Grounding

 What follows are my thoughts on grounding. There is a lot of misinformation around on

grounding. Some of it is just wrong. Some of it is also dangerous. There are also some grey

areas where we may not know what to do! In that case we try to error on the side of safety.

To fully understand grounding you need to have a knowledge of basic electrical principles.

Without going into detail, you absolutely need to know that current flows from a higher

potential to a lower potential. There must be a complete path for current to flow. This is easy to

visualize with DC and a battery, a little harder with AC and downright difficult with RF.

To make up a simple example, if there are two wires supplying current to your house, one black

and one white, current is considered to flow from the black or hot wire to the white or neutral

wire. There is a “source” where those two wires are connected. Current leaves the source on

the black wire and returns to the source on the white wire. That’s the simple case. In the real

world current leaves the source on the black wire and it’s objective it to find a path back to the

source ( the point where the white wire is connected). In a simple case it’s would be just the

white wire, but in reality it is partly the white wire and also any other conductive path that might

also exist in parallel with the white wire. ( the white wire is connected to the earth ground and

so are a lot of things)

Let’s take a metal light pole as a good example. Two wires can be used to light the light at the

top of the pole. The source is back somewhere up the street in the power system transformer

or substation. It does not matter exactly where, just that there is a source somewhere. The

black wire has 120 volts on it, the neutral is said to be zero. It is in fact connected to the

ground back at the power panel that feeds the light. Now let’s suppose the black wire

accidentally comes in contact with the metal pole. The white wire is not touching the pole.

The metal pole then becomes very dangerous. It has 120 volts on it. Anyone touching the pole

can be killed. Sometimes, in ignorance, the installers of the power pole will drive a ground rod

and connect the pole to the ground rod thinking that makes it safe. All that does is make it

more unsafe! Current will indeed flow from the black wire to ground, but it will only be a few

amps at most. It will not be enough to trip the circuit breaker. So the power stays on. The light

stays on. The pole remains energized with 120 deadly volts. In this case we have current from

the source supplied to the black wire going to the light and returning through the white wire to

the source and we also have additional current supplied going through the pole to the ground.

That current is trying to find find a way to get back to the source. If the pole is only grounded

with the ground rod, the current will flow through the ground back to the source, because in all

cases the source should be grounded. However, the amount of current will not be high

because the return path through the ground rod has significant resistance to limit the current to

only a few amps. What also occurs is a voltage gradient in the vicinity of the pole where

dangerous voltages occur. The voltage at the copper ground rod will be 120 volts. Just a few

inches away from the ground rod, the voltage might still be 100 volts. As you move farther from

the ground rod the voltage decreases until at somewhere from 25 to 50 feet it becomes zero.

We call that the zero ground potential. Remote earth ground is always at zero volts. So the

voltage from remote earth to the light pole is 120 volts. The voltage from the ground right at the

pole to the pole is more like 100 or 110 volts. There have been many cases of people being

killed by touching a metal pole that has been energized like this. The existence of a ground rod,

grounding the metal pole, does nothing to make that pole safe. What does make it safe is to

have that third conductor which is called a safety ground connected to the metal pole and

running all the way back to the power panel. With that ground, the breaker will trip if and when

the black wire inadvertently makes contact with the metal pole. Never cut off or defeat the

grounding prong on an ac electrical cord or you will create this dangerous situation on

whatever equipment that power cord supplies.

If a person were to touch such a power pole with a fault as I have described, their body would

provide a parallel path for the current to travel to ground. The current would then divide up

between the ground connection and the body path. How much current goes which way would

depend on the resistance of each path. It does not take much current to kill. Even though the

ground is considered to be a conductor, making a good contact with the ground is very

difficult. A ground rod does not make very good contact. The path back to the source through

the ground rod to earth path is nowhere near as good as that single wire used as a safety

ground.

The National Electric code only requires the ground rod to have a resistance around 25 ohms.

The fault current in that case (black wire connected directly to the ground rod) would be 120/25

or 4.8 amps. That would not be enough to trip the circuit breaker. In most cases a single

ground rod will not be that good.

