All about Lightning protection Identifying the issue (I)

Among all activities practiced by radio amateurs, the problems of grounding and the lightning protection of radio equipments are probably the sole fields that have no room for experimentation; dame Nature doesn't like amateurism...

We have indeed to take this subject very seriously being given that amateurs unaware of the danger they incurred without protecting themselves or their installation have suffered of the anger of dame Nature up to see explode all their domestic installation ! In the worst cases, they rejoined the Silent keys family. So take care, the subject is at risk...

An aerial placed outdoor and powered through your transceiver constitutes a conductive electrical circuit offering very few resistively. This is of course very fine to work on the air in good conditions but this property has only one drawback.

That means that during thunder weather an antenna conducts very well electricity and if you do not take care, a lightning striking its structure can very rapidly reach and damage your entire ham shack if it is not properly protected against lightning and grounded. In the same way, if you try to touch the ends of an antenna or the rungs of a tower during a thunderstorm, you can endure huge discharges of static and be injured at the 1st degree if not worst. At last during these events if the tower or the antenna elements are too close of a metallic object, including distribution power lines, you can damage these materials due to arc and other sparks. These very dangerous phenomena mainly concern metallic towers, beams, verticals and very long dipoles, as you have few chance to be concerned if you work with an indoor antenna or if you use a wire antenna shorter than about 10 m.

The price of the security We cannot conceal the fact that a good lightning protection cost a few money, and even much if you

desire to protect a large installation. Best to know it... A dozen PolyPhaser surge protectors cost $500, as much copper ground rods cost $100, some clamps and other angle adaptor kits cost about $100, the copper straps can largely exceed $500. You have to add tools and maybe some technical books. Hopefully for a small amateur radio station like mine the investment is still tolerable. But when the total cost exceeds $3000 most of us think about it at twice before investing. But you must compare the price to pay for an efficient lightning protection to the price of potential repairing and administrative annoyance. Here are real-life examples.

Encircled, is the last trace of damage that we can

still see in W0ZUX.

Andy Flowers, W0ZUX, experienced a direct strike on his house and show us his shack at left. He accepted to explain to us what happened when the lightning stroke. Here are his comments.

"I had a surge suppressor on one of the AC outlets, and it was not damaged. The other outlets were destroyed. But I had no surge protectors on the antenna wires. My 2-meter transceiver directly in front of the main outlet was damaged beyond repair. On the desk, below and to the right, is a Heathkit SB-200 linear that was not damaged. Next to the linear is a Kenwood PS-30 power supply. It was damaged and had to have several parts, including the on-off switch replaced. To its left is a Kenwood TS-850S transceiver. It had some damage and was

repaired. More to left is a CDR antenna rotator control box. This had exploded and the case was nearly destroyed as were many of its parts".

To continue, "Nothing else on the desk was damaged. At the time lightning struck, I had two computers turned on and both of them had to be repaired. One coaxial cable end was on the floor and it burned a hole in the carpet about a foot in diameter. The noise and light in this flash were horrible! The room was filled with smoke and the lights were out as the circuit breakers to this room had tripped. There was some other damage in other parts of the house also. The total damage was about $3000 that was covered by my insurance, but $200". Hopefully for Andy his insurance agent paid the replacement value, or actual repair cost, without taking into account the depreciation.

On his side, Harry Bloomfield's ham shack, M1BYT, was stroke by an indirect strike: "A few years ago, the steeple of our local church was hit by a massive direct strike at about 2 am when I was fast asleep. The church is about 100 m from my home, but the noise was unbelievable and I must have caused me to almost jump out of bed. I remember landing back down on the bed. The strike was so intense it had traveled down the lightning conductor, through the walls and caused a large area of plaster to fall. The church repairs took 6 months. Many phone lines were damaged within a 1 km area and it took BT a week to reinstate many of them. None of my equipment was turned on, but the pulse wrecked my internal modem, traveled through my PC, out the parallel port, and then wrecked the port IC on my laser printer. I have a remote dish satellite system which was turned on and the pulse took out the front end of the receiver, but it did not damage the LNB. I had a range of receivers and transceivers (HF and VHF), most were connected to antennas, but all of these surprisingly escaped any damage". Thus in this case, without be protected, Harry's equipment was partly damaged although it was switched off but not disconnected from the line.

After have lost, or almost, so much money and lost many time in administrative tasks, investing the same amount in a good lightning protector looks "more normal" and certainly justified.

But can such events occur again or did they each occur by pure chance? It is good to know whether this risk of thunder is real or really negligible, in what case the investment could be delayed, with the risk of course to get a new visit of your insurance agent...

Frequency of thunderstorms If I remember well my meteorology studies at the Air force, in average there are 20 millions

thunderstorms on the earth during one year, so in average 55,000 thunderstorms each day! We mean by thunderstorm, the recording of at least one clap of the thunder (corresponding in the SYNOP weather code to group 7, WW=17). Taking into account the duration of a thunderstorm (a few hours) we can say that some 2600 thunderstorms rage on earth at each instant.

In general, the frequency of thunderstorms increases from the poles to the equator due to a progressive increasing of the period of sunshine and moisture. In tempered European countries or in the northeastern coast of the U.S.A. including New York, there are 4 to 7 thunderstorm days per year at spring, 9 to 14 in summer, 2 to 5 in autumn and only one or none in winter. Reported on the year we observe 18 thunderstorm days per year on the seaside and 25 at a distance of about 300 km inlands. For your information, the California coast records the less thunder events compared to all other states, with a maximum of 5 thunderstorm days per year, when the central Florida supports up to 90 thunderstorm days each year!

Without taking into account the influence of the latitude and moisture, being given the higher instability of the atmosphere over lands in summer, the frequency of thunderstorms is usually higher than over the ocean. At the seaside, thunderstorms mainly occur at night.

Crawlers, leader channels and CG lightning are three common appearances of lightning. Documents Chris VenHaus, WPOD and Fiche W.L.

Driven up by the convective movements caused by a strong instability of the air, quite rapidly friction occurs inside a thunderstorm cloud between droplets or ice particles. These sheerings and collisions lead to charge the cloud of static electricity, the negatives values gathering at the lowest level as the ground is charged positively, while positive particles gather on top of the cloud, near the famous anvil. When the static charge reaches a threshold, a leader channel is created between the cloud base, searching to reach the ground, and its counterpart in the ground, from which ions escape, searching the negative particles in the cloud base. This channel contains ionized atoms, ions and free electrons; this is conductive plasma.

