Los receptores experimentales de AM son muy fáciles de montar y no son críticos, convirtiéndose así en proyectos ideales para cursos técnicos, materias electivas y para el experimentador principiante. El circuito propuesto en este artículo es ideal para ello, presentando buena sensibilidad y excelente calidad de sonido.

   Dos circuitos integrados de bajo costo se utilizan en la elaboración de un receptor que, en su versión básica captará las estaciones locales de ondas medias, pero que puede ser adaptado para captar estaciones de la banda de ondas cortas.

   Su sensibilidad es excelente de modo que, en la mayoría de los casos, no tenía ni siquiera utilizar la antena externa.

   La potencia de salida de audio es alta, dada por un amplificador integrado de excelente calidad de sonido.

   Como se trata de proyecto dedicado a los experimentadores y tiene finalidades didácticas mostraremos el montaje hecho en una matriz de contactos.

 

   Como funciona

   Las señales captadas por la bobina de antena o la antena externa se seleccionan de modo que permanezca sólo la señal de la estación que desea escuchar.

   La señal se detecta y el audio resultante se aplica a la entrada de un amplificador operacional de alta impedancia de entrada y de alta ganancia.

   La ganancia de este circuito se ajusta en P1, resultando así en una señal capaz de excitar fácilmente el amplificador de potencia de audio que es el segundo circuito integrado del proyecto.

   Este circuito integrado, que en realidad no necesita ser el TDA7052, pero hasta otro que el lector disponga, amplifica la señal y lo aplica directamente a un pequeño altavoz.

   La alimentación se realiza por 4 pilas pequeñas.

   

Montaje

   En la figura 1 tenemos el diagrama completo del receptor.

 

   Figura 1 - Diagrama completo del receptor
   Figura 1 - Diagrama completo del receptor

 

   El montaje, basado en una matriz de contactos, se muestra en la figura 2.

 

Figura 2 - Montaje en matriz de contactos
Figura 2 - Montaje en matriz de contactos

 

  La bobina está formada por 30 + 70 espiras de hilo 28 o más fino en un bastón de ferrita de 1 cm de diámetro y de 12 a 20 cm de longitud.

   El capacitor variable se puede aprovechar de una radio AM fuera de uso y el altavoz de 8 ohms puede ser de 2,5 a 10 cm de diámetro.

   Los capacitores son todos cerámicos, excepto C4 que es un electrolítico para 6 V o más.

   El diodo debe ser de germanio y se puede utilizar una segunda bobina de 20 espiras del mismo hilo en el mismo bastón de ferrita para conectar una antena externa y conexión a tierra.

   

Prueba y uso

   Sólo tienes que conectar el circuito es ajustar CV para capturar una estación, P1 para una mejor fidelidad de sonido y P2 para el volumen deseado.

   Para captar ondas cortas, cambie la bobina a 5 + 15 espiras del mismo hilo en el mismo bastón de ferrita.

   Comprobado el funcionamiento es sólo utilizar el aparato.

   

CI-1 - CA3140 - Circuito integrado JFET

CI-2 - TDA7052- circuito integrado

D1 -1N34 - diodo de germanio

S1 - Interruptor simple

B1 - 6 V - 4 pilas pequeñas

CV - capacitor variable - ver texto

L1 y L2 - bobinas - ver texto

P1 - 1 M - potenciómetro

P2 - 47 k - potenciómetro

R1 y R2 - 22k ohms x 1/8 W - resistores - rojo, rojo, naranja

C1, C2 y C3 - 100 nF - capacitores cerámicos

C4 - 220 uF - capacitor electrolítico

FTE - 8 ohms - altavoz pequeño

 

Varios:

Matriz de contactos, soporte de pilas, hilos esmaltados, bastón de ferrita, hilos, soldadura, etc.

 

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