Short-Wave Superregenerative Receiver Circuit Diagram

Short-Wave Super regenerative Receiver Circuit diagram. Super regenerative receivers are characterized by their high sensitivity. The purpose of this experiment is to deter-mine whether they are also suitable for short-wave radio. Super regenerative receivers are relatively easy to build. You start by building a RF oscillator for the desired frequency. The only difference between a super regenerative receiver and an oscillator is in the base circuit. Instead of using a voltage divider, here we use a single, relatively high-resistance base resistor (100 kΩ to 1MΩ).

Super regenerative oscillation occurs when the amplitude of the oscillation is sufficient to cause a strong negative charge to be applied repeatedly to the base. If the regeneration frequency is audible, adjust the values of the resistors and capacitors until it lies somewhere above 20 kHz. The optimum setting is when you hear a strong hissing sound. The subsequent audio amplifier should have a low upper cutoff frequency to strongly attenuate the regeneration signal at its output while allowing signals in the audio band to pass through. This experimental circuit uses two transistors. A Walkman headphone with two 32-Ω earphones forms a suitable output device. 

Short-Wave Super regenerative Receiver Circuit diagram :

Short-Wave Super regenerative Receiver Circuit Diagram

The component values shown in the schematic diagram have proven to be suitable for the 10–20 MHz region. The coil consists of 27 turns wound on an AA battery serving as a winding form. The circuit produces a strong hissing sound, which diminishes when a station is received. The radio is so sensitive that it does not require any antenna to be connected. The tuned circuit by itself is enough to receive a large number of European stations. The circuit is usable with a supply voltage of 3 V or more, although the audio volume is greater at 9 V. 

One of the major advantages of a super regenerative receiver is that weak and strong stations generate the same audio level, with the only difference being in the signal to noise ratio. That makes a volume control entirely unnecessary. However, there is also a specific drawback in the short-wave bands: interference occurs fairly often if there is an adjacent station separated from the desired station by some-thing close to the regeneration frequency. The sound quality is often worse than with a simple regenerative receiver. However, this is offset by the absence of the need for manual feedback adjustment, which can be difficult. 

Author :Burkhard Kainka  - Copyright : Elektor

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Signal Injector Circuit Diagram

This is the simple Signal Injector Circuit Diagram. This circuit is wealthy in harmonics and is good for testing amplifier circuits. to seek out a fault in an amplifier, 

Connect the planet clip to the 0v rail and move through each stage, beginning at the speaker. a rise in volume ought to be heard at every preceding stage. This Injector will bear the IF stages of radios and FM sound sections in TV's. to Index

Signal Injector Circuit Diagram
 

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Simple AM Receiver Circuit Diagram

This is a compact three transistor, regenerative receiver with fixed feedback. It is similar in principle to the ZN414 radio IC which is now no longer available. The design is simple and sensitivity and selectivity of the receiver are good.

Notes:

All general purpose transistors should work in this circuit, I used three BC109C transistors in my prototype.The tuned circuit is designed for medium wave. I used a ferrite rod and tuning capacitor from an old radio which tuned from approximately 550 - 1600kHz. Q1 and Q2 form a compund transistor pair featuring high gain and very high input impedance. This is necessary so as not to unduly load the tank circuit.

The 120k resistor provides regenerative feedback,between Q2 output and the tank circuit input and its value affects the overall performance of the whole circuit. Too much feedback and the circuit will become unstable producing a "howling sound". Insufficient feedback and the receiver becomes "deaf". If the circuit oscillates,then R1's value may be decreased; try 68k. If there is a lack of sensitivity, then try increasing R1 to around 150k. R1 could also be replaced by a fixed resisor say 33k and a preset resistor of 100k. This will give adjustment of sensitivity and selectivity of the receiver.

Transistor Q3 has a dual purpose; it performs demodulation of the RF carrier whilst at the same time, amplifying the audio signal. Audio level varies on the strength of the received station but I had typically 10-40 mV. This will directly drive high impedance headphones or can be fed into a suitable amplifier.

Construction:

All connections should be short, a veroboard or tagstrip layout are suitable. The tuning capacitor has fixed and moving plates. The moving plates should be connected to the "cold" end of the tank circuit, this is the base of Q1, and the fixed plates to the "hot end" of the coil, the juction of R1 and C1. If connections on the capacitor are reversed, then moving your hand near the capacitor will cause unwanted stability and oscillation.

Finally here are some voltagee checks from my breadboard prototype.This should help in determining a working circuit:-

All measurements made with a fresh 9volt battery and three BC109C transistors with respect to the battery negative terminal.

