Written by Dr. John Gregory, CEO & Founder of CruiseEmail
Co-authored by John Sloop, Network Manager & Systems Designer
There have been numerous instances of RF grounding for HF/SSB
installations as far back as Noah‟s Ark. Many great scientists have
mathematical equations named after them. Einstein's Law of Relativity
(E=MC2), Newton‟s law of gravity, and Elijah's Law of Grounding (i.e., using
100 square feet of copper screen in the bilge of a vessel).
Elijah was the marine dock technician who installed the copper sheets in
Noah's Ark. That was the right thing to do, for in those days there was
always water sloshing around in the bilge which made good contact with the
copper sheets. Times have changed, but unfortunately some installers still
believe in that law.
This article will address these issues from both the theoretical
viewpoint and actual use proven by many hundreds of hours of testing,
retesting and more testing.
For operating an HF radio in a marine environment, the authors highly
recommend the purchase of a "Marine Radio". Many owners look for the least
expensive way out and try to modify a ham radio for marine applications. Bad
decision! Marine radios are designed and manufactured with protection
against salt water and sea air conditions. Marine radios are FCC Type
accepted, and meet the requirements of frequency stability and RF radiation.
Ham equipment does not need to meet these standards, and its use is
prohibited by law on Marine bands.
When using Terminal Node Controllers (TNC) such as a Pactor modem,
frequency stability and accuracy are critical. The further off frequency,
the worse will be the reception. This limits the ability to connect and to
data at the maximum rate for email. When tuning to a frequency, a marine
radio has a highly stable Numerically Controlled Oscillator (NCO). This
means it is EXACTLY on frequency. Ham radios use a Variable Frequency
Oscillator (VFO) that does not have circuitry capable of automatic frequency
The radio should be connected directly to the batteries via a proper
fusing system. Today‟s radios have fast-acting fuses that will react far
more quickly than the circuit breakers on your panels. Many times the radio
is connected to a breaker in the fuse panel marked "Radio". Usually the
breaker is the same as the other breakers, i.e., 20 amps. Marine radios that
transmit 150+ watts need at least 30-35 amp breakers. Install the radio by
connecting it directly to the batteries or to the closest battery switch and
install your fuses (yes, fuses, plural). Connect one on the hot side and the
other on the ground side. In my experience most radios are lost by a power
surge, lightning strike or corona hit to the ground side of the radio. Using
fuses on each, should there be a high voltage surge the radio is protected
on both positive and negative supply sides.
Not all fuses are the same. There are fuses made specifically for DC
applications. The 110 volt fuses available at hardware stores and even some
well-known Marine stores are not adequate. The correct DC fuse for a marine
application is marked for 32 VDC or Volts D.C. When installing the fusing
circuits to the radios, the authors prefer the new Plastic blade fuses that
are specifically made for the auto industry. Not only are they designed for
12-volt use, but they are sealed to protect against poor environmental
conditions. Glass fuses start to rust and corrode open causing problems
because the fuse and fuse holder are made of dissimilar metals. The
molecular difference in potential in the damp marine environment causes
electrolysis. When the author was designing and overseeing the installs in
Europe, he noticed the introduction of a new blade fuse that has a small red
button on the top, a re-set button. This is the way to go: if the short is
major, the fuse will melt and open, yielding a "blown fuse", but if it is a
short transient surge, the fuse will trip, and it will only need to be
Remember to calculate the distance from the radio to the battery source.
Countless times when radios have low power output or modems that do not
work, the cause is a wire size too small that is preventing the 12.6 volts
from reaching the radio. To accurately measure the voltage, place the
transmitter in the "FSK" mode and press the "PTT" button. Measure the
voltage at the
radio in the transmit mode, NOT just while it is in standby mode. This
test is extremely important. It demonstrates why the radio panel goes dim,
and the Pactors (TNCs) do not work. Antenna tuners will not work when they
do not receive 12 VDC.
Another note: when operating in the marine bands, the radio MUST always
be in the USB "Upper Side Band" position.
