2 Transistor Transmitter Schematic

A compact 2 transistor transmitter for use at VHF frequencies.

2 Transistor Transmitter Schematic Circuit Diagram

Notes:
Transistor T1 works as an audio preamplifier, gain is fixed at approximately R2/R1 or 100 times. The audio input is applied at the points LF in (on the diagram). P1 works as gain control. After amplification this audio signal now modulates the transmitter built around T2. Frequency is tunable using the trimmer CT and L1 is made using 3 turns of 1mm copper wire wound on a 5mm slug. The modulated signal passes via C6 to the antenna. A dipole can be made using 2 lengths of 65cm copper pipe. A DC power supply in the range 3 to 16 volts is required.

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Wideband Two Pole High Pass Filter Schematic

The circuit provides a 10MHz cutoff frequency. Resistor R3 ensures that the input capacitance of the amplifier does not interact with the filter response at the frequency of interest. An equivalent low pass filter is similarly obtained by capacitance and resistance transformation.

Wideband Two-Pole High-Pass Filter Schematic

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Room Noise Detector Schematic Circuit

This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively. Current drawing is 1mA with LED off and 12-15mA when the LED is steady on.

Circuit diagram :

Room Noise Detector Circuit diagram

Parts List :

R1____________10K 1/4W Resistor
R2,R3_________22K 1/4W Resistors
R4___________100K 1/4W Resistor
R5,R9,R10_____56K 1/4W Resistors
R6_____________5K6 1/4W Resistor
R7___________560R 1/4W Resistor
R8_____________2K2 1/4W Resistor
R11____________1K 1/4W Resistor
R12___________33K 1/4W Resistor
R13__________330R 1/4W Resistor

C1___________100nF 63V Polyester Capacitor
C2____________10µF 25V Electrolytic Capacitor
C3___________470µF 25V Electrolytic Capacitor
C4____________47µF 25V Electrolytic Capacitor

D1_____________5mm. Red LED

IC1__________LM358 Low Power Dual Op-amp

Q1___________BC327 45V 800mA PNP Transistor

MIC1_________Miniature electret microphone

SW1__________2 poles 4 ways rotary switch

B1___________9V PP3 Battery

Clip for PP3 Battery

Use :

• Place the small box containing the circuit in the room where you intend to measure ambient noise.
• The 50 dB setting is provided to monitor the noise in the bedroom at night. If the LED is steady on, or flashes bright often, then your bedroom is inadequate and too noisy for sleep.
• The 70 dB setting is for living-rooms. If this level is often exceeded during the day, your apartment is rather uncomfortable.
• If noise level is constantly over 85 dB, 8 hours a day, then you are living in a dangerous environment.

Source by : Streampowers

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Wideband Two Pole High Pass Filter Schematic

The circuit provides a 10MHz cutoff frequency. Resistor R3 ensures that the input capacitance of the amplifier does not interact with the filter response at the frequency of interest. An equivalent low pass filter is similarly obtained by capacitance and resistance transformation.

Wideband Two-Pole High-Pass Filter Schematic

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4 Transistor Transmitter Schematic

This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor. ( Click here for Colpitt Oscillator Resonant Frequency Equation.) Frequency is around 100Mhz with values shown.

4 Transistor Transmitter Circuit Diagram

Audio modulation is fed into the tank circuit via the 5p capacitor, the 10k resistor and 1N4002 controlling the amount of modulation. The oscillator output is fed into the 3.9uH inductor which will have a high impedance at RF frequencies.

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 sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.

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Glitch Detector Schematic

In the circuit, two op amps (half of an LM324 quad op amp) and an SCR are direct coupled in a de-voltage monitoring circuit. Op-amp U1-a is configured as a voltage follower, which feeds the bridged inputs of the second op amp, Ul-b. A resistor/capacitor combination (R2/C1) connected to the negative input of U1-b forms an RC time-delay circuit.

Glitch Detector Circuit Schematic

As long as there is no change in the de-voltage level at either of U1-bs inputs, its output is near zero. If a voltage glitch occurs, the RC timing circuit will delay the voltage change at the op amps inverting input, causing its output to go high, triggering SCR1 and causing LED1 to light. The circuits sensitivity allows it to detect voltage changes in the millivolt range. Pressing S1 diverts the SCRs holding current to ground, causing it to turn off and reset the circuit.

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Low Forward Drop Rectifier schematic

A
TMOS power FET , Q1 , and LM393 comparator provide a high efficiency
rectifier circuit. When Va exceeds Vb1 U1s output becomes high and Q1
conducts. Conversely, when Vb exceeds Va1, the comparator output
becomes low and Q1 does not conduct.

The
Forward drop is determined by Q1s on resistance and current I. The
MTH40N05 has an ON resistance of 0.028 Ω ; for I = 10 A , the forward
drop is less than 0.3V .Typically , the best Schottky diodes do not even
begin conducting below a few hundred mV.

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