Attenuate variable radio frequency
 
This circuit can be designed to attenuate signal frequency. Customizable from 1 to 40 dB.If you want to use the band uhf, should be fitted within the frame shield, and C1 to C3 type feeds true.The line should be as short as possible, and the diode should be a kind of low capacity on high speed. The potentiometer can be installed separately, if desired, as well as R3 and Zener diode
Noise limiter signal
 
Interference from ignition noise pulse of the engine, it can cause various problems associated with radio communication equipment installed in the car.This circuit improves signal to noise ratio (S / N-ratio) was better, To connected between the output of the detector circuit with the audio input (if high impedance) or region of the impedance between the high dance audio section.
The diode D1 and diode D2 is there any way to direct the resistance is quite low and very high back resistance.
This circuit for the rf receiver have low bandwidth still 2kHz also 3 kHz
Simple AGC for radio receiver
 
The automatic Gian control circuit also AGC with audio signal is simplest for compress to signal in the Radio receiver. It is ideal for short wave radio receiver used in areas with weak signals.
You should adjust the master volume control dress until the desired signal intensity. While tuning the receiver to the station light, then gradually tuned to the power station and adjust the AGC pot until the pressure in the hearing as needed
Video Tracer For Trouble-Shooting
 
This circuit was designed as an aid to installers and maintainers of video systems. It is basically a video sync separator (IC1) followed by a LED and buzzer driver (IC2, Q1 & Q2). In use, the device is connected to a video cable and if there is video present, the LED will flash at about 10Hz. If there is no video, the LED flashes briefly every couple of seconds. A buzzer can also be switched in to provide an audible indication. The buzzer is particularly useful when tracing cabling faults or trying to find a correct cable amongst many, where it is difficult to keep an eye on the LED.
Another use for the buzzer option is to provide a video fault indication. For example, it could be inserted in bridging mode, with switch S1 in high impedance mode (position 2) across a video line and set to alarm when there is no video present. If someone pulls out a cable or the video source is powered off, the alarm would sound. IC1 is a standard LM1881 video sync separator circuit and 75? termination can be switched in or out with switch S1a. The other pole of the switch, S1b, turns on the power. The composite sync output at pin 1 is low with no video input and it pulses high when composite sync is detected
A frequency multiplier in depth
 
Most of the frequency multiplier circuit using IC phase locked loop (PLL).It will increase the frequency to an integer only.
But this circuit can double the frequency, in the integer to a fractional number.This circuit has an IC phase locked loop number NE565.
It changes frequency as the incoming voltage,Frequency control. That, from the IC Oscillator NE566. IC phase locked loop circuit is in the nature of Demodulator.The output at Pin 7 and is connected to the IC op amp 741. Which is connected in a manner of Voltage-follower circuit. to the driver IC 566 to work.
The voltage passing through the pin 6 of IC op amp, will be entered into a 5-pin of the IC 566.To control the frequency of leg 3 of the IC NE566. the multiplication of frequency equal to R1, C1, R2, C2. For the operation of the circuit stability.Therefore the value of R1 and C1 should be chosen to suit the frequency.
The input entered. Boost up the value frequency is selected by the value of R2 and C2
Direct Coupled Radio
 
Here is the circuit of an excellent direct coupled radio ideal for listening to near by stations.The circuit uses Q1 as a diode detector and first audio amplifier.The detection is across the first emitter base junction which operates as a diode.The base emitter capacitance provides the radio filtering.The resistor R1 is adjusted to obtain the least distortion with consistent volume.Transistors Q2 and Q3 also serve as audio amplifiers
AM Transmitter circuit
 
Here is the circuit diagram of a simple AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited the power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs.You will love this!.
The circuit has two parts , an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz. These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again. The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground. Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5
QRP antenna tuner circuit
 
Low power ( 3 to 30 MHz) transmitters constructed by hams are generally called QRP’s. For such transmitters a well tuned antenna is a must.If the impedance is not properly matched there will be a little or no output.But if properly matched there will be great results.A circuit for matching the antenna properly with the transmitter id given below.
The output of the transmitter is given to the input of the tuner( connector BNC1). The output of the tuner(connector BNC2) must be connected to antenna.Then adjust the L1 and C1 to obtain the maximum transmission power.The transmission power can be checked using a SWR meter
VHF field strength meter
 