Circuit diagram

Parts
Q1 (b) 1.31V
Q2 (b) 0.71V
Q2 (c) 1.34V
Q3 (b) 0.62V
Q3 (c) 3.87V

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AM transmitter using Integrated Circuit Diagram

Many beginners give up playing with RF due to the difficulty of building coils and problems with self oscillations that are common in many electronic circuits of RF. I always point out to beginning the construction of a small FM transmitter, myself have made available a simple circuit and an explanatory tutorial in Article Micro FM Transmitter and Micro Spy FM Transmitter Spy Bug in SMD.

The RF is really a very critical area, but on the other hand, it is the most rewarding, especially when we see one of our creations give the air of grace and drop its waves through the air. I always say that we learn more from mistakes and making mistakes is part of the electronics, I even today burst capacitors and transistors see loose tufts of smoke, the difference is that today I have fun with these errors.

Here I will publish a simple electronic circuit RF, so simple that does not use a single coil. This is a small tone transmitter modulated (AM) for the band of medium waves (AM) using an integrated inverter hex 4049 and a crystal circuit. The circuit is very simple, but effective, as can transmit smoothly.

AM transmitter using Integrated Circuit

 

 

The operation of this AM transmitter is simple, the RF oscillator in the transmitter circuit uses an inverter (7-6), whose frequency is determined by the 1 MHz crystal, as we see in the scheme. Two more drives (9-10 / 11-12) amplify the 1MHz oscillator signal.

Have the two inverters (3-2 / 5-4) produce an audio tone, which is modulated with the RF signal by the last inverter (14-15). You can use a piece of wire as an antenna, the signal, a buzz, should be easily capitate until a few meters from the transmitter at 1000 kHz in any AM radio.

With this circuit it is possible to work with the fundamental frequency and its harmonics at all integer multiples of a 1 MHz (or 2 MHz, 3 MHz, ... 10 MHz). This circuit can also be used as a frequency standard to verify the calibration of the display of a short wave radio.[Link]

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SMD FM Transmitter Circuit Diagram

Let’s construct a low-power FM transmitter using surface-mount devices (SMD) that will be received with a standard FM radio. Soldering surface mounted devices is not so hard and actually is quite easy. There are many designs for small FM transmitters but they have some problems. First, you need an audio amplifier to get enough modulation. Second, the antenna is attached directly to the collector.

Third, the coil L must be wound by hand and adjusted by stretching. It all ads with a weak signal that tends to drift in frequency. In contrastm the transmitter schematic we present here eliminates some of those problems, using varactor diode for tuning and modulation, givind great sensitivity without an audio amplifier.

FM Transmitter – How it works
The figure below shows the schematic of the transmitter which consists of two stages: an oscillator and an output amplifier. Modulation is from an electret microphone but you can use a low power audio source.

Oscillator stage
Transistor Q1 is a Colpitts oscillator where the frequency is determined by the parallel resonant circuit formed by inductor L, varactor V1 and capacitors C7 and C8. Q1 is a common-collector amplifier where the power gain counts. V1 is actually a dual varactor that eliminate the possibility of forward conduction at the sinewave peaks.

The frequency of oscillation is set by adjusting the DC voltage on V1 with potentiometer R2. R4 and C3 form a low-pass filter to prevent RF from feeding back onto the DC.
Capacitors C7 and C8 form an AC voltage divider to provide feedback at the emitter of Q1 to sustain oscillation. A necessary condition for oscillation to start is for the radio (C7+C8)/C7 to be sufficiently bigger than 1.

SMD transmitter circuit schematic

Frequency Modulation
Modulation is done by superimposing an audio signal from the electret mic onto the DC bias applied to V1. R3 and C1 form a low-pass filter to prevent RF from feeding back to the mic. R3, R4 and R2 form a votage divider for the audio.

Transmitter output stage
The output of the oscillator is fed through C9 to the Q2 emitter-follower. The output of Q2 drives the antenna through C11. The Q2 emitter-follower it ensures that the oscillator is not loaded down by the impedance of the antenna and it provides power gain to drive the antenna.

