text: Chapter 6
  Figure 6-12. Omni-directional antenna pattern.
  CONSTRUCTION AND SELECTION
  6-100. Antenna construction is limited only by the imagination. There are many types and configurations.
  However, the operator must be careful not to construct an antenna that has a high standing wave ratio,
  which could damage radio equipment. He should use standing wave ratio meters when testing or using
  unfamiliar antennas. In selecting an antenna for an HF circuit, the operator must know the type of
  propagation.
  GROUND-WAVE PROPAGATION
  6-101. Ground-wave propagation requires low takeoff angles and vertically polarized antennas. The whip
  antenna provides good omnidirectional ground-wave radiation. If a directional antenna is needed, the
  operator selects one with a good low-angle vertical radiation.
  SKY-WAVE PROPAGATION
  6-102. Sky-wave propagation complicates antenna selection. After first finding the distance between
  radio stations, the radio operator can determine the required takeoff angle. The takeoff angle-to-distance
  tables give approximate takeoff angles for day and night sky-wave propagation. If the circuit distance is
  966 kilometers (600 miles) during the day, the required takeoff angle is about 25 degrees. At night, it is 40
  degrees. Therefore, the operator selects an antenna that has high gain from 25 to 40 degrees. He omits this
  step if the propagation predictions give the takeoff angles. For NVIS-constructed antennas and short-range
  HF communications, he subtracts 20 percent from these predictions and uses a planning range of 0 to
  300 miles.
  COVERAGE
  6-103. The radio operator determines what type of coverage to use. If the radio circuit consists of mobile
  (vehicular) stations or of many stations at different directions from the transmitter, an omnidirectional
  antenna is required. If the circuit is point to point, he can use a directional or bidirectional antenna.
  Normally, the receiving station locations dictate this choice.
  CONSTRUCTION
  6-104. Before he can select an antenna, the operator must examine the materials available to build one.
  He needs two supports to build a horizontal dipole, and a third support in the middle for frequencies of 5
  mega hertz (MHz) or less. If he has nothing he can use for a support, he cannot build a dipole antenna.