FM Transmitter

L1 is 0.112uH (this tunes to the middle of the FM band, 98 MHz, with VC1 at its centre value of 33pF). L1 is 5 turns of 22 swg enamelled copper wire close-wound on a 5mm (3/16") diameter former. Alternatively, you can have a fixed 33pF cap instead of VC1 and have L1 as an adjustable molded coil (eg UF64U from Maplin). VC1 will give you a tuning range of 85 - 125 MHz, and a possible choice is the Philips type polypropylene film trimmer (Maplin code WL72P). Two sets of.....

Views: 233 | Votes: 104 | Comments: 1 | Rating: 8 | Rank: 4 | Added: Oct 22, 2012 |

My 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.....

The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up and amplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (the 5 turn coil and the trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a.....

Here is a simple yet very useful circuit which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier. One important feature of this circuit is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its.....

Here it is a brand new TX300 FM transmitter. The amplifier has exactly the same architecture as TX500 with the difference that TX300 has only one stage variable VHF amplifier. It is a cute schematic that was made for all of you who wanted something even simpler than TX500 and with not as many necessary parts. It is a perfect circuit for transmitting your music around the house and yard. Interesting feature is a gain control P1 that lets you adjust your desired output power.....

Here is the schematic, PC board pattern, and parts placement for a low powered FM transmitter. The range of the transmitter when running at 9V is about 300 feet. Running it from 12V increases the range to about 400 feet. This transmitter should not be used as a room or telephone bug...

This is an image Schematic. No Description available...

Views: 5532 | Votes: 41 | Comments: 0 | Rating: 4 | Rank: 4 | Added: Sep 27, 2012 |

This bugg is based on my previous 3-transistor transmitter. This bugg unit has many advantage. The transmitter use a crystal 46.515MHz to hold a steady frequency. The frequency can be fine-tuned by some 100kHz. The transmitter can send data and audio-signal with +/- 10kHz FM modulation. The output power is about 10mW into 50 ohm. The crystal I used is a 3:th overtone crystal. The coil L1 is a slug tuned coil. The primary winding is 8 turns and the second winding is 2 turn......

This is a small but quite powerful FM transmitter having three RF stages incorporating an audio preamplifier for better modulation. t has an output power of 4 Watts and works off 12-18 VDC which makes it easily portable. 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 to experiment with. The circuit of the preamplifier is very simple and is built around TR4. The input sensitivity.....

Views: 2416 | Votes: 87 | Comments: 0 | Rating: 8 | Rank: 2 | Added: Sep 14, 2012 |

This new stereo FM Micromitter is capable of broadcasting good quality signals over a range of about 20 metres. It`s ideal for broadcasting music from a CD player or from any other source so that it can be picked up in another location. Because it`s based on a single IC, this unit is a snack to build and fits easily into a small plastic utility box. It broadcasts on the FM band (ie, 88-108MHz) so that its signal can be received on any standard FM tuner or portable radio......

A composite stereo signal, as transmitted by FM radio stations, is composed of at least three parts: A base band mono signal, a double sideband channel difference signal, and a pilot carrier. The signal composition is somewhat analogous to an NTSC composite color television signal. I said "at least three parts" because some stations transmit other things such as data and background music that our normal FM receivers do not decode. The base band signal falls between 30 Hz.....

Views: 1670 | Votes: 12 | Comments: 0 | Rating: 6 | Rank: 2 | Added: Sep 1, 2012 |

This small FM transmitter includes a limiter, a microphone amplifier and a PLL digital tuning. All the parts are placed on one circuit board. The RF power is switchable between 1 W (HI) and 0,2 W (LO). Technical specifications: Supply voltage: 12 V from accumulator or regulated power supply. Supply current (HI/LO): 270/170 mA. RF power HI: 1 W. RF power LO: 0,2 W. Impedance: 50-75 ohm. Frequency range: 87,5-108 MHz. Modulation type: wide-band FM. Modulation inputs: line,.....

This circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Circuit draws about 30 mA from a 6-9 volt battery and can be received to about 100 yards. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less.....

This transmitter was designed from the ground up to provide very high sound quality, coupled with excellent frequency stability, reliability, etc. It can be used as a standalone transmitter to serve a medium-sized town, or as an exciter to drive a kilowatt-class power amplifier to serve a large city. It is designed to work from 13.8V nominal voltage, so that it can be run from a common communications power supply in parallel with a backup battery. In the event of a power.....

Views: 5061 | Votes: 14 | Comments: 0 | Rating: 3 | Rank: 7 | Added: Aug 24, 2012 |

The inductor is made by winding 8 turns of #24 insulated solid copper wire on a 5 mm screwdriver. I used a conductor from a piece of category 5 quad twisted pair, left over from wiring the house with Ethernet and this seems to work well and to be easy to handle. Stripping the vinyl insulation is much easier than scarping or burning off enamel. This was easily tuned up and down the bottom of the FM band using a 10 turn panel mounted potentiometer. The upper limit to the.....

This section describes an experimental low power, low bandwidth data signaling system that operates at 100 MHz (In the FM broadcast band in the U.S.). Before operating a radio transmitter, find out what kind of transmitter operation, if any, is permitted in your locality. Radio transmitter operation is a serious legal matter. In the United States, operation of unlicensed intentional radiators is covered by Part 15 of Title 47 of the Code of Federal Regulations. This.....

A frequency reference for tuning up the RS-232 to 100 MHz RF desktop channel adapter elsewhere on this site, when I found this Saronix crystal oscillator in my junk box. A few minutes with AVRStudio produced an ATtiny12 to make a tone - even fewer parts than using an NE-555. With the addition of a transistor to gate the output, I was set to go. Quick and dirty, but it was useful. The Saronix oscillator has an open emitter output. When the 330 Ohm load resistor on the.....

Views: 3028 | Votes: 4 | Comments: 0 | Rating: 9 | Rank: 2 | Added: Aug 13, 2012 |

TR1 (BC547) is an inverted Hartley oscillator which based upon an inductor fabricated on the PCB. This makes it megga-stable, and setable anywhere in the VHF FM band (76MHz to 119MHz) and the BB105 varicap makes it voltage tuneable over about 8MHz of that band. The inductor has one tapping for feedback and a second to feed an optional prescaler. TR2 is a buffer/amplifier and TR3 it the PA stage...

The main oscillator is printed in blue and is voltage controlled. In this construction the VCO range is 88 to 108 MHz. As you can see from the blue arrows, some energy goes to an amplifier and some energy goes to the PLL unit. You can also see that the PLL can control the frequency of the VCO. What the PLL do is that it compare the VCO frequency with the reference frequency (which is very stable) and then regulated the VCO voltage to lock the oscillator at desired.....

This new FM transmitter is very easy to make and doesn't need any RF tuning. First of all ,we have used an integrated VCO: The POS150 from Mini-circuits. This excellent RF circuit covers all the FM Band in a voltage range of 4V to 8V. The Kvco factor is very stable all over the FM band, consequently, we have applied the AF signal directly on the control voltage line coming from the PLL. A 4dB attenuator allows the VCO to drive the MSA1105 RF power stage without exceeding.....