MULTIWIRE RHOMBIC

A rhombic antenna improves in performance if each leg is made up of more than one wire. An improved antenna, known as a curtain rhombic, uses three wires spaced 5 to 7 feet apart for each leg and connected to a common point (figure 2-30).

SLEEVE ANTENNA

The sleeve antenna is used primarily as a receiving antenna. It is a broadband, vertically polarized, omnidirectional antenna. Its primary uses are in broadcast, ship-to-shore, and ground-to-air communications. Although originally developed for shore stations, there is a modified version for shipboard use. Figure 2-31 shows a sleeve antenna for shore stations.

Sleeve antennas are especially helpful in reducing the total number of conventional narrowband antennas that otherwise would be required to meet the requirements of shore stations. With the use of multicouplers, one sleeve antenna can serve several receivers operating over a wide range of frequencies. This feature also makes the sleeve antenna ideal for small antenna sites.

CONICAL MONOPOLE ANTENNA

The conical monopole antenna (figure 2-32) is used in HF communications. It is a broadband, vertically polarized, compact omnidirectional antenna. This antenna is adaptable to ship-to-shore, broadcast, and ground-to-air communications. It is used both ashore and aboard ship.

When operating at frequencies near the lower limit of the HF band, the conical radiates in much the same manner as a regular vertical antenna. At the higher frequencies, the lower cone section radiates, and the top section pushes the signal out at a low angle as a sky wave. This low angle of radiation causes the sky wave to return to the Earth at great distances from the antenna.

Figure 2-30.-Three-wire rhombic antenna.

Figure 2-31.-Sleeve antenna (shore stations).

Therefore, this antenna is well suited for long-distance communications in the HF band.