SMD Transmitter layout
The figure below shows the layout of the PCB and it uses surface-mounted devices like resistors and capacitors (non-polar devices). All the caps are size 0805 and all resistors are size 1206. use through-hole components for Q1, Q2, IC1 and V1. You can use an SOT-89 device for IC1 and an SOT-23 device for V1. Use MPSH10 or a transistor equivalent. Here you can learn how to solder smd chips

The inductor
A coil would consist of two or three turns of wire but for this schematic we will use an inductor with loops of copper on the PCB. Such flat spiral inductor are common at these frequencies.
One formula for flat spiral inductors is:
flat spiral inductors formula where
L = inductance in uH
r = radius of coil (outer radius + inner radius divided by 2 ) inches
N = number of turns
d = depth of coil (outer radius minus inner radius) inches

Tuning range
While commercial FM band goes from about 88 MHz to 108 MHz, the L and C values used in this design allow tuning up to 100 MHz.

Transmitter testing
You will need a portable FM radio and an assistant. First, find an empty spot on the FM dial and set your radio about 30 feet away (9 meters). The radio’s volume control should not be set too high to prevend feedback. Next, power-up your transmitter and talk to yourself as you adjust the frequency with the trim-pot. When your assintant hears you, your transmitter is tuned. You might have to adjust the radio’s tuner slightly for best reception.

Have fun with it but remember that using the transmitter as a bugging device may not be legal in your country. To use the circuit as a wireless microphone, increase the value of R3. The transmitter range is about 100 feet (30 meters) inside a building.
Parts list

 

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RF Generator 6 GHz Circuit Diagram

RF Generator 6 GHz Circuit Diagram. When we talk about high-frequency, everything seems to be difficult, a simple coil becomes a feat. Doing a search on the Internet found that generator "comb" (comb generator), which is a signal generator that produces multiple harmonics of your input signal. The appearance of the output on a spectrum analyzer resemble a comb, hence the name.

Comb generators are simpler to build and seem to work well up to 1 GHz This generator I found surprised me because he was 6 GHz has a crystal oscillator 96 MHz (third overtone), capacitively coupled to a broadband amplifier using IC mar3 and capacitively coupled to a back-to-back diode set low capacitance PIN. According to the creator of this circuit was originally designed to produce a reference signal in the amateur radio band of 2.4 GHz, hence the 96.013 MHz crystal

RF Generator 6 GHz Circuit Diagram

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Cell Phone Detector Circuit Diagram

This is a simple cell phone detector circuit diagram, this is a pocket-size mobile transmission detector or sniffer can sense the presence of an activated mobile cellphone from a distance of one and-a-half meters. So it can be used to prevent use of mobile phones in examination halls, confidential rooms, etc. It is also useful for detecting the use of mobile phone for spying and unauthorized video transmission. Sourced: EFY

 Simple Cell Phone Detector Circuit Diagram
 

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Single Chip FM Radio Circuit Diagram Using IC TDA 7000

To day i share cheapest cost FM radio circuit using IC TDA 7000. This Single Chip FM Radio Circuit Diagram is designed as per the data sheet and the result is excellent. Ideal for all category of electronic enthusiasts.

The TDA7000 is a monolithic integrated circuit for mono FM portable radios, where a minimum on peripheral components is crucial. The IC TDA 7000 has a Frequency-Locked-Loop system with an intermediate frequency of 70 kHz. The intermediate frequency selectivity is achieved by active RC filters. The only function which needs alignment is the resonant circuit for the oscillator, thus selecting the reception frequency. Spurious reception is avoided by means of a mute circuit, which also eliminates too noisy input signals. Special steps are taken to meet the radiation requirements.

 Single Chip FM Radio Circuit Diagram Using IC TDA 7000

Notes

• For L1 and L2 wind 5 turns of 0.6 mm enameled Copper wire on a 4 mm dia plastic former.
• For antenna use a 50mm long insulated copper wire.
• IC TDA 7000 can withstand up to 10 V supply voltage.But I recommend 6V.
• Use an 8 Ohm speaker or Headphone at the audio output.

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1W Long Range FM Transmitter Circuit Diagram

How to Build a 1W Long Range FM Transmitter Circuit Diagram. This is a simple1W Long Range FM Transmitter Circuit Diagram. This is a long range, very stable, harmonic free, FM transmitter circuit which can be used for FM frequencies between 88 and 108 MHz. With good antenna transmitter can cover 5km range. 

 1W Long Range FM Transmitter Circuit Diagram

It has a very stable oscillator because it uses LM7809 voltage regulator which is a 9V stabilized power supply for T1 transistor. Frequency adjustment is achieved by using the 10K linear potentiometer. The output power of this long range RF transmitter is around 1W but can be higher if you use transistors like KT920A, BLX65, BLY81, 2N3553, 2SC1970 or 2SC1971.

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Four-Stage FM Transmitter Circuit Diagram

This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built around transistor BF200 (T2), a driver built around transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4). A condenser microphone is connected at the input of the oscillator. 