This is a simple and low cost wide band VHF field strength meter. The field strength is measured by converting the radio signal to DC and measuring it. The RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal. The meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal. This circuit is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters( ideal for theoretical demonstrations)
FM Radio jammer
 
Circuit shown here can be used to jam FM radios in its vicinity. The circuit is nothing but a classic single transistor oscillator operating in the VHF region. Working principle of the circuit is very simple and straight forward. Powerful VHF oscillations from the circuit will interfere with the FM signals to nullify it. Jammer circuits like this are illegal in many countries and you must assemble this circuit on your own responsibility. This circuit is intended only for fun and i request you not to misuse it
Low cost AM radio
 
Here is the circuit diagram of a simple and low cost AM radio. The working of this radio circuit is straight forward. Inductor L1 and capacitor C1 forms the necessary tank circuit. Diode D1 performs the job of de-modulation. Transistor T1 is wired as a preamplifier whose output is further amplified by the IC LM386 to drive the head phone Z1. The 10K POT R3 can be used as a volume controller
Voice Bandwidth Filter
 
This circuit passes frequencies in the 300Hz – 3.1kHz range, as present in human speech. The circuit consists of cascaded high-pass and low-pass filters, which together form a complete band-pass filter. One half of a TL072 dual op amp (IC1a) together with two capacitors and two resistors make up a second-order Sallen-Key high-pass filter. With the values shown, the cut-off frequency (3dB point) is around 300Hz. As the op amp is powered from a single supply rail, two 10kO resistors and a 10µF decoupling capacitor are used to bias the input (pin 5) to one-half supply rail voltage.
The output of IC1a is fed into the second half of the op amp (IC1b), also configured as a Sallen-Key filter. However, this time a low-pass function is performed, with a cut-off frequency of about 3.1kHz. The filter component values were chosen for Butterworth response characteristics, providing maximum pass-band flatness. Overall voltage gain in the pass-band is unity (0dB), with maximum input signal level before clipping being approximately 3.5V RMS. The 560O resistor at IC1b’s output provides short-circuit protection
TV transmitter with transistor BC547
 
The TV transmitter given here uses UK standard 1 FM modulation for sound and PAL for video modulation. The audio signal to be modulated is pre-amplified using the transistor Q1 and associated components. The transistor Q2 has two jobs: production of carrier frequency and modulation. The pre-amplified audio signal is fed to the base of transistor Q2 for modulation. Capacitor C5 and inductor L1 forms the tank circuit which is responsible for producing the carrier frequency. The video signal is fed to the emitter of transistor Q2 via POT R7 for modulation. The modulated composite signal (audio+video) is transmitted by the antenna A1
Simple FM Receiver Pocket FM Radio by BF184
 
It is a pocket receiver that I built. The idea was to use a simple receiver, but can be used to escape to 3 times viewed. My previous 6-transistor receiver was more complicated and requires 12 volts. This means that 10 AA batteries. I designed and built acircuit board, and built a small aluminum box will hold Comact as possible.
There is nothing wrong with this design. The detector has a simple Colpitts oscillator is of a type often used in other receptor super-regeneration. It’s natural for yourself. The sensitivity for this type of detector is relatively low, but it’s simple and easy to get work. As always, gave me a feedback control to determine the optimum point of operation, ie. maximum sensitivity and minimum SCA / stereo subcarrier beat
VHF Preamplifier 15-20 dB
 
The actual preamplifier in this circuit is a practical wideband amplfier that gives about 15 – 20dB of gain from 1.8 MHz through to well over 200 MHz. You will no-doubt replace this circuit for your own favorite amplifier for the band you are interested in. The 2.2mH chokes should have an absolute minimum reactance of 5000 ohms at the lowest frequency to be used. For 145 MHz these may simply consist of a few turns of wire. I personally used a 10-turn 4mm Dia. coil in series with a 2.2mH torroidal inductor
mini amplifier for computer music
 