When both channels encounter at mid height, a huge discharge occurs in a few microseconds (typical 1.8 μs). When the connection is established, the leader channel free its energy, reaching temperatures exceeding 50,000° during one microsecond, compressing highly the surrounding air. This phenomenon creates a huge explosion developing a shock wave that propagates a few kilometers away.

Now that a channel is created between the cloud and the ground, a discharge can occur. These discharges can burst out either between the cloud and the ground as in our example (CG lightning) or between the different parts of a same cloud (CC lightning of Crawler), or at last between different clouds constituting a super cell.

When the channel is triggered off, the lightning strikes the ground following the path of least resistively, hence its path in zigzag. In the case of a CG lightning, only the first return lightning displays a tree structure while the successive discharges will always use the same channel, giving to the lightning the impression of flashing like in the film displayed at left.

We can record up to 30 return discharges coming from the ground in a period of one to two seconds, giving the feeling that the lightning is persistent and very bright. When the lightning stroke, the cloud reload itself a few times depending its maturity and its activity. Some thunderstorms cells can generate more than 100 lightning per minute while the less active emit only one lightning during all their life cycle, so in a period of one hour.

These lightning find their origin in the high value of the local electrical field that can reach a potential exceeding some thousands volts per centimeter just before the discharge! Discharge currents display a peak energy ranging between 18 and 31 kA including short variations up to 24 kA/μs. But they can also reach more than 200 kA during a few microseconds! The conductor (a wire or a tower) is subject to huge voltage too that can reach 750,000 V! Induction generated in electrical circuits of a house can generate voltages exceeding 100,000 V!

A tower or any elevated structure is also a huge generator of voltage. The potential difference between the top and the base of a 10m high (33 ft) tower is about 30,000 V during thunder weather. If this energy is not dispersed away, the least object showing the lowest impedance will be seen as a perfect sink. If you

are just in contact with your equipment in such a circumstance, you will endure a severe strike although all is well grounded, excepting you.

At last, a typical thunderstorm releases as much energy as 1 MT of TNT and up to day nobody has find a mean to stock and exploit this energy yet. When one tells you that trying to resist to this energy is a lost fight this has nothing exaggerated...

The bright lighting that we observe during a thunderstorm is accompanied by several huge impulses of energy that spread in the electromagnetic spectrum 1[1]. During a lightning, most signals are pulsed DC that are often preceded by the release of radio electrical energy (RF) during the first rise of the pulses. A lightning strike lasting as short as 0.25 μs radiates a radio electrical energy at 1 MHz audible on a shortwave receiver. As the duration increases, the signal slowly drifts down in frequency. A 12 μs impulse for example radiates a RF signal at 20 kHz. Listen to a shortwave receiver during such events, these low frequencies crackle for dozen of minutes as if there were spark in the air! And this is well what happens, and much more...

These low frequencies radiations can be picked-up by a small LF antenna and directed to a computer that will analyze the signal intensity and it is distance. Some manufacturer like Boltek provide a "lightning detection tracker" (using a PCI card or the serial port of your PC completed with a software) that warns you when the energy reaches a threshold.

If we are able to see and hear these lightning, due to their extremely high currents and voltages, there is no doubt that they also produce undesired effects on equipments powered on the main that is a great friend of dame Nature and Jupiter, famous for holding the lightning’s in his hands. I have thus only one recommendation to suggest you: protect you against their angry!

Thor's hammer... This is the story of an amateur radio whose house was stroke by a violent lightning during spring months. He thought that he was well protected but he wasn't... Indeed, the strike was such that the shock was felt in a nearby house and the noise what so loud that the OM thought that his pylon 15m high collapsed. Hopefully the pylon was up but... ...all the electrical head exploded : all 64 amps fuses, the meter, the circuit breaker, the relay, including the TV, the video recorder, the digital phone, the computer screen and its video board, the modem, and last but not least, the computer motherboard burnt, although all these devices where switched off and linked to a lightning conductor that exploded too ! The VHF RTX that was switched off was stroke also and the fuse equipping the HF RTX blew out. Its 30 Ah power supply was hit and the switch on/off button was damaged. At last the motherboard of the small rotator AR-40 burnt also but as strange as it is all antennas were preserved and continue working like usual ! The sole common point between all these devices is that all they were linked to the same ground. In other words, the lightning went up by the ground! So the lesson is next: never say that a good ground can preserve you from a direct strike. In such circumstances this accident confirms that a difference of potential can always exist between two grounded objects and damage your ham shack. You’re only safe protection 100% sure is to unplug all your electrical

devices from the power line, switch off your devices, and get a good insurance... Hope this helps!

How to protect your assets? We must make a difference between the electrical protection provided by your house electrical circuit

and a radio electrical protection suited to HF needs of an amateur radio station. But in all cases, as you will probably be connected to the main, that you will maybe install some domestic gears, a telephone, additional lights, and why not a TV in your shack, the lightning protection will have to protect all these equipments too and not only your transceiver and your antenna system.

In this article we will not review the domestic protection consisting for example in installing lightning conductors on the high points, breakers in the electric distribution panel, etc. This subject requests however a specific study.

In theory, a good lightning protection must protect all your radio electrical equipment, for short your entire ham shack. A similar but independent protection should of course cover all your domestic devices (fridge, cooker, microwave oven, TV, VCR, DVD, portable radio, Hi-Fi, computing network, answering machine, lighting, etc), both being interconnected on a perimeter ground surrounding your house via the utility entrance.

