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Antenna Amplifier (ART411E)

  This circuit helps to increase the intensity of signals picked up by an antenna before being brought to the receiver. It is designed to operate with signals between 200 kHz and 30 MHz, which corresponds to the range of medium waves and short waves. The current demanded by this circuit is extremely low, so the battery life used in your power supply is very great. The signals are applied to the base of a transistor and removed from its collector.

   The amplified signals can then be applied to the input or antenna of the receiver with which it will operate. Grounding is very important for maximum circuit performance.

   The transistor used can be any type of RF such as the BF494 or its equivalents.

 

ASSEMBLY

In figure 1 we have the complete diagram of the apparatus and in figure 2 its assembly realized in a bridge of insulated terminals.

 

Figure 1
Figure 1

 

 

Figure 2
Figure 2

 

   The appliance can be installed in a closed box for ease of use. The resistors are 1/8 W or larger and the Capacitors must all be ceramic.

   In figure 3 we have two ways of connecting the amplifier to the receivers.

 


 

 

   The first is for receivers that have antenna and ground input. If the earthing is not accessible, it can be made at the negative pole of the battery holder or at any point in its chassis that corresponds to earth.

   The second is for receivers without antenna. In this case, we make a radiating "frame antenna" which consists simply of rolling 2 to 8 turns of ordinary wire around the radius. The external antenna must be at least 5 meters long and the ground connection can be made in a water pipe, at the neutral pole of the outlet or in an iron bar buried in the ground. If you do not get amplification when you connect, reverse the connections of the plug that goes to the antenna.

 

Q1 - BF494 or equivalent - RF transistor

C1, C2-10 nF - ceramic Capacitors

C3 - 1 nF - ceramic capacitor

C4 - 100 nF - ceramic capacitor

R1 - 1 M - resistor - brown, black, green

R2 - 100 k - brown, black, yellow

B1 - 9 V - batteries or battery

S1 – On-Off switch

E, E2 - Input and output jacks

 

Several:

Terminal bridge, battery holder or battery connector, wires, solder, etc.