Last but extremely important is NOISE. What is excessive noise in the HF/SSB
This is where the radio manufacturers have "missed the boat"! There is no
signal strength meter on marine radios. Only the bars on the screen of the
radio give an indication. When in the receive mode, if 4+ bars are shown on
the radio, there is TOO much noise. (This has been independently verified by
the author and a colleague who repairs most of the popular HF radios on the
market.) The source of the noise may be on the vessel or simply nearby, such
as welding machines or a faulty bleeder resistor on a power line pole near
To verify the noise level, turn on all the DC panel breakers. Now slowly
start turning them off, one at a time. Wait 15-20 seconds between breakers.
Some electronics have high voltage capacitors and need time to bleed down.
The bars on the radio will change with each breaker. As the bars decrease
the amount of noise each circuit is contributing can be identified by the
change in the bars displayed. Once the circuits which contribute the most
noise are identified, investigation of the individual items on each circuit
will reveal which are the sources of the noise. Major contributors are
battery chargers, inverters, fluorescent lamps, some makes of halogen lamps,
and certain DC fans.
The next important device is the auto antenna tuner. This part covers
almost all the auto-antenna tuners, and how they should be connected to the
radio and the ground system.
The antenna tuner should be mounted within 5-7 feet of the ground plate,
the closer, the better. For owners who do not want to use a ground plate,
connecting the 2-3-4 bronze through holes together will work, but the green
bonding wire needs to be disconnected and butted to bypass the through
With 0.123 inch copper strap, a standard paper punch can be used to make
holes for attaching to the tuner and the ground plate. Again remember to
attach the copper strap to all the thru bolts from the ground plate. There
are only two straps connected to the ground plate, one to the antenna tuner
and the other to the radio.
Connect a copper strap (yes strap not wire) from the grounding lug on the
antenna tuner neatly to the ground plate. If using a ground plate that has
4-5 bolts on the inside, then use the copper strap to bond all those bolts
together; allowing maximum RF grounding to be transferred to the outside
RF resistance between the antenna tuner end of the ground strap and the
ground plate should measure 4-12 ohms as measured with an RF ohm meter. The
copper strap should be 1 to 1 ½ inches wide, and made of pure copper for
There should be two cables from the radio to the antenna tuner, a coaxial
and a control cable. Exception, there is an antenna auto tuner that only
needs the coax cable and is powered by the DC fed down the RF coax line.
Almost all problems associated with systems working improperly are
directly related to the PL-259 coax fittings. If there is a very fine wire
from the shield, not touching but near the center conductor, when 150 watts
of RF energy passes through the coax, it will arc to the center conductor
and cause an RF short. To confirm a good connection, install a 52-ohm
dummy-load on the coax at the antenna tuner end before you connect it to the
antenna tuner. Check for 1.6:1 Standing Wave Ratio (SWR). Now remove the RF
dummy load and connect to the antenna tuner.
Connecting to the antenna
Elijah‟s law and a California myth recommend using GTO-15 to run from the
antenna tuner to the antenna and that the GTO-15 will protect from RF burns.
Not true at all! GTO-15 was manufactured for neon signs like the type used
inside diners. To ignite the neon signs, it takes high voltage, and GTO-15
was used because owners wanted to prevent a shock to their customers should
they inadvertently brush against the sign. GTO-15 cable is not shielded and
will radiate just as much RF as an open backstay or wire. The GTO-15 center
diameter is no larger than the size of a hat pin. It is about the size of #
18-20 gage wire and provides high resistance.
The optimum design for antenna connection is copper tinned braid, like
that used at broadcast stations. This braid will provide minimum resistance
from the tuner to the antenna with very little RF lost. Cover the ¼ inch
braid with high voltage blue-stripe-plastic auto-loom. It is available in ¼
diameters and easy to install. This braid will allow maximum transfer of RF
energy to the antenna with very little resistance.