This concept of a potential gradient in the vicinity of a ground rod is significant not only in a

case like this where 120 volts is inadvertently connected to it but also in a great many other

cases such as a lightning strike. More about that as I get into details about grounding in a ham

radio station.

The circuit or that part of a circuit that is made up by the copper ground rod, it’s contact

resistance with the earth touching the bare copper and the actual dirt, concrete, and other

materials that make up the ground in the vicinity of the ground rod out to some distance of 25

or more feet to the point that can be called remote earth ( where the normal potential is that

theoretical zero potential) has a resistance. That resistance is never zero, but can be made

fairly low. It can be thought of as several series resistors. For example, in the case of a single

long copper ground rod, that resistance might total 25 to 50 ohms. In a simplistic case, as a

start in understanding it, it could be thought of as a 20 ohm resistance ( the contact resistance

of the rod to the dirt it actually touches) in series with maybe a 10 ohm resistor representing the

next foot or so of dirt, then in series with maybe a 5 ohm resistor representing the next 10 feet

of dirt and finally a 2.5 ohm resistor representing the rest of the distance out 50 or so feet to

remote earth. Add those up and the resistance to our estimated zero potential earth point is 20

+ 10 + 5 = 35 ohms. The reason I have used decreasing resistors as we moved away from the

ground rod is that as we spread out from the rod we will have more and more parallel paths for

the current to take. Any time you provide a parallel path, you decrease the resistance. For

instance if one chunk of earth has 10 ohms of resistance and you add another chunk

alongside it where the current can also flow, you cut the resistance down to 5 ohms. As the

current travels away from the ground rod there is more and more dirt available creating less

and less resistance. Consequently the voltage gradient that exists around and out from the

ground rod is not a set number of volts per foot. To keep it simple, the resistance decreases

each foot you move away from the ground rod, therefore the voltage drop or change in

potential is less and less per foot as you move away from the rod. The first 6 inches is a high

resistance and a large voltage drop can exist very close to the rod. The voltage drop across

each foot of earth becomes less and less as you move away. You can look at this several ways.

First of all, what is significant is the difference in potential or voltage between two points. If you

get across two points with a high enough potential you can be shocked or killed. If the ground

rod is energized with 120 volts and you touch it with your feet on the ground you will get a

shock. If you are insulated from the ground you may not feel a shock. To take the unknown

shoe resistance out of the equation, let’s say you are barefooted. Standing with your feet 50

feet from the ground rod and if you could touch the rod with a long stiff copper wire, you would

get shocked with the full 120 volts. Move in to about 5 feet from the rod and you would be

shocked with about 100 volts. Move even closer to 1 foot away. At one foot you would be

shocked with only 82 volts! Still enough to be lethal! Move in to within 6 inches. At that point

you would be shocked with 62 volts. What you are feeling is the difference in potential caused

by the voltage difference created by the current flow through the resistance of the ground to

the point where your feet are touching the ground.

Suppose you do not touch the ground rod. Let’s say you are standing on the ground five feet

away and bend over and touch the ground that is 3 feet away from the rod. The potential

difference of those two points is what could shock or kill you! It is quite possible that that

voltage would be 15 volts more or less. You would feel that. How bad the shock would be

depends on moisture on you skin, the ground composition and other vague factors. However, if

the voltage on the ground rod was 1200 volts instead of 120 volts, you would be killed, as the

potential difference between those two points would be 150 volts instead of only 15.

This is why you never want to get close to a live power line that touches the ground or even

concrete. It causes a voltage gradient in the nearby earth.

You can illustrate this by placing a dot in the center of a piece of paper to represent the ground

rod and drawing 10 concentric circles around the dot. The outer most circle represents the zero

potential point and the dot can represent 120 volts. The first circle would be 90 volts, the

second circle would be 100 volts, the fourth circle 110 volts, the eighth circle 115 volts and the

last circle 120 volts. These numbers represent the voltage measured from that point on the

ground to the rod. It is called the touch voltage. The voltage you would feel if you touch the

ground rod when it is energized with 120 volts.

