Impedance matching

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Impedance Matching is required to maximise energy transfer from an AC source to a device.


  • Transform 240V AC to 12V AC for a power supply.
  • Transform a 7 Kohm audio source (from an amplifier for instance) down to 16 Ohms for a headphone or loudspeaker.
 - both of these can be done by using a transformer.
  • Couple an antenna with impedance other than 50 Ohm and non-zero reactance to a transceiver with 50 Ohm purely reactive impedance.

This is done by an ATU. The simplest form of an ATU consists of a variable capacitor between TRTX and ground followed by a series variable inductor, which in turn is followed by a series variable capacitor which leads to the antenna (in case of an unbalanced feed line).


Design Beam * Dipole * Dish or Parabola * DDRR * Log Periodic (LPDA) * Loop * Mobile and portable * Omnidirectional * Panel * Quad and Quagi * Screwdriver * Small tuned loop * Vertical * Yagi-Uda * Wire and random wire antennas
Installation Antenna Tuners * Capacity hats and loading coils * Cavity filters * Coaxial Cable * Feedlines * Rotators * Towers and Masts * VK2ACY - G5RV coupler
Theory Front-to-back ratio * Impedance matching * SWR * Tower design * Vertical Antenna efficiency * Wire comparison tables