Tenemos otro artículo en el sitio de una radio experimental AM utilizando un circuito integrado AM. En este artículo, el proyecto descrito tiene sólo un transistor adicional y capta bien las estaciones locales con reproducción en un pequeño altavoz.

   Describimos el montaje de un sensible receptor para las estaciones de onda medias utilizando un circuito integrado 741 y un transistor.

   El receptor necesita una pequeña antena externa y para las estaciones más débiles, también de una conexión a tierra.

   La alimentación puede ser hecha por batería (grande) o fuente y los componentes utilizados son comunes.

 

   Como funciona

   Las señales captadas se llevan al circuito de sintonía formado por L1 y CV de donde se aplican a la entrada del amplificador operacional a través del potenciómetro de volumen.

   La amplificación depende de la resistencia de retroalimentación R3.

   La señal amplificada se aplica a la base de un transistor donde recibe una nueva amplificación y se lleva al altavoz para la reproducción.

   Cambiando la bobina a una con menos espiras se pueden captar estaciones de onda corta.

   

Montaje

  En la figura 1 tenemos el diagrama completo del receptor.

 

   Figura 1 - Diagrama del receptor
   Figura 1 - Diagrama del receptor | Haga click en la imagen para ampliar |

 

   El montaje se puede realizar en una matriz de contactos o en una placa de circuito impreso con el patrón mostrado en la figura 2.

 

   Figura 2 - Placa de circuito impreso
   Figura 2 - Placa de circuito impreso | Haga click en la imagen para ampliar |

 

  En el montaje, observe la posición del circuito integrado y del transistor.

  La polaridad del diodo también debe ser observada y los resistores son de 1/8 W.

   La bobina está formada por 30 + 70 espiras (desde el lado de la tierra) de hilo 28 o 30 en un bastón de ferrita de 10 a 20 cm de longitud.

   El capacitor CV puede obtenerse de cualquier radio AM fuera de uso, así como el altavoz.

   

Prueba y uso

   Para probar y usar, basta con conectar la antena, conectar la alimentación y buscar captar alguna estación local.

   Para una recepción mejor, la antena puede ser larga, consistente en un pedazo de hilo estirado.

   

CI-1 - 741 - circuito integrado

Q1 - TIP31 - transistores de potencia

D1 - 1N34 - diodo de germanio

L1 - Bobina - ver el texto

CV - capacitor variable - ver texto

P1 - 100 k ohms - pote

R1, R2 - 22 k ohms - resistores - rojo, rojo, rojo

R3 - 2M2 ohms - resistor - rojo, rojo, verde

R4 - 1 k ohms - resistor - marrón, negro, rojo

C1 - 1 nF - capacitor de cerámica

C2 - 100 nF - capacitor de cerámica o poliéster

C3 - 10 uF x 12 V - capacitor electrolítico

 

Varios:

Placa de circuito impreso, hilos, caja para montaje, soldadura, etc.

 

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