Typical application circuit diagram analysis of three wireless microphones

Introduction to the small power emission typical application circuit diagram of the 88-108MHz frequency modulated range of 88-108 MHz frequency modulation ranges in a number of represented sponsors. Introduction to the small power emission typical application circuit diagram of the 88-108 MHz frequency modulation range in the range of 88 to 108 MHz frequency modulation, which is easy to produce a single-range amateur, which has a simple single tube transmit circuit, and a stereo transmit circuit using an integrated circuit. Mainly used in FM wireless headphones, telephone wireless recording forwarding, remote control, wireless alarm, monitoring, data transmission and campus frequency modulation broadcasting, etc. Mono FM Emitting Circuit Figure 1 Figure 1 is a more classic 1.5km single tube frequency modulated voltage circuit. Key components in the circuit are transmitted transistors, multi-use D40, D5O, 2N3866, and the like. The operating current is 60--80mA. But the above triodes is difficult to purchase, and the price is high, and there are many fakes. The author chooses other triode experiments, relatively priced trioders C2053 and C1970 are quite good, and the actual distance communication distance is greater than 1.5km. The author also replaced D40 to ordinary triode 8050, and the working current is 60--80mA, but the emission distance is less than 1.5km. If it is changed to 9018, the working current is smaller, the emission distance is also shorter, the circuit In addition to the transmitting tripod; the parameters of the coil L1 and the capacitor C3 are more important. If it is not properly selected, it does not control the void or the operating frequency exceeds the range of 88--108 MHz. Among them, L1, L2 can be used on a round rod of 3.5 mm in a single layer of about 5 and 10 hinders, and C3 is selected from 5 to 20 pF of porcelain or polyester adjustable capacitance. When actually produced, the capacitor C5 may be omitted, and the L2 can also be replaced with a normal inductor coil of 10-100MH. If the emission distance is tens of meters, then the battery voltage can be selected from 1.5-3V, and the D40 tube is replaced by a cheap 9018, etc., the power consumption will be less, or the "Electronic News" 2000 No. 8 The fifth edition (simple long-distance wireless frequency modulated microphone) is slightly changed. The single tube transmitter introduced in Figure 1 has a simple circuit, the output power is large, and the production is easy to make, but it is inconvenient to send the high frequency cable to transmit the RF signal to the outdoor transmit antenna, which is generally a rod of 0.7--0.9m. The antenna is directly transmitted on C5. Due to the Doppler effect, people move around the antenna, the frequency drifting is very serious, making the sound of the receiver that the radio is normal. The sound is distorted or silent. If the transmitter is used as a wireless microphone, when the antenna is pinched, it can be imagined. Figure 2 Figure 2 is a 2km frequency modulation transmitter circuit. This circuit is divided into oscillation, multiplier, and power amplification. In the circuit, V1, C2 - C6, R2, R3, and L1 constitute a capacitor three-point oscillator, and its oscillation frequency is mainly determined by the parameters of C3, C4, and L1, and its oscillation frequency is 44 to 54 MHz, which is tapped from the center of L1. Output, the C7 is coupled to V2 amplification, and 44 to 54 MHz is selected from the C8 and L2, ie 88-108 MHz, which is coupled to V3 by C9, and V3 consists of 3 3DGL2 triodes. The output power can be expanded. When the circuit is working normally, the current is about 80-100mA. Three 3dg12 constituting V3 can add an appropriate heat sink to prevent overheating. When the production, L1 ~ L3 was formed with a 0.31 mm enamel wire on a single layer of 3.5 mm round. Figure 3 Figure 3 is a crystal transmitter circuit. J. , VD1, L1, C3 ~ C5, V1 constitute a crystal oscillation circuit. Since the frequency stability of quartz crystal J is good, the temperature has a small impact, so it is widely used in a cordless telephone and an AV modulator. The VL is a 29-36 MHz crystal oscillation triode. The emitter output contains rich harmonic components. After V2 amplification, the collector is selected from the C7, L2, which is constituted by a network of 88-108 MHz, and selects 3 frequency signal (ie 87 to 108MHz. The signal is the strongest), and then amplified by V3; L3, C9 is selected to obtain a desired frequency band signal. The process of frequency modulation is such that the change in the audio voltage causes a change in capacitance of the VD1 pole; since the VD1 and the crystal j are connected in series, the crystal has a slight change, after three times, frequent paragraph is 29-36MHz Three times the crystal frequency is passed. In actual application, in order to obtain a suitable modulation degree, a quartz crystal or ceramic vibrator having a large modulation frequency is selected can be selected, or a 6-12 frequency circuit of the circuit is slightly complex. If the input audio signal is weak; can add a first-stage voltage amplifying circuit. Due to the 1.5km FM transmitter (see Figure 1), the antenna parameter will occur when the antenna parameter is slightly changed, and the racefire phenomenon will occur, and then, since it is a single tube self-excited oscillation, the working current is large, when work After several seconds to several minutes, the temperature rise of the triode causes a change in the pole capacitance, and the oscillation frequency is changed (in general, the oscillation frequency is lowered), and sometimes the float is from 0.2 to 1 MHz. It is poorly reliability when used as FM broadcast or long-distance remote alarm, but the components are less, low cost, and easy to debug, suitable for primary enthusiasts. 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