Proper
grounding of radio stations is probably one of the least understood
aspects of ham radio. It almost has a certain aura
of mystique or
magic about it instead of being the pure science it should
be. This
is a very important aspect of any radio installation. There
are two
major criteria we need to consider when doing the planning for this
installation. The primary reason has to be safety, both for
ourselves
as the operator who will be seated at the controls, but also for our
equipment and possibly the structure….probably our
home. The second of
course has to do with the performance of our antenna system and it's
ability to radiate an efficient signal. Let’s treat
these separately
for now and they will combine into a total plan at the end.
Surge
(or Safety) grounding.
We
need to protect our installation and ourselves from lightning.
There
is no protection against a direct lightning hit!
It has way more power than we can
shunt to ground safely or our budget
can handle. That is what insurance is for. We CAN
however make our
installation an unattractive target to lightning. We can also
take
care of any secondary surges and static build up that can destroy
equipment and give healthy zaps enough to more than get your
attention. There is nothing more frustrating than trying to
talk on a
radio and you keep getting zapped on the chin while doing so!
I speak
of personal experience here. Let’s let it go at
that. The Safety
ground has to consist of enough ground contact surface area to safely
dissipate the surges into the soil safely. Multiple ground
rods
connected with solid 1 ott ground wire is best. You should
have one
rod where your antenna support structure is, whether it be a tower or
mast or roof tripod, etc. It must have at least 4 gauge bare
or
insulated, NOT stranded wire. These surges can easily be
hundreds of
amps. DO NOT scrimp on the wire. This is your life
you are dealing
with. If stranded wire is used it should be no more than 8
conductors. Heavy bolt type connectors should be used for all
connections. You should also employ a non corrosive type
coating. All
of these connectors and grease are available at your good home supplies
or electrical supply houses. All grounds for the installation
should
be bonded together at the ground. NEVER daisy chain
grounds. ALL
connections from devices should go DIRECTLY to closest ground
point.
Use eight foot copper ground rods for all. Bond the rods with
single
ott solid bare copper wire. Drive a ground rod for electrical
supply
to house if you do not already have one. Bond it to others
with
aforementioned wire. If you have overhead service to house,
run wire
direct to neutral wire at feed point and use split bolt connections
with grease for corrosion. If you have underground service,
ground at
meter box. If your power company objects, run it to your
service
panel. You need a minimum of one eight foot ground rod for
every
protected structure, ie, every mast, tripod, vertical antenna,
etc.
These must all be connected together AT THE GROUND. Run bare
copper
between the separate ground rods to form a ground system. The
bare
copper provides additional surface contact area for the ground
system.
It should be underground, but does not need to be deep for any
engineering reasons. Make sure you make yourself a map of the
runs for
future projects to avoid hitting and digging up the system in the
future. Use heavy duty bolted connectors designed for this
service.
If you have access to a ground megger or ground tester the system
should be less than 15 ohms. In sandy soil this can take
several rods
to achieve. I have had to put down 3 32 foot rods (consisting
of four
8 foot rods with couplers and driven in with a power driver) in sand to
get the measurement needed. This should take care of our
safety
grounds.
RF
Grounding.
Rf
grounding is considerably different than surge grounding.
First thing
is you are working with RF. Since it is an AC signal it has
impedance. The length of the ground runs has much more to do
with the
fraction of a wavelength at the frequency involved than the DC
resistance of the wire. While the DC resistance of a ground
wire may
be only a fraction of an ohm, the impedance (or the AC resistance at RF
frequency) can easily be hundreds or thousands of ohms on the same
wire. This can make it pretty difficult to get an effective
RF
ground. Remember an RF ground wire is just a short
antenna! We want
to make it as LOUSY an antenna as possible! We
really don’t need it
radiating extra RF inside our shack. It is supposed to remove
this
stuff not cause it. An effective RF ground needs to be less
than a
quarter wave length at the highest frequency used. As you can
see
there is no such thing as an effective ground for VHF or UHF.
We will
concentrate our efforts to 10 meters and above. This means
our ground
wire from radio to ground must be about 9 feet or less! This
is still
pretty difficult. All radios, tuners, meters, etc in radio
system
should be grounded in a star ground configuration. The common
point
should be at the tuner if one is used, otherwise a ground bus bar can
be purchased at an electrical house. All Connections to
radios should
be with either insulated or bare wire with as few strands as
possible.
