Works
As shown, the low-frequency amplified by the transmitter , the varactor bias oscillation circuit. After amplified by the audio signal BG1 , to the varactor, with the capacity to change the signal , the direct frequency modulation of the oscillation circuit , eliminates the parasitic transistor junction capacitance AM FM phenomenon , less harmonic components . Frequency modulated radio frequency signal to the direct radiation from the space L1 .
Components Selection
Inductor L1 with ∮ 1mm enameled 5 turns on the tube ∮ 8mm , bodiless hollow . L2 with ∮ 0.1 ~ 0.3mm in wire resistance is greater than about 100 turns 1/4W carbon film resistor 100kΩ made of welded joints across the resistor , C2, C11, C4, C3, C5 should be of high quality ceramic capacitors . Resistors are used 1/8W, 0.01μF decoupling capacitance ceramic capacitors can be ordinary .
Installation and commissioning
Recommended etching produced circuit boards, soldering first resistive and capacitive components , semiconductor components and then welding , weld inspection has been completed correctly, pass on the +6 V power supply , measuring 9014 -emitter voltage of the ground should be 0.47 ~ 0.9V , except for should be adjusted R1. Test-retest 9018 -emitter voltage to ground should be 1 to 2V , except for adjustable R6, and then measuring the varactor should be no voltage bipolar or bipolar voltage is less than 0.25V. If the pressure is too large poles , adjust , or R3 R4. After adjustment of the above items , turn on the radio FM segment , receives a signal emitted by the transmitter , opened to more than 5 meters away , if the transmitter sends a signal is found, adjust L1, stretching L1, fundamental frequency increased compression L1, fundamental frequency decreased, so that the transmitter away from the local radio station transmitting frequency , but also a reliable receiver . Connect the output signal of the multiplayer and other equipment , carefully adjusted W1, make music at high volume without distortion as well ( non -player and other devices will be open to the maximum volume , and the volume to be opened in the common position ) . After adjustment of the above items , commissioning basically ended, load it into a solid plastic or wooden box ( not available metal box ) , to be decorated , used to listen to music or audio transmitters for television , FM radio signals are no different , clear and stable, can be called a " professional amateur transmitter ." And without the antenna , it's small , home use need not worry because the transmission range .
I use it for TV audio transmitter, audio input connected to the TV audio output , with 6V battery-powered , with an alligator clip to make the switch . Circuit board with a rubber band tied to the battery, continuous use dozens of days , do not worry about power running out .
Experiment Review
The transmitter making simple, reliable performance and low cost. The specific production, I used a small circuit board for the high-frequency loss of epoxy boards , commissioning is completed, each high-frequency coils are made of high quality wax seal , with good results . 5pF capacitor can be used instead of double-sided copper-clad ( by 1pF = 1平方millimeters ) .
Our other product:
