Coax cables are intended to be pathways for low voltage and low wattage RF energy to and from your antenna. However, it is an adequate
pathway for destructive and deadly lightning strokes to enter into your home or laboratory. Proper planning is required to minimize
Most RF users don�t ever consider the life/safety liabilities a company assumes when it authorizes the installation of communications cables from outside antennas, to inside equipment. Direct or near lightning strokes can introduce immense voltages into such cables which inadvertently provide a pathway of destruction INSIDE the building. Any nearby comm cables e.g. CAT6, security, building automation, fire systems and even electrical distribution wiring can become charged with damaging voltages which could potentially damage entire infrastructure systems. Such considerations are rarely understood or even considered by amateur installers. Facilities personnel should NEVER install coax cables from outside without seeking advice from someone that understands the risks as well as damaging voltages management. Saturn Antennas can be your companies resource.
What kind of Arrestor is best?
Since there are no definitive rules on design/form/function or testing methods for Arrestors, their performance could largely be a leap of faith in a manufacturers credibility. Direct shorting style Arrestors offer the ultimate in protection but as mentioned previously, they are only available for a few bands and only for passive antennas. This is where Saturn Antennas can be of assistance. With decades of experience installing base and mobile protection, we have developed a common sense recognition of what constitutes quality products, which devices lend themselves well to reliable installations and which devices do not.
Other methods may use spark air-gaps or sealed gas tubes or more novel filter circuits that replicate the above QWS Arrestor but perhaps in lower frequencies than would be practical for a QWS because their size quickly becomes prohibitive at low frequencies. It is unlikely that the circuits are as robust as a thick metal stub however. Sometimes a series of same or different type Arrestors comprise a high performance Arrestor system, but must be carefully planned as even the best designs will add at least a little insertion loss as will the additional connectors that must be used.
There are 3 basic methodologies to providing coax protection: Other methods can also be employed to increase your probability of survival.
1) Properly ground your antenna array and provide multiple low impedance and low DC resistance alternate paths to ground.
2) Properly ground your coax shield at the array and especially at the building entry point.
3) Provide an adequate alternate pathway to outside Earth ground off of the coax center conductor at least at the building entry point.
For more information on lightning characteristics, click on the link below or see the �Links� button on the main page.
Example cutaway of a typical Direct Shorting style Arrestor
also referred to as a �Quarter Wave Stub�. This method provides the ultimate in protection as it shunts ALL currents below AND above the pass band. They are very robust, and virtually fail proof, offering a reduced chance of failure from actual use. They are unfortunately narrow band devices and therefore are the antithesis of other Arrestors in that other designs shunt a narrow band of currents to ground and pass a wide band of currents to your radio.
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