Many radio amateurs and shortwave listeners haven't protected their antennas against lightning, because their house is never hitted by a lightning stroke. They forget, that mounting an outdoor antenna has increased the chance on a direct hit. But a direct hit is not needed to destroy the transceiver or receiver. With a thunderstorm in the vicinity (up to 10 miles away), very high voltage spikes are induced in every metallic structure, including the antenna. The same can happen during dry weather with low air-humidity and during static charged rain or -snow. Although the induced power is not very high, the voltage spikes can reach values of thousands of volts, and can destroy the sensitive input circuitry of the receiver. Every repair shop can confirm that blown-up front-ends due to static discharges is a very common problem.
These static discharges must have a way to ground. Therefore it is very important, that the antenna it selves or at least the shield of the coaxial lead-in cable is connected to a low impedance ground, outside the house. Not many amateurs have such a ground point, for instance a metallic pipe of at least 3 mtrs, banged into the ground. They seem to have confidence in the safety ground of the mains wiring, to which most receivers are connected.
The safety ground is sufficient for induced statics, but very dangerous in case of a direct hit of the lightning. With a direct hit, the lightning bolt will flow along the coaxial cable, through the receiver and than thtough the mains wiring in the house to the grounding point in the fuse box. All the mains wiring in the house will melt down, all appliances which are connected to the mains become defective and the chance of fire is very large...
So, an outside grounding point is in fact a necessity for every antenna installation. But a good grounding point is not enough to protect your receiver. If you use for instance a dipole, trap dipole (W3DZZ) or G5RV antenna, one leg of the antenna is connected to the (grounded) shield of the coaxial cable. The other leg of the antenna is connected to the centre conductor of the coax and thus directly to the antenna input of the receiver. With a direct hit or with just static discharges, this direct connection is the reason that the receiver will not survive.
Some companies sell so-called lightning protectors, which must be inserted in the coaxial lead-in cable. They have a metallic housing, which has to be connected to a good outside ground. Inside, the centre conductor is connected to a gas-arrestor. That is a kind of neon-lamp which ignites at 230 Volts. In case of a static discharge or direct hit, the gas-arrestor ignites and the discharge flows to the ground. These devices, provided that they are properly installed, can keep the lightning bolt out of your house. Unfortunately, they cannot always protect the receiver. Reason is the reaction time of the gas-arrestor. It takes time before the neon gas in the arrestor ignites. The rise time of an induced static discharge or a direct hit is so fast, that the voltage over the arrestor rises to 600 to 1000 volts, before the arrestor forms a short-circuit to ground. That short during high voltage spike was no problem in the good old days of tube receivers with high voltage capacitors, but modern solid state receivers cannot withstand such spikes.
For amateurs, it's always wise to disconnect the receiver from the lead-in coax during a thunderstorm in the vicinity, but professionals often don't have that choice. They must continue their operations, regardless the weather conditions. With the financial help of the Dutch Government, RF Systems has solved this problem with the Power - Isolator.
The Power - Isolator is a completely new device to protect transceivers and receivers from static discharges and direct hits of the lightning. It separates the antenna totally from the receiver. There is no conducting connection any longer, so discharges cannot reach the transceiver or receiver. The transfer of radio signals (or transmitter power) takes place by means of a magnetic field only. This Magnetic field Technology (MT) act also as a screen of Faraday, with a strong reduction of static- and man-made noise as result. See for more info :
* Power - Isolator: Noise reducer & Lightning protector
These static discharges must have a way to ground. Therefore it is very important, that the antenna it selves or at least the shield of the coaxial lead-in cable is connected to a low impedance ground, outside the house. Not many amateurs have such a ground point, for instance a metallic pipe of at least 3 mtrs, banged into the ground. They seem to have confidence in the safety ground of the mains wiring, to which most receivers are connected.
The safety ground is sufficient for induced statics, but very dangerous in case of a direct hit of the lightning. With a direct hit, the lightning bolt will flow along the coaxial cable, through the receiver and than thtough the mains wiring in the house to the grounding point in the fuse box. All the mains wiring in the house will melt down, all appliances which are connected to the mains become defective and the chance of fire is very large...
So, an outside grounding point is in fact a necessity for every antenna installation. But a good grounding point is not enough to protect your receiver. If you use for instance a dipole, trap dipole (W3DZZ) or G5RV antenna, one leg of the antenna is connected to the (grounded) shield of the coaxial cable. The other leg of the antenna is connected to the centre conductor of the coax and thus directly to the antenna input of the receiver. With a direct hit or with just static discharges, this direct connection is the reason that the receiver will not survive.
Some companies sell so-called lightning protectors, which must be inserted in the coaxial lead-in cable. They have a metallic housing, which has to be connected to a good outside ground. Inside, the centre conductor is connected to a gas-arrestor. That is a kind of neon-lamp which ignites at 230 Volts. In case of a static discharge or direct hit, the gas-arrestor ignites and the discharge flows to the ground. These devices, provided that they are properly installed, can keep the lightning bolt out of your house. Unfortunately, they cannot always protect the receiver. Reason is the reaction time of the gas-arrestor. It takes time before the neon gas in the arrestor ignites. The rise time of an induced static discharge or a direct hit is so fast, that the voltage over the arrestor rises to 600 to 1000 volts, before the arrestor forms a short-circuit to ground. That short during high voltage spike was no problem in the good old days of tube receivers with high voltage capacitors, but modern solid state receivers cannot withstand such spikes.
For amateurs, it's always wise to disconnect the receiver from the lead-in coax during a thunderstorm in the vicinity, but professionals often don't have that choice. They must continue their operations, regardless the weather conditions. With the financial help of the Dutch Government, RF Systems has solved this problem with the Power - Isolator.
The Power - Isolator is a completely new device to protect transceivers and receivers from static discharges and direct hits of the lightning. It separates the antenna totally from the receiver. There is no conducting connection any longer, so discharges cannot reach the transceiver or receiver. The transfer of radio signals (or transmitter power) takes place by means of a magnetic field only. This Magnetic field Technology (MT) act also as a screen of Faraday, with a strong reduction of static- and man-made noise as result. See for more info :
* Power - Isolator: Noise reducer & Lightning protector
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