Production of cell FM (stereo) transmitter, FM Transmitter
Keywords: stereo FM transmitter production, frequency modulation machine circuit
The cell range referred to here refers to the radius of 1-3 kilometers, such a FM transceiver system is more suitable as a campus or unit broadcast. This article will detail the cell FM (stereo) emission device produced by the micro-efficient wireless microponic module MEC002A produced by Lifong Technology. The MEC002A miniature high-efficiency wireless microphone module developed by the Fuzhi Technology has the advantages of small volume, high radio frequency output, high sound sensitivity, and relatively stable output frequency. It is simple, easy to produce, debugging. Convenient, only the frequency range transmitted in three kilometers can be achieved by adding a radio frequency power amplifier circuit composed of C1971. Circuit construction is quite simple, and thus compares the production of amateur radio enthusiasts.
Fig. 1 is a three-kilometer mono frequency modulation circuit composed of MEC002A, which can be seen that the radio frequency circuit is actually only two levels, and the first stage is a radio frequency oscillation output circuit composed of MEC002A and peripheral correlation frequency control devices. It is a co-radio frequency power amplifier composed of C1971 and related components, and other components are mainly used in power and filters and microphone amplification. Although MEC002A contains a microphone amplification circuit, for some units, it is necessary to plug-in microphone without using a high-sensitivity microphone amplifier circuit in the module. In order to obtain a stable operating frequency, the circuit sets a multi-stage power supply regulator and filtering. Circuit, where u1 (7812) provides a stable 12V voltage for the MEC002A module, and C12-C15 is a power filter capacitor to ensure that the operating voltage is more stable to ensure that the MEC002A module does not generate a frequency drift due to changes in the operating voltage. R3, R7, and L3 are stage decoupling devices, which can effectively overcome mutual interference between the levels of the same power supply. Q1 and its peripheral components constitute the microphone amplification circuit, the audio output is coupled to W1 to control the volume size of the microphone, and the controlled microphone volume is coupled to the MEC002A modulation end (7th foot), the internal high-frequency oscillation circuit of the MEC002A Perform frequency modulation. The 6th feet of the MEC002A are the internal microphone audio-enlarged output feet. After the W2 controls its sound sensitivity, it is adjusted by C9 to 7 feet, and the internal high-frequency oscillation circuit internal high-frequency oscillation circuit is also modulated. If you want to make MEC002A's internal microphone does not work, only It is necessary to hang up its 4 foot can be achieved when the internal microphone circuit needs to be started. The CV1 is the RF output frequency control capacitor of the MEC002A, and the output frequency of the MEC002A can be changed in the range of 68-118 MHz by changing the capacitance capacity. Basically covered the entire campus broadcast and frequency band broadcast band. However, once the output frequency changes, the radio frequency power amplifier of the later level is also adjusted to make the RF output power, the farthest transmission distance. Therefore, it is recommended that it is recommended to specify the desired operating frequency so that the manufacturer adjusts the post-level power amplifier circuit to the maximum gain. The third pin of the MEC002A is its RF output pin. The modulated frequency modulated wave is outputted from the foot of the C16, CV2, L1 to the base of the C16, CV2, and the base, MEC002A, which is composed of Q2 (C1971). 1 pin is a power supply, and 5 feet are power supplies. Q2 works in a co-based state, the bias resistance provides a negative bias to its base, which can cause the circuit's output efficiency than the A, and the prerequisites are required to have enough excitation power, and 12V work The MEC002A under the voltage is nearly 200MW, which can be pushed to the co-amplification circuit. U1 provides a stable 15V operating voltage, L5, L6, CV3, CV4 constitutive frequency network, by adjusting CV3, and CV4 can efficiently transmit Q2 output power to the transmit antenna, the whole machine operates at 18V operating voltage For 800mA, the RF output power is about 3W. This circuit also provides the mainstream power supply function, and D1-D4 forms a full bridge rectifier circuit, and C30-C33 is a filter capacitor to reduce the exchange of alternating flules from the city. The input AC voltage is controlled around 18V. The whole machine working DC voltage is 18V, and the U2 can be unused when using a 13.5-18V voltage, and the 1,3 foot pad is shorted directly with the jumper.