Four-Stage FM Transmitter Circuits diagram :

Four-Stage FM Transmitter Circuits Diagram

Working of the circuit is simple. When you speak near the microphone, frequency-modulated signals are obtained at the collector of oscillator transistor T1. The FM signals are amplified by the VHF preamplifier and the pre-driver stage. You can also use transistor 2N5109 in place of 2N2219. The preamplifier is a tuned class-A RF amplifier and the driver is a class-C amplifier. Signals are finally fed to the class-C RF power amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground plane antenna. Use a heat-sink with transistor 2N3866 for heat dissipation. Carefully adjust trimmer VC1 connected across L1 to generate frequency within 88-108 MHz. Also adjust trimmers VC2 through VC7 to get maximum output at maximum range. 

Regulator IC 78C09 provides stable 9V supply to the oscillator, so variation in the supply voltage will not affect the frequency generated. You can also use a 12V battery to power the circuit.

Assemble the circuit on a general-purpose PCB. Install the antenna properly for maximum range. Coils L1 through L5 are made with 20 SWG copper-enamelled wire wound over air-cores having 8mm diameter. They have 4, 6, 6, 5 and 7 turns of wire, respectively.  

EFY note. This transmitter is meant only for educational purposes. use of this transmitter with outdoor antenna is illegal in most parts of the world. The author and EFY will not be responsible for any misuse of this transmitter.

Author : Pradee G.  - Copyright : EFY

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SW Converter for AM Radio Circuit Diagram

SW Converter for AM Radio Circuit diagram. Apart from chucking it in the bin, what can you do with old AM car radio or clock radio in your junkbox? How about turning it into a crystal controlled, stable, short wave radio receiver, for a minimum investment in time and money? Read on. The heart of the circuit shown here is an IC which goes by the name NE602, NE612 or SA612. It is a double balanced mixer that includes an oscillator that can be crystal-controlled, free running or even driven externally from a PLL, etc. It was originally designed for mobile telephones and is probably available in junked car phones from the tip. The NE602/612 contains a differential input amplifier (called a Gilbert Cell), an oscillator/buffer, a temperature compensated bias network and a power regulator. Typical frequency response is in excess of 500 MHz for the input and 100 MHz for the oscillator.

SW Converter for AM Radio Circuit diagram :

SW Converter for AM Radio Circuit Diagram

 

Supply current is 2.4 mA and the absolute maximum supply voltage is 9 V. Input and output impedances are approx. 1.5 kΩ. As you can see from the circuit diagram, the input from the aerial is passed through a 10.7 MHz IF (intermediate frequency) transformer. This gives isolation from the aerial and reduces the effect of strong local AM radio breakthrough.The transformer can be salvaged from a dead FM radio or stereo or even the FM section of an old clock radio. (The AM section is what we want to use anyway so ratting a bit from the FM section saves cost). A number of 10.7 MHz IF coils from Toko and other far-Eastern manufacturers may be used, including the 94AES30465N and 94ANS30466N, but obtaining these as new parts may be more costly than a complete radio rescued from the tip. There is usually a small capacitor under the IFT coil, between the pins. If so, remove it by crushing it with a pair of pliers and ripping out the remains. The capacitor is not needed as we add an external one according to the band wanted. The input signal is fed into the balanced input of the IC.

 

The crystal is connected to pin 6. It oscillates at its fundamental frequency and is mixed with the input signal giving a number of outputs. The mixer output signal appears on pins 4 and 5. Here, only pin 5 is used for the output. By the way, the inputs and outputs are internally biased with pull-up resistors, so there is no need to tie the unused pins to ground or power. The 220 pF capacitor gives isolation to any DC into the AM radio aerial input. Note also that the same circuit can be used to extend the range of an existing short wave radio receiver in exactly the same manner. The AM radio is used as a tuneable intermediate frequency amplifier, with a tuning range of about 1.6 MHz. You can try different values for C1 to get resonance at the NE602 input: 150 pF for up to 5 MHz, 47 pF for up to 8 MHz, and no capacitor for up to 10 MHz. In practice however 33 pF should do for all ranges. Almost any crystal can be used. The author tried many types from FT-243 WW2 surplus ones to 27 MHz, 3rd overtone CB crystals. Every crystal tried worked. TV sub-carrier crystals work well, as do large oven types. Several crystals can be connected through a switch, giving a convenient way of switching bands. Keep the leads to the switch as short as possible though to prevent radiation of the crystal oscillator. There are many ways to build the circuit. You could make it into an external metal box that can be connected to several radio’s, depending on your location. For instance, if you are a traveller, make it in a small box with an internal 9-volt battery, and leave enough wire on the output to wrap a few dozen turns around the clock radio in your Hotel room.

