Because communications gear includes an antenna, which works best unobstructed at a high elevation, odds are that the antenna is higher than anything else in the area. In addition, the unit may be deployed at sea or in the desert where there is nothing else around. Consequently, lightning or transient surges will strike the antenna. Without protection, the radio will fry probably causing an aborted mission, or worse a hole in the communications infrastructure.

A direct lightning strike involves an enormous release of power -- millions of volts and 200,000+ amperes; nothing but extreme engineering designed devices can survive a surge of this magnitude. What's required is to provide the surge a direct path to ground, and provide secondary protection against the strike's cousin -- the transient surge. A transient surge is defined as the secondary effects of the lightning strike - the energized field surrounding the lightning bolt itself, or the ground potential rise.

The device below was developed specifically for a mobile launching vehicle with a 100' retractable antenna mast. Because of the deployment locations, there would be a high probability of a direct lightning strike.

Even though a substantial grounding structure was developed for the vehicle, it was determined that a significant surge on the transmission line would be inevitable. The challenge was to protect the equipment regardless of the surge size - and to do it repeatedly!

The specifications called for a protector that could withstand multiple 150kA surges and survive at least one 200kA pulse - A tall order!

The antenna attaches directly to the large 7-16 connector on the exposed antenna end of the arrestor. In the event of a large direct strike the antenna and jumper cable is sacrificed to save the 100' cable and the subsequent equipment.

A spare antenna aerial, jumper cable, and, if necessary, a new arrestor can be on hand for a rapid replacement, with the overall system back on-line in minutes.

Although the system is protected from a direct strike to the antenna mast, the radios are still vulnerable to transient surges that can be coupled over from the grounding structure into the coaxial cables. The current of these transients can reach upwards of 40kA. To safely protect the overall system arrestors need to be installed at each end of vulnerable cables. The design on the right (click for a larger image) generically illustrates a complete coaxial protection design for the mobile vehicle.

With the exception of the upper antenna mast, each subcomponent is protected and will be operational after a direct strike to the upper most antennas. With the addition of the optional quarter wave stub units and the fine protector closest to the radio equipment, the transient surge has been reduced to about 30 volts peak going into the radio.

For more information on how NexTek can help you protect your system design please contact NexTek for a free consultation.

Coaxial protectors are intended to pass through a desired RF signal with minimum loss or disturbance. When RF energy enters a protector, the energy is, in some combination, passed through, reflected back, and dissipated within the device. The fundamental RF performance parameters of a coaxial connector are RF frequency and the corresponding insertion loss and VSWR (or return loss). The loss of signal level through the protector is called Insertion Loss and is measured in decibels (dB). The reflection of a signal back to the source is measured as VSWR (or return loss in dB).