Practical Grounding Systems|
for Amateur Radio Stations
A ground is defined as a low-impedance electrical connection to earth.
Beside a common reference point in electronic circuits, also all transmitting
antenna systems need a properly functioning ground system to provide for proper
operator safety and efficient radiation of the maximum amount of RF energy into the air.
There are 3 principle forms of ground :
Power Line Ground : is the ground you see at the power box where your
home's electrical service is connected.
It is required by law to ensure the safety of life and property surrounding
DC Ground ( Safety Ground ) : is familiar to the amateur as
the strap or wire placed from equipment to a convenient cold water pipe
or ground rod to reduce the risk of electrocution or radio equipment damage
by short circuited "power mains", or from lightening strikes to the antenna
or "feedline" system.
In the car, it is the wire which connect from the ground stud on the rear
of the radio to the negative terminal of the battery, or ideally the engine block.
An effective safety ground system is necessary for every amateur station.
It provides a common reference potential for all parts of the ac system and reduces
the possibility of electrical shock by ensuring that all exposed conductors remain at
that (low) potential. Three-wire electrical systems effectively ground our equipment
for dc and low frequencies. Unfortunately, an effective ground conductor at 60 Hz
(5,000,000 m wavelength) may be an excellent antenna for a 20 m signal.
RF Ground : is a low-impedance path for RF to reach earth and which is
designed to dissipate rather than radiate RF energy.
Not all radio antenna systems should be grounded to enhance their radio performance.
If grounding these antennas was for the purpose of safety is ok, but if
grounding an antenna will automatically make it a better communications device
is completely wrong.
On certain lower frequency longer wavelength bands an RF ground is not only a
reasonable consideration but, it is fundamental to getting the best
communications performance from the radio station. At other higher frequency
and shorter "wavelength bands" however, RF grounds are either superfluous, or
even harmful to overall communications performance.
Keep in mind the concept of thinking about the physical length of the
"grounding conductor" in relationship to its comparative "wavelength dimension"!
Many troublesome harmonics are in the VHF range.
At VHF, a ground wire length can be several wavelengths long - a very effective
Any VHF signals that are put on a long ground wire will be radiated.
This is usually not the intended result of grounding.
For decades, amateurs have been advised to bond all equipment cabinets to an RF ground
located near the station. That's a good idea, but it's not easily achieved. "Near" in
this use is 10 ft or less for HF operation, even less for higher frequencies.
At some stations, it is very difficult to produce an effective RF ground.
When levels of unwanted RF are low, an RF ground may not be needed.
Don't use power line ground as an RF ground!
In most stations, safety ground and RF ground are provided by the same system.
If you install ground rods, however, bond them to each other and to the power line ground
at the electrical service entrance. In older houses, water lines are sometimes used for
the service entrance panel ground. It is a good idea to check that the pipes are electrically
continuous from the panel to earth. (Consider that Teflon tape is often used to seal pipe
joints in modern repairs.)
Some think that RF grounds should be isolated from the safety ground system-that is not true!
All grounds, including safety, RF, lightning protection and commercial communications,
must be bonded together in order to protect life and property.
Ground loop is a condition where all the electrical equipments "grounds" aren't at
the same electrical potential, namely zero volts AC and DC.
When two or more devices are connected to a common ground through different paths,
a ground loop occurs.
Currents flow through these multiple paths and produce voltages represents unwanted
The unwanted signal radiation can cause Radio Frequency Interference (RFI), Television Interference (TVI), noise or hum, etc.
To prevent ground loops :
- The station should be on the ground floor of the house.
- The lowest possible resistance or Alternating Current (AC) impedance grounding conductor
should have considerably less than a quarter wavelength of total length between
the radio and the first ground rod.
- If the soil or other conditions in the yard allowed only short length rods,
should have used several of them all tied in a line.
Making an effective ground
Station ground :
The first step in building an RF ground system is to bond together the chassis of all equipment
in your station.
Choose conductors large enough to provide a low-impedance path.
Avoid solid conductors as they tend to break.
