[Photo] BA1404 modulator circuit

BA1404 is a product of Toyo Corporation, Japan, with an operating voltage range of 1 ~ 3V . The circuit is a monolithic integrated circuit composed of an FM stereo mixer , a 38KHZ oscillator, an FM modulator, and a high-frequency amplifier.

Working principle (see Figure 1): The stereo audio signal is input by pins 1 and 2 through the emphasis and matching network , and then enters the FM stereo mixer after being amplified , generating a stereo composite signal composed of the L + R main signal and the LR secondary signal After buffer amplification, it is output from pin 14 (pins 16 and 17 can adjust the parameters of the composite signal and can control the left and right balance); the external discrete components of pins 4 , 5 , 6 and the internal circuit form a 38KHZ oscillator to generate a 38KHZ signal after buffering After amplification, they are supplied to the mixer and 1/2 frequency divider respectively . The 38KHZ signal gets a 19KHZ pilot signal through the frequency divider and is output from pin 13 ; the composite signal and the pilot signal from pin 13 and pin 14 are output from pin 11 through the matching network. Enter the FM modulator ( 9 , 10 external peripheral components to determine the oscillation frequency) to generate a frequency modulation signal, amplified by the output of 7 feet; 2 feet for AF bias, 3 feet for AF ground point, 8 feet for RF connection Location, 15 feet is the positive pole of the power supply. (Note: a reference voltage output pin 11 to facilitate separation of the peripheral elements of the oscillation frequency control, not employed here.) Pin 7 μ pc1651 signal and finally by the amplified output.

Production points: The circuit can be densely installed on the universal circuit board, and the extra copper points should be removed; the resistance on pins 13 and 14 is only a reference value, because its value is related to the stereo separation, it should be set according to the actual situation ; L is the adjustable inductance of the iron shell, its parameters are related to frequency, here is the key to frequency stabilization, be careful; if you want to use commercial power supply, pay attention to the power supply, because the current is not large, you can use a discrete filter power supply ; The working voltage of μ pc1651 is 5V, which should not be exceeded, and it is easy to burn.

Summary of experiment: Because many netizens in the "Electronic Newspaper" BBS request detailed FM stereo transmitter information, I have re-collected relevant information and experimented with simple discrete, combined and integrated FM stereo transmitters. I feel that this combination of BA1404 + μ pc1651 is the easiest to make and debug, and the frequency stability is quite high (relative to the previous BA1404 circuit), and the transmission power will not exceed the legal range.

Since I am still a student, my technical level is limited, and the experimental data is collected and the current knowledge is used to design the circuit. There are definitely many improper points, and I hope that those with common interests can give me pointers.

parameter

unit

Test Conditions

Minimum value

Typical value

Maximum

Quiet   state   Electricity   flow

IQ (mA)

3.5

3

5

lose   Enter   Electricity   Hinder

Rin (K Ω )

f = 1KHZ

360

540

720

lose   Enter   increase   beneficial

GV (dB)

Vin = 0.5mv

30

37

sound   Tao   level   Scale

CB (dB)

2

Mixer output maximum voltage

Vom (mvp-p)

THD = <3%

200

38KHZ leakage voltage

Voo (mv)

When there is no signal

1

Pilot output voltage

Vop (mvp-p)

When there is no load

460

580

Channel separation

Sep (dB)

25

45

lose   Enter   noise   sound

Vin ( μ V)

1

Maximum output voltage

Vosc (mV)

350

600

Figure 1

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