BA1404 is a low-voltage, low-power design with a maximum power consumption of 500mW.
It integrates stereo modulation, FM modulation, and radio frequency amplification on one chip; it requires few peripheral components;
The two-channel separation is high, with a typical value of 45dB;
The input impedance is 540Ω (fin=1kHz), and the input gain is 37dB (Vin=0.5mV);
The RF output can reach 600mV.
The circuit uses a very classic diagram, and the output at the back is tuned and amplified to meet the power requirements. Here the transmitter circuit should be careful not to have too much power. If it is too large and affects other frequencies, it is against the law. It is legal only in some frequency bands with high power. I don’t understand the law here, and the power at that time was generally high.
Stereo pre-stages are audio amplifiers for two channels. When the input is 0.5mV, the gain is as high as 37dB, and the frequency bandwidth is 19kHz.
I was afraid that the output power of the 1404 would not be enough, so further amplification was added later.
The erected inductive type above this picture can be adjusted. By changing it, he changes the resonant frequency, which is the frequency of the output. It can be calculated according to the formula. But the inductance was not calculated at that time. So just tune in and receive it on the radio. Adjust the receiving frequency of the radio when fixed. As long as there is the sound I emitted, it is right. The effect of jumping out is still pretty good. In addition, it is important to pay attention to the parameters of the capacitor here, and the parameters in the indicator of the subsequent amplification and tuning need to be adjusted step by step. It took a while too. Generally speaking, the sound received is quite clear.
I was afraid that the output power of the 1404 would not be enough, so further amplification was added later.
The erected inductive type above this picture can be adjusted. By changing it, he changes the resonant frequency, which is the frequency of the output. It can be calculated according to the formula. But the inductance was not calculated at that time. So just tune in and receive it on the radio. Adjust the receiving frequency of the radio when fixed. As long as there is the sound I emitted, it is right. The effect of jumping out is still pretty good. In addition, it is important to pay attention to the parameters of the capacitor here, and the parameters in the indicator of the subsequent amplification and tuning need to be adjusted step by step. It took a while too. Generally speaking, the sound received is quite clear.