It is mini old power amplifier circuit low power at have strip zone frequency wide. It develop upward for apply to change digital signal to analog signal circuit (DAC) and change low filter circuit . For be born the sound of music. Which build by Chinese gambling cow staggers to stagger, By the circuit composes op-amp IC LM3900 perform amplify at the beginning, as a result driver the sound with dual transistor subsequently submit go to still a loudspeaker next. see other detail in the circuit
Valve Transmitter 7 watt 3.5-30 MHz
 
The oscillator is un-tuned so the only tuning procedure required is to select the band (coil tapping) and peak it for maximum RF output. The valves used were selected because they had B7G bases and were the first I put my hand on when I reached into my junk-box. Virtually any pentode valves will work in this application. An EL84, for example, will deliver over ten watts in this circuit but the valves quoted will deliver seven watts from 3.5 to 30 MHz. If you should use another tube then don’t forget to check the screen voltage. If it is less than 250v then you will need a resistor in the screen supply to the valve
12 Watt CB linear amplifier
 
The amplifier has a wide bandwidth, from 1.8 MHz through to over 30 MHz. The drive level required is only about 2 – 5 mW under 14 MHz, rising to 10 mW at 30 MHz. You can therefore make a good QRP CW rig with nothing more than this PA and a simple crystal oscillator. I can achieve 12 watts out of mine using a 10-turn loop around my Grid Dip Oscillator! I can get over 15 watts from my Marconi signal generator, but above about 12 watts it is being over-driven an may not be very nice to look at on the spectrum analyser. The bias generator transistor, TR4, is marked TIP31 in the circuit diagram, but here you can use just about anything that will fit. You could even use another 2SC2078, if you had money to burn, but more practical components would be TIP41, TIP3055, MJE3055
AM-CW ham bands transmitter
 
This is a small transmitter is a good stable QRP transmitter, which has many uses, from the HF bands AM transmitter, radio control models, or AM / CW ham-band transmitter. Circuit is almost ridiculously simple, and construction is even simpler. It is basically a single transistor oscillator with very low output impedance, suitable for driving the base of another transitory stage amplifier. Oscillator uses a single coil and crystal. The coil is tuned to a frequency output, which may correspond to the crystal frequency, or harmonics
FM Wireless Microphone by BC557
 
FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike. It has been used inside guitars and as the basis of a remote control system. I do however, receive many requests for a higher powered circuit and better microphone sensitivity. Now I can introduce the new FM Wireless Microphone (v5), which also has a better frequency stability, over 1Km range (under ideal conditions) and is good on microphone sensitivity. This has been achieved by adding an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little
HF 300KHz-30Mhz Linear Amplifier
 
This is a rather unusual QRP Power Amplifier design, with a wide frequency response; within three dB’s from 300KHz to 30MHz. Overall gain is in the region of 16dB and the final output power may be well over four watts. This PA will deliver 4 watts continuously (with a suitable heatsink), and may be loaded into a short-circuit or open circuit without causing damage. This makes it almost the ideal PA for outdoor/field use. Above is the full circuit diagram of the RFPA and the coil winding pattern. This PA may be used for for SSB
LED FM Tuning Indicator
 
Usually already the circuit F.M. Discriminator the majority will give output that can modify tall and lower 0V depend on something tuning and often use drive Tuning meter at have junction universal position. This circuit designs by use LED 3 pcs. Replace which regard as suit very with the usability. By when institute off-tune output of Discriminator change go to tall more or lower 0V make LED1 or LED3 shine respectively. When output of Discriminator equal to 0V LED2 stick for inform that something tuning best effective both of transistor Q1 with Q3 that use circuit model silicon PNP small signal the multi-purpose and Q2 with Q4 be model silicon NPN small signal the multi-purpose
Active Antenna by MPF102
 
