The 7001 (Q2/Q3) oddly enough also reference towards the NTE123AP. Some substitutes for the 2N3904 are: NTE123AP, 2N4401, BC547 (watch lead orientation), and so on. Check to see that the voltages in the automatic diode matrix switching circuit are good (likely the 'bridge looking affair' you mentioned), but otherwise, poor sound quality from the mono signal will be poor adjustment of Z5 and/or poor adjustment of Z5 relative to that of the first four IF. The emitter resistor and 1k base resistor avoid instability and thermal runaway in this stage. The mono audio comes directly off of Z5 - the MPX circuit has nothing to do with the Mono FM signal. The output stage operates as a ‘Class D’ amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is enough to drive this stage. The oscillator output is fed in to the 3.9uH inductor (L1) which will have a high impedance at RF frequencies. Description Fm Radio Receiver 4 Transistors Fm Radio Receiver 4 Transistors Here is a very simple and effective circuit using only 4 transistors. Frequency is about 100Mhz with values shown.Īudio modulation is fed in to the tank circuit via the 5p capacitor, the 10k resistor and 1N4002 controlling the quantity of modulation. The oscillator is actually a Colpitts stage, frequency of oscillation governed by the tank circuit built from two 5pF ceramic capacitors along with the L2 inductor. The input microphone pre-amplifier is designed close to a pair of 2N3904 transistors (Q1/Q2), and audio gain is restricted by the 5k preset trimmer potensiometer (trimpot). This circuit delivers an FM modulated signal having an output power of about 500mW. 元 = aircoil, 8.5 turns air space, 1/4 inch diameter The following diagram is the schematic diagram of 4 transistors FM transmitter circuit designed by Paul K.
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