If you want to see the absolute earth potential, you can label the first circle 110 volts, the

second circle 100 volts, the forth circle 90 volts volts, the eights circle 10 volts and the outer

circle zero volts to represent the absolute remote earth potential of zero. This is a better way of

looking at it from an engineering point of view, but the touch voltage may be better from a

practical understanding as it indicated what voltage you could actually feel.

If the wire contacting the ground is a 7200 volt power line, then the ground potential five feet

away is probably 6000 volts and very high voltages extend out considerably farther! There is a

term called step potential. It is the voltage difference between your feet. If that voltage

difference is high enough it could be very dangerous. For example, in a car accident involving a

downed high voltage power line, you should stay in your car. Just walking on the concrete or

earth near a high voltage wire could likely kill you. If you must get out of your car, the

recommendation is to jump out with both feet together. Then continue jumping with both feet

together away from the wire. It is possible that there could be extremely high voltage points

existing just in the distance of one step. By keeping both feet together you are trying to be like

that bird on a high voltage wire that does not get shocked! Even though the voltage on the

earth may be several thousand volts, if you keep both feet together, you can minimize the

voltage difference. Only do this if you must leave your car due to fire or smelling gas and fear of

an explosion.

We can now bring into this discussion a lightning stroke. When the lightning hits the ground,

either directly or through a tree or tower, it causes a potential gradient to exist out significant

distances from the strike. It also sends out a short duration pulse of electromagnetic wave.

If you have two ground rods, say 50 feet or so apart, the ground potential at those two points

could be a thousand volts or more apart. This will cause significant current to want to flow from

one rod to the other. If it has no other choice it will flow through the ground. However if there is

a better path, some or maybe most of the current will take it. That path could be through

equipment that is connected to both ground rods. The ground rod at the power panel is the

primary ground rod. The one that hams put at the radio is a secondary or auxiliary ground rod.

In order to minimize (Note I did not say prevent) damage, the auxiliary ground rod must (by the

electrical code) be bonded or connected to the primary ground rod with at least a number 6

copper wire (or equivalent capacity aluminum wire).

In addition to the potential problems caused by lightning hitting the ground, the strike will

create an electromagnetic pulse. It is a short duration pulse. Such a short pulse will contain

high frequency components and may be at the equivalent frequency of one megahertz. It will

induce currents into nearby conductors. Since it is what I will call a high frequency pulse, the

voltages created by the current are not simply current times the resistance of the wire, but

current times the impedance. This impedance includes reactance. Inductive reactance of a wire

may be minimal under normal ac or dc situations, but can be significant where lightning pulses

are concerned. We need to be concerned with voltages on wires ( whatever they are normally

carrying is not important here) rising high enough in potential with respect to anything they are

in close proximity to where there will be damage caused by this over voltage situation. If the

radio chassis is connected to a ground rod that rises several thousand volts above the power

wires from a panel grounded to a different rod, we most likely will have damage. If the ground

rod rises in potential, thus elevating all the power from it to your radio, but the radio chassis is

held at a lower potential by its ground rod, we again could have a problem. Bonding the two

ground rods with as short and straight a No. 6 wire as possible will help somewhat.

Why is a number 6 wire required? The answer is that the lighting pulse is a short duration,

equivalent to about a 1 MHz frequency and the surface area is more significant than the cross

sectional area of the wire. The NEC has deemed a No. 6 copper wire is what is required.

Next there are three reasons to ground.

The first two concern the power system ground.

First of all, there is the safety reason. This applies when we are connected to 120 or 240 volt

ac. The commercial power at your house or building will have a single point ground. For 120

volt ac there will be a black wire, a white wire and a bare (or green wire). The black wire is

referred to as the “hot” wire. The voltage (or potential) between the black and white wire will be

