Keywords: 2km FM transmitter amateur production
2km FM transmitter amateur production
First, the main feature of this machine
1. The frequency is relatively stable because it is a multi-stage amplifying circuit, unlike a single tube circuit from oscillation to the same stage circuit, the segment parameters of its output stage can easily affect the oscillation circuit, and the frequency is unstable. This may be the reason why the single tube frequency modulation circuit cannot enter practical significance. The unit is in the middle of the frequency modulation to the antenna, and there is a few magnifier isolation, and the intermediate-level distribution parameters are not as easy to change as a single tube, so it is not easy to affect the predecessor.
2. The amplifier stage transistor is not directly selected to increase the transmit power in parallel with a small power transistor. High-power high-frequency launch tube is not only expensive, but more important is that it is not good, this machine is 2N3904. The quality of this tube is relatively guaranteed, as it is small, the parameters of 2N3904 are VCB = 60V, IC = 0.2a. Pc = 0.36W. TF = 300MHz.
3. The voltage stability of Ba1404 is used as the TL431, which is better than the regulator of ordinary regulator diode. Here you need to say that the grounding feet of the TL431 must be welded and cannot be soldered. Once this foot is soldered, the A point voltage in Fig. 1 is raised to about 6V, and it is easy to burn the BA1404. I started using an old TL431. Due to the non-welding of the lead, in addition to the soldering other components, they scrapped a piece of Ba1404 at once. The working voltage of BA1404 is 1-3V. More than 3V will have possible possible. It is recommended to use the new tube to TL431.
4. For the A1404 circuit, the most difficult component is 38kHz crystal. The circuit is designed as a non-stereo, so that the hard-to-seese crystal is removed, and it is an ordinary 47PF capacitor (i.e., C9 in Figure 1).
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Pay attention to the circuit diagram needs to be complete! !
Second, the production method
1. Interception of a 40 mmx140mm of the copper-copper standby.
2. Reduce the circuit to the paper box of 40mmx140mm, draw a good line diagram, the line go to follow the signal input - FM modulation - push-amplifier-emission antenna law, otherwise the high frequency circuit is easy to be self-excited and burn the power amplifier tube .
3. The fan is difficult to draw while drawing the circuit board, because the pin of the integrated block is made in English, and there are no feet in the hands of many enthusiasts. Here you introduce a better way to find the old board with the same integrated block with the BA1404 pin number and shape. Remove the above integrated block, this empty board is a good integrated block template that presses the integrated block template on the drawing of the line map, and the position of the two integrated blocks is aligned. Then, the pins are then stamped by sewing needles, so that the needle print is left on the drawing, which is the pin position of the integrated block BA1404.
4. After the drawings are described, they are passed onto the copper plate. When drawing, you must pay attention to the order of the integrated block pins, because the drawing is drawing, while the texture is attached to the welding surface, the drawing is sticking After taking the hole according to the position of the component, take the drawing carefully remove the drawings and then draw the line and the small oily marker in the copper according to the position of the lead hole according to the position of the lead hole.
5. After the circuit board is described, it will start the line, and the enthusiasts generally use the steel saw blade, and the saw blade is not easy. The author introduces you a tool very well, and the steel saw bar is used, and this tool is used. This kind of tool is a pull knife for cutting the organic plate used in the art store. The blade needs to be small. The blade of the original blade is triangular, and it is only necessary to convert it into a word.
6. The engraving of the circuit board, with a miniature small tab tongs instead of the tiger plurpets, pull the steel tape together, pulling the line along the steel side, all after all, finishing the light Carefully check that there is a place where there is no connection. After the line is engraved, it will be shining with fine sandpaper above 1,000, and then put the circuit board in the clean water, then wipe the water, put it under the sun. Dry or put it under the bulb.
7. Formulation of flux and protective agent: Put the rosin into a powder into a vial, add alcohol, and make alcohol saturated solution. Apply rosin solution on a circuit board. When the solution is dried, it can be soldered.
8. Debug: Figure 1A point is 2.5V. The spacing of the adjustment L1 coil can change the transmit frequency. R7 is a L00KΩ fine-tuning potentiometer, the whole electric current is less than 200mA. 4 measuring units 2N3904. It is better than using 9018, and C3355 is easy to burn. First, use the hand-conditioned frequency modulated radio to search the native signal in the FM band, and then fine adjust the L1 after the signal is queued to adjust the set frequency point. General enthusiasts do not have a dedicated measurement, but there are many mobile phones with FM radio function. We can use your hand to match the FM phone to accurately adjust the frequency to the set frequency. First use your hand radio to capture the signal and then slowly adjust the L1, and the tuner is adjusted. When the radio tracks to the vicinity of the set frequency point, open the phone radio, use the phone to be fixed, set the frequency on the frequency you need to transmit, then slowly adjust L1 until the voice is clear, loud, and frequency it is good.
9. Production of the launch antenna: the transmit antenna has a big impact on the entire electricity, produced with a TV antenna coaxial cable, and cut off the outer plastic sleeve in the top 0.75m of the cable. Pull to pull it, then use the transparent tape to dress up the entire antenna. The launch antenna is more than 5m from the unit. The higher the antenna, the farther the emission distance.
10. If the sound is blocking phenomenon, you need to add an attenuation network on the signal input. If you want stereo to transmit, just disconnect the connection between C3 and C4 to increase an input circuit, replace C9 to 38kHz crystal, if this crystal is not yet, the output stereo separation will be affected.
Author: Du Yong
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