When attaching the RF feed line to the antenna, do not tie rap or tape it
to the backstay. The RF line radiates and it will couple to the lower part
back stay which is grounded and that will reduce the output of your
The average length for the RF feed line should not exceed 5-7 feet in a
mono-hull and should be much shorter in a CAT if the tuner is mounted a mid
Definition: A system of wires "insulated" from the vessel‟s ground system
and whose purpose is to be an artificial ground for the antenna. There are
many different lengths which represent the primary operating frequencies.
This subject is probably the most misinterpreted and misunderstood in the
entire installation. It is by far the most important part of the system
related to the antenna.
The counterpoise is the mirror image of the electrical side of your
antenna. It can be minimized in length, as long it is resonant to the
Remember that the antenna tuner wants to match the antenna and transfer
as much RF energy to it as possible. Auto antenna tuners will match between
80 to 1200 ohms to the antenna at frequencies from 2.8 MHz to 22 MHz. It is
important that this same RF impedance be established on the counterpoise
A few years ago the author introduced using 450 ohm ladder line for the
counterpoise. When it is cut to the correct length, it has the same
impedance (80 to 1200 ohms) to mirror the impedance to the auto tuner.
Also introduced was a counterpoise using two ladder lines, each connected
to the same grounding lug of the antenna tuner, but one line running in the
port side of the bilge and the other in the starboard side. The lines should
be separated from each other throughout the entire length of the vessel and
be at least 3 feet apart. (If they run together for a few feet it is
When these counterpoises are built, signals of the desired frequencies
are injected into the lines using a digital signal generator. The individual
lines are then cut to resonate with the tuner and give the best performance.
Interestingly, the impedance of the ladder lines is not always what is
stated by the manufacturer. Consequently, the length cannot be copied from
another vessel. By the design of these lines, the SWR match will be
approximately 1.6:1 or better throughout all assigned frequencies.
Once again, the counterpoise is not the RF ground that gets connected to
your systems DC ground and absolutely not bonded to the engine.
As you can see, the concept of 100 square feet of copper in the bilge has
long ago been thrown out, although there are still those who believe in this
ancient myth. Of course, if the vessel is a re-constructed Noah‟s Ark, then
Elijah‟s law of Grounding just might work, because there will always be lots
of water inside the hull!
Counterpoise in Bilge
RF Ground Plate
Ground plates are a very important part of a radio system, and also a
major grounding connection for other important instruments on the vessel,
e.g., the radar system. The RF resistance of the ground plate should be 4 to
12 ohms between the ground plate and the salt water and about the same for
fresh water. The ground plate represents that copper or brass 8 foot stake
that one would pound into the dirt to ground radio equipment on land.
The ground plate should be located about 5-7 feet from the antenna tuner,
and deep enough under your vessel that when the vessel heels, the ground
plate remains underwater. Now consider the surface area. There are some
manufacturers who claim major surface areas by counting the dimples in
their plates. From a technical standpoint the dimples do not do anything. In
reality what counts is the total RF surface area. RF current does not look
at each and every dimple on a ground plate; it looks at the surface area as
a whole. For example, if a 4 x 18 inch plate is mounted solidly against the
hull you cannot count the back as surface area.
Next consider the connection from the tuner and the radio to the ground
plate. The average power is 65 watts using an Amateur radio or 150 watts
using an authorized Marine Radio. The ground strap from the tuner and radio
to the ground plate should be copper foil 0.123 to 2.0 mils thick and 1 to
1.5 inches wide. Anything more is a waste of time, money, and a painful
exercise running the foil through those tiny scupper holes in the bilge.
The tuner has a "large" wing nut on a porcelain stand-off to attach the
copper strap. Use the copper foil between it and the ground plate. If the
plate has 4-5 through bolts, tie them all together with the copper strap.
When making the connection, apply an anti-oxidant paste at the connection
point only. This is because some copper foil is really only copper coated,
and the molecular difference will start a small corrosion point. The author
always uses Lanakote™. It is a grease that will last for a very long time in
the bilge area.