This be Active Antenna circuit for boost frequency all signal give the power goes up. By this circuit has tall rapidity cover the frequency about 10Mhz – 110MHz by have electronics equipment the important be FET and Transistor the small-sized. It make a signal that change antenna the power goes up plentiful.
Antennas that are much shorter than 1/4 wavelength present a very small and highly relative impedance that is dependent on the received frequency. It is difficult to match impedances over a decade of frequency coverage. Instead, input stage Q1 is an FET source-follower. A high-impedance input successfully bridges antenna characteristics at any frequency
Lightning Storm Detector
 
Detects approaching lightning storms by monitoring the RF spectrum
Reverse engineered schematic diagram of a mass produced lightning detector. The RF signal from lightning is quite strong and broad in spectrum so a tuned circuit is not required at the antenna input stage. Too much sensitivity will cause false alarms in a simple receiver such as this one. The circuit uses clever pulse timing and intergration techniques to discriminate between real lightning and other RF interference. The short antenna provides bandwidth limitation towards the low end of the spectrum, while the metal gate CMOS logic running on a mere 6 volts caps the high frequency response. Latch-up is not a problem for the metal gate CMOS logic during normal operation because the operating voltage is only 6VDC, but if you happen to turn the unit off and then back on extremely quickly while the alarm is sounding, then CMOS gate B might get destroyed by the discharge of the 47uF capacitor at pins 1&2. Put a large capacitor between pins 1&14 of one of the the CMOS gates to prevent this
Single Channel RC Cars TX and RX
 
Simple RC Cars – Single channel Transmitters and Super Regenerative Receivers at 27MHz and 49MHz
Here is the 9 volt GS transmitter which does not use a crystal. This clever design allows only two transistors to generate both the carrier and and the modulation. Shown below at 27MHz 40MHz and 49MHz
House fm transmitter 88-108MHz at 4 Watt
 
This is Fm transmitter circuit for house. It is modulation type Mono FM and Frequency range 88-108 MHz. By it have Working voltage range 12-18 VDC and use current max at 450mA only. This circuit convenient for , because , have good small-sized. It is the ideal project for the beginner who wishes to get started in the fascinating world of FM broadcasting and wants a good basic circuit. This circuit use the transistor the important , be the number is 2N3553
Low Pass Filter For FM 88-108 MHz
 
Filter used for eliminate unwanted harmonic frequency at second and third. Notch filter, Band Pass Filter (BPF), and High Pass Filter (HPF) sometime combined in constructing LPF design. Schematic below for FM Broadcast Lowpass Filter 88-108 MHz. It has been tested with a good result. Note : Make the coils at 74 nH and trim them to adjust exact value
AM Transmitter by BC109
 
The circuit is in two halfs, an audio amplifier and an RF oscillator. The oscillator is built around Q1 and associated components. The tank circuit L1 and VC1 is tunable from about 500kHz to 1600KHz. These components can be used from an old MW radio, if available. Q1 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q1 to opposite ends of the tank circuit. The 1nF capacitor C7, couples signals from the base to the top of L1, and C2, 100pF ensures that the oscillation is passed from collector, to the emitter, and via the internal base emitter resistance of the transistor, back to the base again. Resistor R2 has an important role in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q1, and also increases the input impedance so that the modulation signal will not be shunted. Oscillation frequency is adjusted with VC1.
Q2 is wired as a common emitter amplifier, C5 decoupling the emitter resistor and realising full gain of this stage. The microphone is an electret condenser mic and the amount of AM modulation is adjusted with the 4.7k preset resistor P1.
An antenna is not needed, but 30cm of wire may be used at the collector to increase transmitter range
Car Burglar Alarm system with radio wave signal
 
When steal open automobile door relay K1 and K2 work make have voltage 12V give radio transmitter and origin sound part for mix radio waves steal will deaf anything sound. Because radio high frequency. But car owner will hear the sound , by take handbag very small radio, tune the frequency directly with the frequency of a transmitter. Which there is just not mW as a result the enough. A transmitter will still work for 15S (fix the time has with R3 and C1) although the door will open then follow thereafter radio transmitter will stop to work. Because of Transistor stop bias relay contract K2 be scratched. The transistor that use must durable current change relay get. If use battery separate separately and use an antenna model to draw start up the motor this use within a car , steal will can not cut the work has of from the outside
Antenna tunning circuit for 27MHz CB band
 
