DIY Long-range 1W stereo FM transmitter
This paper introduces 1W FM stereo radio diversion circuit audio modulation unit circuit and the modulated wave RF amplification circuit unit composed of two parts. The audio modulation unit circuit with two IC debugging becomes extremely simple. Modulated wave RF amplifier circuit of the main vibration level with crystal off-frequency stability, phase modulation circuit in the local oscillator circuit, high frequency stability of this machine. Selected frequency multiplier level of LC resonant circuit using the pass bandwidth, small rectangular coefficient phase frequency particularity good dual tuner frequency selection circuit has a huge inhibition of the stray unwanted harmonics other than the resonant frequency. The final amplifier output connected to a multiple-section band-pass, low pass filter so that the wireless radio waves transmitted out more pure single, even if in close proximity to work the TV will not be disturbed. Is a high-performance transmitter circuit for radio communication enthusiasts generic.
Circuit as shown. The audio modulation circuit pre-amplifier, IC1 use of high quality and price Qian Jiang Sheng op amp NE5532. Stand break the sound signal synthesis circuit IC2 NJM2035D. To poker dynamic microphone or CD player, high-fidelity audio signals from the L, R-ended input by W1, W2 coaxial potentiometer control the voltage amplitude of the input signal into IC1, high-fidelity amplification. IC2 ○ 1 foot, ○ 14-pin stand off-sound audio signal input terminal, stand break acoustic signal output from ○ 9 feet synthesis after a series of processing of the IC internal functional circuits. Select the amount of signal components output signal ○ 8 feet 19KHZ pilot signal superimposed by W3 sent to the phase modulation of the RF circuit level.
The vibration level transmitter circuit of crystal V1, crystal JX2 components. Oscillation frequency FO = 15.3MHAZ. V2 is a buffer amplifier stage, the output signal T1 coupled to the phase modulation level until the audio signal to be modulated. Varactor diode D2, inductor T2, resistor R24, R25, the R26 composition of the bridge phase modulator. R24, R25, R26 were three bridge arm of the bridge phase modulator, the fourth bridge arm T2, D2. Audio modulation signal by C20, R18 to the bridge arm. Phase modulation FM signals sent by the C30 V3, the V4 buffer amplifier after T3, C34, C35, T4, C36, C37 dual tuner frequency selection circuit elected three times the FO of the sine wave signal, that is, FO × 3 = 15.3 × 3 = 45.9MHZ. V5 this frequency signal of the second harmonic amplification, T5, C39, C40, T6, C41, C42 dual tuner frequency selection circuit elect (45.9 × 2 = 91.8MHZ) second harmonic signal sent to the V6 power amplifier. The V6 output RF amplifier signal of L2 ~ L5, C45 ~ C54 band-pass, low pass (impedance matching) filter to filter out unwanted harmonic components sent to the antenna can radiate radio frequency energy to the surrounding space.