120 volts. The white wire will be at about the same potential as ground. It will be connected to

the ground rod through the power panel. This used to be all there was in a home. As long as

you connected your lamp, tv, radio, power saw or whatever to the black and white wire you

had power and your device worked. This was not very safe. Sometimes you could plug in your

radio set the wrong way and the hot wire would be connected to the metal case and you could

get a nasty shock. At some point they started using polarized plugs so you could not plug

things in the wrong way. This helped. Eventually we got to where we are now. We normally

have plugs with three prongs. One to the black (hot) wire, one to the white wire and one to a

third wire, which is usually bare or green. If your device has a metal case or metal chassis, the

third wire is connected to it. The black wire and the white wire are intended to carry the current

to operate your device. The black wire is referred to as the hot wire or hot conductor. The white

wire is the grounded conductor. It is a conductor like the black wire but it is also connected to

the ground rod back at the power panel. The “third” wire is called the grounding wire. It is not

supposed to carry current. If there is some problem where the black wire comes in contact with

the case of the device current can flow through this third wire back to the power panel and trip

the circuit breaker. This third wire is usually smaller than the conductors carrying current to run

your device, because it only has to carry short circuit current for however long it takes to trip

the breaker. Small wires can carry 15 or 20 amps for short periods of time while they would

overheat if they had to carry that current for a long period of time.

So for safety we have a ground at the power panel and two of our wires from every outlet run

all the way back to the power panel where they all connect together at one place where there is

another wire that runs to the power ground rod. This is all for safety. Mostly personal safety.

The second reason for the power ground is to protect the equipment from lightning surges.

Note I did not say protect anything from a direct hit by lightning, I said protect equipment from

damage by a lightning surge. That is protection from a nearby lightning strike.

Strange things happen when lightning is nearby. We think of ground as at zero volts. We think

of the white wire as at ground potential and the black wire as -/+ 120 volts from the white wire

and the same from the grounding wire. However, in an ungrounded system during a nearby

lightning strike, the voltage induced on the power wires can rise to extremely high values. For

example, inside a machine that is bolted to the concrete floor, the voltages on the power wires

can get so high that current may arc through the 600 volt insulation to the machine case or

foundation or whatever happens to be connected to the foundation. Major damage can occur

to the equipment. It is possible for anyone nearby to be also hurt or killed due to this lightning

surge. The solution was to use a grounded power system so that when the voltage on the

power wires increased due to the surge, everything in the area also increased in potential. In

that case there would be no large potential developed between the power wires and the

equipment case or foundation.

Originally electrical systems were ungrounded, but these types of problem caused a change to

be made to grounded systems. It can be confusing at first.

Even though we think of the ground, everywhere, being at the same potential, there are some

subtle issues. First of all, even though the resistance of the ground from one place to another

may be really low, connecting to the ground is not easy. When a ground rod is driven into the

ground, there will be a contact resistance. Let’s suppose we go to one of our receptacles in our

house, that is not protected by a ground fault breaker and do a simple test.

We take a long black wire and connect to a standard 120 volt plug on the hot side. Then we

run that black wire out to the middle of our back yard and connect it directly to a ground rod.

What will happen when we plug it in to the receptacle? Most people think it will trip the 15 or

20 amp breaker. Let’s think about what we have. We do have a complete circuit. There is a

path for current to flow from the breaker through the black wire to the ground rod, into the

ground, through the ground and to the power system ground and ultimately back to the source.

If we take our volt meter, and measure voltages we will read 120 volts ac from the breaker to

the ground bus in the panel where all the white wires are connected. We will read 120 volts

from the ground rod in the middle of our back yard to the ground bus in the power panel. No

surprise in those measurements. If we measure from the power system ground rod to out

ground rod where we connected our black wire we will also get 120 volts ac. This voltage is

pushing a current through the ground. If the ground had no resistance we would trip the

breaker. Current equals 120 volts divided by the resistance. If the resistance was 6 ohms we

would have 120/6 equals 20 amps. That would trip our 15 amp breaker. However most of our

resistance will be at the point where the ground rod contacts the earth. That contact resistance

will be in series with the actual resistance of the ground or moist dirt. It is quite possible that

we will only have a few amps flowing. There will be what is called a voltage gradient around the

ground rod. Remember we will have a total voltage drop in this (or any circuit) equal to the

source voltage. In our case the source voltage is 120 volts ac. We start at the end of our black

wire with 120 volts with respect to the white wire or white wire bus. As we move away from the

ground rod, that voltage will decrease until it reaches zero (the same as the white wire or white

wire bus. This change in voltage as we move away from the ground rod is not linear. It changes

rapidly in the first few feet then the change in voltage per feet will be less and less.

