2 Watts FM transmitter

This is a nice 2 Watts FM transmitter. It has a Super-Sensitive pre-amplification with BC109 and BC177 with more than 100% signal modulation. The job finish the 2N2219 by Motorola. For the Coils you should use 1mm wire(enameled), L1= 3 turns - 10mm diameter, L2= 1 turn - 10mm diameter. R9 trimmer controls the modulation gain. The tunning is easy by controlling C9 trimmer (88-108 MHz). The RFC J should be the VK220J with ferrite (VK200 is not suitable). You will be amazed how well this little monster can transmit several kilometers excellent quality sound. Feed input from a simple cd player or PC (win amp) or just connect a microphone. Enjoy!

1W Linear FM Booster

That RF Amplifier is for boosting small fm transmiters and bugs. It use two Philips 2N4427 and its power is about 1Watt. At the output you can drive any linear with BGY133 or BLY87 and so on. Its power supply has to give 500mA current at 12 Volts. More voltage can boost the distance but the transistors will be burned much earlier than usual.! In any case do not exceed the 15Volts. The Amp offers 15 dB in the area of 80Mhz to 110 Mhz. L4, L5, and L6 are 5mm diameter air coils, 8 turns, with wire 1mm wire diameter.An easy project, with great results.

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.

If you use 1/2 wave length antenna (5.5m) then C3 has to be set to highest capacitance. The connection with the receiver can be done using the SO-239 connector (UHF) or with BNC's. Keep the distance of the cable between the transceiver and the tunning circuit the shortest you can.

USB FM Transmitter MAX2606

This USB FM transmitter can be used to listen to your own music throughout your home. The transmitter circuit use no coils that have to be wound. 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.

This FM transmitter use a chip made by Maxim Integrated Products, the MAX2606. 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.

MP3 FM Transmitter Parts List

Resistors (all SMD 0805)
R1,R2 = 22kO
R3 = 4kO7
R4,R5 = 1kO
R6 = 270O
P1 = 10kO preset, SMD (TS53YJ103MR10 Vishay Sfernice, Farnell # 1557933)
P2 = 100kO 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 = 2200O @ 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)

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. A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply.
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 transmitter 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.

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

Small Single Chip FM Transmitter

This FM transmitter circuit is small, similar to our previous single chip FM transmitter, but this FM transmitter is monophonic. You can see in the circuit’s schematic, the left and right signals is mixed before modulate the radio frequency. Here is the schematic diagram of the circuit:

The core of this FM transmitter circuit is a MAX2606 IC chip, a compact, high-performance intermediate-frequency (IF) voltage-controlled oscillators (VCOs). This FM transmitter will output -21 dBm radiation power, and work with 3 volts power supply. Two small 1.5V battery cells should be enough to power this FM transmitter circuit. The best part of this FM transmitter circuit is that you just need a potentiometer to tune the frequency within commercial FM broadcst band 88-108 MHz. This chip provide all the necessery frequency tuning circuitry, you don’t even need an external varactor. You can use this FM transmitter circuit to extend your mp3/CD player in your room to your portable set around the house, a simpler way than using wires. [Circuit's schematic diagram source: Maxim Integrated Products Application Notes]

UHF Antenna Booster

UHF antenna booster can be used for better reception, especially when you’re far from TV station / relay transmitter. This UHF antenna booster works in 400-850 MHz range. Here is the circuit diagram of the UHF antenna booster:
The circuit use only one transistor, but it gives you 10 to 15 dB amplification, enough for many situation. The most important part is that the transistor circuitry should be shielded from the input circuitry, as shown in the schematic diagram by the dashed line. This ircuit is powered via the signal cable, since the antenna booster circuit must be wired as close as possible to the antenna. This is very important since the amplifier should amplify the signal acquired by the antenna, not the noise picked by the cable from the antenna to the circuit. The antenna and the booster circuit can be installed above your house’s roof. Long 75 ohm coaxial cable can be drawn from the this booster circuit output to the power supply unit close to TV set.

AM/FM Antenna Booster

This antenna booster circuit can be used to amplify the weak signal received by the antenna. Antenna for AM/FM is usually not tuned for the optimal dimension of 1/4 wavelength, since we prefer small portable size. This untuned antenna has very low gain, so the antenna booster circuit here is very helpful in getting better signal reception. Here is the schematic diagram of the circuit:

Use around 470uH coil for L1 if you use for AM frequency (700kHz-1.5MHz) and use around 20uH for SW or FM receiver. For short wave performance, using this antenna booster, you’ll get a strong signal as we get from a 20-30 feet antenna, with only a standard 18″ telescopic antenna and this booster circuit. The power supply should be bypassed by a 47nF capacitor to ground, at a point that should be chosen as close as possible to L1