Copper strap, sold as “flashing copper,” is excellent for this application.
Coax braid is a popular choice; but it is not a good ground conductor unless tinned,
and then it’s no longer very flexible.
Rather use commercially made copper braid ground strap that is tinned and ampacity rated—
wider straps make better RF grounds.
Grounding straps can be run from equipment chassis to equipment chassis, but a more convenient
approach is illustrated in Fig 1. In this installation, a 1/2-inch-diameter copper water pipe
runs the entire length of the operating bench.
A wide copper ground braid runs from each piece of equipment to a stainless-steel clamp on
After the equipment is bonded to a common ground bus, the ground bus must be wired to a good
earth ground. This run should be made with a heavy conductor (copper braid is a good choice
again) and should be as short and direct as possible.
In most cases, the best approach is to drive one or more ground rods into the earth at
the point where the conductor from the station ground bus leaves the house.
Multiple ground rods reduce the electrical resistance and improve the effectiveness of
the ground system.
The best ground rods to use are those available from an electrical supply house.
Don't use steel or iron pipe for ground rods!
A minimum RF ground system will use at least three 8 foot or longer ground rods.
If you can't sink a rod that long, than you must use many more shorter rods, or bury a splayed
out radial system of wires. In this last case you must terminate this wire radial screen within
less than a quarter wavelength at 29.7 MHz (which is 94.5 inches or 2.4 meters).
Once the ground rod is installed, clamp the conductor from the station ground bus to it with
a clamp that can be tightened securely and will not rust. Copper-plated clamps made specially
for this purpose (and matching the rods) are available from electrical supply houses.
If have antenna tower, the tower ground also must be connected to the station ground.
The length of the conductor between the ground bus and the ultimate ground point becomes
a problem. For example, the ground wire may be about 1/4 wavelength (or an odd multiple of
1/4 wavelength) long on some amateur band.
A 1/4-wavelength wire acts as an impedance inverter from one end to the other.
Since the grounded end is at a very low impedance, the equipment end will be at a high impedance.
The likely result is RF hot spots around the station while the transmitter is in operation.
In this case, this ground system may be worse (from an RF viewpoint) than no ground at all.
For some installations, especially those located above the first floor, a conventional ground
system such as that just described will make a fine dc ground but will not provide the necessary
low-impedance path to ground for RF.
Tower & antenna ground :
Because a tower is usually the highest metal object on the property, it is the most likely
Proper tower grounding is essential to lightning protection. The goal is to establish short
multiple paths to the Earth so that the strike energy is divided and dissipated.
Connect each tower leg and each fan of metal guy wires to a separate ground rod.
Space rods at least 6 ft apart. Bond the leg ground rods together with a enough large copper
Connect a continuous bonding conductor between the tower ring ground and the station ground.
Make all connections with fittings approved for grounding applications.
Do not use solder for these connections. Solder will be destroyed in the heat of a lightning
strike. Tower ground is shown in Fig 2 below.
Unless the tower is also a shunt-fed antenna, use grounded metal guys. For crank-up or
telescoping towers, connect the sections with strap jumpers. Because galvanized steel
(which has a zinc coating) reacts with copper when combined with moisture,
use stainless steel hardware between the galvanized metal and the copper grounding materials.
To prevent strike energy from entering a shack via the feed line, ground the feed line outside
Ground the coax shield to the tower at the antenna and the base to keep the tower and line at
the same potential. Several companies offer grounding blocks that make this job easy.
Important Tip: Don't install the ground rod within the
concrete! One reason is that it is connected to the earth via the high
resistance of the concrete. The other reason is that a lightening strike to the
tower may well blow the concrete block to bits!
Ground in Vehicles
In the environment of the mobile antenna system many factors contribute to the radiation
of an excellent RF signal, but none more than the quality of the RF ground.
The RF ground represents the "unseen half" of your antenna system.
The visible half is the whip or other radiating element.
Failure to construct a good RF ground inhibits the efficiency of the system's
radiation and can present danger to the operator through RF feedback.
