7-2. ANTENNA AND GROUNDING

7-2-1. Antenna

The following describes various antenna types and their installation.

•Long Wire Antenna

This is the simplest antenna, using about 30 – 100 feet (10 – 30 m) of wire installed between poles, trees or other convenient supports. The antenna wire should be heavy 8 gauge vinyl insulated, stranded wire or 4-gauge copper wire or copperweld. This type of antenna must be installed horizontally to a length of 60 feet (20 m) or more, and be positioned as high as possible. Note that it should be as far away as possible from AC power lines, buildings, trees and other objects.

Fig. 7-1 shows an inverted L antenna. Other antenna types such as sloping, vertical, etc. are also possible.

A long-wire antenna, when installed in an open area, is suitable for all-band operation.

•Doublet Antenna

This type of antenna is suitable for reception of a specific band.

The relation between the overall length "L" and the tuned frequency is:

•Inverted V Antenna

This is a modified doublet antenna, designed to be installed on a single pole or support. The characteristics of this antenna are almost the same as those of a doublet. The overall length "L" is a little more than that of a doublet, and is computed thus:

•Multiband Antenna

This antenna uses more than one doublet for multiband re- ception. The overall length "L" is the same as that of the doublet. If the lengths L1, L2 and L3 are cut for 7 MHz, 14 MHz and 28 MHz, then L1 is tuned to 21 MHz (3 x 7 MHz), permitting reception on 4 amateur bands 7 – 28 MHz. When used only for reception, this antenna will cover the 6 – 30 MHz SW bands. (See Fig. 7-4)

This antenna is directional. Signal strength is maximum when the antenna is at a right-angle (broad-side) to the desired signal and the frequency for which the antenna is cut. It must be used with a 75-ohm coaxial feeder. (See Fig. 7-2)

• Trap Vertical Antenna

Antennas designed exclusively for BCL are available com- mercially, or may be built yourself. Antennas designed for HAM band (3.5 . 28 MHz or 7 – 14 MHz) operation will provide satisfactory broadcast reception for stations near the SW bands. Antennas of this type are most suitable for the listener who does not have enough space for installation of a doublet or long-wire antenna. (See Fig. 7-5)

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