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.

FM Transmitter

18w FM Transmitter
 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.

Share this article


Post a Comment

Copyright © 2018 • All Rights Reserved.
back to top