Reform to campus broadcast radio ----- TDA7012 FM Radio

Some college campus broadcasting modifications are a problem that many teachers and students have a headache. The original 72MHz is changed to 52.5MHz. The radio bought by the teacher is less than 52.5MHz, and people who do not understand the radio change technology Flower money to change or find someone else. Now introduce the modified method. There are now 6 campus broadcast radio, looking at the use of the use of the single-chip TDA7021 integrated circuit, so the modification is very simple. Be First, TDA7021 external circuit TDA7021T mounting circuit diagram is not seen. The headset is replaced with the antenna in the figure. It feeds the high frequency signal via C12 into an integrated circuit, and the variable circuit selection of the C4, L1 selects the radio signal frequency, and the BG is low-frequency amplifier to have sufficient output power. L2, L3 is a high frequency blocking ring, which prevents passage of high frequency signals, and allows the audio signal to reach the headset. Component selection: BG can be selected from C9014, β is 120 or so, L2, L3 with φ0.51mm enamel wire on the waste medium circle coordinate magnetic core around 30 laps. If you are troublesome, you can buy a commercially available 1μH color code inductor. C3, C6, C9 are monolithic capacitors. C14, C15 is an electrolytic capacitor, and other porcelain capacitors. The oscillation coil can be used on a diameter of 5mm, and then removes the hollow coil, then removes from about 0.08μH, E1, E2 is 32Ω ordinary stereo headphones, and the power supply 2 is 5 Enter the battery case. Second, the modulation After the circuit analysis and circuit assembly we can see that C4, C5 and L1 determine the selection of reception frequencies, and the campus radio can also choose FM and campus broadcast, which is to pick up a switch at 4 feet. The inductor coil is selected, and the disassembly can see the switch at the switch at the number of different numbers, respectively, the frequency reception of FM and campus broadcast, and we have to change it. Method 1: Mandatory change (single adjustable capacitor, the minimum frequency is 70 MHz): 13-14 turns around the 5 mm round rod with φ0.5mm to φ0.65 mm. Remove the paint on the two leaders of the wrap, remove the small knife, and unpack the radio with a lot of solders. The coil is soldered by soldering iron, and then weld the inductance that is just doing. If your radio has frequency display, check it, the frequency display can be lowered below 50MHz. Method 2: Easily change (double-tension capacitor, the minimum frequency is 58MHz): There are two radio machines for a double capacitor, large. There are 4 rounds in the back, there is 2 no copper pieces, the other can be tune with a word screwdriver, pay attention to the first hole of the bronze slice counterclockwise, turn the left of the fan Copper sheets (can be seen) make it right below 30. Left and right, the counterclockwise rotate 180 degrees, so that the received frequency is lowered from 58. MHz to about 51.0MHz, containing 52.5 MHz? Author: from friends