Marine MF/HF SSB Radio HF Antennas & Installation Which SSB?
Marine MF/HF system
There is no black magic to installing an SSB radio onboard a yacht and this page should give you a guidance on installing an MF/HF (SSB) transceiver on an average size yacht.
Every yacht presents it’s own challenges and issues, so do give consideration to the location of the equipment, the antenna and grounding and power requirements, what works on one yacht may not work so well on another.
The MF/HF (SSB) installation can cause issues on-board a yacht with receiver interference from other equipment and on transmitting interfere with other equipment around the yacht.
MF/HF (SSB) Installation: Getting it right!!
There are 3 main parts to a marine MF/HF installation:
The Power Supply
An MF/HF (SSB) transceiver requires peak currents of 25 to 35
Amps at 12 volts, depending on transceiver and power output.
Hence the voltage drop between the power source and the SSB transceiver should be no more than half a volt.
Good ground
For
any MF/HF (SSB) transceiver system to work a good connection to
ground or salt water is required.
On a steel yacht this is not a problem as you can connect directly to the steel hull of the yacht, but just be aware of any electrolosys issues this may cause.
On a plastic yacht you
need to mount one or more 300mm by 75mm ground plates to the
outside hull of the yacht and connect them to the ATU with 50 mm by
0.5 mm copper strip.
Inside the hull
internal grounding such as wire mesh or inductive paint and
KISS-SSB, but these types of systems do not perform so well at
lower frequencies and can induce RF current into the boats
electrical systems.
Never use the boats DC electrical ground as the MF/HF antenna grounding system as this will course interference to other on-board equipment.
The Antenna
The
start of the antenna is at the Antenna Tuner
Unit (ATU) , so mount the ATU close to the external antenna
as you can, but at the same time keeping the ATU and antenna
connecting cable well clear of other electrical equipment and
cables.
A 7 metre long marine whip antenna works best as it
gives vertical polarization which is good for long range
communications on higher frequencies, 8MHz and above depending on
the whip length.
The backstay can be
used, if properly insulated and a good RF connection is made. Due
to the length of the backstay, performance is usually better than a
whip on the lower frequencies, 2 MHz and 4 MHz.
Try and keep
the antenna well clear of any metal, including the bottom section
of backstay.
The ATU can produce some very high RF voltage
which can cause burning if touched. It is therefore highly
recommend that a high voltage weatherproof single core cable is
used between the ATU and the antenna.
Marine MF/HF (SSB) Antennas
Whichever
antenna you are going to use, backstay or whip, this page is
intended to give some hints on how to get the best
performance.
First thing to consider is that your SSB
antenna is like a musical instrument, if you want to sound good
(transmit well) then you must get it right. Although it may receive
stations does not mean that it will transmit or radiate well.
The
antenna starts at the top of the ATU (antenna tuner unit) and ends
at the top of the antenna, if using the back stay then the top
insulator. Therefore the cable from the ATU to the antenna itself
is part of the antenna and it is recommended that a high voltage
single core weatherproof cable is used.
An
MF/HF SSB works on a wide range of frequencies (2 MHz to 25 MHz)
which are wavelengths between 12 metres to 150 metres. The ATU
matches an antenna from 7 metres to 15 metres long to the right
wavelength, but it is not practical to get an antenna system to
perform well across all wavelengths.
An antenna which
works on 12MHz may not be so good on 2 MHz.
A good antenna on
2 MHz is harder to achieve due to the long wavelength of 150 metres
but may not be effective on 12MHz due the multiple wavelength of 6
wavelengths.
When considering the antenna system, decide what
frequency you are going to use the most and optimize the antenna
for that frequency.
Avoid multiple wavelengths or half
wavelengths, as the ATU may have problems tuning to these
frequencies.
If the antenna length is 15 metres long then the
ATU should tune across a frequency range of 1.6 to 25 MHz with no
problems.
NOTE: The antenna on an SSB systems starts at the Antenna Tuner Unit (ATU) !
If properly
insulated the backstay can be used as an antenna.
Due to the
length of the backstay, performance is usually better than a whip
on the lower frequencies (2 MHz and 4 MHz).
Try and keep the
antenna well clear of any metal, including bottom section of
backstay.
Mount top insulator at least 1 metre or more from top of the mast.
Mount the bottom insulator close to deck level.
The antenna length (from top of the ATU to the top insulator) should be no shorter than 7 metres and no longer than 15 metres.
To avoid half wavelengths on marine frequencies, the antenna length should be no longer than 15 metres, if the antenna is longer than 15 metres then the ATU may have problems tuning the antenna on higher frequencies.
Use a high voltage weatherproof single core cable between the ATU and the antenna and keep the antenna as far away from other cables and metal objects as possible. Also keep the antenna cable from the antenna tuner to the backstay 75 mm clear of the uninsulated part of the backstay.
Connection
to backstay:
The weakest
electric link in any backstay insulation is the connection to the
backstay.
It is recommended using a good quality riggers clamp or sometime called bulldog clamp. Do not us a Jubilee clip as they can trap water in the connection which in turn can cause corrosion.
The
connection must be kept clean and free of rust and corrosion.
Depending on the frequency, you may loose transmit
power if you do not stand off the antenna cable from the bottom
backstay section.
It is highly recommend that a high
voltage weatherproof single core cable is used between the ATU and
the antenna.
Standing
antenna cable off the bottom of the backstay
NOTE: The antenna starts at the ATU and therefore the antenna is between the ATU and TOP insulator of the backstay!
Ground Plates
A good antenna
system requires a good ground, on a yacht this means having a good
connection to salt water. On the fibreglass yacht this is achieved
by fitting 1 or 2 ground plates to the outside of the hull which is
always under the water line.
A good quality Ground Plate
(Dynaplate) should be used. Good quality Ground Plates have lots of
small holes in them allowing sea water to seep into them increasing
the surface area and therefore giving good contact with sea water.
To reduce drag the Ground Plate should be mounted flush
to the outside of the hull of the boat with no gaps showing
otherwise weed and small animals get caught in the gap which can
increase drag on the yacht.
The Ground Plates should
then be connected to the antenna tuner unit (ATU) by means of 50 mm
copper or wider strip copper strip. The length of the copper strip
should be kept as short as possible. To reduce possible RF earth
loops, the Ground Plates should NOT be connected to any other part
of the SSB or boat electrical system.