This project looks complex at first sight, and it can be for a contest station or a repair desk including dozen of gears and a true antennas farm. So, to achieve this job we must divide this project in several small steps, easier to manage. Here is an example:

A. Theoretical study and brainstorming 1°. Identify all radio equipments and their accessories to protect 2°. Identify all circuits (I/O lines with power requirements) to ground in common 3°. Identify all antennas and anchorage systems to protect 4°. Select the right protector device for the right circuit

B. The indoor installation 1°. Create a special panel called a "single point ground" (common to all devices to protect), or SPGP 2°. Lay on the SPGP all lightning protectors 3°. Connect the I/O lines to the protectors (protected and unprotected sides) 4°. Mount your SPGP on a wall with an access to the external ground system 5°. Attach a large copper strap between the SPGP and the external ground system

C. The outdoor installation 1°. Select an earth ground at 15m or more from the house 2°. Create a perimeter ground around the house 3°. Create a ground system (radials bonded to rods or using the tower Ufer ground) 4°. Bind your copper strap coming out the ham shack to this perimeter ground 5°. Bind the perimeter ground to the ground network 6°. Check any possible difference of potential (tower side, close to the Telco, etc)

In addition, in large stations you will probably have to take in consideration the fact that the shack is maybe distributed across several rooms and thus that you will have to install multi interconnect copper strap buses to ground all these gears; the concrete floor conductivity impacts also the location of the SPGP; and at last the constraints of your environment do not always allow you to run the wires or the copper strap to the ground as you want in terms of accessibility, length or esthetic.

Let's review now each step individually, it is not so difficult.

Identifying the devices to protect (II) To avoid spending too much money in a lightning protection

system, usually we need to identify the assets to protect in creating a priority list. It will contain if not all, at least the most expensive or important radio equipments installed in your ham shack that you desire to protect against lightning. The ones that will stay without protection would be unplugged for security as soon as a thunderstorm will approach within 10 km (6 miles) of your area.

Begin with your more expensive gear, probably the transceiver, then its power supply, your HF amplifier, SWR-reader, the rotator control box, the packet interface, the scope, etc.

After a first identification of all big and expensive devices you have to look closer and identify also all accessories attached to these devices, the key, the coax switch, the external speaker, maybe some CW filters, etc. Then examine each unit and list its connections, the I/O lines in both input and output, without to forget of course the feed line coming from the antenna and maybe the rotator control cable.

Then proceed the same way with all other equipments installed in the ham shack: your computer and all its wired peripherals, including the screen, the keyboard, the modem or the DSL connection, the optional printer, the digital cam, the scanner or your webcam. Add to the list your stereo system and its wired connections and maybe your TV, the telephone and its answering machine and a digital clock. Don't forget the secondary power supplies that recharge your GSM or your digital cam as well as all external input devices permanently attached to your computer like the mouse, the memory card reader, an external DVD reader, maybe a router or a wifi station, etc.

At last do not forget to draw a ground line from the chassis of each metallic gear, from the transceiver, from the amplifier, from the tuner, etc to the outside of the diagram. For more clarity I have represented them with a small ground symbol ( ) close to each equipment.

Excepting if it is integrated in your rack; does neither add the lighting to the list nor any other domestic device like the fridge or the alarm system. For this first installation we focus only on the radio electrical equipment that you use in the ham shack because it should protected by a grounding system independent, but bonded to it later, from the domestic grounding system.

After a first look at your material you will quickly discover that your ham shack is invaded by dozen of devices and twice as much wire. To manage this installation that can quickly become complex, you must draw this installation on paper in a

block diagram like the one displayed at right, including all peripherals, all I/O lines, all ground lines from chassis, and power requirements. Now, whatever the

complexity of your installation, you have under the eyes a very simple representation of all interconnections. The red box contains all devices that you

desire to protect. The green bus represents all I/O.

For this case study I took my own small ham shack as practical example. As you can see it exceeds rapidly 20 gears and this one doesn’t practically include any workshop equipment (no oscilloscope or any other test or measurement device). This is really a very simple installation that most active amateurs know probably very well. But how to remember all their I/O circuits, their gingival power requirements to purchase the suited protectors? This is simple.

We are going to place all these equipments and their I/O lines in a block diagram. This drawing will represent the electrical circuit that the lightning might potentially follow to destroy your equipment if there is an entry point of less resistively. Therefore you must include in this diagram all devices to protect and all electrical connections made between them. Represent each device by a rectangle and write its name inside. Represent the wires by simple lines. Do not forget to draw a ground wire from the chassis of each equipment. Even passive components, USB devices and the antenna coaxial switch must be included in the diagram.

Knowing that a lightning can jump from one metal object to another within a radius of 1.2m (4 ft), insert also in the diagram all metallic devices located within 1.2m around your radio equipment. That can be a metallic frame, a metallic desk or a chair, a metallic bin, a telephone or even the case of your computer. Don't forget any device because the lightning is very clever to find the least weak point of your radio electrical installation and the path of least resistively.

Then project all I/O connections and feed lines, what we call the circuits, to one side of the diagram for a better clarity. Align them along a bus as displayed above. In addition, on each feed line write the maximum power sustained, the range of frequencies, the type of feeder, the type of connector and its gender if required (i.e. Coax, PL-259, 1kW, HF). At last, circuit’s side and close to each I/O device write the voltage and current requirements (i.e. 220 V, 2A). These indications will help you later to select the appropriate protector.

When your diagram is complete, reflecting all electrical devices and I/O of your ham shack verify each of them to check if you don't forget a connection or left a peripheral aside. Once done, take your largest red pen and draw a large frame around all devices. All wires entering this frame must be protected!

In identifying all devices and I/O lines of your ham shack, you have already realized 1/4th of your project. But we have still to protect each of these devices with a good system, then create a single ground point and bind this "point" to a ground system located outdoor in order to dissipate the lightning energy away from the house. Let's examine each step separately.

Identifying and protecting I/O lines Until now a surge can easily reach each device installed in your ham shack in following simply either

your coaxial, the telephone/DSL line or the AC line if they are not properly grounded. As we told, dame Nature is smart enough to find the path the least resistive like water find always the lowest point.

A lightning protection is in fact very simple. In case of threat on one of your device, if the voltage suddenly increases for example or if appears a point of lower impedance, it purposes is to short-circuit the entry conducting to this device, and this for all gears installed in your ham shack. But not necessary in the same way.

If the individual protector can be a simple electrical component like a shunt device, its sensitivity is of the uttermost importance to protect your assets. Indeed, like you cannot block the water flowing in your sink with a too small stopper, you cannot install any kind of protector on your devices.

The front-end stage of a transceiver for example consists in FET transistors like the ones displayed at left from Zetex. These small components are known to be very sensitive to overdrive (i.e. high VSWR). They display in fact a maximum tolerance just a few volts above the operating value. The I/O ports (serial, etc) of you computer are also very sensitive and it happened that plugging simply the mouse in its port, amateur short-circuited their mother board. That means that the protector must be selected with a great attention to let pass through the least energy as possible in respect with the specifications of your device. Find the proper protector capable to limit the lightning discharge is your first objective.