A ground loop not only causes possible electrolysis to your radio, but
also distortion of your radio signal that is most noticeable in sending data
such as emails. To prevent this from happening, a DC Block should be
inserted by cutting the copper strap near either the tuner or the ground
plate. This block will prevent a ground loop from your radio to the tuner
and back to your radio.
At the radio side on most radios is an RF ground screw or lug that should
also be connected to the RF Ground Plate. Cut another copper strap and run
it from the radio to the same ground plate. If this is not possible, then
connect the strap to 2-3 bronze through-hulls. If you have green 10-12 gauge
bonding wire connected to the through-hulls, cut it away from and by-pass
the through-hulls by terminating the connecting wire. Tie the 2-3 bronze
fittings together with the copper strap, and clamp it with a "real"
stainless steel hose clamp. Apply Lanakote™ and you are done.
Now to will address the mounting of the ground plate correctly to the
hull. After extensive research, testing, measuring, and addressing some of
the major rumours about grounding plates mounted on the hull of vessels,
here are the facts. Review the diagram. It is the best way to have all the
surface area that you need.
The ground plate should be off-set from the hull by 3/8 inch. Some years
ago, a major vessel insurance company which shall remain nameless came to a
false conclusion. They stated that vessels which had ground plates and were
hit by lightning blew major holes not only in the fibreglass, but also in
bronze through-holes. After an intense investigation the Department of Navy
determined that this was not the case. There were improper connections to
the ground plates. The 4-5 bolts that took the major portion of the direct
hit from the lightning actually heated the through bolts so much, that it
melted the fibreglass hull. After 6-7 months of exhaustive testing, it was
found that by mounting the plate off-set by no more than 3/8 of an inch,
the water behind the plate not only provided additional RF surface area
but also cooled the bolts sufficiently to prevent damage to the hull. This
is also the reason to run an extra ground plate for lightning discharge.
Remember that it is not just a lightning bolt hitting your mast, but the
corona from lightning which can hit as far away as 18 miles and it can put
enough electricity in the air to blow out all of the vessel‟s electronics,
including it‟s radio. There is a good work-around to this problem which will
be addressed in a future article. So remember, mount the plate, at least 3/8
of an inch off the hull and 5-7 feet from the antenna tuner.
Ground Plate through hull installation
Single Side Band Antennas
Single side band antennas are an extremely controversial subject. The
authors have conducted tests on various antennas for the past 8-10 years.
Numerous styles, makes and models of SSB antennas and their efficiency have
been tested. The Rope Antenna was determined to be the most efficient,
economical, and the simplest to install.
With any antenna, the installation of a good counterpoise provides the
greatest efficiency and maximum output from the transmitter and the
antenna tuner (whether a manual or auto tuner). The transmission line to
the antenna should not be running parallel to any rigging and should be
spaced at least 2-3 feet away. This practice prevents the effects allowed by
vessels that have poor filters in the power supply of refrigerators and
inverters. The power supply of these devices oscillates into the grounding
system which ties to the ground side of the battery. This pulsing oscillates
at such a high level that it is coupled into the antenna system of the
vessel. When listening to the HF radio, this noise sounds like someone
sending Morse code. (If you turn off these appliances and equipment the
noise will stop.
At the antenna tuner all that is needed is a flat copper ground strap 1 -
1.5 inches wide and no more than 0.130 thickness, going from the tuner to
the Ground Plate. A DC Block should be inserted in the line from the antenna
tuner to the ground plate. This stops the induced noise current from looping
back through the antenna tuner to the radio, and reduces the noise caused by
For efficient and reliable H.F. communications it is extremely important
to pay close attention to the details of the system installation. Equipment
mentioned in this article may be obtained from www.ropeantenna.com and email
service from www.cruiseemail.com. Both authors are available for design,
installation, troubleshooting, and consulting.
Dr. John Gregory John Sloop
No part of this article may be reproduced in any manner without written
permission of the authors.