The voltage at the ground rod will be 120, about a foot away it will be around 80 volts, 3 feet

away it will be 90, 5 feet away it will be maybe 103, at 25 feet away it will be 120. So it will take

about 25 feet to zero volts or in other words get back to ground potential, which is zero volts.

There are well established power tables that give this information.

Another example is metal power poles. With the old two wire systems, if a pole was energized

with 120 volts by a fault or any other reason, you could get shocked touching it. The first

answer was to drive a ground rod and ground it. Problem solved. NO! With a contact

resistance of 25 ohms the ground rod did not protect anything. The solution was to run a

grounding conductor back to the same place as the white wire! Standing at the pole with only a

ground rod could still pose a severe electrical shock or death.

Note the utility has multiple grounds on their side ( service side) of the home panel box. It’s ok

for them to do it but it’s not ok on the load side of the panel box.

We think of the neutral or white wire as being zero volts because it’s grounded, but that’s not

really true. While the neutral (white wire) might be zero at the transformer, the neutral wire

carries load current and has resistance. Therefore because it carries current and has

resistance, there will be a voltage drop. Current times resistance or IR drop.

In reality there will be a voltage on the neutral wire. It should be small, but it can be measured.

It will vary depending on the load on the utility. It is called the NEV or Neutral to Earth Voltage.

The neutral wire will carry load current back to the substation transformer. There is a resistance

in that wire, however there are parallel paths through the ground where current will also flow

back to the substation. In fact there are many many parallel paths and they all reduce the

current flowing in the neutral conductor and therefore that reduces the IR drop in the neutral

conductor.

Let’s think about the concept of neutral earth or remote neutral earth. That is a place where no

current is flowing and therefore the potential can really be zero. For all practical purposes that

is probably 50 feet or so from any ground rod that is connected to a neutral. You can go and

stick a meter lead in the ground at that point and then connect the other lead to your panel box

and read a small voltage. Could be .5 volts or it could be 2 volts. It is simply the result of

neutral current flowing in the utility system multiplied by the resistance of the neutral path. It

typically increases the farther you are from the substation. It will also be constantly changing as

the load on the utility system changes.

One important note here. If the potential between the black and white wire is 120 volts and the

voltage from the white wire to ground is zero, then the voltage from the black wire to ground is

120. However, if the system neutral is at 2 volts, then the voltage from the black wire to ground

becomes 120 plus 2 or 122. This might not seem significant at this point, but if for some

reason, like a nearby lightning strike some ways from away, voltages are induced in the power

cables they we could have several thousand volts on the black and white wires above ground,

while still having 120 volts between them. If we have a dedicated ground on our equipment

(radio) then the chassis of the equipment will be held to the potential of the local ground. Let’s

call that zero or near zero volts. In that case we can have equipment failure because it can not

handle the power wires inside the equipment being several thousand volts higher than the

chassis. We need the chassis of the equipment to “ rise up” so, for example, the insulation in

the power transformer does not arc to the chassis, thus at a minimum blowing the transformer.

In a similar manner, a nearby lightning strike could cause the local ground to raise up much

higher than the ground back at the substation. In that case the chassis ground could rise up

while the power lines are still 120 volts above the utility ground but become significantly

different than the dedicated equipment ground causing similar equipment damage.

You never ground a piece of equipment to a ground that is different ( not bonded to) the system

ground at the power panel.

The third reason is the ham radio or antenna reason. This gets even more vague and

complicated than the electrical safety and lightning reasons.

First of all a ham radio does not need a ground to work. There are cases where a ground may

compensate for some other problem and appear necessary. There are cases where the ground

is actually used as half of the antenna. I will try and address all these cases.

The transmitter is a source of power similar to the utility power generators. At the output

connector of the transmitter there is a push and a pull of current. However much current leaves

the transmitter at any given instant an equal amount of current must return. With a balanced

dipole it is easy to see. We can visualize current going out to one side of the dipole escaping

into the air and returning back on the other side of the dipole and down the transmission line to

the transmitter ( source) .