This will give you your short-wave reception on the go. It is also possible to build the converter right into the car radio. Any sort of construction method can be used, from a small piece of perforated board that I used, to a more elaborate printed circuit board and even just lash all the small components underneath the IC socket. A small switch may be used to change from AM to short-wave. Connect the circuit to the car radio with screened cable to prevent or lessen the effect of strong station breakthrough. To couple the output of the converter to a radio without an external AM aerial input, wind several turns of wire around the internal ferrite rod aerial. As suggested before, winding a dozen or so turns around the plastic radio case will also couple the converter to the radio. This will work at the expense of increased AM signal breakthrough. Connect the positive power lead to the switch on the radio so that it switches the converter on and off as well.

The short-wave aerial can be 2 to 3 meters of wire strung around the room, but better results will be obtained with a outdoor aerial. The test aerial was about 100 meters long and 10 meters high. At night there is a lot of activity on the short waves after dark. Find a weak station around 1 MHz on the AM dial and adjust the core of the IFT for minimum volume from the broadcast station. That’s the only adjustment. SSB signals can be heard, but as no beat frequency oscillator is fitted, you hear the “duck talk” of the signal. The 10 kHz bandwidth of the radio means that on the ham bands, signals do overlap, but it also makes the broadcast stations sound better as most of them do broadcast with reasonable quality audio. Digital tuned AM radios are usually not suitable for the circuit as presented, because the tuning steps are 9 or 10 kHz apart and we want much smaller steps. The old manually tuned types of car radio are what you want. The idea of the circuit is not to get too complicated, but to just enjoy listening on a simple, stable, cheap, short wave receiver. Experiment and enjoy!

Author : P. Laughton, VK2XAN – Copyright: Elektor Electronics

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Simple Radio Band Position Display Circuit Diagram

This is a project of Simple Radio Band Position Display Circuit Diagram. This circuit is an add-on unit for radio receivers that lack band-position display. The circuit presented here can show up to nine bands. It also incorporates a novel feature to make the display dance (blink) with the audio level from the receiver. The power-supply for the circuit can also be derived from the radio-set. The conversion of selected channel to BCD format is achieved using diodes D1 through D15 in con-junction with resistors R4 to R7. The voltages developed across these resistors (R4 through R7) serve as logic in-puts to BCD inputs of BCD to 7-segment de-coder IC1 (CD4511).

Radio Band Position Display Circuit diagram :

Radio Band Position Display Circuit Diagram

When all switches are in  ‘off’ state, the volt-age across resistors R4 through R7 is logic zero, but when any of the switches S1 through S9 is slided to  ‘on’ position, the output across these resistors changes to output proper BCD code to represent the selected channel. This BCD code is converted to 7-segment display by IC1. By this arrangement of diodes, the need for another decimal-to-BCD converter IC and associated parts is obviated. Switches S1 through S9 are actually parts of existing band-switch of the radio. 

Usually, one or two changeover contacts would be found extra in the modular pushbutton-type band-switches of the radios. IC1’s display blanking pin 4 is connected to a display-blinker-control circuit wired around transistors T1 and T2. A small part of the audio signal from the speaker terminals is applied to rectifier diode D16 and filter capacitor C1 to pro-duce a pulsating DC across preset VR1. The sliding contact of preset VR1 is connected to the base of emitter-follower stage comprising transistor T2. The out-put of transistor T2, as amplified by transistor T1, is connected to pin 4 of IC1.Thus turning  ‘on’/‘off’ of display is con-trolled by the pulsating voltage developed from audio output of radio.

The power-supply regulator stage is needed only when radio power-supply is greater than 6V DC.

Author : M.K. Chandra Mouleeswaran Copyright : Electronic for you 2000

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MP3 FM Transmitter Circuit Diagram

MP3 FM Transmitter Circuit Diagram. Here's a simple VHF FM transmitter that could be used to play audio files from an MP3 player or computer on a standard VHF FM radio. The circuit use no coils that have to be wound. This FM transmitter can be used to listen to your own music throughout your home. When this FM transmitter used in the car, there is no need for a separate input to the car stereo to play back the music files from your MP3 player.

