Describimos un radito experimental para la banda AM con buena sensibilidad usando el TDA7052. El circuito es alimentado por pilas comunes y tiene un buen volumen en un altavoz.

   Si bien las estaciones de AM convencionales están con los días contados dada la llegada de las transmisiones digitales en esta franja, todavía podemos montar receptores experimentales para aprender o incluso para operar con transmisores que montemos.

   El circuito tiene como base un circuito amplificador de audio bastante versátil, pues utiliza pocos componentes externos y ofrece excelente calidad de sonido en un pequeño altavoz.

   Si el reproductor todavía disfruta de AM (donde las transmisiones de partidos de fútbol siguen siendo muy atractivas), podrá montar esta radio.

   En la figura 1 tenemos el diagrama completo del receptor.

 

   Figura 1 - Diagrama completo de radio AM
   Figura 1 - Diagrama completo de radio AM | Haga click en la imagen para ampliar |

 

   Si bien el montaje también puede realizarse en una matriz de contactos, una placa de circuito impreso, como la de la figura 2, es ideal para un montaje definitivo.

 

    Figura 2 - Placa de circuito impreso para el montaje
    Figura 2 - Placa de circuito impreso para el montaje

 

   En el montaje, observe la posición del circuito integrado y de los transistores.

   Los resistores son de 1/8 W con cualquier tolerancia y el electrolítico para 6 V o más.

   La bobina consta de 80 + 20 espiras de hilo 28 a 30 en un bastón de ferrita con las 20 espiras del lado de tierra.

   El capacitor variable puede ser retirado de una radio AM fuera de uso, así como el altavoz y el bastón de ferrita.

   El diodo puede ser de cualquier tipo de germanio y para las estaciones locales la antena consiste en un pedazo de hilo de 2 a 5 metros de longitud.

   Una buena conexión a la tierra mejora bastante la recepción, principalmente de las estaciones más débiles.

   

CI-1 - TDA7052 - circuito integrado

Q1 - BC548 - transistores PNP de uso general

D1 - 1N34 o equivalente - diodo de germanio

CV - capacitor variable para AM - ver texto

L1 - Bobina - ver el texto

FTE - 4 ó 8 ohms - altavoz de 5 a 10 cm

S1 - Interruptor simple

B1 - 6 V - 4 pilas

P1 - 22 k ohms o 47 k ohms - pote

R1 - 1M5 ohms - resistor - marrón, verde, verde

R2 - 47 k ohms - resistor - amarillo, violeta, naranja

C1, C4 - 100 nF - capacitores cerámicos

C2 - 100 pF - capacitor de cerámica

C2 - 220 nF - capacitor de cerámica o poliéster

C5 - 220 uF -capacitor electrolítico

Varios:

Placa de circuito impreso o matriz de contactos, soporte de pilas, hilos, soldadura, etc.

 

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