Manufacturers sold probably as many protectors as there are devices to protect, or almost. They come in different shapes, several range of frequencies, suited for AC or DC power, Telco, IT network, in single or multiple circuit lines. We must thus well define our scope. We can divide protectors in five major categories:

- The coaxial surge protector - The AC power protector (most devices powered on main) - The Telco protector (for the telephone, modem, ADSL, etc) - The circuit breaker (a shunt for all external devices, i.e. the antenna rotator or elevator) - The ITW Linx surge protector and alike (for IT networks in UTP)

The coaxial surge protector Sometimes called a lightning arrester, the coaxial surge protector is designed to join two segments of

coaxial cable. Inserted in-line on your feeder it protects your antenna. A quality product should not add to system neither SWR (the worst display a VSWR 1.2:1), nor insertion loss, nor return loss and it must operate in a wide range of frequencies and be compatible with your emitting power, match to the load and using the right connector type (i.e. 1.5-50 MHz, 2 kW, 50 ohms, SO-239). Note however that some models are not suited for transmitting or do not provide both genders M/F. Of course like most protectors there are two sides, to not reverse if you want that your protection works properly!

At left a gas-tube protector with N-connectors from Nex Tek. At center and at right the classic coaxial surge protectors equipped with UHF connectors and a bulkhead mounting

from respectively Industrial Communication Engineers and PolyPhaser.

Dipole fed with an open-wire must be protected in another way, using a shunt-type protector for example instead of an in-line model. How that works? Use two identical gas-tube surge protectors and install them at each leg of the feed line near the entry point (usually approximatly 10m below the dipole). Most are capable to sustain a current peak of 40-50 kA (on 8/20 μS IEEE standard) and voltage exceeding 1000V. They work in frequencies ranging from DC to 2 GHz; they provide a bi-directional protection and are weatherproof.

Aside the HF, V/UHF or broadband surge protectors, there are models specialized for repeater duplexer antennas, GPS, radio, TV, CCTV antennas, etc. They are usually available with a flange or a bulkhead mounting like the model displayed above, allowing screwing it easily on the single point ground plate (see below).

The AC power protector This is a protector well know by amateurs and other handyman. Most devices of your shack are

probably powered on the main, 220V or 110V. Like the telephone outlet, the AC power outlet is specific to each country due to the non-standardization of the connectors at worldwide scale. So you must buy it in your country to prevent any hardware compatibility problem. But this is not enough. Many "AC Lightning protector" are not what they claim to be but simple outlets protected against voltage surge, sometimes coupled to an uninterrupted power supply or even simple multi adaptors equipped with a power switch. If some use a safety ground wire, this latter is unable to carry away the surge of a lightning strike. Even a ground wire made of #14 AWG is too inductive with respect to the short interval during which the current intensity "explodes" in a strike. None of these products will ever protect your equipment excepting against line noises.

A good AC power protector able to redirect the RF energy of a strike to the ground must be placed in-line with your device and protected with a metallic housing to avoid melting under the strike conditions. It must match your voltage and current requirements. In my block diagram there are 7 devices powered on 220V at 2A maximum, plus the transceiver and the amplifier that draw each 220V at 16A maximum.

You can combine all small devices powered under 220V at 2A maximum on a single AC power line protector. You can combine them up to the limit of the circuit protector current limit (usually 15 or 20A in using a model similar to the one displayed at right).

Once protected, the AC power can then be distributed to each of the equipment elements using a multi adaptor optionally equipped with a switch. Drawing high current, I would recommend a separate protector for the amplifier power feed (15A) and another similar protector for the transceiver. Some high-end equipment might require a more powerful protector, up to 200A.

At last GPS, TV, CCTV and other repeater feed lines require also a dedicated AC or DC protector able to separate the RF energy form the current and protect each device in respect to its requirements.

The Telco/datacom protector Like the power outlet seen previously, the telephone line connector comes also in many types specific

to each country. There are also technical differences, to name the classic old POTS to the digital terminal including a built-in answering machine or a video system. The oldest use a balanced line powered at -48V DC while modern devices are powered either via the line or on the main. Depending the model, an in-line DC protector (for POTS) or an in-line AC power protector (for devices powered on 220V AC) will be effective.

This telephone line will be probably also used for the asynchronous modem or your DSL connection. Most of the time these interfaces use modular connectors RJ-11 or RJ-45. Using a plastic housing, from an electrical point of view these connectors are very fragile and they cannot sustain the surge energy of a lightning strike. In such occasions either the connector is welding or is fusing.

At last, plugged in an interface card, in case of surge these connectors can short-circuit, burn the printed circuit boards, and create arcs on equipments.

So, as long as you can, avoid using these connectors and select a telephone line protector accepting bare wires like the model displayed above. This model protects also DSL connection or your UTP home network. In case of technical problem, call your phone distributor for help.

The circuit breaker All devices located outdoor must also be protected, beginning with the antenna rotator and maybe the

antenna elevator. The rotator of the antenna system can be driven by a relay, an electronic system or even optical encoders in the most advanced systems. Each model requires an in-line shunt device appropriate to the type of interface and voltage requirements.

Three lightning primary surge protectors. At left a device suited to a rotator controller with 8

lines, IS-RCT from PolyPhaser. At center a network protector ITW Linx category 5. At right an ITW Linx protector category 6, one of the first models suited to a router.

The network surge protector Although not all amateurs have installed a computing network at home, many amateurs use at least one

home computer and maybe a portable. If you connect your computer to a network, there is some chance that you have selected a UTP (unshielded Twisted Pair) architecture. Of course, like the computer installed in your shack, its I/O must also be protected.

For an ordinary 10/100 Mbits UTP network, ITW Linx and Tripp-Lite provide what they call a Category-5 LAN cable. This is a protector to wire in series with the network and grounded the same way as the other protectors. Recently ITW Linx introduced a surge protector for routers too, a category-6 model.

The single point ground panel (III) We have practically achieved half of our project. The theoretical part

consisting in the identification of your equipment and the selection of lightning protectors is done. Now it is time to lay down your protectors on a single ground point and bind all this equipment to an external earth.

