Nuestro proyecto de transmisor consiste en un pequeño aparato de bolsillo que se puede utilizar para comunicaciones a poca distancia. El alcance y el orden de 50 metros y las señales se pueden recibir en cualquier aparato de sonido o radio que sintonice la banda FM.

Este es uno de los muchos proyectos de micro-transmisor que el lector encontrará en este sitio. Este fue influido en uno de nuestros libros de espionaje de la década de los 80 y luego actualizado en 2015.

La alimentación es hecha por dos pilas pequeñas, pero se pueden utilizar pilas ultraminiatura que reducen mucho el tamaño final del aparato, pero también tienen menor autonomía.

En la figura 1 tenemos el diagrama completo de nuestro pequeño transmisor.

 

Figura 1 - Diagrama del transmisor
Figura 1 - Diagrama del transmisor

 

En la figura 2 tenemos el montaje en una placa de circuito impreso.

 

Figura 2 - Placa para el montaje
Figura 2 - Placa para el montaje

 

Para el rango de FM entre 88 y 108 MHz la bobina y formada por 4 vueltas de hilo común (22) rígido en forma sin núcleo con diámetro de 1 cm. Para el rango inferior de VHF entre 50 y 88 MHz utilice 6 espiras y para la banda superior superior a 108 MHz utilice 2 o 3 espiras.

Se debe observar el micrófono y el eletreto y su polaridad. La antena puede ser telescópica de 20 a 50 cm o un pedazo de hilo rígido.

 

SEMICONDUCTORES

Q1 - BF494 o equivalente - transistores de RF

 

RESISTORES

R1 - 4,7 k - resistor (amarillo, violeta, rojo)

R2 - 6,8 k - resistor (azul, gris, rojo)

R3 - 3,9 k - resistor (naranja, blanco, rojo)

R4 - 47 ohms - resistor (amarillo, violeta, negro)

 

CAPACITORES

C1 - 10 uF - capacitor electrolítico

C2 - 22 nF - capacitor de cerámica

C3 - 4,7p - capacitor de cerámica

C4 - 100 nF - capacitor de cerámica

CV - trimmer 3-30 pF

 

DIVERSOS

MIC - micrófono de electreto

B1 - 3 V - 2 pilas - ver el texto

S1 - Interruptor simple

L1 - Bobina - ver el texto

Placa de circuito impreso, soporte para pilas, caja para montaje, antena, cables, soldadura, etc.

 

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