Active Antenna for FM AM and SW

Active antenna for FM, AM and SW . The antennas active are very useful in areas where some stations are at a very low level.


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  • 1 Active antenna concept
  • 2 Difference between active antenna and passive antenna
  • 3 Circuit
  • 4 Food
  • 5 Description
  • 6 Components
  • 7 Source

Active antenna concept

The active antenna concept encompasses a wide variety of possible architectures composed of radiating elements and active components, all with the aim of minimizing the effect of losses between the radiating part and the transceiver (transmitter / receiver)

Difference between active antenna and passive antenna

The passive antenna is the one that captures the radiological signal and supplies it to any equipment (radio, television, telephone, etc.) and this equipment internally amplifies that signal to make it useful. The active antenna carries an amplifier itself, which amplifies the weak signal and supplies it already with a certain value, for a single equipment or for several, that is, if it is television, so that it reaches all the receivers in a building) They have more “range” because if the signal is very weak at a certain distance the passive antenna would not work, and it would not be enough and they would not work, but the active one, that very weak signal, when amplified, is already enough to be able to use it and for the receivers.


This circuit constitutes an ideal active antenna to replace the common ones, totally passive. It is special for areas where certain stations are received at a very low level. The value of L1 depends on the application. For SW and FM L1 it must be 20 mH. On the other hand, for Am its value is 470 mH.


It can be provided by a 9V battery. In case of using a source, it is necessary to place a capacitor to ground of 1mF, to avoid the introduction of the ripple.


The active antenna consists of:

  • a short rod, about 1 meter, mounted on a small plastic box in which the amplifier is located. Outside, a clip can be attached, with which the box can be attached to a post, to the roof of the house, the fireplace, or to the window frame.
  • a coaxial cable both for the power supply of the antenna amplifier and for the transport of the amplified antenna signal. Although loss of some signal is inevitable, there is no objection to using up to 20 meters of this cable.
  • a power unit, which is powered by local means (electrical network) or by batteries. This feeder unit supplies 42 volts DC to the coaxial cable to power the antenna amplifier.
  • a short coaxial cable, which runs from this feeder unit to the antenna and ground pins of the receiver.



  • Resistance: R1 = 1MW,
  • Capacitors: C1 = 470pF, C2 = 470pF
  • Semiconductors: T1 = MPF 102
  • Others: Antena.L1 (see text), 9V battery.


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