By: T. Ellison, W4TME
Description, Terminology, and Definitions.
An EMP or Electromagnetic Pulse is defined as a brief burst of electromagnetic energy. The origin of an EMP can be natural or artificial and can occur as an electromagnetic field, as an electric field, as a magnetic field, or as a conducted electric current.
The electromagnetic interference caused by an EMP can disrupt communications and damage electronic equipment. An EMP such as a direct or indirect (near) lightning strike can physically damage objects such as buildings and aircraft.
The first recorded damage from an electromagnetic pulse came with the solar storm of August 1859 or the Carrington Event.
The brief surge of energy contained in an EMP covers a wide range of frequencies, sometimes referred to as "DC to Daylight" and can induce strong currents in electrical wiring.
Common Types of EMPs on Earth
- Lightning - electromagnetic pulse (LEMP). The discharge is typically an initial huge current flow, at least mega-amps, followed by a train of pulses of decreasing energy.
- Electrostatic discharge - (ESD), is a result of two charged objects coming into proximity or even contact.
There are also EMPs in extraterrestrial in nature caused by events such as coronal mass ejections (CME) or the discharge of electromagnetic energy resulting from either the impact of a meteoroid with a spacecraft or the explosive breakup of a meteoroid passing through the Earth's atmosphere. These are a lot less common and generate lower levels of localized energy.
Why Should I Care about EMPs?
As alluded to in the previous section, terrestrial EMPs can result in damage to electronic equipment. Radios in particular, are especially vulnerable because they are electrically connected to the A/C wiring in your home and have an RF collection device (aka "an antenna") connected to them.
We see an increase in damaged radios coming into the FlexRadio Service department in the spring when thunderstorm activity picks up, be EMPs can damage radios at any time of the year.
In some cases, damage caused by a build-up of DC charge on an antenna resulting in an electrostatic discharge resulting from "rain static" (due to particles of rain, snow, or dust striking antennas), results in minor damage to the radio.
In the case of direct lightning strikes, where enormous qualities of energy are transferred from the atmosphere to and from the earth, the damage can be catastrophic and result in significant damage to the dwelling and/or personal injury.
Indirect lightning strikes, while much less physically dangerous and damaging, can significantly change the ground potential causing currents of upwards of 1000s of volts to flow in electrical wiring. The EMP from both direct and indirect lighting strikes can cause significant damage to electronic equipment.
Repairing equipment damaged by lightning or ESD can be quite challenging due to varying electrical and mechanical stress levels that may not manifest as faulty at the time of service but could fail days, weeks, or months later. Consequently, FlexRadio does not normally repair equipment damaged in this way.
What Can I Do To Prevent EMP Damage to the FLEX-6000?
In the case of a direct lightning strike, there is really little you can do unless you spend tens of thousands of dollars on sophisticated lightning protection systems. The enormous amount of energy transferred during a direct lighting strike requires significant infrastructure and specialized engineering to prevent damage.
For EMPs caused by indirect lighting strikes and electrostatic discharges, there are some cost-effective measures that can be taken to mitigate the possibility of damage to your FLEX-6000.
Physically disconnecting the coax from your radio during a thunderstorm is a good practice, but you may not be able to do that every time a thunderstorm is near. If you can hear the thunder, the indirect EMP is already too close.
Also, EMP currents can be induced in any type of wire or cable connected to the radio, including grounds, so the only absolute protection would be to completely disconnect the radio from all cables. But, just like disconnecting the coax when you hear thunder, this may not be convenient or practical.
Taking Some Precautions is Better Than None.
The ARRL has a collection of very good resources for protecting your shack from lighting damage, available from their website: ARRL Lightning Protection.
The proper use and installation of lightning arrestors on the incoming coax is one technique to mitigate high-frequency alternating-type currents. The effectiveness of lightning arrestors is only as good as the low-impedance, high-current carrying capacity of the external earth ground used to shut damaging voltages and currents to ground.
There is a class of lightning arrestors that bleed off DC static electricity responsible for electrostatic discharges, such as the ones based on the Industrial Communications Engineers (ICE) design. The ICE-type arrestors are DC blocked and include static and DC discharge capabilities. ICE-type lightning arrestors are manufactured by Morgan Manufacturing and are available from several different distributors, such as Array Solutions and KF7P Metalwerks.