No ground is involved is this situation. Ground does get involved in reflecting the radiated

wave, but that’s another issue.

In most antennas, we can easily understand where the current that is leaving the transmitter

goes. It goes out on one wire of the transmission line and out on the antenna to (hopefully) be

radiated. In all cases, an equal amount of current must return to the transmitter (source). I can

state that another way, however much current returns to the transmitter will be exactly equal to

the amount of current that left the transmitter. If no current returns then no current can leave.

It’s just that simple.

Let’s take the extreme case of a simple end fed wire. It can be a half wave or any length.

We visualize current going up the coax center conductor and out on the wire. Where is the

return current. We need to see the complete circuit. In the dipole it came back to the opposite

half of the antenna. In this end fed example we do not see that half. In all cases that current is

looking for a path back to the transmitter ( source). If it only finds a high impedance or high

resistance path that will limit the current that can even go out on the antenna in the first place.

One path that will exist is the outside of the coax feed-line. In this case the outside of the feed-

line acts like the other half of a dipole. Current will flow on the outside of the coax and back to

the transmitter (source). Current may enter the ground and return through the ground rod and

up the ground wire that was installed at the station for whatever reason. Maybe it was installed

for this very reason. Another way for current to return to the source is by entering a ground

radial system or a set of counterpoises that were designed to capture these return currents.

However it is done, some means must exist for return current to get back to the source.

I think it’s a mistake to think of a ground as some sort of attraction for radio frequency energy

that will send unwanted signals to ground. Remember that current only wants to get back to

the source. That “source” will be a potential difference. If a potential difference (voltage) exists,

it wants to push the current from the high potential to the low potential. Looking at the output

of a transmitter as a source having two terminals, one terminal wants to push current out and

the other wants to pull it in. The ground is not necessary.

A power substation wants to push current out (eventually to the black wire in your house) and

suck it back from wherever it can. The transmission line for the dipole wants to push it out on

one wire and suck it back on the other. The transmission line for the end fed antenna wants to

push it out on the wire and suck it back from wherever it can.

Charged clouds in the atmosphere build up larger and larger charges until the air can no longer

act as an insulator and the clouds discharge through the air to the earth or something

connected to the earth. I really don’t know or care which direction it goes. Electrons go one

way, positive ions go the other way and current is defined to be in the direction that a positive

test charge will move when placed in an electric field. It really doesn’t matter.

We do know that lightning is an electrical arc of high current for a short duration.

The best we can do is to bleed off excessive charge ( static electricity or induced electricity)

with some sort of “spark plug” device on our feed-lines. That stops the buildup of excessive

voltage between the two conductors of whatever kind of feed-line we use.

We also should have a device to bleed off charge in the feed-line to ground. This can also be a

spark plug type of device or a direct ground.

Any direct ground to the radio equipment (if you chose to use one) needs to be bonded to the

power panel ground. In recent years there is a device installed at most building grounds for that

purpose.

Assume lightning could strike the antenna and route feed-lines and take normal precautions

accordingly. Actually lightning could strike anywhere.

In my station, I accept some risk. I physically disconnect antennas and power cords at what I

deem the appropriate times. Always in spring through fall. Usually in winter, but less careful

then. All of my feed-lines run down to the ground before coming to the house. An exception is

that one dipole coax hangs on the house then runs to my antenna switch. I need to have a

better place to support it. That bothers me a bit.

I do not yet have spark plug devices installed nor are my feed-lines grounded before they enter

the house. This is something I might eventually do. At the moment I deemed the risk I am

taking is acceptable to me. I feel simply driving a ground rod outside my radio shack without

bonding back to the power panel is taking unacceptable risk. I do have a ground rod but it is

not connected. I used it for a temporary end fed wire test. At some point I should run a wire

from it back to the panel and connect the shields of my coax there. That is low on my list of

priorities.

I did have a 160 meter dipole struck by lightning twenty years ago. The wire was destroyed.

The coax also severely damaged and had to be replaced. My main radio was disconnected. No

damage. One radio had its power supply plugged in to a wall outlet. It was blown out of the

wall outlet. The plug was an old black plug with a fuse in each side. It was shattered into many

pieces. Ten years later I found part of the plug on the opposite side of the room. No damage to

the power supply other than needing a new plug and fuses! It still works as of December 2021.

