Describimos el montaje de un pequeño transmisor para el rango de los 11 metros o 27 MHz, donde los radioamadores conocidos por "PX" en Brasil operan. El transmisor tiene un alcance que depende de la sensibilidad del receptor, pudiendo llegar a cientos de metros e incluso más.

   El transmisor que describimos puede ser alimentado por pilas comunes o baterías, debiendo su señal ser recibida en un receptor especial para el rango del ciudadano o 11 metros.

   El circuito es simple de montar, pues utiliza componentes comunes y no es muy crítico admitiendo hasta un montaje no convencional en puente de terminales.

   Sin embargo, el aparato debe instalarse en una pequeña caja con una antena telescópica.

   Tenemos sólo dos transistores en el proyecto, siendo un modulador y otro oscilador de alta frecuencia.

 

 

   Montaje

   En la figura 1 tenemos el detalle de la bobina que puede ser enrollada con cable esmaltado de 24 a 26 AWG, o incluso hilo telefónico rígido en un tubo de 0,5 a 0,7 cm de diámetro con núcleo de ferrita.

 

Figura 1 - Detalle de la bobina
Figura 1 - Detalle de la bobina

 

   

El diagrama completo del transmisor se muestra en la figura 2.

 

 

Figura 2 - Diagrama completo del transmisor
Figura 2 - Diagrama completo del transmisor | Clique na imagem para ampliar |

 

   

Una primera versión para el montaje, utilizando un puente de terminales, se muestra en la figura 3.

 

Figura 3 - Versión en puente de terminales
Figura 3 - Versión en puente de terminales | Clique na imagem para ampliar |

 

   Para esta versión los terminales de los componentes deben ser mantenidos lo más cortos como sea posible.

   La placa de circuito impreso para el montaje se muestra en la figura 4.

 

Figura 4 - Placa de circuito impreso para el montaje
Figura 4 - Placa de circuito impreso para el montaje | Clique na imagem para ampliar |

 

   

En los dos montajes, las posiciones de los transistores y la polaridad de los capacitores electrolíticos deben ser observadas.

   Los resistores son de 1/8 W con cualquier tolerancia y los capacitores más pequeños deben ser cerámicos.

   El trimmer puede ser del tipo antiguo aprovechado de una radio u otro equipo o moderno cilíndrico de plástico.

   La antena es telescópica de 80 a 150 cm de diámetro.

   Para probar hable delante del micrófono (que debe ser piezoeléctrico) y ajuste CV para captar la señal en el receptor.

 

Q1 - BC548 - transistores NPN de uso general

Q2 - BF494 - transistores NPN de RF

R1- 2M2 ohms - resistor - rojo, rojo, verde

R2 - 22 k ohms - resistor - rojo, rojo, naranja

R3 - 5k6 ohms - resistor - verde, azul, rojo

R4 - 4k7 ohms - resistor - amarillo, violeta, rojo

R5 - 47 ohms - resistor - amarillo, violeta, negro

C1 - 100 nF - capacitor de cerámica o poliéster

C2 - 10 nF - capacitor de cerámica

C3 - 4,7 uF x 12 V - capacitor electrolítico

C4 - 2n2 F - capacitor de cerámica

C5 - 47 pF - capacitor de cerámica

C6 - trimmer de 4 - 40 pF o cerca

C7 - 100 pF - capacitor de cerámica

C8 - 47 uF x 12 V - capacitor electrolítico

L1 - Bobina - ver el texto

S1 - Interruptor simple

B1 - 6 V o 9 V - pilas o batería

MIC - micrófono cerámico o cristal

A - antena - ver texto

Varios:

Placa de circuito impreso o puente de terminales, soporte de pilas o conector de batería, caja para montaje, hilos, soldadura, etc.

 

 

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