TDA7000 FM Receiver / TV Tuner / Aircraft Receiver
This simple one chip FM receiver / TV tuner will allow you to receive frequencies from 70 up to 120 MHz. With this small receiver it is possible to pickup TV stations, entire 88 - 108 MHz FM band, aircraft conversation and many other private transmissions. It is a perfect companion to any FM Transmitter especially if FM band in your area is very crowded. TDA7000 receiver offers very good sensitivity therefore it will even allow you to pickup weaker signals that cannot be heard on conventional FM receivers.
A neat feature of presented TDA7000 FM receiver is a voltage controlled oscillator similar to TV tuners that are used in television sets. Frequency is tuned by varying the input voltage to the oscillator. The advantage of this type of oscillator is that you can use regular 100K potentiometer to precisely tune to a given broadcast. Tuning can be performed much quicker and precisely than by using a trimmer (variable capacitor). Trimmers will also shift the frequency as you touch them where potentiometer will not. Trimmer also needs to be placed on receiver's PCB to minimize the stray capacitance where potentiometer can be conveniently placed anywhere you want because it will not be affected by any external capacitance.
TDA7000 Block Diagram
TDA7000 is a great chip because it includes RF input stage, mixer, local oscillator, IF (intermediate frequency) Limiter, IF filter, amplifier, Phase demodulator, Mute detector, Frequency-Locked-Loop system and voltage controlled oscillator (VCO) all in a single chip, so you don't have to do so much tuning and tweaking as you would normally do in super-heterodyne receivers. TDA7000 is also a great choice for folks that don't have great experience with RF circuits due to the fact that there are few external capacitors & resistors needed, no external IF filters, and only one variable coil and varicap diode.
The IC has an FLL (Frequency-Locked-Loop) system with an intermediate frequency of 70 kHz. The IF selectivity is obtained by active RC filters. The only function which needs alignment is the resonant circuit for the oscillator, thus selecting the reception frequency.
Spurious reception is avoided by means of using a muting circuit similar to squelch. This eliminates and rejects other input signals around selected frequency so that even remote stations can sound clear just as if they were located near by.
Audio Output
TDA7000's audio output signal is only around 70mV which might be enough for driving crystal earphones or high impedance headphones. For higher power audio signal you can easily connect audio amplifier built around LM386 or just about any amplifier chip that will suit your taste.
Reception of stereo audio signal is possible by connecting an external stereo decoder circuit (LM1310) to audio output.
Frequency Selection
Audio Output
TDA7000's audio output signal is only around 70mV which might be enough for driving crystal earphones or high impedance headphones. For higher power audio signal you can easily connect audio amplifier built around LM386 or just about any amplifier chip that will suit your taste.
Reception of stereo audio signal is possible by connecting an external stereo decoder circuit (LM1310) to audio output.
Frequency Selection
Frequency selection is very straight forward. Use L1 variable coil to tune to the lower or upper frequencies that you want to receive and then use just 100K potentiometer to fine tune to any specific frequency. Potentiometer doesn't have to be mounted on the PCB. You can conveniently mount it on enclosure and use leads to connect it to the PCB. If you intend to use TDA7000 as regular 88 - 108MHz FM receiver the recommended voltage supply is 4.5 - 5V.
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