2km FM transmitter Amateur
One, the main features of the native
1. Frequency is relatively stable, because it is a multi-stage amplification circuit, unlike the single tube circuit from the oscillator to the transmitter in the same stage circuit, so its output level segment parameters easily affect to the oscillation circuit of the frequency instability. This is perhaps the single-tube FM transmitter circuit can not enter the practical significance. Native from FM antenna transmitter middle, there are several stages of amplifiers isolation, middle-class distribution parameters, unlike single-pipe machine as easy to change, it is not easy to affect to the previous level.
2. Amplifier stage transistors than direct selection of high-power high-frequency transmitter transistor to increase the transmission power, but with a small power transistors in parallel output. High-power high-frequency transmitter tube is not only expensive, but more important is that it is not good to buy the machine with low power tube 2N3904. This tube quality protection, because it fakes the 2N3904 the parameters VCB = 60V, Ic = 0.2A Pc = 0.36W. The Tf of = 300MHz.
3. BA1404 voltage regulator power supply TL431 for better effect than ordinary Zener diode voltage regulator. It should be said that TL431 GND must be firmly welded, not Weld. Once this pin Weld, will make 1 point A voltage rises to about 6V, it is easy to burn BA1404. I start with a disassemble old TL431. Pin oxidation welding is not strong, in addition to its Weld in the welding of other components, and suddenly scrapped a BA1404. BA1404 operating voltage is 1-3V. Over 3V will have burnt possible. TL431 recommendations or with a new tube.
4. A1404 circuit, the most difficult with the components is 38kHz crystal oscillator, the circuit will be designed to be non stereo, so I removed the hard to find the crystal, is a common 47pF capacitor (Figure 1 C9) .
Second, the method of making
1. The interception of a 40mmx140mm Bonded Copper spare.
2. Miniaturization 40mmx140mm the paper box, draw a good wiring diagram, alignments, to follow the signal input - FM modulation - promote - Amplifier - the law of the transmitting antenna, otherwise self-excited high-frequency circuits and burn amplifier tube .
3. Lovers drawing board integrated circuit pin position is very difficult to draw accurate, Manifold pin made in accordance with the British system, and many fans did not feet. To introduce a better way to find one with the same old circuit boards Manifold with BA1404 pin count and shape. Remove the manifold of the above piece of empty plate is a good Manifold template, Manifold template pressure in the drawings to draw a line graph above two Manifold alignment. And then one by one with a needle to poke Manifold foot hole, so that the needle is left on the drawing India, these needle India is Manifold BA1404 pin position.
4. Drawings described with double-sided adhesive paste to the Bonded Copper on, the drawing must pay attention to the order of Manifold pin, drawing plug-surface mapping, and the texture is affixed to the welding surface, drawings paste After the component location to lay the hole, lay the hole after the drawings carefully taken down not torn, and then according to the position of the pin hole with a ruler and trumpet oily marker to draw lines on the copper clad laminates.
5. Circuit board described after the engraving lines, enthusiasts are generally steel saw blade to engrave broken saw blade is bad. I introduce to you a tool to good use, hacksaw engraved lines push, this tool is used to pull. Broach this tool is commonly used in arts and crafts store cutting organic boards, blades need to make a few small restructuring, the original blade of the knife-edge triangle simply converted into a font can be.
6. The engraving of the circuit board, and replaced with a miniature vise hand vise clamp with steel rule and circuit boards, with Broach along the edge of a steel rule line one by one pull carved, engraved after all front lights carefully check the line attached to the place, the line all engraved with fine sandpaper No. 1000 be polished bright, the circuit board into the clear water rinse, clean water, in the sun dried in the sun or on the bulb dried.
7. The flux and the protecting agent formulation: rosin crushed into powder in vials, adding alcohol to prepare the saturated solution of the alcohol rosin. Rosin solution was coated on the circuit board. Etc. can plug-in solution dry after welding.
8. Debugging: Figure 1A voltage of 2.5V. Adjusting the spacing of the L1 coil can change the transmission frequency. R7 for l00kΩ fine-tune potentiometer, the whole current of less than 200mA. 4 amplifier tubes 2N3904. Better than the 9018 effect, C3355, burn easily. First hand to tune the FM radio in the FM band search for the signal of the machine, when found to signal and then fine-tune the L1 its tune in the frequency set point. General enthusiasts do not have a dedicated frequency measurement instrument, but the mobile phone with FM radio function but it is a lot of. We can hand tune the radio frequency accurately transferred to the frequency set with the FM phone. First hand to tune the radio to capture the signal and then slowly adjust L1, tune the radio tracking adjust. When the radio tracking to set the frequency near the open phone radio, phone no fixed frequency, the frequency set in the frequency of launch, then slowly adjust L1 until the phone sound clear, loud, frequency even if the tone better.
9.The production of transmit antennas: the transmitting antenna entire electrical properties have a great impact, turning the skin to produce TV antenna coaxial cable ring in the top of the cable 0.75m at Peel week deprived of the outer layer of plastic wrap, cable outwardturn pull to pull them to, then the entire antenna bandage layer of transparent tape. The transmitting antenna away from this machine is greater than 5m. The antenna higher the emission farther distances.
10. If the sound is blocked, you need additional attenuation in the signal input terminal network. If you want stereo transmitter, an input circuit simply disconnect the connection between the increase in C3 and C4, C9 replaced 38kHz crystal oscillator can output stereo separation will be affected if not this crystal....