Project image :

USB FM transmitter

To keep the circuit simple as well as compact, it was decided to use a chip made by Maxim Integrated Products, the MAX2606 [1]. This IC from the MAX2605-MAX2609 series has been specifically designed for low-noise RF applications with a fixed frequency. The VCO (Voltage Controlled Oscillator) in this IC uses a Colpitts oscillator circuit. The variable-capacitance (varicap) diode and feedback capacitors
for the tuning have also been integrated on this chip, so that you only need an external inductor to fix the central oscillator frequency.

t is possible to fine-tune the frequency by varying the voltage to the varicap. Not much is demanded of the inductor, a type with a relatively low Q factor (35 to 40) is sufficient according to Maxim. The supply voltage to the IC should be between 2.7 and 5.5 V, the current consumption is between 2 and 4 mA. With values like these it seemed a good idea to supply the circuit with power from a USB port.

Circuit diagram:

USB FM transmitter schematics Circuit diagram

 Parts List
Resistors (all SMD 0805)
R1,R2 = 22kΩ
R3 = 4kΩ7
R4,R5 = 1kΩ
R6 = 270Ω
P1 = 10kΩ preset, SMD (TS53YJ103MR10 Vishay Sfernice, Farnell # 1557933)
P2 = 100kΩ preset, SMD(TS53YJ104MR10 Vishay Sfernice, Farnell # 1557934)
Capacitors (all SMD 0805)
C1,C2,C5 = 4μF7 10V
C3,C8 = 100nF
C4,C7 = 2nF2
C6 = 470nF
Inductors
L1 = 390nF, SMD 1206 (LQH31HNR39K03L Murata, Farnell # 1515418)
L2 = 2200Ω @ 100MHz, SMD, common-mode choke, 1206 type(DLW31SN222SQ2L Murata, Farnell #1515599)
Semiconductors
IC1 = MAX2606EUT+, SMD SOT23-6 (Maxim Integrated Products)
Miscellaneous
K1 = 3.5mm stereo audio jack SMD (SJ1-3513-SMT
CUI Inc, DIGI-Key # CP1-3513SJCT-ND)
K2 = 5-pin header (only required in combination with 090305-I pre-emphasis circuit)
K3 = USB connector type A, SMD (2410 07 Lumberg, Farnell # 1308875)

A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply. There is not much else to the circuit. The stereo signal connected to K1 is combined via R1 and R2 and is then passed via volume control P1 to the Tune input of IC1, where it causes the carrier wave to be frequency modulated. Filter R6/C7 is used to restrict the bandwidth of the audio signal. The setting of the frequency (across the whole VHF FM broadcast band) is done with P2, which is connected to the 5 V supply voltage.

The PCB designed uses resistors and capacitors with 0805 SMD packaging. The size of the board is only 41.2 x 17.9 mm, which is practically dongle-sized. For the aerial an almost straight copper track has been placed at the edge of the board. In practice we achieved a range of about 6 metres (18 feet) with this. There is also room for a 5-way SIL header on the board. Here we find the inputs to the 3.5 mm jack plug, the input to P1 and the supply voltage. The latter permits the circuit to be powered independently from the mains supply, via for example three AA batteries or a Lithium button cell. Inductor L1 in the prototype is a type made by Murata that has a fairly high Q factor: minimum 60 at 100 MHz.

PCB Layout :

 USB FM transmitter Layout PCB

Take care when you solder filter choke L2, since the connections on both sides are very close together. The supply voltage is connected to this, so make sure that you don’t short out the USB supply! Use a resistance meter to check that there is no short between the two supply connectors before connecting the circuit to a USB port on a computer or to the batteries.

P1 has the opposite effect to what you would expect (clockwise reduces the volume), because this made the board layout much easier. The deviation and audio bandwidth varies with the setting of P1. The maximum sensitivity of the audio input is fairly large. With P1 set to its maximum level, a stereo input of 10 mVrms is sufficient for the sound on the radio to remain clear. This also depends on the setting of the VCO. With a higher tuning voltage the input signal may be almost twice as large (see VCO tuning curve in the data sheet). Above that level some audible distortion becomes apparent. If the attenuation can’t be easily set by P1, you can increase the values of R1 and R2 without any problems. 

Measurements with an RF analyzer showed that the third harmonic had a strong presence in the transmitted spectrum (about 10 dB below the fundamental frequency). This should really have been much lower. With a low-impedance source connected to both inputs the bandwidth varies from 13.1 kHz (P1 at maximum) to 57 kHz (with the wiper of P1 set to 1/10). In this circuit the pre-emphasis of the input is missing. Radios in Europe have a built-in de-emphasis network of 50 μs (75 μs in the US). The sound from the radio will therefore sound noticeably muffled. To correct this, and also to stop a stereo receiver from mistakenly reacting to a 19 kHz component in the audio signal, an enhancement circuit Is published elsewhere in this issue (Pre-emphasis for FM Transmitter, also with a PCB). Author: Mathieu Coustans, Elektor Magazine, 2009

Notice. The use of a VHF FM transmitter, even a low power device like the one described here, is subject to radio regulations and may not be legal in all countries.

