, but thanks to integrated radio ICs you don't need to know much of it to make something that works. :-) IMO the neatest thing about this project is that everything you need can be scavenged from one transistor radio and a TV. And the TV works afterwards! The above circuit was designed using what I found in the radio and had at hand, so some of the components values may seem arbitrary, which they are.


Completed 38,9MHz IF demodulator. Notice how the volume and input jacks were recycled.

In the end I was able to pick up all of the local FM stations, along with several unidentified signals in the other bands. The number of signal sources I could find increased greatly after building the circuit on a PCB. The PCB files aren't provided because chances are the radio IC, SAW filter or audio amplifier you find will be completely different. I plan on finding a digital TV tuner before making a project box for this.

TV Tuners

Analog:
The particular tuner I used for this project has the serial number UVE33-EW51 and was found in a small 12 volt TV. I couldn't find any information on it, which I assume is the case with any tuner found out there, but fortunately the pins were labeled as seen in the above schematic. Every analog tuner will have equivalent pins so it's just to find out which are which. Pins Bu, BH and BL select the band you are listening on. Knowing what the frequency range of these bands isn't easy though, and they're not always standard to make things worse. I can only place the frequencies in the FM band, so I'm guessing that BL goes from 40MHz to 106MHz, and BH continues from there up to 180MHz. Bu could be anywhere in the UHF band. I know the channels on the TV were 1-26, so using this knowledge I could probably find the exact band frequencies if I wanted to. MB is the 12V supply voltage, AGC is automatic gain control, which sets the gain. Set this to 6-10V and you should pick up something. Below 6V and my tuner didn't receive anything. VT is the tuning voltage input, and varies from 0 to 13V to get the full range on my TV tuner. Most tuners use 0-30V however, so keep this in mind. Taking the 30V supply from the TV might be a good idea. IF is intermediate frequency out, of course. So as you see using the old analog tuners is great to get things up and running, but not so great when you want to actually use the device. :-) Frequency is unknown, you'll drift because Vtuning isn't constant, etc.

Digital: All of the flaws and benefits of the analog tuner are nullified by the digital tuner. In this tuner the receiving frequency is set digitally, and maintained by a PLL. This means you can tell which frequency you are listening too quite easily. However interface is much more difficult, because you need to communicate with PLL and synthesizer chips to set the receiving frequency. The plus side is these things use I2C, which is a standard.

Update 11 July 2013

33V Tuner power Supply
The digital TV tuner I found required a 33V source to function, so I built a simple boost converter to step up the voltage to the required level. I was having severe problems with noise when using the tuner with this power supply, until placing a few decoupling capacitors in the circuit. A 100nF cap was placed at the supply, while a 10nF capacitor was placed directly across the vTuning leads on the tuner. This eliminated noise problems altogether, and the tuner is now run from a mains powered supply.
33V source schematic

Digital TV tuner Radio
I found a digital tv tuner of the type UV1316, which is I2C compatible. It requires a +33 and +5 volt supply, but is otherwise quite easy to use. The intermediate frequency output can be plugged into the circuit above. To control the tuner, I constructed a simple circuit consisting of a microcontroller which received control signals over bluetooth. The circuit would then decode the bluetooth data, and write data to the appropriate registers in the tuner via the I2C interface. An Android app was written which would translate the desired listening frequency into the correct register values, which are then sent to a connected bluetooth unit.  The required circuit is nothing but support circuitry, so no schematic will be provided. The android app and microcontroller firmware can be downloaded here.






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Disclaimer: I do not take responsibility for any injury, death, hurt ego, or other forms of personal damage which may result from recreating these experiments. Projects are merely presented as a source of inspiration, and should only be conducted by responsible individuals, or under the supervision of responsible individuals. It is your own life, so proceed at your own risk! All projects are for noncommercial use only.