Keywords: high frequency head, frequency modulation, FM radio
Author: wjh0023
The receiver has a high sensitivity line simple, easy to install and debug, powered by the battery, low operating stability, small size, easy to carry. The electrical material diagram is shown in Figure 1. Working Principle: A weak frequency modulated signal received by the high frequency header and mixed, and the 31.5 MHz sound intermediate frequency signal generated after mixing is output from the IF end. IC1 collects into blocks for the FM (due to the high frequency head has good tuning reception performance, and the TDA7010T is a dedicated frequency frequency receiving 1C, and the sensitivity is 3UV, thereby ensuring high receiving sensitivity), the intermediate frequency signal input IC1 ( 11) Feet, via the IC1, output audio signal by 2 pin after the frequency modulation is used, and IC2 is used to amplify the audio signal power amplification. T1, T2 and LEDI, etc. constitute a tuning indication circuit. Be
T3, DWI, T4, and related components form a 6V voltage regulator circuit, providing a stable operating voltage for high frequency head and IC1. T5, T6, B and related components constitute a boost inverter circuit, detect the output voltage through T6, D3, DW3 to control the oscillation intensity of T5 to achieve regulatic energy saving. The inverter circuit outputs a 33V tuning voltage for high frequency head tuning settings. RT is a temperature compensation resistor, which is used to compensate for the initial initial charging of the boot caused the 33V tuning voltage to be slightly insufficient (very slightly, and it is not measured by the multimeter). Figure 2 is a pre-selection stage circuit and is used in conjunction with K1. Component selection and production: High frequency heads can be used with TDQ-3 type 470MHz full increase of high frequency heads, and the AFC foot leaves, R1, R2, C1 use micro or patch elements, which can be directly soldered in the high frequency head shield. The tuning potentiometer W2 selects 100K multi-circle potentiometers to make tuning settings more convenient and more stable. IC1 peripheral circuit should be installed with a patch component, and the 23 homogenesis is formed by a 3 mm ballpoint pen with a 0.4 mm enamel. The boost inverter B is magnetized with a 10mm small magnetic ring (can be removed from the old electronic ballast), using a transparent adhesive package to be insulated, with 0.25 mm enameled wire, and data is shown in Figure 1 Numerical value. The role of the L3 is to provide a bias voltage that is slightly high (about 0.8V) than the supply voltage to ensure that the battery voltage is lowered to 6.2V, there is still 6V stable voltage output. T4 is used as a constant current pipe, and DWI provides a stable bias current. Since the power supply circuit has adopted corresponding measures, the 6V output voltage and the 33V tuning voltage are very stable, and the high band of high frequency head and medium placement frequency circuit are guaranteed. The power supply is selected from the 6-segment nickel-hydrogen charge battery or two lithium rechargeable batteries, and CZ2 is an external power jack. The speaker is used in 50mm in the magnetic, and the whole machine can be installed in a plastic box of 14.5 cmx8cmx2.2cm. Debugging this receiver uniquely need to debug is the reception frequency of IC1. In order to ensure its tuning of 31.5MHz, it can be commissioned with a normal receiving TV: 用 use the wire to connect the TV high meal IF end with the TDA70iot antenna input (ie (11) foot), and connect to the ground; adjust L Make it to receive a sound signal. The working current of the pressure inverter circuit is about 12 mA; the thermal quiescent current should be less than 45mA; the power supply voltage is changed between 6.2 to 9V, the whole machine current is basically unchanged. Using the effect This receiver has been used and inspected for more than half a year, and the effect is very satisfactory. High receiving sensitivity (receiving local FM broadcasts and television signals can only be a few centimeters long), the work is stable and reliable; low power consumption, small and exquisite, love is not released. Since the high frequency head has adopted a low voltage power supply, its operating current is greatly reduced. Therefore, the whole machine operating current is small, which is beneficial to use the battery. The shortcomings of this receiver is that the initial need for starting from about 3 seconds can enter a stable operating state.
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