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SW Converter for Digital AM Car Radio Circuit Diagram

SW Converter for Digital AM Car Radio Circuit Diagram This circuit is purposely presented with many loose ends (not literally, of course) to stimulate experimenting with RF circuitry at a small outlay. Looking at the circuit diagram you may recognize a modified version of the SW Converter for AM Radios described elsewhere in this issue. The modifications were necessary to make the circuit compatible with a digital rather than analogue AM car radio. The main difference between digital AM radios and their all-analogue predecessors is that tuning is in 9 kHz (some-times 4.5 kHz steps) in compliance with the international frequency allocation for the band. Obviously, that particular step size, desirable as it may be on MW, is a stumbling block if you want to use a digital AM receiver in combination with a frequency step-up converter for SW, where chaos reigns and there is no fixed step size. The first attempt was to make the crystal oscillator variable by about 5 kHz each way.

 

SW Converter for Digital AM Car Radio Circuit diagram :

 

SW Converter for Digital AM Car Radio Circuit Diagram

 

Unfortunately, despite serious efforts, the crystal could not be pulled more than 1 or 2 kHz so another solution had to be found. After studying the NE/SA602/612 datasheet, it was found that a variable LC based oscillator was the best alternative. The circuit worked after winding a resonant LC circuit and adding a 0.1 µF series capacitor to block the DC component on pin 6 of the NE602 (612). When the tuning was found to be a bit sharp with the original capacitor, a simple bandspread (or fine tuning) feature was added by shunting the LC resonant circuit with a lightly loaded 365 pF tuning capacitor (C10) which, like the main tuning counterpart, C8, was ratted from an old transistor radio. The tuning coil, L1, consists of 8 to 10 turns of 0.6-0.8mm dia. enamelled copper wire (ECW) on a 6-8 mm dia. former without a core. With this coil, frequency coverage will be from about 4 MHz to 12 MHz or so. Details on Tr1 may be found in the referring article.

 

Note that no tuning capacitor is used on the secondary — the input stray capacitance of the NE602 (612) does the trick. A BFO (beat frequency oscillator) was added to enable SSB (single sideband) signals to be received. The BFO built around T1 is simple, has a heap of output and is stable enough to hold an SSB signal for a few minutes without adjustment. The BFO frequency is tuned with C3. Tr2 is a ready-made 455 kHz IF transformer whose internal capacitor was first crushed and then removed with pliers. When S2 is closed the BFO output signal is simply superimposed on the NE602 (612) IF output to the MW radio. The converter should be built into a metal box for shielding. If you find that the BFO gives too much output, disconnect it as suggested in the circuit diagram and let stray coupling do the work. Sensitivity, even on a 1-metre length of car radio aerial, is quite amazing. Bearing in mind that most of the major international SW broadcasting stations like Radio NHK Japan, Moscow, BBC etc.) generate enough power to make sure that you will hear them, it is still quite exciting to hear such signals for the first time on your car radio. 

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4 Transistor FM Transmitter Circuit Diagram

 

 4 Transistor FM Transmitter Circuit Diagram

Build a  4 Transistor FM Transmitter Circuit Diagram. This 4 Transistor FM Transmitter Circuit Diagram provides an FM modulated signal with an output power of around 500mW. The input microphone pre-amp is built around a couple of 2N3904 transistors (Q1/Q2), and audio gain is limited by the 5k preset trim potentiometer. 

The oscillator is a colpitt stage, frequency of oscillation governed by the tank circuit made from two 5pF ceramic capacitors and the L2 inductor. 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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1 Watt PLL FM Broadcast Transmitter Circuit

To day i share a little power for my friends.This is a Simple 1 Watt PLL FM Broadcast Transmitter. The RF output varies from 500mW to about 1.2W depending on the frequency selected and RF output transistor used. Motorola 2N4427 always seems to work well. Transmitter uses CMOS PLL VCO that prevents the frequency drifts. The frequency is selected via DIP switches. The transmitter is supplied by 12V DC and can also be powered from the battery. 

 Simple 1 Watt PLL FM Broadcast Transmitter

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Tuned Radio Frequency (TRF) Receiver Circuit Project

This is a simple project of Tuned Radio Frequency (TRF) Receiver Circuit diagram. Super heterodyne receivers have been mass-produced since around 1924, but for reasons of cost did not become successful until the 1930s. Before the second world war other, simpler receiver technologies such as the TRF receiver and the regenerative receiver were still widespread.