As we explained on the previous page, the purpose of a lightning protection is to short-circuit when threatened by a surge. In addition the excess of energy will have to be rerouted away, towards a grounding system. By shorting all wires running to the devices, physically no current can reach your equipment. If in addition all the protectors are mounted in common, no current can flow between the I/O devices. In other words, no lightning surge current will flow up to your radio equipment.

K5GS's single point ground panel with its protector

devices, cables and the strap at right.

For reaching this objective we need to create a "single point ground panel", SPGP for short. As its name states, it will be the sole ground point in your ham shack. It is important that this ground displays the lowest electrical potential of your room, what we already introduced when speaking about RFI and equipotent.

To achieve this you need to buy a copper plate (some use a copper pipe) large enough to lay down all your surge protectors, say at least 50x50 cm (1.6x1.6 ft) if your protectors are not numerous and not too large. I displayed at left one of the models sold by PolyPhaser, a US company represented worldwide. This plate comes with a fiberboard back and it suited to small to medium radio stations. Two copper straps 38 mm wide (1.5") and their accessories are also provided, the first to make the junction to the external grounding system, the second to bind the chassis ground of all your equipment.

Of course for a large contest station you can bind several plates together or use a wider copper strap (up to 15 cm wide or 6" at PolyPhaser).

We saw in the previous page that each of your equipment chassis had to be connected to the SPGP. To make this possible in a small station you can run a bus bar along the back of the station desk and connecting it to the SPGP second strap. The bus bar can be a piece of copper water pipe, a wide flat copper braid or, better, a copper strap too. The width of this strap should be between 30 and 80 mm (1-3"), the larger the best to keep the inductance as low as possible as the RF tends to travel on the outside of the conductor (the famous "skin effect").

As you ham shack will probably grow with years, think to buy an oversized SPGP. You will maybe install a second tower with its rotator in the future; get new gears powered on the main, new coaxial cables, etc. So instead or having to rearrange all these devices on a plate became too short, it is wiser to foresee now this expansion, and to leave some room left for an additional AC power protector, one or several coaxial protectors and maybe one more rotator or line shunt device. The alternative is to foresee now the place and connections for a second SPGP that will be linked to the first.

Do not add protector for your input devices like the microphone, the key, the headphone or the mouse or any other device connected to a controller. Indeed these controllers, to name the transceiver or the computer are already grounded to the SPGP through the ground strap and the input devices will be automatically grounded to their chassis by design.

An AC/DC ground is not an RF ground Remember that a "perfect" DC ground like the electrical plug has nothing to do with a RF ground, except at very low frequencies. Such a plug ground will probably be useless as an RF ground for HF and V/UHF bands. At the very least, however, it could be effective as an AC ground for the station and can be used for that purpose. It will not be a good lightning ground however, and it shouldn't be relied upon for that purpose.

Last but not least, it is time to mount your surge protectors on the SPGP. Like on the above picture try to separate the protected side of the SPGP (above center) from the unprotected one (below center). To accomplish this, coaxial protectors and most other devices are provided with a label stating what side must be connected to the "outside world" and which one must be connected to the equipment. For example, on the coaxial protector is its labeled "↑Antenna” on one side and "↓Equipment" on the other one. For a telephone or a network protector, the label states "←Lines" and "Equipment→", thus there is no risk either of inverting the device. At last for an AC power protector it is not always labeled, but the power cord must be placed on the outside, "Antenna" side like on the above image as your multi-adaptor cord will be plugged in the outlet(s), thus "Equipment side".

The spark-gap level

Security side, many installations create functional SPGP but they forget to respect some basic security rules. For example, in order that the SPGP works properly, you must maintain a physical separation of approximatly 50 cm (1.5 ft) between the unprotected cabling (rotator cable, antenna coax, incoming AC power, etc) and the protected wiring of the same connections. Why? Because during the short time that the voltage flows through an in-line protector, there is a voltage difference when it crosses the input to the output side of the protector. At 66% of the velocity of light in using coaxial of low velocity factor, a duct 30 cm long (1 ft) is crossed in about 1.7 nanoseconds. In this short interval, any significant potential difference (if a device is not grounded for example) or inductance increasing can be a sink and thus experiment a lightning strike. This "spark-gap level" is established in respecting this separation of 50 cm. If you attach your cables well in-line, thus in opposite direction, you prevent this problem.

In the same way, if you place the SPGP vertically, the thick cables like the coaxial will have, due to the gravity, a tendency to bend down and come close, and sometimes to touch the wire on the unprotected side of the plate. If this happens during the strike event, there is a chance for a spark-gap breach of the protectors between the cables, thus a failure of your protection plan.

This SPGP is not fully secure as it does not respect the "spark-gap level". Above left for

example the gray coaxial located on the unprotected side is bending down too close its

protected counterpart. Idem with the two coaxialmarked in red below left. There are all chances

that the protectors failed due to a too short spark-gap during an intense strike event.

This rule can be somehow pushed if your tower is located a few hundreds meters from your house. Over 200 or 500m away for example, any strike will be dissipated to a large degree before it gets to the

house. That has some effect in reducing voltage at the SPGP, allowing attaching all cables near each other. However the potential risk of an arc will remain. Remember Murphy's Law.

How to attach the surge protectors on the SPGP? Usually protectors come with a flange or a bulkhead mounting. This latter allows to easily screwing the

foot in L-shape to the panel. Depending on the thickness of the panel metal and the characteristics of the underlying support material (if any), it may be necessary or appropriate to drill a small pilot hole so that the machine screw does not buckle the surface or raise the panel from the backing material (what might happen using a fiberboard-backed copper panel). What is important here is that the protectors have a consistent, clean, flat, low impedance connection with the SPGP. If the panel is located in a non-controlled environment, say lock up in a box outdoor, then it may be appropriate to use a small amount of conductive grease or simply Vaseline between the protector mounting bracket and the panel to ensure that moisture does not deteriorate the connection.

When all devices are screwed or bolted in the SPGP, you still have to find a place in the ham shack to attach it, after which you can screw and plug all your cables and wires in their respective surge protectors. Ideally the SPGP should be placed within a few meters (1 to 10 ft) of the radio station equipment, inside of an external wall, close to a window or mounted in a full-fledged through-wall entrance panel. It should be placed between and inline with the entrance of the coax cables and the radio equipment. Assuming that it is in a controlled environment, there is no need to have a protective cover or box. Most amateurs mount the panel on the radio station wall midway between the coax entrance into the room and the operating desk. This helps to achieve a cable path layout that minimizes the potential to mix protected and unprotected cables. Creating the layout of the protectors on the panel will require some thought.

