Production of all-channel FM receivers

The receiver introduced in this article only uses an integrated block and a compact high-frequency head with a power supply voltage of +5V. It consumes less power and is easy to carry when going out. It truly realizes the compactness of the receiver.

The working principle is as shown in the attached figure. The tuner amplifies and mixes the signal received by the antenna. The 31.5MHz audio intermediate frequency signal generated after mixing is output from the IF1 terminal and enters the (12) pin of the IC. After being amplified by the IC, it is mixed with the 42.2MHz second local oscillator to generate a 10.7MHz second intermediate frequency signal. After being filtered by the 10.7MHz three-terminal filter, it is sent to the IC (17) pin, and then is put through the IC mid-amplifier and demodulated. The (24) pin of the IC finally drives the speaker to work through the internal power amplifier of the IC. The power supply required for the high-frequency head of this machine also uses a boost circuit composed of a triode 2SC8050 and a high-frequency transformer to provide working and tuning voltages. Due to the use of a low-voltage powered tuner. The power supply voltage can be lowered. Experiments have proved that the power supply voltage can work at around 3.6V. It can be powered by three AA nickel-metal hydride rechargeable batteries or a 3.6V lithium battery.

Component selection: The selection of the tuner is very critical for this machine. The fully supplementary tuner TDQ36-5V with high sensitivity, low voltage power supply and small size should be selected. The name and voltage of the lead-out terminal of TDQ36-5V are shown in Table 1. Note that this tuner has two signal output terminals, IF2 is not used. Only use IF1. The IC uses the FM and AM radio special integrated circuit CXA1O19 produced by Sony Corporation of Japan. Only the FM part is used here. It adopts a 28-pin dual-in-line package. The functions of each pin are shown in Table 2. CXA1019 is fully functional and includes all the circuits of an FM and AM radio. It has the advantages of fewer external components, low power consumption, high sensitivity, and low distortion. The tuning potentiometer w uses a 100kΩ multi-turn precision potentiometer. A miniature digital voltmeter is connected between the high-frequency head VT and the ground to display the receiving frequency of the machine to achieve miniaturization of the machine. The high-frequency transformer B1 and oscillation coil B2 use mid-circuit TRF1445. B1 does not need to be modified, and B2 removes one turn. The remaining components should also be miniaturized as much as possible.

The debugging of this machine is very simple. Just adjust B1 and B2 to get a 10.7MHz IF signal.

The receiver only needs to be connected to an external telescopic antenna on an ordinary radio to receive all nearby FM radio stations and TV audio signals.