Este artículo forma parte del libro Transmisores y Generadores de RF de Apollon Fanzeres de 1985 que reproducimos en su totalidad para descargar en este sitio, pues la parte teórica todavía es actual y algunos circuitos todavía pueden ser reproducidos con facilidad.

   El circuito de la figura 1 es de un transmisor transistorizado, para operar con una potencia de salida de 1 watts en FM. El lector no debe, como ya dijimos anteriormente, mirar con indiferencia los proyectos de pequeña potencia. Por un lado, la construcción de transmisores de baja potencia cuesta poco y cualquier equívoco no acarreará grandes pérdidas. Por otro lado, los desajustes no causarán grandes males en la vecindad, si bien es sorprendente el alcance de un transmisor de sólo 1 w, con una antena adecuada.

 

Figura 1 - Circuito de transmisor transistorizado
Figura 1 - Circuito de transmisor transistorizado | Clique na imagem para ampliar |

 

   

En la figura 2 se muestra la disposición de los componentes en el circuito impreso.

 

   El punto crítico es la bobina L1. Deberá tener un diámetro de 3,5 mm. Para obtener este diámetro, se puede utilizar, como molde, la parte no cortante de una broca de 3,5 mm (9/64 "), donde se enrollan las espiras de hilo esmaltado de 1 mm de diámetro.

 

Figura 2 - Disposición de los componentes en el circuito impreso.
Figura 2 - Disposición de los componentes en el circuito impreso. | Clique na imagem para ampliar |

 

   

El número de espiras, junto con el condensador variable (trimer) C6, determina la frecuencia de irradiación. En el caso de que se produzca una disminución de la frecuencia, es decir, que va de 60 a 120 MHz, con 7 espiras de 70 a 100 MHz. 50, 40, etc. Mismo. Menor número de espiras, aumenta la frecuencia, es decir, va caminando a los 100, 120, 140, etc. MHz.

   El choque de RF (RFC 1) se constituye de 15 espiras, con hilo de 0,20 mm de diámetro sobre núcleo con ferrita de 4 mm y extensión de 7 mm. El micrófono debe ser de buena calidad, tipo cristal. Los transistores TR1 y TR2 no necesitan disipadores. La antena debe ser una pequeña varilla con 1/4 de longitud de la frecuencia irradiada, la frecuencia esta determinada por L1 y C6.

 

Cristales

   Afortunadamente en Brasil, que es uno de los mayores productores de cristal de cuarzo del mundo (a pesar de las depredaciones que hace largos años se hace ...) existen industrias que producen este componente, a precio razonable y en la frecuencia deseada. Una de las fábricas tradicionales es la Radio Cristal Brasil, situada en Río de Janeiro, Av. Brasil, 5966 (En la época en que el artículo fue escrito).

 

 

 

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