As displayed at left on the installation of Bill Otten, KC9CS, it is not necessary to protect your SPGP with a cover or to place it in a box. If it is well grounded and each of the chassis is connected to the panel, there are no safety issues or problems since no current must flow on its surface. If you place the SPGP outdoor with AC protectors, of course in this case you must place it under cover, i.e. inside an electrical weatherproof plastic box.

Then take all your ham shack cables and plug them in their respective protected devices. From the outside do the same and connect all your unprotected wire on the other side of the SPGP. Attach also the ground wires of your chassis to the ground strap. If necessary label each connector or identify each pair with a colored strap if the protector is hidden. If the cables bend attach them with mini-clamps or straps to respect the spark-gap level.

SPGP impedance Theoretically to prevent any energy sink, all devices and conductors must display the same electrical

potential. As we have already told and will say again, if during a surge event the energy finds a path of lower impedance than another, be sure that it will follow that conductor to the end, what is maybe not the function of your ground system... So to be sure that your ground connection offers the lowest resistively, all wires connections must run on the shortest distance, in straight line (with a minimum of bends in the wire) and as wide as possible, hence the utility of installing a wide copper strap to the outside instead of using a simple AWG wire, even of large diameter (at least #10 AWG). Due to its design this latter is inadequate to disperse the energy quickly and safely.

The fact to run the copper strap ground from the SPGP in straight line to the external grounding system is easier to say that to do. Indeed, most of the time the environment forces you to divert from the straight

line due to an obstruction, a wall, a door or even for esthetic considerations. So, knowing that, run the strap... as straight as possible to the outside!

Be only aware that no conductor like to be compressed, what modify its impedance, nor change of direction. In bending a conductor at 90° for example its inductance will increase of approximatly 0.15 μH on a distance less than 25 mm (1"). Repeated on a few meters this cumulative effect can significantly increase the transmission line inductance. Then, due to the nature of the field components, a wide wire like a strap as a lower inductance per length, compared to a rounded conductor, and has minimal inductance for turns. The electromagnetic field doesn't like change direction neither. Each bend or turn represents a large change in the field orientation over short distance. If the change is large enough, some of the electrons traveling in the conductor can leave the wire and find by themselves a path to the ground: there is an arc. Therefore if you desire that the grounding system works properly you need, here also, to respect the laws set by Nature.

Whatever the size of the conductor, a wire has inductance. However larger is the wire size, lower is its inductance. Then to reduce the skin effect, the fact that the RF energy travels near the surface of the wire instead of using the central core, we should use oversized conductors to get the best path to the ground. That means that a railroad bar should be the best connector; it is massive and offers a large surface. Unfortunately this solution is not really conceivable as such a bar is first prohibitively expensive but also extremely heavy and cumbersome. So we need to find a cheaper solution but offering similar performances if possible.

To meet all these criteria at low cost but without impacting the security, there is a solution, and very easy to handle. It is using a copper strap in #26 AWG or 0.4 mm thick and at least 38 mm wide (1.5"). Displaying a lower inductance than the big #4/0 AWG cable (Ø16.4 mm), it is also much cheaper and lighter (14 kg/100m vs. 110 kg/100m). With its 38 mm wide, its cross sectional area is similar to the #6 AWG wire (Ø6.95 mm, over 9 kg/100m) and almost as light. If you install a Belden 9913 coaxial cable, its perimeter represents about 32 mm or 1.27" of incoming conductor surface. Our wide copper strap is still larger and its surface makes it ideal for conducting the strike's RF energy to the ground. Of course, if you use 2 or more such coax, you can purchase a 10 cm wide (4") strap. For a 7/8" Hard-line (Ø22 mm) a minimum strap width of 8 cm (3") is needed but 10 cm (4") would be better. If you work with three Hard-lines, triple these numbers.

KC2TN's SPGP. Note above left the braid grounding all chassis and very below the large copper strap going to the external grounding

system.

To be sure to have the best path, inductance is calculated on the length of the connections between the SPGP and the ground, as well as on the number and sharpness of the turns. In practice this is the inductance of the coax cables between the antennas and the SPGP that you need to compare to the calculated inductance of the ground conductor.

At last, to please dame Nature and present her a path of least resistively, we need to offer a ground path larger than the total amount of coaxial surface area coming to the SPGP from the antennas. Why take the coaxial for reference? Simply because since the most likely place for the surge current to originate is the antenna, and the coax cables represent a relatively low inductance connection to the surge, it is important that the connection to the earth ground be a more attractive (lower inductance) path than the path in any other direction. The other wires (AC, telephone, etc.) are small and inductive in comparison to the

coaxial and can usually be ignored in figuring the width of the ground conductor. For that reason the use of a copper strap larger that the perimeter of all coaxial is recommended.

We have now achieved our indoor installation. We have selected our surge protectors, learnt how to mount them of the ground plate to get an effective protection against the lightning energy. Remain to bind this ground to the external ground system.

The external grounding system (IV) After have created our single point ground panel, SPGP, in the

ham shack and attached on it our surge protectors as well as all cabling, take a look at the outside. We have now to develop a good external grounding system.

Quite regularly we read on forums that an external grounding system can be made in burying simply a copper rod in the ground close to the ham shack. But if you read the other articles, you know how subtle can be the properties of the conductors and electromagnetic fields. I would like to know how a so light installation could be efficient in dispersing the energy of a lightning and its side effects, not to mention any voltage difference generated by a tower. I do not bet the least buck on this protection, inadequate to protect your radio equipments.

Grounding straps installed at WX3K

Indeed, after have read this article, you know that an external efficient grounding system has for main purpose to dissipate the most lightning energy as possible before it finds the path to your amateur station... Good news, in the best ham installations, taking advantage of an extended estate, high conductive soil and of a lot of money, up to 90% of the lightning energy can be dissipated into the ground if it is properly installed. This is a high value that even some commercial sites do not reach! However such results are hard to achieve for an amateur radio who is not necessary willing to spend more than $5000 in his lightning protection!