RF likes smooth surfaces best. DO NOT USE braid for RF
connections.
This is an old wives tale! Your ground run should go directly
to the
ground where you should have a ground rod for the connection
point,
(which will be connected to all your other ground rods in the system as
discussed above). This run must be less than nine feet to be
effective. If you are on the second floor this will make this
length
impossible. Use of a shielded ground* wire
can stop radiation of the ground wire but you will still have a lousy
ground. Nothing can change this. Ground wire tuners
only turn your
ground wire into a counterpoise for your antenna, meaning it WILL
radiate. This will only ensure that the low voltage point of
your
antenna will be at your radio. Next we need to form
our RF
counterpoise outside at our ground system. You will next need
to add
some bare copper wire at the RF feedpoint where your shack ground wire
connects to. I prefer to use bare 8 gauge copper ground wire
here. It
is single conductor, bare copper and easily bent and run around
house.
Single strand is best but it should definitely be bare even if you have
to strip insulation off wire. Run it around the house or
anywhere it
will stay out of the way fo lawn equipment but not buried deeper than
½”. This is CRITICAL. RF will
not penetrate soil deeper than this at
these frequencies. Those bonding wires you have
between ground rods
and ground rods do not exist to the RF! Burying
this wire under wood
chips or similar non conductive landscaping, etc is the way to
go.
This counterpoise should be as long as the wire antennas you have in
the air. For most hams this will be about 130 feet.
Longer is
better. I run all the way around my house. I have
found the eight
gauge will push into the spacing used between driveway and foundation
when persuaded with the proper tool, (READ HAMMER). You can
connect
the loop back on itself at the feed point. This can add
several S
units to the receive signal and dramatically reduce noise on the
signal, though nothing will help all the noise on 80 or 160
meters.
Years ago I installed a long wire antenna that was about 250 feet long
and about 50 feet in the air. This should work fantastic you
say. I
had three ground rods outside window of shack with single ott solid
copper ground wire direct to tuner. Ground wire length was only six
feet. All three rods were spaced about eight feet
apart with
connecting bare wire interconnecting them….in other words, a
really
good surge ground. What I did not realize at that time was
how lousy
my RF ground was. We could not tune the antenna on most
frequencies
and we kept getting zapped from the radio or microphone when we
transmitted. Also, our signal reports were lousy.
SO, after
consulting some experts, I added 250 feet of counterpoise around the
building consisting of some bare 6 gauge copper wire I had.
The radio
was on while I rolled it out and a friend was listening to the
broadcast on 40 meters, (OK it was night time---best time to do antenna
work right!) Anyway he reported the broadcast was only about
S 4-5 on
meter. As I rolled out the counterpoise it rose to 40 over S9
and came
in much clearer. We were able to tune everything easily now
and SWR
was rock stable. When
we did a signal test, the station we had talked to before accused us of
running a contest amplifier. We could not convince them it
was only
100 watts, same as before and the same antenna!
SUMMARY.
Don’t
underestimate the importance of a good ground system.
Include
it into the planning of that ultimate shack you are working
on. Don’t
scrimp on good copper wire and connectors. Aluminum can be
used above
ground but never in ground. Add one size to aluminum to
achieve same
current capability. Ground everything to the
system. A ground run to
ductwork in house can alleviate a lot of noise. A run to
water pipes
should go direct to ground….NEVER to radios, NEVER
connect radios to
ANYTHING inside the house for ground purposes. Always run all
grounds
from everything to ground directly. In other words, your
furnace ducts
will get one run, your water pipes will get one, etc.
Don’t daisy
chain to save wire. If you have a chain link fence in back
yard, run a
bonding wire underground from ground system to it and bond
well. A
solid aluminum or copper wire run along bottom of fence as a bonding
device will make it a great addition to the system. Weave it
through
the bottom fence fabric and bond every few feet with a split bolt
connector. The power company does this with all their fences
around
their power stations.
*
A shielded ground can be made using RG 8 or similar coax to replace the
ground wire. Connect both inner and outer shields to the
Ground rod
and connect the center only to the radio. Add a .1uf 1000
volt cap
between ground and shield at this end.
73 Bill - N8SA
Questions? Email Bill here