Low-Cost 3 volts FM Transmitter

This very Simple Electronic Project and useful circuit diagram of an FM transmitter is sown in this schematic. This fm transmitter circuit is very simple and it has a acceptable transmission. The signal transited from this fm transmitter circuit can be received at almost 300 meters in open air The circuit require a 3volts operating voltage and can be tuned anywhere in the FM band.

Low-Cost 3 volts FM Transmitter Circuit Diagram:

 
You can use this rf transmitter circuit to transmit signal from your house to garden or from room to room . To listen the signal you can use any radio (portable or not ) that can work on FM band . The coil should be about 3mm in diameter and 5 turns. The wire is tinned copper wire, 0.61 mm in diameter.

After the coil in soldered into place spread the coils apart about 0.5 to 1mm so that they are not touching. If you don’t have a trim cap you can use a fixed value capacitor and you can vary the TX frequency by adjusting the spacing of the coils or placing a small piece of ferrite inside the coil, but the better way to change the transmission frequency is to use a variable capacitor.

Connect a half or quarter wavelength antenna (length of wire) to the aerial point. At an FM frequency of 100 MHz these lengths are 150 cm and 75 cm respectively. The calibration of this rf transmitter circuit is very simple and you need just to place a radio at some distance from the transmitter and set it somewhere about 89-90MHZ (chose the transmission frequency) and after that vary the transmitter oscillator frequency, by modifying the value of the capacitor. The transmission frequency is set to the desired frequency just when you can hear the transmitted signal.

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Low-Cost 9V FM Transmitter

A very simple and useful circuit that require few external components and operates in FM band ( above 100 MHz ). This circuit diagram transmitter needs to be powered from a 9 volts battery or from another 9 volts regulated power supply . The tuned coil L1, has two output tappings for the antenna connection, marked "A" and "B". These are both low-level outputs and you choose which tapping you want to use ( stable low range, or more unstable but higher range).

Tap B (2.5%) takes just a very small portion of signal from the oscillator circuit and therefore gives a very frequency stable transmitter. The output level (around 2.5mW) and range are therefore somewhat reduced.  Tap A (10%) delivers very much more power (around 10mW) to the antenna load. This gives you a greater range, but at the expense of frequency stability.

All component leads should be kept as short as possible. The LINK wire on the PCB should lay flat on the PCB. Use the cutoff from a resistor leg. Antenna length for circuit diagram transmitter varies with frequency for optimum distance: 90MHz 80 cm, 95MHz 75cm, 100MHz 70 cm, 105 MHz 68 cm. The frequency determining elements (L1, C5 and C6) form a simple LC tuned oscillator. The inherent problem with this type of circuit diagram transmitter is that any external load (antenna) will change the operating frequency.

The inductor L1 must have around 5.5 turns of enameled 0.5 mm Cu wire , and must have a diameter ( coil diameter) around 5 mm.

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Simple 3 Volts FM Transmitter Schematic

This is a simple and useful circuit diagram of an FM transmitter is sown in this schematic . This FM Transmitter software is very simple and it has a acceptable transmission . The signal transited from this FM transmitter can be received at almost 300 meters in open air The circuit require a 3volts operating voltage and can be tuned anywhere in the FM band.

3V FM Transmitter Circuit Diagram

You can use this emitter circuit to transmit signal from your house to garden or from room to room . To listen the signal you can use any radio (portable or not ) that can work on FM band .

Connect a half or quarter wavelength antenna (length of wire) to the aerial point. At an FM frequency of 100 MHz these lengths are 150 cm and 75 cm respectively.

The calibration of this FM emitter circuit is very simple and you need just to place a radio at some distance from the transmitter and set it somewhere about 88-107MHZ( chose the transmission frequency ) and after that vary the transmitter oscillator frequency , by modifying the value of the capacitor . The transmission frequency is set to the desired frequency just when you can hear the transmitted signal.

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How to Build a Fox Hunt Transmitter

It is a very Simple Build a Fox Hunt Transmitter. This 2 meter 144 MHz fox hunt transmitter is used in amateur competitions where a hidden transmitter is to be “hunted” using mostly home brewed receivers and antennas. The foxhunt electronic circuit is the transmitter. It radiates a high quality signal without unwanted harmonics. Transistor T1 and the crystal together make the oscillator that generates a 36MHz signal.

