![]() ![]() This is by no means a stable and predictable oscillator at 100 MHz. T5 is the carrier LO and T8 is the FM modulator. In an fm transistor, modulation is accomplished at the oscillator stage. The TW100F transceiver is a solid-state, high-frequency, single-sideband transceiver operating in the. 86 20 Download By CableGuy Follow More by the author: Hello Im gonna show you How to make a Simple FM Transmitter that works with only an AA battery. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. Distortion in single sideband transmitters is usually the result of improper. (VC1 variable capacitor is meant to modify frequency, but 100pf seems somewhat too large). Single Transistor FM Transmitter Design In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency. ![]() Then you vary component values in an attempt to move frequency up or down. Tolerance of small-value inductor and capacitors is often poor, and their values are modified by inductance of connecting wires.Īt 100MHz, the 2N3904 hasn't much gain, and is likely running close to its gain*bandwidth limit: a carefully-done internal model would be required.Īs others have said: you build it and verify that it oscillates by searching for its frequency with measurement tools. Besides strays, the inductor's self-resonant frequency is likely unknown. Not shown on the schematic are stray capacitances and inductances, and the reactive component added by the antenna. ![]() In this circuit, collector-to-base capacitance would be close to \$C_ \$ has a relatively minor affect on frequency, compared to other capacitances. To get the total capacitance in parallel with L1, I need to add VC1 and B-C capacitance.īut how do I know the capacitance of the B-C junction? Let's say I want to know the base frequency (no sound signal), how much capacitance is there? I don't see C-B capacitance as a function of C-B voltage on datasheets. So therefore we have, in effect, L1 directly parallel with VC1 and B-C capacitance. I know that C1 is large enough so it offers no impedance for the FM signal and therefore the base is effectively grounded for the FM signal. The resonant frequency of this circuit changes as B-C capacitance changes, and so the signal is FM modulated with the sound signal.īut how do I work out the frequency of the FM signal by reading this schematic? Let's say there is no sound signal. This internal capacitance forms a resonant circuit with C1, C3 and L1. As the internal base-collector capacitance of a BJT depends on the base-collector voltage, the B-C capacitance changes with the sound signal. I understand that this work in the following way: the sound picked up by the mic is translated into a voltage at the base of the Q1 transistor. I understand that this work in the following way: the sound picked up by the mic is translated into a voltage at the base of the Q1 transistor. Here is a schematic of a simple FM transmitter. Here is a schematic of a simple FM transmitter. ![]()
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