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Varactor FM wireless transmitter

Published on Jul 20 2010 // FM Transmitter Circuits


Varactor FM wireless transmitter

As shown, the transmitter is amplified by the low frequency , varactor bias , the oscillation circuit. Audio signal amplified by the BG1 , sent to the varactor , its volume changes with the signal on the direct FM oscillator circuit , eliminating the use of the parasitic transistor junction capacitance frequency modulation amplitude modulation phenomenon , less harmonic components . Has FM radio frequency signals directly from L1 to space radiation. Components Selection Inductor L1 with ? 1mm enameled wire in the tube on ? 8mm around 5 turns , bodiless hollow . L2 with ? 0.1 ~ 0.3mm enameled wire is greater than 100kO resistance in the carbon film 1/4W resistor made around 100 turns , resistance weld at both ends , C2, C11, C4, C3, C5 should be Capacitor quality tiles . Resistors are used 1/8W, 0.01µF decoupling capacitor capacitance can use ordinary tiles . Installation and commissioning Recommendations made by etching the circuit board , the first welding RC components, semiconductor components and then welding , welding inspection is completed correctly , the links on the +6 V power supply , measuring 9014 emitter on the ground should be 0.47 ~ 0.9V voltage , if not on Should be adjusted R1. Retest 9018 emitter should be 1 ~ 2V to-ground voltage , if not on the adjustable R6, and then measured the bipolar varactor should be no voltage , bipolar voltage difference is less than 0.25V. If the polar pressure is too large, adjust R3 or R4. Adjust the above items, turn on the radio FM section , received signals from the transmitter , opened to more than 5 meters away , if can not find the transmitter sends the signal , adjust L1, stretching L1, fundamental frequency increased , compression L1, fundamental frequency decreased , so that the transmitting power of the transmitter to avoid the local radio station , but also a reliable receiver . Afterwards , on -player and other equipment, the output signal , careful adjustment of W1, so that ‘s in large volume without distortion as well ( not to -player and other equipment down the volume to maximum , and to open the volume in the common position) . After the adjustments above , the basic end of debugging , to mount strong plastic or wooden box ( not with the metal box ), to be decorated , used to listen to music or for TV audio transmitter and FM radio signals are the same, Clear , stable, and can be called a ” professional amateur transmitter . ” And without antenna , size small, as for use at home need not worry about firing range . I use it for TV audio transmitter , audio input connected to the TV audio output , with the 6V battery powered , with a crocodile clip to switch . Circuit board with rubber bands tied to the battery , continuous use of several tens day oersted did not worry about power running out . Experiment Comments The transmitter produced a simple , reliable and low cost. Concrete production , the author used for the loss at high frequency circuit board epoxy board , debugging is completed, the coils are of high quality wax seal high-frequency , very good. 5pF capacitor can be used instead of double-sided Bonded Copper (at 1pF = 1??millimeters ) . As shown, the transmitter is amplified by the low frequency , varactor bias , the oscillation circuit. Audio signal amplified by the BG1 , sent to the varactor , its volume changes with the signal on the direct FM oscillator circuit , eliminating the use of the parasitic transistor junction capacitance frequency modulation amplitude modulation phenomenon , less harmonic components . Has FM radio frequency signals directly from L1 to space radiation. Components Selection Inductor L1 with ? 1mm enameled wire in the tube on ? 8mm around 5 turns , bodiless hollow . L2 with ? 0.1 ~ 0.3mm enameled wire is greater than 100kO resistance in the carbon film 1/4W resistor made around 100 turns , resistance weld at both ends , C2, C11, C4, C3, C5 should be Capacitor quality tiles . Resistors are used 1/8W, 0.01µF decoupling capacitor capacitance can use ordinary tiles . Installation and commissioning Recommendations made by etching the circuit board , the first welding RC components, semiconductor components and then welding , welding inspection is completed correctly , the links on the +6 V power supply , measuring 9014 emitter on the ground should be 0.47 ~ 0.9V voltage , if not on Should be adjusted R1. Retest 9018 emitter should be 1 ~ 2V to-ground voltage , if not on the adjustable R6, and then measured the bipolar varactor should be no voltage , bipolar voltage difference is less than 0.25V. If the polar pressure is too large, adjust R3 or R4. Adjust the above items, turn on the radio FM section , received signals from the transmitter , opened to more than 5 meters away , if can not find the transmitter sends the signal , adjust L1, stretching L1, fundamental frequency increased , compression L1, fundamental frequency decreased , so that the transmitting power of the transmitter to avoid the local radio station , but also a reliable receiver . Afterwards , on -player and other equipment, the output signal , careful adjustment of W1, so that ‘s in large volume without distortion as well ( not to -player and other equipment down the volume to maximum , and to open the volume in the common position) . After the adjustments above , the basic end of debugging , to mount strong plastic or wooden box ( not with the metal box ), to be decorated , used to listen to music or for TV audio transmitter and FM radio signals are the same, Clear , stable, and can be called a ” professional amateur transmitter . ” And without antenna , size small, as for use at home need not worry about firing range . I use it for TV audio transmitter , audio input connected to the TV audio output , with the 6V battery powered , with a crocodile clip to switch . Circuit board with rubber bands tied to the battery , continuous use of several tens day oersted did not worry about power running out . Experiment Comments The transmitter produced a simple , reliable and low cost. Concrete production , the author used for the loss at high frequency circuit board epoxy board , debugging is completed, the coils are of high quality wax seal high-frequency , very good. 5pF capacitor can be used instead of double-sided Bonded Copper (at 1pF = 1??millimeters ) .