Ground radials and rods Let's take the case your are a lucky amateur having assembled an antenna on top of tower placed close

to your shack, knowing that a simpler installation will not require a protection as large as the one we are going to describe.

As its name states, the external grounding system is... a system. That means that a ground rod is not a system! To get efficient energy dissipation and a good protection we need to create a network of interconnected rods and radials. It should be divided in several parts:

- The perimeter ground - The ground radials - The rods From a pure electrical point of view there can be only one ground system for a facility (house or

building). The fact of having more than one, separating for example the domestic from the radio ground, will permit current to flow between the different grounds and it will usually flow through your radio equipment since it will most likely be bridging multiple grounds.

To get the best lightning energy dispersion, it is recommended to build the external grounding system as a thick network in shape of goose foot (X) away from the house, at both the tower base and the anchorage bases. All radials and perimeter ground lines use either a copper bare cable or, preferably, a wide copper strap (38 mm or 1.5" or larger). The strap is less inductive than #4/0 AWG cable and also less expensive. Ground rods should be as thick as a finger, 16 mm or 5/8" in diameter minimum, and

2.4m or 8 ft long, copper clad. Each ground rod should have a cylindrical shape, sharp angles providing area of potential arcs. You can also replace the rods by the ground steel frame that you’d have sunk in the concrete base of your tower. At last a cheap solution, but that we do not recommend, should be to connect your copper strap to the grounded metal frame of a building or to the water-piping system, although an external duct is far more secure.

All rods should have their connection with the copper strap exothermically bonded. Among the manufacturers supplying the molds and fusing material, in the U.S.A. name Erico, Inc and Alltec Corp. If you are not equipped for this operation, a locking system made of clamps could be used like lockers provided by Tyco Electronics.

At left a way to bind a guy wire to the ground using a connector from Petuniaco. At center, a standard roll of copper strap (2.2m x 38 mm or 75 ft x 1.5") sold by

PolyPhaser. At right if you cannot drive in the ground over 30 cm deep, the sole alternative is to do for the best, driven for example a rod as deep as you can and

attach the strap just at ground level using a Tyco Electronics "Shear-Lok" connector.

To disperse as much lightning energy as possible we need first to bind the domestic and the shack/tower equipment grounds together creating a perimeter ground buried around the house and interconnecting the utility ground with the panel/tower ground. This perimeter ground solves two problems: it connects the otherwise separate utility and radio station grounds, and it minimizes the energy potential beneath the house so that the structure is not forced to carry some of the strike energy.

Then you need to dissipate away the energy from the house and grounding your tower. To accomplish this, ideally the tower should be separated from the house by 6 to 15m (20-50 ft) minimum. For security reasons, if it can stand up independently of the house (self standing in the field or using guy-wires) the tower must be erected 1.5 times its height away from any housing or public infrastructure as explained on these pages dealing with this matter.

The fact to move the tower away from the house reduces also the magnetic energy flowing in the tower that can couple with the wiring of the house. In addition you reduce the inductance of the coaxial line in limiting the surge energy heading towards your equipment.

How to assembly the external grounding system? You need a lot of cooper straps, rods and either large clamps or another means to connect the different parts together, good pliers and a hammer to drive rods (and useful to fight against Thor's hammer.

Based on Roger R. Block's recommendations, PolyPhaser Corp., here is a general view of the

ground radials, rods and perimeter ground.

From two opposite corners of the tubular base of your tower spread out a two set of 4 radials in X-shape as displayed at left. The radials length should be longer than 10 m without exceeding approximatly 24 m (80 ft), a value balancing the cost of installation vs. the benefit of a lower impedance system. However, if you are on a low conductive soil and if you experiment too high ground impedance, in this case you can add more radials. Like using ground radials with vertical antennas, it is preferable to add more short radials than few long ones.

If you have several towers or metallic housing within 30m (100 ft) of each other, interconnect their respective radial systems.

Do not forget to ground each guy anchor to the ground system too (3 rods 50 cm long and 1 m of strap). Bind the central rod to the anchor or easier, to the guy wire just above the electrical insulators (above the turnbuckle for example) using a strap.

Radials don't have to go in straight line; they can flow around obstacles but make turns as large as possible (30 cm or 12" radius minimum).

The perimeter ground should go all around the house but some obstacles can be insurmountable (walkway, driveway, etc). In this case a 3/4 of perimeter going around the house is better than no perimeter ground.

Radials should be buried 15 to 45 cm deep (6-18") and connected to vertical copper rods. These rods should be spaced approximatly twice their length. For a rod 2.4 m long (8 ft), the space would be thus 4.8 m (16 ft). Thus if you install four 10m long radials at the base of your tower, you should have to drive 12 rods, 3 per radial, and bind them with clamps. If you cannot drive into the ground deeper than 30 cm (1 ft) or so due to rocks, drive short rods 30 cm long and place them closer, in respect with the twice-their-length rule, thus each 60 cm from each other.

Being given that a rod display a cylindrical region of influence along its axis, placed too close, their respective influence begin to overlap and the capability of the ground rod to disperse the strike energy will diminished. Side effect; in trying to increase the number or rods you only increase the cost of your installation without derive advantages.

The recommended grounding using a copper strap 38mm (1.5") wide bonded to a 16 mm (5/8") rod at

N3RR.

If you drive a long rod into the ground, drill preferably the hole mechanically in order that the rod achieves a reasonable "connection" to the earth. Back filling a hole manually should be avoided for the same reason.

That said, there are a lot of things that influence the quantity and length of the radials like aesthetics, finances, property boundaries, vegetation, soil type, installation difficulties, to name just a few. PolyPhaser for example has a whole service dedicated to just measuring and doing the calculations appropriate to designing an effective ground system! However the general recommendations are usually more than acceptable for an amateur radio station, both from an RF and safety perspectives.

Tower and coaxial grounding To prevent you creating a specific external grounding system, and if you have not started yet

construction of your tower, you should take advantage of the tower's connection with the earth as part of your external ground or Ufer ground. But be aware that if the Ufer ground is improperly constructed you do run the risk of exploding portions of the concrete! This is to prevent such an accident that it is required that the pieces of RE-bars that constitute the framework be electrically connected to each other, whatever can write some radio amateur handbook on this subject. In our example this was accomplished by welding them to the horizontal steel loops. In addition, the anchor bolts must also be electrically connected to the RE-bars. This is a bit more difficult to accomplish since many manufacturers do not permit them to be welded due to the possibility of changing their mechanical strength. A simple mechanical clamp will work. As we told in tower assembling, in addition there must be at least 10 cm (4") of concrete left between the framework and the surrounding earth.