The antenna tunning circuit can accommodate 1/2 wave length antennas or higher, for input resistances of 50 Ohms which make it suitable for CB (Citizen Band) transceivers. C1 is for fine tunning and C2 is just for tunning. Turning C3 with the help of C2 you can set the SWR to 1:1. The Coil L is made of 11 turns of insulated copper wire with diameter of 1mm
UHF TV linear amplifier 4W by BF136
 
That Circuit is a UHF TV linear amplifier for small TV transmitters with output aroun 100-200mW. The transistor BGQ136 comes with SOT-122 case has gain of 13dB at 800MHz. So with input 100mW you get 2W output and for 200mW you get 4W
UHF TV Linear amplifier 5 W by BLW98
 
This small circuit is a Linear amplifier for driving small UHF TV transmitters. Its gain is 7dB and can amplify a signal between 450-800 MHz. You can drive the circuit with 1 to 1,5 Watts signal. Better use double layer PCB with the second layer connected to earth. Use a stabilized power supply 25 volts and at least 5Amps
PAL Colour Encoder TEA2000
 
A PAL color encoder and video summer which requires just composite sync and composite blanking inputs, and a 6-bit binary coded input giving the color information. The inputs are organized as 2 bits per primary color with gamma correction automatically applied to the resultant luminance and chrominance levels
Simple Coil-less AM receiver by LF356
 
This AM receiver is working perfectly without the need of coils or even a variable capacitor. The LF356 is the basic component. P1 and P2 are the frequency selectors. Use a small telescopic antenna. The stations selectivity is not perfect but is acceptable. This circuit can be very small and you can power the circuit with a 9 volt battery
FM IF Subsystem with CA3189E
 
TheCA3189E is a comprehensive FM-IF system designed for high fidelity FM tuners. It includes a three stage FM-IF amplifier/limiter configuration with level detectors for each stage, a double-balanced quadrature FM detector and an audio amplifier that features the optional use of a muting circuit. The advanced circuit design includes desirable special features such as delayed AGC for the RF tuner, an AFC drive circuit, and an output signal to drive a tuning meter and/or provide stereo switching logic. In addition, internal power supply regulators maintain a nearly constant current drain over the voltage supply range of +8V to +16V. Distortion is primary a function of the phase linearity characteristics of the external detector coil
FSK Demodulator-Tone Decoder with RC2211N
 
A monolithic phase locked loop for data communications. The IC contains a basic phase locked loop for tracking an input signal within the pass band, a quadrature phase detector which provided carrier detector and an FSK voltage comparator which provides FSK demodulation. In the circuit shown, the IC is used as an FSK demodulator such as would be found in the receiver circuit of a modem. The table below shows the component values required for a modem demodulator using standard European tones on the public switched network
TV Pattern Generator by ZNA234
 
This Circuit uses the ZNA234E IC which makes available all the waveforms necessary to produce the crosshatch, dot and greyscale test patterns on a television screen. The composite video output can be injected directly into the video input of a receiver or used to drive a modulator for connection to the aerial socket
AM reciever with TDA1072A
 
This reciever uses the TDA1072A which is a complete AM reciever on a chip and it only requires comparitively few peripheral components to complete a high quality AM radio Circuit. Unlike some other AM radio ICs, a minimum number of external tuned inductors are used to preserve reasonable performance, selectivity and quality of output. Only two of these, an RF input transformer and a single winding oscillator coil need be tuned either capacitively or inductively
FM radio with TDA7000
 
An FM radio on a single chip requiring only a few simple peripheral components. In particular the ship requires only one simple coil and alignment is very easy. The chip includes an RF input stage, mixer, local oscillator, IF amplifier/limiter, phase demodulator, mute detector and mute switch. The output will directly drive a crystal earpiece or could be used with a TBA820M to form a complete portable radio
TV and FM jammer schematic using 2N2222