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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.



M802 system overview

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) !

Insulated Backstay Antenna for Yachts.

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.

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
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.

dynaplates