Several wireless microphone circuit analysis

Introducing a number of small power transmitting circuits within 88-108 MHz frequency modulation ranges that are easy to produce a successful amateur situation, including a simple single tube transmit circuit, as well as 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 is a more classic 1.5 km 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 is a 2km frequency modulated 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 is a practical 50m frequency modulated wireless headset emission part circuit. This circuit is divided into oscillation and signal amplification. L1, C2-C5, V1, etc., similar to the black and white television high frequency head vibration circuit similar to the high frequency head vibration circuit, the frequency stability is good, long-term work is not running frequency, the practice proves, in amateur, this improvement Type capacitors three-point oscillators are fully competent. After the number of electric soldering iron is solder, the number of electric soldering iron is solder, and the normal radio is still normal, and there is no runoffring in the case of high temperature in the triode. The frequency of the oscillator is mainly determined by L1 and C2, and the range of 88-108 MHz can be covered by fine-tuning L1. The audio signal passes the base, the E, and B poles of the V1 of the V1, which causes the oscillation frequency to change the oscillation frequency with the variation of the audio voltage, and achieve frequency modulation. The circuit is l, ~ L3 is spymatically surrounded by a 3.5 mm round bar in a 3.5 mm round bar. The adjustment of the T1 turns inter-turning spacing is fine-tuning the oscillation frequency, the oscillating spacing of the restraining of L2, L3 is obtained by the resonator oscillation frequency, and obtains the maximum output power. Figure 4 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. 2km FM transmitter (see Figure 2 above) Adoption of oscillation, frequency, power amplification three-level circuit, relatively independent, frequency stability is superior to a 1.5km transmitter emission of single tube self-exciting oscillation, but the number of boot After minute, there are still 0.2-0.4MHz frequent floats, mainly due to the large working current of V3, temperature rise, causing the pole capacitance to change, this change causes a resonant network composed of C8 and L2 through C9 The parameter changes, and the V2 temperature also causes the resonant network parameters composed of C8 and L2, which is transmitted to C3, C4, L1, C5, C6, V1, etc., which ultimately make oscillation through C7. The frequency also changes (in general, the oscillation frequency is lowered), and the heat dissipation of the triode can be reinforced, and the inter-stage coupling can be reduced, and the capacity of C9 and C7 can be reduced, and a transistor, resistance, resistance, and a resistance of the effect is selected. Capacitance, etc., but frequent drifting is still more serious. The wireless headset transmitter shown in Figure 3, due to the use of an improved capacitor three-point oscillator, compared with the transmitter of the transmitter shown in Fig. 1, Fig. 2, the frequency of the transmitter, and the fidelity requirements such as TV wireless headset are not very high. It is very suitable in situations. Since the crystal oscillating transmitter shown in Fig. 4 is made of a crystal, the frequency stability is very good, but when the frequency modulation broadcast and wireless headset are applied, the modulated frequencies are much smaller than the LC oscillator, listening to the radio When the volume is small, the sound is not round, it is generally more suitable for frequent mapping cordless phones and walkie-talkies. The sound spismillar has been widely used in a transmitter of various wireless remote control and wireless data transmission devices, but the frequency of 88 to 108 MHz is difficult to purchase, and the transmission mechanism of various performance excellent frequency synthesis is more troublesome. Interests can refer to (Electronic News) No. 41 of the 2000 (TGF-Type 10 FM Broadcasting Transmitter Digital Frequency Synthesizer Modulation Unit Circuit), the broadcast-level transmitter adopts universal Motorola frequency synthesizer As the core, the chip MCL45152P is the core, and the high stability frequency of 84 to 108 MHz can be obtained by an external dial switch. FM (DESCRIPTION OF THE INVENTION Figure 5) The core device of the circuit is a stereo special chip BAL404. Many FM stereo modules are packaged in a plastic or metal housing, which only expose power input, audio input, and radio frequency output leads. Just understand how BAL404 will know how the FM stereo module is. . The stereo audio signal from the source is coupled to the BAL404 by a network of R1, R2, R5, C1, C3, C5 (R4, R3, R6, C2, C4, C6). The left (right) channel is enlarged, and the balanced modulation is enlarged, and the modulated composite signal is output from the 14th foot of the IC, and the pilot signals on the 13th feet are composed of B9, C15, B10, C16, C17. The network