Tuned Radio Frequency (TRF) Receiver Circuit diagram :

 

Tuned Radio Frequency (TRF) Receiver Circuit Diagram

The circuit described here is based on the old technology, but brought up-to-date a The most important part of the circuit is the input stage, where positive feedback is used to achieve good sensitivity and selectivity. The first stage is adjusted so that it is not quite at the point of oscillation. This increases the gain and the selectivity, giving a narrow bandwidth. To achieve this, the potentiometer connected to the drain of the FET must be adjusted very carefully: optimal performance of the receiver depends on its setting. In ideal conditions several strong stations should be obtainable during the day using a 50 cm antenna. At night, several times this number should be obtainable.

The frequency range of the receiver runs from 6 MHz to 8 MHz. This range covers the 49 m and the 41 m shortwave bands in which many European stations broad-cast. Not bad for such a simple circuit! The circuit employs six transistors. The first stage is a selective amplifier, followed by a transistor detector. Two low-frequency amplifier stages complete the circuit. The final stage is a push-pull arrangement for optimal drive of the low-impedance loud-speaker. This circuit arrangement is some-times called a ‘1V2 receiver’ (one preamplifier, one detector and two audio frequency stages).

Setting-up is straightforward. Adjust P1 until the point is reached where the circuit starts to oscillate: a whistle will be heard from the loudspeaker. Now back off the potentiometer until the whistle stops. The receiver can now be tuned to a broad-caster. Occasional further adjustment of the potentiometer may be required after the station is tuned in.  The receiver operates from a supply volt-age of between 5 V and 12 V and uses very little current. A 9 V PP3 (6F22) battery should give a very long life.

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Electronic Central Image Canceller Circuit Project

This is a Electronic Central Image Canceller Circuit diagram Project. The circuit allows you to eliminate the vocal portion of an audio signal, while leaving the instrumental portion. The circuit mixes two channels that must be 180° out of phase, so the signals that form the center-stereo image is canceled out. 

 Electronic Central Image Canceller Circuit Diagram

Those signals usually appear in phase. Resistor R3 biases the non inverting input of Ul from a center tap formed by resistors Rl and R4, and capacitor C3. Resistor R4, capacitor C3, and potentiometer R6 form a negative-feedback circuit that establishes the closed-loop voltage gain of Ul at unity. The signal is inverted between the input and output. Signals applied to the right input are coupled to the non inverting input of Ul through C4 and attenuating resistor R5. 

Resistors R3 and R5 make up a 6 dB attenuator, so once again, there is unity voltage gain between the input and the output. However, the right input signal is not inverted. Therefore, a signal appearing at both inputs is phased out by the circuit and will not appear at the output. Even if the two input signals are at slightly different levels because of different source impedance's, you can still adjust for full cancellation by carefully tweaking R6.

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Project of Scheme RF Attenuator Circuit Diagram

The RF attenuator is used to attenuate an RF signal that can be output from a generator, transmitter or receiver. This RF attenuator can be used without problems at a frequency of up to hundreds of MHz The key must be of good quality and with low inductance resistors. Table 1 shows the values ​​of the resistors impedance attenuator with 50 and 75 ohms. read full 

Scheme RF Attenuator Circuit Diagram

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Priject of Receiver and Transmitter Low Cost Data Circuit Diagram

Priject of Receiver and Transmitter Low Cost Data Circuit Diagram. Here are two simple circuits that can be used for transmission and reception of data via RF to UHF frequency (433MHZ). Two circuits are super simple, no special components and has a good performance, but short range. It is set to the frequency of 433MHZ, but nothing prevents that with some modifications it works on other frequencies. 

Receiver and Transmitter Low Cost Data Circuit Diagram 1

The range is small, ideal for data transmissions within an environment like office, garage, laboratory, workshop or room. This system of data communications short-range 434MHz can be used in projects of alarms, electronic gates, trigger devices from a distance, Arduino, etc. .. X1 is working on a crystal harmonic (433.92Mhz) and L1 receiver comprises 1.5 turns of wire must be tested diameter and thickness to reach the perfect reception of the transmitter. 

Receiver and Transmitter Low Cost Data Circuit Diagram 2

You can mount two of each and create a full duplex transceiver module, ie, it transmits and receives data at the same time.

With a suitable antenna it is possible to improve the performance of receiver, transmitter.

Sourced by : Circuitsstream

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