In mobile installations, the chassis or body represents a ground plane: a
common circuit return or reference point for your signal. The signal radiates
outward from the radiating element and flows back to the radio via the ground plane.
Then the polarity switches and this process reverses, back and forth, in synchronization
with the transmitted sine wave.
In constructing an efficient antenna system for your vehicle always make sure that
your frame or car body are at RF ground by connecting them electrically and physically
with the engine block. The engine block acts like a terminal strip or "bus" for your
car's electrical system: the negative terminal of the battery and all other electrical
grounds are connected to it as the central meeting point.
The engine, in turn, is bound to the vehicle chassis through the engine mounting bolts,
though not necessarily grounded! In today's modern vehicles insulating elements,
i.e., rubber motor mounts, are used to cushion vibration. At DC a solid path to ground exists,
and even if this path should somehow fail, the car's body ground can act as a reserve.
At RF frequencies however, an acceptable DC ground can sometimes present such a high
impedance to your antenna system that it is, in effect, no ground at all!
To ensure your mobile antenna environment is at RF ground, simply bind the block to
the chassis with tinned copper braid.
Use short runs so as to avoid introducing any inductive reactance which will impede
the flow of the RF current to ground.
Signs that the quality of RF ground may be lacking :
- Difficulty or inability to tune to an acceptable SWR match with your
manual or automatic antenna tuner. (Assumes you have confirmed in
advance that the antenna is already resonant "off the system".)
- Noticing a waving up and down of the SWR reading on the meter during
transmitting while the vehicle is in motion.
- Noticing that the radio is "kicking", (cutting out and turning itself
off) during transmission, an indication of significant RF feedback.
- Getting an RF "bite" on the radio equipment or code key during
transmission, an indication that excessive RF energy is feeding back
from the antenna system or that the system is floating above ground
Remedies require a review of how your antenna system is mounted to the
car, specifically :
- Is there a good physical and electrical connection between your
antenna's ground and the vehicle frame/body?
- If utilizing the body as the ground plane is there isolation from RF
ground which may be causing the RF return path to float above ground
- Do you have faulty shield connections along your transmission line?
- Are ground loops present in your system?
Based upon your assessment of the above, take action as necessary to clean
up any weak points you uncover.
Ground Loops in The Mobile Environment
In your vehicle ground loops are often unknowingly created as a consequence of frantic attempts to ground out noise sources by braiding "everything" one can think of to the nearest metal available.
This is most likely when working under the hood to suppress noise in the antenna and power supply systems,
but can also occur when your antenna is inadequately mounted to the frame/chassis.
In reading the nature of the formation of ground loops above, you can see how,
in braiding to the nearest available metal, series connections could very well have crept
into your design.
Remember: if you are not at ground potential, RF currents may still be circulating within your
ground system which may then be re-radiated as RF noise that can be received by the antenna system.
To eliminate any loops in your ground, the concept of applying a centralized ground point,
as described earlier for a home station, applies to the mobile configuration as well.
In adopting a single point for your vehicle, use the frame/chassis as your "ground stake",
if you will.
It is the common metal to all other metal points of your vehicle, and provides an excellent
ground plane for your vertical element to work against.
Large body sheet metal surfaces can float above RF ground if they are electrically
insulated by rubber body and engine-cushioning devices designed to absorb road noise,
rattles and vibration.
As a result, RF currents can be encouraged to circulate on your hood, trunk, quarter-panels
or other body surfaces which can act as small antennas,
re-radiating noise signals from the ignition system and associated components.
To solve the problem, follow the steps :
- Bonding body sheet metal parts to ground by utilizing a ˝" to 1"
wide tinned flat copper braid, connect the :
- Hood and trunk lid to car frame (chassis);
- Exhaust system (at several points along the length of the system) to the frame;
- Bumpers (metallic) to the frame;
- Engine block to the frame.
- Shielding the spark plug wires.
- Shielding the distributor and/or ignition module with allumunium foil.
For details on suppression of automotive RFI, please visit the K2BJ Website.