Ground systems


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From the transmitter

In addition to the buried or mounted transmission lines, a buried copper strap should run from the transmitter to each individual tower. To save money, this strap connection is sometimes omitted. It is a great mistake to rely on the outer conductor of the transmission line to form the return path for the antenna current. A flat copper strap has nominally very little inductance while a round transmission line outer conductor can have appreciable inductance. In some cases, where a separate ground strap connection was not used, instability has been observed. This strap should go directly to the base of the tower and be brazed to the copper straps that come down the four sides of the tower base from the bottom of the base insulator to the origin of each tower's radial system.

When constructing directional antenna systems, doghouses are decidedly preferable to free-standing metal cases containing ATU equipment. Antenna adjustment is far more comfortable and more quickly completed when there is a protected area in which to work. A few cold and stormy nights very quickly prove this point. It is important to have 120Vac power, and two or three spare pairs of conductors running to the transmitter from the doghouse generally find a use.

The ground strap at the tower base

Figure 2. The ground strap at the tower base.

Figure 2 shows a doghouse located within the tower fence. A copper strap should be run around the base of the building and connected by another copper strap to the ground ring around the tower base. Radials should originate at this ring, be brazed to this doghouse strap and continue out from the other side of the doghouse. Maintaining continuity is very important in this. Cathodic protection, similar to that used for ships, has been mooted for ground/antenna systems but has not been widely used.

Metal fences around the tower base are far more satisfactory than wooden fences. Wooden fences absorb moisture and can cause changes in tower base operating impedance as the moisture dries and changes the resistance of the fence. The posts of metal fences must be connected to the ground system by means of copper strap. This ensures a stable electrical environment around the tower base and is important for the comfort of people touching the fence.


E-mail Battison at batcom@ohio.net.




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