The unwanted 12MHz basic frequency of the oscillator is suppressed by the filter circuit made of L1, C3, C2. The L2/C4 circuit is set to the fourth harmonic or 144 MHz. The signal goes to the dual-gate-FET driver stage before finally radiating through the transmitting antenna. The output power is from 10…40mW. The radiated signal is also modulated by the gate circuit made of U1, U2, U3, U4. Gate U1 is a low frequency oscillator which generates a signal from 0.1 to 0.5Hz. This signal modulates the transmitter through the transistor T3.

Fox Hunt Transmitter Circuit Diagram

If the U1 output is “0″, transistor T3 is off and the transmitter is also off. On the other hand, if the U1 output is “1″, transistor T3 is on and the transmitter is on. During the “1″ period, gate U2 generates a square wave signal with a frequency form 0.1 to 1Hz. Gate U3 works as an inverter only. It determines whether gate U4 generates a 1KHz signal or not. A periodic burst signal is now present at the gate FET T2 to modulate the transmitter used at foxhunt.

Calibration of the foxhunt transmitter: Adjust the three trimmer capacitors to produse a maximum signal amplitude at the output.

Coil Data:
L1 = 470 nH
L2 is made of 5 windings of 0.8mm copper wire, 8 mm winding diameter. It is tapped at the first winding from the ground.

L3 is made of 0.8mm copper wire, 8mm winding diameter, 3 windings at the FET side and 2 windings at the antenna side. Adjust the coupling between the two windings sides to get a maximum signal output amplitude.
The circuit can be powered with a 9 volt battery. It consumes around 20mA only.

Fox Hunt Transmitter Active Components.

T1 = 2SA256
T2 = 3N205
U1, U2, U3, U4 = IC1 = 4093

Source: Circuitsdiagramlab

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How to Build a 18w FM Transmitter

Build a 18w FM Transmitter. Here's a transmitter for commercial FM band provides up to 18 watts of power. Entering an audio signal 1 Vpp standard , which may come from a mixer or stereo coding stage , this system can cover an entire medium of low houses people or an entire neighborhood in a city. If required you can build more power and interconnect output stages to increase the coverage area of the station. 

Since the electronic diagram is too wide for placement on screen we decided segregated into two , in order to be seen without the need to move from side to side of the screen. The point where we cut only two drivers ( represented by A and B ) which are marked with arrows.

 
 See the Complete Circuit Diagram
  
The Coils and Shocks Should Be Made According to the Following Table:

L1 ------- 3 Turns on ferrite of 5x10mm
L2 ------- 3 Turns on air 9mm ( 10mm long )
L3 ------- 1 Return on 12mm air
L4 ------- 4 turns on air 9mm ( 12mm long )
L5 ------- 2.5 laps on ferrite of 5x10mm
L6 ------- 1 Return on 12mm air
L7 ------- 2.5 laps on HF type ferrite 10x5mm
L8 ------- 3 Turns on air L8 9mm ( 8mm long )
L9 ------- 1 Return on 12mm air
L10 ------- 2.5 laps on ferrite of 5x10mm
L11 ------- 2.5 laps on ferrite of 5x10mm
L12 ------- 7 laps on air 9mm ( 19mm long )
L13 ------- 3 Turns on air L13 13mm ( 7mm long ) 

The variable capacitor connected to the collector of transistor BF199 to adjust the transmission frequency of the circuit. 2K2 potentiometer (which is linear ) serves fine tuning. Once the output frequency should be adjusted following variable capacitors to calibrate the remaining stages of the transmitter. Remember that these settings are made from the capacitor on the left to the one on the right. Remember that the initial settings should accomplish with phantom loads and not the ultimate antenna to avoid interference to other stations.

With respect to the feeding circuit 14V and 2.5A provides 15W , whereas 18V and 3.5A provides 18W, in all cases the source must be stabilized.

The circuit must be built on an epoxy printed with the upper face (components ) reserved for interconnecting tracks and the bottom (solder ) to the ground plane. We have no printed circuit design . If someone builds this transmitter would appreciate email send us the design of the board. 

Transistors 2N3924 , 2N4427 and BLY88 must be mounted heatsinks . In this type of components used sinks star-shaped circular . In the case of transistors 2Nxxxx the ideal size is 20mm in diameter and 10mm in height, while for the BLY88 must be 75mm diameter by 100mm tall. It is mandatory to use silicone grease to optimize the transfer of temperature of the transistors to their sinks . Remember that excessive heat (a part of the output instability ) can cause damage to components.

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