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TBA120 demodulator circuit

2018-02-26 12:25  
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The TBA120 Series ICs provide a high-gain limiting IF amplifier and a quadrature coincidence detector in one package. These ICs are primarily intended for extraction of TV intercarrier sound, which (in Europe) is frequency modulated onto a 5.5MHz or 6MHz subcarrier. The TV waveform constitutes an extreme interfering signal, and the TBA120 provides superior performance in comparison to early Foster-Seeley and Ratio Detector systems, with a considerable reduction in component count.

TBA120 as AM demodulator. Equivalents are SN76660N (TI) and S041P (the latter is a low power version). It is in fact a CW/SSB/AM-multimode-detector, but the BFO line is connected to the signal from the IF. Believe I tested it in my Drake 2-B. Please note that TBA120AS, TBA120S, TBA120C, TBA120D etc are different and may not function satisfactorily in this construction. It is also suggested the change for use as SSB detector,
but it is an old device and the circuit has more interest as a reference IF level is supposed to be maximum 50mV RMS. MC1351 should not have more than 10-20mV, and TDA1576 is overloaded with higher levels than 100mV RMS. NE/SA604/614 could also well be used, but have not been tested.

The TBA120U is an i.f. amplifier with a symmetrical FM demodulator and an a.f. amplifier with adjustable output voltage. The a.f. amplifier is also provided with an output for volume control and an input for VCR operation.

TBA120 demodulator circuit wiring diagram

tba120 demodulator
The input and output of the TBA120U are especially designed for LC-circuits, but the input can also be used with a ceramic filter.

TBA120U demodulator

tba120u demodulator

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