I would be grateful for a professional translation or correction of the following text!

Circuit of micro transmitter of FM using transistor bf494 or bf495

That project is of a micro transmitter of FM using bf494 of easy assembly, so that any one can obtain success in your assembly.


micro fm transmitter details of the mounted circuit, circuit using bf 494

Operation of the circuit of the transmitter of FM with transistor bf494

The Schematic of the circuit is basic of micro transmitters of FM of low potency. Where consists of an oscillator of of high frequency. That frequency is determined by the resonant circuit L / CV. Cv is one it can be adjusted for the oscillator to cover the fm strip.
The feedback to maintain the oscillation comes from the capacitor of 4,7 pF, the capacitor in parallel with the source is to do the desaclopamento. The audio is captured by a sensitive microphone of electrets of two terminals and coupled to the the base of the transistor bf494 through capacitor C5. That sign makes the modulation of the circuit. The antenna for the circuit is a piece of rigid thread of + / - 20 cm. Para to test the transmitter it ties a radio FM and tune in in a free strip, then adjust the trimmer with a of plastic key to capture a stronger sign, when it tunes in a stronger sign it moves away of the radio if the sign disappears it re-does the.

The components for assembly of the transmitter of FM with bf494

The transistor bf494 can be substituted by the bf495 without problems, that transistor easy of being found in the trade.
Attention with the value of the capacitors, so that there is not a position change, C1, C2, C3, C5 should be ceramic. CV is a trimmer for 3 to 30 pF. it can be ceramic or of plastic.
L is the coil, it consists of 4 you exhale of enameled thread 20 AWG, nucleus of air, use a pencil to wind the coil. (that thread type you find in the scrap, of an old transformer or of  it winds found in an old plate). If you have a Lcmeter or Inductimeter, that coil it should present inductance of + / - 0.3µH.

Schematic of the circuit of the transmitter of FM with transistor bf494

Suggestion of Printed circuit board for assembly of the circuit

Circuit of micro transmitter of FM using transistor bf494 or bf495

Printed circuit board for the transmitter in pdf

Printed circuit board side of the components

Circuit of micro transmitter of FM using transistor bf494 or bf495

It lists of components for assembly of the transmitter of FM

Components Value
BAT Two to four piles (3 to 6 volts)
C1 47nF (47n, 473, 0.047)
C2 4,7pF (4.7, 4p7, 4r7)
C3 100nF (104, 100n, 0.1)
CV1 3pF - 30pF
T1 * bf494 or equivalent *
L1 * See text
MIC Electrets microphone
R1 2k7 (red, violet, red, gold)
R2 8k2 (gray, red, red, gold)
R3 5k6 (green, blue, red, gold)
R4 47 (yellow, violet, black, gold)
*See text.

Related tips:
How to identify capacitors with numeric code of three digits + program of capacitor calculation.
Practical calculator to convert capacitors values among pF, nF, µF and vice-versa.
Download of datasheet notes of application of the transistor bf494 and of other several components in the all datasheet, datasheet catalog and datasheet archive using datasheet search.

Other transmitters in that site:
Tv1 transmitter - video Transmitter (DVD, video cassette, camera, computer) of the type video link, using the ci Lm1889n, for 500 meters.
Transmitter of TV 2 - micro transmitter of TV to be used internally, for 100 meters.
micro transmitter of FM - Mini transmitter of FM, good for espionage and amusement in general, for 50 meters.
Potent transmitter of FM with 2n2218. This transmitter can arrive the more than 1 km in favorable conditions of emission.

[index] [Circuits] [Downloads] [Tips] [Links] [sitemap] [Privacy]
©2008 tonieletronica