The ethernet modem in my computer had the top blown off of several integrated circuit chips. I

simply replaced the modem card and the computer still worked. A laptop computer was

plugged in and I had to replace the power supply. Computer still worked. Two TV sets were

affected by the pulse and simply had to be degaussed. They were probably within 50 feet of

the strike or strikes. I feel that what I did then and what I am doing now is sufficient for me. I

have been close to enough lightning strikes to have a healthy respect for its power. I think it

can strike most of my antennas and although the antenna may not survive, I expect my

equipment to survive. That is unless I forget to disconnect it.

I have all my equipment chassis connected together (K3, Drake L7 amplifier and Ranger II ).

Normally the Drake L7 is unplugged from the wall. With the bonding wire all the chassis on my

desk are at the same potential for safety and tied to the main power panel through the third

wire ground.

Everything is also connected by virtue of the coax shields. The one feed-line that enters the

shack is disconnected for lightning.

The two receive antennas are BOGs (wires running on the ground). There is no ground

associated with the feed-lines at all. Each end of the receiving wire is grounded, however it is

isolated from the feed-line by a transformer. A nearby lightning strike could fry the terminating

resistor and the transformer. Since the feed-lines are either on the ground or in the ground, I

feel fairly safe. I suppose I could do more, but in 60 years of having antennas I don’t see the

value of doing more, yet. Of course these antennas are also normally disconnected from the

receiver.

Antennas

A dipole antenna does not require a connection to ground in order to function as an effective

radiator. Neither does any Yagi or other balanced antenna. They are what I call complete or self

contained antennas.

There are come “incomplete” antennas that need either a counterpoise, ground plane or some

sort of image antenna to complete the antenna or antenna circuit. Without the intentional

addition of such circuit, the RF energy pushed out on the antenna will attempt to find its own

way back to the source and whatever conductive or semi conductive path it takes will, in

effect, become a part of the antenna. I suggest that in most cases this will not be the best

situation. Seemingly unrelated changes can then have significant effects on antenna

performance. The same antenna, moved or installed elsewhere may have totally different

performance. In some cases a ground is used in order for the antenna to work reasonably well.

In these cases, the length of the ground wire is significant and frequency sensitive. The ground

wire is also a radiating part of the antenna. The coax shield, if such an antenna is fed with

coax, will also become a radiating part of the antenna.

Even with so called balanced antennas as well as antennas that use a ground system to

complete the antenna circuit, the coax could inadvertently become a part of the radiating

antenna system. It all depends on the impedances of the ground system, impedance looking

down the outside coax shield, and the physical orientation of the coax feed-line in the antennas

radiation field. Again the length of the ground wire as well as the length of the coax feed-line

and any other conductors that may be connected affect how much current flows and where it

flows.

It is always best to install a complete antenna and attempt to not have any radiating portions

running to the operating position. Not only is safety from shock important but radiation safety

becomes a consideration with power over a certain threshold depending on frequency. When I

used end fed antennas, I limited my high power operations to only the lower bands. I still have

one end fed antenna. Is is really a ground mounted top loaded vertical commonly called an

Inverted L for 160 meters. The coax runs out, partly underground and along the ground, to the

base of the antenna where I have a ground rod and one or more radials. The antenna wire is

series fed through a capacitor, so if the voltage on the wire built up high enough it could arc

across the capacitor and from the center conductor to the shield of the coax to get to ground. I

think a direct lightning strike would find its way to ground at the ground rod near the base of

the antenna. I accept the chances that the coax would be destroyed along with the antenna

wire and the capacitor. A spark gap should be installed to discharge the wire to the ground rod.

With balanced antennas, you are concerned with keeping common mode currents off the

outside of the shield. You look at the shield as two conductors. The inside of the shield and the

center conductor being the two conductor feed line and the outside of the shield being the

third conductor. Current on the inside of the shield would be equal to the sum of the current on

the side of the antenna connected to the shield plus the current flowing on the outside of the

shield. To avoid current flow on the outside of the shield there are several things that can be

done if necessary. Basically, you want the impedance that the current “sees” looking back

down the outside of the shield to be several times greater than the impedance looking out on

the antenna wire.