is mixed, and the mixed composite signal enters the 12 foot of the IC, the comparison 8, ⑨, ⑩ foot, C20 - C22 and the calculus composed capacitor three-point oscillator for frequency modulation, the IC's foot is modulated The RF signal is output from the top 7 after the internal amplification, and is sent to the antenna TXL after C18, L2. To achieve the frequency of the FM stereo, BAL404 5, 6 feet require external 38 kHz crystals, but it is difficult to purchase 38kHz for special crystals when the amateur production, so it can be referred to the circuit within the dashed line without the crystal, and is made with discrete components. A 38kHz oscillator, the 38kHz signal passes the R8, C10 to the 5th foot of the IC. When making, the LL can use radio frequency transformer ITF-2-1, TTF-2-2 or TFF-2-9, etc., pay attention to the connection of the pin should not make the wrong, 3 feet, 2 foot link V1 emitter, 1 Feet is feedback and output feet. The frequency is more stable by adjusting its magnetic core, and a 38 kHz signal having a high amplitude is high. It is particularly noteworthy that the C8 should be selected from 0.33uF polyester capacitance, which is not appropriate to select a porcelain capacitor because the stability of the porcelain capacitance is poor, and it is easy to have an oscillation frequency instability, and the frequency modulated stereo work is not normal. Since the high frequency of BAL404 is a three-point oscillator, the frequency is poor, so the circuit does not have the original high-frequency oscillator, and the method of improved the three-point oscillator with a more stable external frequency, can meet the amateur The requirements of FM broadcast and FM wireless headphones. For example, the transmitted portion of the Zn-2001 FM stereo wireless headset uses an improved capacitor three-point oscillation circuit. After the stereo composite signal is enlarged by the V2 voltage, the frequency modulation is directly added to the V3 base by C26, R14. It is characterized by the user needs, can be adjusted to the case of L4 outside the casing, so that it can freely adjust in the range of 88 to 108 MHz, avoiding the frequency of the local FM radio station. Another feature of the machine is that the board has a 1-5W power extension section, such as the campus broadcast, can be put on, and then put it after debugging. However, it is worth noting that if the wireless earphone is still transmitted in the machine after increasing the power; the strong RF signal will produce itself; causing distortion, communication or silent, so be sure to pass 50 Euro-special communication cable transmits RF signals outdoors. In the assembled power extended partial shot, the range of resonant states are adjusted by the RF detector as shown in FIG. The input terminal (one end of the 1K resistor) of the radio frequency detector is first connected to the collector of the triode, adjust the inductor coil on the collector, so that the voltage of the radio frequency detector is highest, then step by step by step by step. Level adjustment, reconfers the antenna side, finally tonate the inductor coils, so that the output voltage is the highest, that is, the completion. Compared to infrared wireless headphones, the host (transmitter) of the FM stereo wireless headset can be used in normal use in the wall, while the infrared earphone cannot be used. In addition, ordinary infrared earphones have no stereo function, so the FM stereo wireless headset is more suitable, and when you enjoy music, you can listen more. If an outdoor antenna is installed, even if the very weak radio frequency signal is very far, the production of a good antenna is much more effective than simply improving the emission power. Making a pair of water-wide polarization, the entire antenna is more troublesome, and the general frequency modulation broadcast station also uses a horizontal polarization method. In order not to create interference, the author introduces a simple and efficient vertical and high efficiency. Polarized antenna. Since people use the earphone line as the radio antenna in the mobile phone, the earphone cable is vertical; the antenna of the car radio is also approximately vertical, so the vertical polarization is more suitable for mobile reception. The antenna uses a 50-ori-umbrella antenna dedicated to the communication machine. As shown in FIG. 6, there are 4 or 7 vibrators on the antenna seat, with a total length of about 0.75m, and a main vibrator of the transmit antenna. The down three or 6 vibrators constitute a simulated ground, and the angle between them is uniform, and the angle between the main vibrators and the vibrators constituting the simulated ground is fixed as required, and the impedance of the entire antenna is 50 Euros. The 10MHz bandwidth gain is about 2 dB, and the standing wave is less than 1.2. Many occasions are transmitted to digital signals, so they can refer to the circuit of the field 7, add several components to realize wireless digital transmission of the transmitter, and the circuit is simple and easy.

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