Two transistor fm receiver8/9/2023 ![]() ![]() I see regeneration until the base/collector comes out of saturation, into active mode, limiting the growth. All I can imagine is a small voltage increase at the collector, from thermal noise, lessens the forward bias, and the small voltage increase is passed down to the emitter (reduced), and is inversely reciprocated back to the base, reducing the forward bias on the base/collector even more, thus increasing the collector voltage even more. Figure 2 The tuner with forced quenching. The quench frequency of this oscillator is about 21 kHz. The adjustment of the quench-level control is critical, so a good single-turn potentiometer should be used in this position. Since VCEO for this transistor is around 40V, we choose a much lesser Vcc, of about 9V. I know it's to extract the IM (100Khz), but placing it there seems to lower the saturation current, putting the transistor into "saturation" - the base/collector junction is forward biased. This makes a three-transistor circuit still quite simple for an FM radio ( Figure 2 ). This is a simple wireless FM transmitter circuit which uses RF. If R2 was not in the picture, I understand how the common base configuration, with positive feedback, in it's active region, oscillations start and build and become self limiting. Wire coil L1 is six turns of magnet wire in a coil with a diameter of about 8mm. Lastly, why is the resistor above the coil 8.6k? Is this the best value to extract the IF (about 100k)? Shown above is a regenerative FM receiver with just a single JFET transistor (MPF102). As with all simple radios like this, use a. At first I was told by the designer this circuit will run near cutoff. This is a two Transistor receiver which has sufficient gain and selectivity to drive a Speaker to adequate volume. For this to happen, the two signals need to go though a non-linear circuit. I am guessing this current change, maybe through the feedback capacitor from the collector to emitter, will act with regeneration and magnify the original voltage change at the collector? This seems unconventional, but I really want to understand how this circuit oscillates! When I run this circuit in a simulator, it indeed does oscillate!įurther, I am trying to understand how this circuit mixes the incoming RF with the LO. As the base collector junction is FORWARD biased, a small voltage change across this junction will induce an exponential current change. This will affect the base to collector voltage. incoming RF and transient noise should show up at the collector. I also don't see how it can amplify incoming RF. Again, if this is correct, I don't see how Q1 will amplify transient noise to begin and sustain oscillation. If this is correct, then the base/collector junction is forward biased. If I am doing my calculations correctly, it seems the collector of Q1 will sit at about 0.2v DC, the base at about 0.8v DC, and the emitter at about 0.1v DC. 4.5x5x1-5/8 deep cardboard box contains 2.5x4x1.25 deep transistor radio with Dick Tracy name and. ![]() I have attached the original version of the schematic, DICK TRACY 2 TRANSISTOR RADIO RECEIVER BOXED SET. But I like the idea of using fewer components (and NO IC's) so I hope someone can assist me. No license is required for this transmitter according to FCC regulations regarding wireless. Q1 and it's supporting components act as an RF (LO) oscillator, as well as an antenna and "RF pre-amp", as well as a mixer (to multiply the incoming RF and the LO to get the IF.) If there was a separate RF pre-amp, a separate LO, and a separate mixer, I think I would understand this better. This circuit is a simple two transistor (2N2222) FM transmitter. The radio works great, but I am having trouble understanding the very first stage: Q1. My goal is to learn about discrete electronics (NO IC's.) I'm very happy with the results! It is the Sinclair Micro FM. Figure 1 shows the complete schematic diagram for the transmitter.I have built an FM radio receiver from a kit. Best results are obtained when using a 3 to 4 ft antenna. The ideal bias for the audio stage can be adjusted using a trimmer potentiometer, allowing the operator to achieve the best performance. The reader can use this transmitter as a wireless microphone for short-range communications or as a “bug” to hear conversations in an adjacent room. The other transistor is used for the audio signals. Observe that only one transistor is used to produce the RF or high-frequency signals. The circuit also implements an audio amplifier stage to increase microphone sensitivity. The range will depend on the supply voltage. ![]() This transmitter can be powered from a 6 to 12 V power supply, dry cells, or a nicad battery. The project was published in a Brazilian magazine and after in one of my books in USA. This small FM transmitter can send the signals to a receiver placed at distances up to 1,500 ft. ![]()
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