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Figure 1 (Click on the map to be enlarged)
figure 2
Figure 2 is a machine assembly, Figure 3 shows the welded layer circuit board of the circuit, Figure 4 is a component assembly, and Figure 10 is a physical fitting diagram.
Figure 3 Figure 4
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Figure 6 (Click on the graph to enlarge)
For cell broadcasts, the current mono broadcast can not meet the needs of the majority of music enthusiasts, and more listeners want to receive high-quality FM stereo broadcast. Fig. 6 is a frequency modified stereo encoding circuit composed of the BA1404 on the basis of FIG. 1, so that the conveying sound quality is further improved, which can transmit the Quasi-frequency stereo signal. The BA1404 is a FM stereo modulation emission integrated circuit, where we discard its high-frequency oscillation part, and directly take the 19kHz pilot signal and 14 foot output of the 13 pin output to modulate the frequency modulation of the MEC002A. . 1 and 18 pin connector constitute a frequency modulation pre-emphasis network, and the frequency modulation of the receiver can effectively obtain the ideal frequency, so that the received sound quality is best. The LED provides a stable operating voltage for the BA1404 in addition to the power supply instruction. The wiring pads of the microphone volume control potentiometer and power switch can be reserved on both emitting boards, and the user can transform according to the schematic, plus the power switch and the microphone volume control potentiometer.
Figure 7
Figure 7 is a machine assembly of the frequency modulated three kilometers of three kilometers, and Fig. 8 is a welding layer circuit board of the circuit, and Fig. 9 is a component assembly, and Fig. 10 is a physical fitting.
Figure 8 Figure 9
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Figure 10
Precautions: (1) Source and antenna: Since the transmit power of this unit is slightly large, the field strength it produces is sufficient to affect the normal operation of electrical appliances that are poorly shielded, and it is recommended to put the above two launches during use. The plates are shielded with a metal box and lead antenna to an outdoor or far from the source. When the circuit board is actually tested, it is directly launched by the pulley antenna directly to transmit, and when the MP3 player is used as the sound source, it is not interfered with the transmitter MP3 player, but when using a Walkman or VCD player as a sound source The launch plate will work abnormal within three meters, and other sound sources are not tested; but there will be no more phenomenon when emitting with outdoor antenna. In addition, using a computer as a source should also remotely depending on the transmitter, especially for the stereo emitting board, noise. The outdoor antenna is preferably used to use the GP antenna introduced by the Lifact website or the "half-wave couple" antenna made from the Yangjiao antenna, and transmit a radio frequency signal with a coaxial cable. The lar rod antenna using 1.5 meters will increase the emission distance of the 1-meter tie rod antenna supporting the original plate. (2) Power supply: Since the operating current of the transmitting board is large, the power supply is high, the output current of the power supply is not less than 800 mA when the output current of the power supply is not less than 800 mA, so the power source of the output power will make the transmitter cannot work properly. For example, using two 9V laminated batteries, the battery will be exhausted in a very short period of time, and the output current is required to be greater than 800 mA when using DC adapter, and the operating voltage must be selected at 13.5-18V. The test power we use is made of TL431 precision voltage reference IC. (3) About the warm drifting: This three kilometers will produce a small range of frequency drift as the working temperature in a few minutes of the power-on, and finally in a working frequency, and more effective solutions are: a . Cap2, CV4 adjustable capacitance in the circuit is replaced by a fixed porcelain capacitor (with black dot high frequency capacitance), and the capacity is in the range of 20-68P. (Note: Changes in the value of CV2 have an impact on the transmit frequency) B. Secure the heat sink to the metal casing to increase the heat dissipation area, allowing heat to dissipate the heat as soon as possible, and the conditional can be installed a small fan for the heat sink. There is two suggestions to effectively overcome the three-kilometer plate due to the temperature caused by temperature.
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