The impedance of the half antenna is pretty much fixed, but the impedance looking down the

third wire ( outside shield of the coax) varies with the length and location of the shield and

whether or not it is grounded at the radio and/ or connected to any other conductors. It can be

next to impossible to predict exactly what this impedance will be. If this third wire is open

ended and a quarter wave long, it will have a high impedance at the end, but back at the

antenna feed point it will have an impedance close to the actual antenna wire impedance, so

theoretically it will carry half the antenna current. In other words the current will see equal

impedances and will split 50/50. I think this is the worst case. If the coax, in this ungrounded

situation, is longer or shorter than one quarter wave then the impedance looking down the

outside of the coax will be greater than the antenna wire and the current will divide accordingly

and more will end up on the antenna.

A choke can be put in the coax near the feed point to insure a high impedance in this third wire

path. That is the only thing I do, if I do anything. Another popular solution is to use a current

balun. Pretty much that is the same thing as a choke. They can be made one of several ways.

One need to be careful that impedances are correct and the voltage, current and power ratings

are not exceeded. What is designed to work under a given set of conditions, may not work if

not used under those same conditions. I have known people to burn up balun so with far less

power than it’s rating.

It is frequently unnecessary to do anything other than connect the coax and see how the

antenna performs. Some radiation from the feed line is not always a problem, however with a

directional antenna, such as a Yagi, it may degrade the directive pattern. With dipoles

directivity is not much of a concern.This may or may not be acceptable in a particular specific

case.

The simplest and probably the most reliable method is to use the feed-line itself to make the

choke. That way there are no connections to make or go bad. This type of choke is simply

several turns of the coax feed-line taped together. The diameter and number of the turns can

be tailored to suit the frequency range of the antenna. This is my preferred method if I choose

to do anything besides feeding the antenna directly with coax.

Notes:

A ground is not necessary for a ham radio station in many cases.

Radio equipment should be connected back to the building electrical panel ground bus

through the “third wire” or ground wire in the power system. This is for safety.

Coax cables should have devices to bleed off charge from the center conductor to ground.

(Poly phasers or “blitz-bug” type of spark gap.

The shield of the coax may be connected to ground outside the radio station. This ground

should be bonded with a number 6 (minimum) copper wire to the building IBT or intersystem

bonding termination.

In most cases the ground is for safety or to provide a path for a lightning surge but not for a

direct lightning strike.

Connecting a piece of equipment to a isolated or stand alone ground rod does not make it any

safer to touch, but most people think it does!

In some cases a ground connection is used to compensate for using half of an antenna, or to

attempt to compensate for a poor design or poor installation.

Currents always return to the source and an antenna circuit is no different. Current leaving one

antenna terminal must complete the circuit by flowing back to the other or opposite terminal.

Antenna currents may return through the ground on their way to that terminal. If that terminal is

connected to only a ground rod, then it will become the return or part of the return. It depends

on the antenna and what other conductors are nearby and may be intentionally or inadvertently

connected or coupled to the equipment / antenna. Although the ground may be a good

conductor, the ground rod only makes contact over a small contact area and that is not good.

For this reason, multiple ground rods and radial systems are frequently used with bottom fed

verticals or monopoles. Typically these verticals are only half of the antenna. They are not what

I would call “self contained” verticals. A vertical center fed dipole would be a “self contained”

vertical. A half square would also be a SCV or self contained vertical. They do not need a

connection to ground or any kind of radial system.

It is important to recognize the different functions that the earth plays under a ground mounted

vertical and several wavelengths out in front of the vertical. The close in earth or ground system

can minimize or cause loss. The far earth or ground (we have no control over that other than

choosing to install the vertical antenna on the ocean shore) has to do with how good the

reflections are and how much gain there is at the receiving station. It does not affect the shape

of the pattern, just how large it is. With horizontal antennas the quality of the near and far earth

( ground) is not very important. Vertically polarized waves are affected quite differently than

horizontally polarized waves when reflected from earth (ground).