Production, audio modulation unit circuit and the RF unit circuit were fabricated in the two circuit boards. The RF unit circuit should be taken to the overall shielding measures. W1, W2 coaxial volume potentiometer, IC1 selection of inexpensive and quality pretty sound op amp NE5532. IC2 use NJM2035D. JX1 selection 38kHZ crystal. D1 use ordinary light-emitting diodes. W3 is a 10K-trimmed resistor. R1 ~ R18 selection of the 1/16W colored ring metal film resistors. C1 ~ C21 selection of high quality capacitors. The JX2 selected 15.3MHZ crystal. C23, C46, C47, are 5/25PF high frequency tuning capacitor. V1, V2, V3 selection 2SC2787 and V4, V5 selected 2SC2026. V6 selection 2SC2538 of the tube parameters: PCM = 3W ICM = 0.4A, the FT 175MHZ. Varactor diode D2 selected IS2236. C23 ~ C56 in addition to C42 and C56 high-quality electrolytic capacitors, the rest are high-frequency ceramic capacitors. R19 ~ R38 selected 1/8W ordinary carbon film resistors and R39 selection 1W carbon film resistors. T1 ~ T6 are on the 7 × 7 weeks of high frequency in the wound on the T1 primary Φ0.21mm the high-frequency enameled around six in the 1-3 slot each turn, sub-tank 3 around 3 turns; T2 with Φ0.21mm the high-frequency enameled wire in 1, 2 tank around each turn; T3, T4, Φ0.38mm the high-frequency enameled in 1 to 3 tank around two turns; T5 , T6 Φ0.38mm the high-frequency enameled wire around two turns each in the 2-3 slot. L1 ~ L5 diameter of 3.5mm high-frequency the enameled core inductors are wound on the with Φ0.51mm high frequency enameled, L1 around 5 turns, L2 around 4 turns, L3 around 5 turns, L4 around three turns, L5 around 5 turns. The IC3 use LM78L067. Antenna with double cross-shaped omni-directional antenna, its aircraft from a height of 10 meters above the ground with a 75-5 high-quality coaxial cable from the RF output of the machine can be.
Debug circuitry, the first load resistor in the RF output access 75Ω high-frequency false no-load to prevent damage to the RF power transistor the V6. High Frequency Voltage 2V high-frequency voltage that the collector measured in the V2 to V1 from the normal vibration frequency of the test rod point measured V2 collector, with no sense of a small screwdriver to adjust the tuning capacitor C23 frequency meter display value is "15.300MHZ" to complete the debugging of the local oscillator, buffer amplifier stage. High Frequency Voltage high-frequency voltage to the 5V that the collector measured in V4 V3, V4 buffer amplifier stage is working properly. Adjustment of T3, T4 in the core of High Frequency Voltage V5 base on a very high-rate meter measured value for the "45.900MHZ" tripler circuit debugging. Adjustment of T5, T6 core V6 base pole when the frequency meter display value "91.800MHZ" to complete the second harmonic circuit debugging. High Frequency Voltage mapping marked point A at the high-frequency voltage, adjust the tuning capacitor C46, C47 A high-frequency voltage ≥ 12V. High Frequency Voltage mapping, marking the point B at the high-frequency voltage, with no sense of a flat screwdriver struck from the L3, L4, L5 turns, so that high-frequency voltage of point B ≥ 10V, the frequency of test rods from dummy load 10 ~ 20cm away sensor, the frequency counter value is stable and unchanging "91.800MHZ" to complete the L3 ~ L5, C49 ~ C54 band-pass, low-pass filter debugging.
Remove the false load access antenna Field emission experiments, I found its output power than the access to false load when the output power is small. Mainly for high-frequency voltage of point B in the figure a lot of shows at this time of the antenna impedance less than 75Ω. Flat with no sense of a small screwdriver to toggle L3, L4, L5, turns away from the point B measured high-frequency voltage ≥ 10V wipe amp output circuit of V6, L2 ~ L5 and other components of formal debugging.
Audio modulation unit circuit debugging needs in conjunction with the FM stereo radio Young. L, R-side into the high-fidelity audio output signal of the CD player, FM stereo radio and then holding a certain distance to listen to. Turbid noise input to L and R side of the signal amplitude is too strong, hear the voice signal in the receiver, then counterclockwise tune W1, W2, knob until the receiver to hear the voice signal clarity right identified up. Listen to restore the voice of the signal limiter distortion, the FM partial modulation potentiometer the W3, until the outgoing voice signal in the receiver until the realistic reproduction.
Above debugging, you can hand-held FM stereo radio to test launch distance. Receiver sensitivity for the 500μV the ordinary FM stereo radio receiver, open space distance of 1.5km around the non-open distance of about 500m, the normal FM stereo indicator light. 0.5μV FM stereo radio receiver using the receiver sensitivity, open distance of more than 5km, and the stereo indicator still normal and light-emitting
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