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We have discussed the lightning event, how sites get damaged, and how to direct this damaging energy to earth ground. But what (in this context) is ground? Ground is the “sink” for electrons in a negative polarity cloud to earth strike.

There are many opinions about how to ground equipment inside the equipment room. Two options are presented here. When a large conductor such as a tower has high peak current flow through it (such as a lightning strike), an intense magnetic field is created around the tower. This field radiates out orthogonally from the tower. Since the building or cabinet is usually close to the tower, equipment in the building is subject to intense moving magnetic fields.

Proper lightning protection for a ham radio station can involve more variables than any other type of radio site. The antenna location will establish the grounding requirements, while the station location will drive the protection requirements.

Wood or fiberglass support structures are not a good idea. They are an insulator. The cabinet earth ground, coaxial cables, and conduits attached to the support would be the only conductive path for lightning energy. If a wood or fiberglass pole must be used, the first step is to provide an alternate conductive path down the pole to earth. A lightning diverter (lightning rod) on top of the pole (above the antenna) with a separate 3 inch copper strap as an earth ground conductor, would provide a low inductance/large surface area conductive path to an earth ground system.

One of the basic ideas in developing a protection strategy is not allowing stray energy to flow through the equipment. There are several ways to accomplish this. One is to totally disconnect the equipment! Another is to provide some form of impulse protector for each of the equipment’s Input or Output (I/O) ports. These ports are usually the ac power connection, a telephone, control, or data line, and an antenna transmission line. A protector on each of the l/O’s will protect that path from damage. However, it is also necessary to be careful about voltages that may exist between the I/O’s during a strike event.

Since the purpose of any coax protector is to equalize the center conductor potential with the shield potential to minimize current flow through the equipment input, how much lightning current will actually be on the center conductor of your coax cable? To answer this often asked question, we need to determine two things:

• How much current is available from the lightning strike?
• In to how many paths will the current divide as it travels towards the site MGB?

The total current available from a direct strike is a given amount. Typically, the 50% occurrence strike will have 18kA or less, and only 10% will have 65kA or more. We will use the 65kA figure for this discussion.

Electromagnetic Pulse (EMP) is an intense electromagnetic field that can instantly overload electrical circuits and damage microelectronics, electrical control and communications systems as well as electric power distribution networks. Produced in the atmosphere by the gamma ray pulse of a nuclear explosion,it is referred to as High-Altitude Electromagnetic Pulse (HEMP) or Nuclear Electromagnetic Pulse (NEMP), which affects electronic equipment over a wide area. Other sources of EMP include nuclear explosions on the ground, man-made weapons like High Power Microwave (HPM) or Directed Energy Weapons(DEW) as well as natural causes like solar storms and lightning.

Combining consists of summing multiple channels together to feed onto a common cable. Low frequencies and higher frequencies will in time reach a peak voltage together of the same polarity. This voltage summation peak can have more peak power than the sum of their RMS powers.

The sudden release of gamma rays (high energy rays) in a nuclear explosion will cause almost instant ionization (the removal of electrons from atoms) of the atmospheric gases that surround the detonation. Free electrons are driven outward. Gamma rays can travel great distances ionizing the atmosphere. This forced movement of electrons, which will again recombine with atmosphere atoms (Compton Recoil Effect), creates a pulsed electromagnetic field (EMP), or “Electromagnetic Pulse.” This is also referred to as “Nuclear Electromagnetic Pulse” (NEMP). About 99% of the NEMP is radiated in a broad spectrum between 10kHz. and 100MHz. Most of the energy is at frequencies below 10MHz. For comparison, lightning’s power density spectrum is from dc to 1 MHz (for the -3dB point).

Outdoor Closed Circuit Television (CCTV) Security Cameras can be a prime target for lightning. They are usually mounted on a building or other vantage point such as a metal o r wood pole. A lightning strike can not only destroy the camera, but can damage your control console due to energy flowing back through the coax and camera power wiring.