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Bredhurst Receiving and Transmitting Society

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Part 2

Learning outcomes of this part

  • Know that the gain of an antenna is measured in dB, and understand how to calculate the e.r.p. for a known RF power and antenna gain (in multiples of 3 dB).

  • Know that a three-element yagi has a half-wave driven element, a reflector that is slightly longer than the driven element and a director that is slightly shorter than the driven element.

  • Know that yagi antennas may have more than one director.

  • Know that electromagnetic radiation comprises both an electrical field and a magnetic field.

  • Know that the two fields are at right-angles to each other and that the direction of propagation is at right-angles to both fields.

  • Know that it is the electrical field that defines polarisation of the wave.

  • Know that VHF and UHF signals will normally be received best when the transmitter and the receiver have the same antenna polarisation.

  • Know that polarisation is less important at HF due the effects of ionospheric reflection.

  • Know the concept of an antenna polar diagram.

  • Know how to recognise the directions of maximum and minimum radiation.

  • Know how  to recognise polar diagrams for the half-wave dipole and yagi antennas.

  • Know the use of a dummy load and its construction.

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