At last, to keep the equipotential leveled, any radial coming within 1.2 m or so (4') from a metallic object (anchor, pole, fence, etc) must be bonded to this object to prevent arcing in a strike event. Check only that the metal properties are compatible when bonding the two objects.

At Tift sheriff radio station one has taken advantage of the tower Ufer ground to bind the tower feet and

radials together. The connection was then coated with zinc to prevent steel

from rusting

Without be informed, you will probably experiment some trouble trying to bind the ends of radials to your tower feet.

Most steel towers are galvanized in plunging them in a bath of liquid zinc. This coating prevents the steel to oxidize. In binding the copper strap to legs with a clamp, you will erode the zinc, allowing the steel to oxidize and become rusty. With time, this will cause a change in the mechanical strength of the tower and will modify its resistance. There is a risk that during high winds exceeding 120 km/h (75 mph) during a dozen years the tower base bend. You can prevent the steel to oxidize in inserting a layer of stainless steel between the zinc and the copper. Among other brands, Brite products will help you in protecting steel thanks to cold galvanizing, coating the metal with zinc to protect it from rusting.

The coaxial running along the tower from the antenna radiator to the transceiver must also be grounded as shown in the previous drawing. The first grounded point is just at the top of the antenna, where the coaxial feeds the antenna. The second point is at the tower feed, just before it leaves the tower to the shack.

The grounding point must be taken off as close to the base of the tower as possible. If you installed a very high tower, additional ground points must be taken off each 25 m or 75 ft as measured from the top.

Due to the height of a tower, that can exceed 33 m or 100 ft at radio contest stations, there can have a voltage difference between the top and the base that exceeds 100 kV! At 10% of that height, thus a bit higher than the height of a man, there is still 10% of that energy or 10 kV that can easily follow the coaxial cable to your shack. Therefore it is very important that this ground connection be established as close to the base as physically possible; 10 cm over the base is a good distance for our tower 33m high since we get a voltage difference of only 30V. For a 10m high (33 ft) tower, the take-off point can be at 30 cm high (1 ft) or so above the base.

The grounding coaxial kit is different from a coaxial surge protector. This is totally other product. It can be purchased to any manufacturer of grounding kit. Don't forget to protect the interface with a weatherproof product. Like with anchors in connecting the ground kit to the tower is aware that dissimilar

metals can corrode the steel of the tower. Coat them with appropriate products like the one sold by Anchor Guard.

I will survive What about the lightest installations? I am aware that not all amateurs have a tower in their garden. If

this is of your concern, you will probably search for an external grounding system close to your house. But do not select any kind of support. Do not use neither the electrical system, nor the metal building skin, nor any pipe (metal cold water or stand pipe) to create your external ground. At worst use the building steel but even this framework is not the best RF ground and is highly inductive compared to a true external grounding system.

The purpose of the lightning grounding system is to survive to the lightning strike by ensuring that no current will flow to your equipment using the I/O wires and cabling system. This is mainly accomplished creating a single point ground panel to keep a same level of potential during a strike event independently of how the SPGP is grounded.

Don't forget neither to leave the ham shack during a threat of a thunderstorm if you installed a SPGP. Even if there is no current that flow between your equipments and on the SPGP, there are static because you are placed above the ground level compared to the external grounding system. If you take the risk to hold your metallic microphone in hand or to touch the chassis of a metallic gear during a strike event, for dame Nature you will be the object displaying the lowest impedance. During the strike event there is no doubt that the current will flow through you from all protected devices, including the chassis of your transceiver to the ground.

Thunderstorms detectors being able to warn you when there is a lightning activity within 15 km around your radio station, it is better to leave the room as soon as you see or hear the thunder. As your equipment is grounded you can leave them powered-on. This is a practice that follows all radio broadcasters and equipments remotely operated like repeaters, which emitters and amplifiers cannot be switched off at each strike event.

Of course like me you have probably heard many people telling that, although they were protected, they were stroke by a direct lightning strike, and more than once coming back via the ground path. Sometimes there was also either a coaxial or another device that was not protected... To reinforce your security, I suggest you to insert a second stage protection in placing surge protectors in each single outlet system as well as lightning controller in your main distribution panel.

An Obo Bettermann lightning controller to place

in your electricity distribution panel.

Artificial ground tuner At last, if you live in a building, accomplishing a good RF ground will be difficult at best. The good

new, however, is that most installations do not necessarily require such a protection. If you have a well balanced antenna/feed line system, your installation is probably safe. If you erected a beam or a vertical antenna on the roof, then of course you need to protect your system. If you use a wire antenna and you have a relatively poor RF counterpoise or ground system, you might look into an "artificial ground", like the MFJ-931 tuner from MFJ Enterprises. This device can successfully resonate a random length ground wire and make the station "see" an effective counterpoise.

At last advice. If you live in an apartment, make sure that your station is at least at DC ground (ground all the equipment chassis to a common point and then to a good DC ground) and keep the lightning ground outside the house.

By way of conclusion

There are some very important notions to remember: - One cannot suppress lightning - It is quasi impossible to build a system strong enough to compensate the effects of lightning. So our sole alternative is to search for solutions to reduce this risk (a direct strike or by induction) in

applying the same rules than the ones used for plumbing: build a drain system to evacuate and dissipate the energy of lightning away from our electrical devices.

The installation of such an electrical system or the modification of a lightning conductor should be made by skilled people or entrusted to a specialized enterprise, expert in HF installations. This work has to overhang all elements to protect. This is a very important subject, complex, which requests deep knowledge.

If you are novice in this field, before investing in this equipment I suggest you to read several technical books about the subject, to follow maybe some courses, to question specialists and to plan on paper all your installation. If you consider that you can handle the project alone, if you are ready to invest the price requested in both time and money, go ahead, otherwise reduce your scope and phone maybe an expert.

When your plan is achieved do ask an expert to check your project before beginning the real installation in the field. That is worth much more than hazards your incur in doing this work "at best", maybe without know-how, and see your ham shack be transformed in a sink and burn at the first strike event ! Take care.