More than 100 bolts of lightning strike the earth every second of every day.

No single protection device can fully protect a communications site. Maximum protection is provided by a comprehensive, fully integrated, low impedance grounding system.

A single lightning flash is often brighter than 10 million 100 watt light bulbs, generates billions of watts of energy and produces temperatures as high 50,000 ºF., five times hotter than the surface of the sun. More than 100 lightning bolts strike the earth every second of every day.

A lightning bolt is created when the electrical energy potential between the earth and an energy source (usually clouds) exceeds the atmosphere's ability to restrict the flow of energy. In the clouds, small streamers of electrical energy, called stepped leaders, begin to shoot rapidly downward in fifty-yard jumps. As these leaders approach the ground, they attract upward streamers from the ground forming a conductive path through the atmosphere. The localized energy potential is released through this path in a return stroke of enormous energy from the ground to the clouds in the form of a lightning bolt or strike.

Stepped leaders take the path of least impedance (resistance + inductance) to ground. Metal towers, antennas, wet trees, wires, and people usually provide a lower impedance path to ground than the surrounding air. The path to ground may or may not be a straight line, and multiple paths to ground may form through each stepped leader. Any object within a fifty-yard spherical radius of the end of any stepped leader is at risk of being included in the main strike or secondary ground path. Secondary paths to ground carry a fraction of the amount of energy of the main bolt but are still powerful enough to easily kill people or destroy communications equipment. The energy carried by the primary and secondary strike paths is not dissipated solely at the point of contact but rather spreads from these points of contact on the earth's surface along paths of lowest impedance until all of the strike energy is absorbed into the earth.

Multiple strikes (energy surges) along the main strike path occur in over 70% of direct strikes at intervals up to 200 milliseconds between surges. These surges are visually perceived as the flickerings of the lightning bolt. Additionally, each surge along the primary and secondary paths generate electromagnetic pulses (EMP) of energy, which radiate from the bolt at the speed of light. Equipment destroying "overvoltage" transients can be induced into any wire or cabling in the path of these electromagnetic pulses. EMP's can also damage sensitive components within equipment if the equipment is not properly shielded.

In the United States alone, damage to equipment is estimated to be in excess of $1 billion annually. Noting the many paths through which the energy produced by lightning can destroy communications equipment, a comprehensive plan, incorporating multiple technologies, to control and direct these energy paths safely to ground is the only way to mitigate the risk of damage from direct lightning strikes and their related transient surges. A comprehensive and effective plan, at a minimum, should include:

A means to effectively capture a direct strike and conduct the energy into a low impedance ground dissipation system that avoids earth loops and ground differentials;

Proper shielding around sensitive equipment and components to protect them from EMP's;

A means to effectively protect equipment from surges and transients on incoming power lines, rf communications lines, and data/signal lines.

Gas Tube Type Surge Suppressors
The in-line coaxial gas tube type of surge arrester is best suited for broadband applications in frequency ranges below 2.5 GHz. During normal operation, the gas tube is in a high impedance state making it effectively transparent to the circuit. When an overvoltage condition occurs, the tube very rapidly becomes highly conductive and effectively and efficiently shunts the overvoltage energy to ground, away from sensitive equipment.

Design Advantages
Properly designed gas tube type arresters provide wide frequency bandwidth coverage, quick turn-on time and high surge-current carrying capacity.

Trade-offs
Limitations of the gas tube design are inherent to the gas tube itself, primarily degradation of the tube both over time and with usage (activation), requiring periodic maintenance and replacement. In high powered systems rf energy in the range bordering the tube's turn-on voltage can cause the tube to become partially conductive (excited) creating "noise" in the system.

dc pass, a flawed design

By design, dc pass type surge arresters will allow the lightning surge current—up to the turn-on voltage of the gas tube—to pass directly into the equipment via the center conductor. To minimize this damage potential, a gas tube with the turn-on voltage closest to the operating voltage of their system must be utilized. Maximization of surge protection therefore requires a gas tube whose excitation range often falls within, or minimally outside, the normal operating voltages of the rf system which often results in the introduction of noise. Additionally, higher powered systems require gas tubes with higher turn-on voltages which permit higher surge currents to pass to the "protected" equipment. Therefore the greater the overall system power the higher the turn-on voltage required by the gas tube resulting in increasingly less the protection for the equipment.

Filter Type Surge Suppressors
The majority of energy generated by a lightning strike falls in the frequency range from dc to 1 MHz. Surge energy above 500 MHz generated by either stepped leaders or the main strike is inconsequential. Applications above 800 MHz are ideal for filter type surge arresters that are designed to provide a sharp cutoff of energy below 500 MHz, effectively shunting all of the potentially harmful lightning strike energy to ground.

Design Advantages
Filter type surge arresters do not employ gas tubes eliminating the problems of maintenance, degradation and excitation noise inherent to gas tubes.

Trade-offs
This design style cannot be used to pass control voltages to tower-top amplifiers and other equipment as the frequency of these voltages falls below the filter cutoff point. This design is also not as widebanded as gas tube designs.

1/4 wave stub, a limited design

This style of arrester utilizes a 1/4 wave stub "tuned" to the band pass frequency. Theoretically, only energy at the desired frequency is permitted to pass through the device. Significant shortcomings include a narrow bandwidth which may not optimally cover the systems frequency range and the need for custom tuning to optimize the arrester for a specific frequency. Another major drawback is that like an antenna, the 1/4 wave stub can resonate harmonics of the tuned frequency, above and below, the desired pass frequencies. These harmonic frequencies would be passed in addition to the desired pass frequencies. Any or all harmonic frequencies below 500 MHz could contain surge energy during a lightning strike. Since this design is also dc pass, the surge energy will pass directly to the equipment along with any stray energy from improper grounding.

SG Series
15-1000 MHz
dc blocked gas tube design

SF Series
800-3500 MHz
dc blocked pass filter design

ALLCOM Surge Suppressors significantly reduce the chance of equipment damage when compared to any dc pass design.

All Feature
Integral mounting bracket for easy wall or panel installation; available 90° mounting adaptor.

Silver plated connectors feature TFE dialectrics and either gold (type N) or silver (UHF style) plated center pins

ALLCOM dc blocked surge suppressors

The superior design: the potential amount of lightning surge energy passed to the equipment is minimized by a surge suppressor utilizing a dc-blocked design.

SG Series

By design, ALLCOM's dc blocked gas tube arresters provide no direct center conductor dc path to the equipment. In the worst case, only small, noncritical, amounts of surge energy exist to be passed to the equipment. Also, by not having to closely match the gas tube turn-on voltage of the rf system peaks, gas tubes with higher turn-on voltages can be utilized thus drastically reducing gas tube induced noise in both analog and digital systems.

SF Series

ALLCOM's dc blocked filter surge arresters do not use a tuned stub to achieve band pass, effectively eliminating the problem caused by resonant harmonics. By design, the center conductor has no direct path to the equipment further blocking any stray strike energy from the equipment. Finally, the removal of the 1/4 wave stub element allows the device to be designed with greater optimized bandwidth.