Reduce Interference

Office of Technology, Services, and Innovation

Reduce Interference

Interference Reducing Antenna for Shortwave Broadcasts

Interference Signals:
Signal interference can annoy listeners. By degrading the quality of reception of the desired broadcast program, evere interference can cause the received signal to be completely unintelligible. Such harmful interference disrupts the broadcasts for dedicated listeners.

An interference-reducing antenna described below has been shown to increase the program intelligibility. It is of simple design, low cost, and can be built from material commonly available to most households.

Construction & Installation

Materials

  • A compact portable receiver radio with its telescoping whip antenna
  • An additional telescoping whip antenna similar to the one used with the receiver radio or a stiff wire
  • Two pieces of aluminum foil having same width and length as those of the portable radio receiver
  • A clean piece of plywood or equivalent, non conducting of electricity, big enough for overall support
  • Two short pieces of connecting wire with screws for connection as required
  • A block of wood or equivalent to support the additional antenna

Installation

  • On the piece of plywood used as overall support, lay the radio receiver on the first aluminum foil pad. Use a rubber band or string to secure the receiver if desired.
  • Fix second antenna into wood block so it stays vertical.
  • Connect the additional telescoping whip or stiff wire to the foil pad on which the radio lays. A small screw can be used to attach the first connecting wire to the aluminum foil.
  • Wrap the other bare end of the wire around the whip and twist the wire to assure that a good electrical contact with the whip is established.
  • Use the second wire to connect the remaining aluminum foil to the telescopic whip of the receiver as described above.

Operation

  • The interference reducing antenna should be operated in a relatively clear area. It works best when people are not near the antenna.
  • The interference reducing antenna is operated by rotating the whole system, receiver and the two whip antennas together with the plywood support, until the interfering signal is minimized and the desired program is as clear as possible.
  • If the desired program cannot be received clearly by rotating the plywood support when the interference reducing antenna is level, then try slanting each of the antenna whips or both, and then rotating the system again. Keep experimenting with different slants and rotations combinations until the desired program clears.

Note: If the interfering signal is coming from the same direction as the desired program, this interference reducing antenna will not work.

 

Schematic Diagram of the Anti-Interference Antenna

 

Schematic Diagram of the Anti-Interference Antenna

A sample of the Anti-Interference Antenna

 

Photo: Courtesy of H. Creech, Radio Free Asia