Sunday, May 27, 2018

Marine Mobile...



A Communicator Reprise: January 2012


Most countries' amateur radio licenses allow licensed operators to install and use radio transmission equipment while at sea. Such operation is known as maritime mobile amateur radio. In most cases the operator's call sign needs to be extended by adding the suffix '/MM' when transmitting at sea.

There are some special considerations when installing and using amateur radio transmitters and receivers afloat. These include power supply, RF ground, antenna design and EMC (Electromagnetic compatibility) with other electronic equipment aboard.

For MF and HF use, the most common antenna design is to add two RF insulators into the backstay of the mast and feed it from the transceiver using a sintered bronze ground plate, bolted to the outside of the hull, well under the waterline, as a ground. On metal hulled boats the ground plate can be dispensed with, and the whole hull used for this purpose. In this case, the thickness of any paint layer is entirely negligible at RF. On a yacht with twin backstays, if insulators are placed in both of them and they are fed from the masthead, they may be usable as an 'inverted vee' avoiding the need to feed the antenna against ground. Either format will require the use of an ATU (Antenna Tuning Unit) to achieve resonance for the HF frequency in use, as the physical length of the antenna will almost invariably be incorrect at the frequency of choice. A few twin-masted sailing vessels have the space to erect a "Tee" antenna or an inverted "L" between masts. These antenna configurations are more common on merchant ships.

For VHF and UHF operation, one option is to mount a small yagi antenna to a pole 1–2 m (3–6 ft) long and haul this to the masthead using a flag halyard. If the halyard is correctly knotted to the middle and bottom of the pole, it is easy enough to make the antenna project above the clutter at the masthead into clear air. The problem is in rotating it - it usually needs to be lowered and re-raised to alter the direction of its beam. For the safety of masthead fittings and lights it is better if these yagis are light in weight and made largely of, for example, plastic tubes supporting internal wire conductors. Operating in this way is best reserved for when in harbour or at anchor, to avoid interfering with the operation of the boat. Repeated loss of signal due to rolling and pitching would make it impractical for useful communication at sea anyway.

For FM operation on the 2m band, the masthead vertical whip that is normally installed for marine VHF operation will provide good omni-directional, vertically polarized signals. The frequency of operation around 145 MHz is close enough to the antenna's design frequency of 156 MHz that most amateur transceivers will not need an ATU and will not suffer unduly from a poor (high) SWR.


Grounding

For a single-ended HF antenna, a good electrical ground connection is essential. It is also necessary from the points of view of safety and EMC considerations on any radio transmitter installation on a boat or ship. As mentioned above, metal-hulled vessels have a natural advantage in that, especially at HF and lower frequencies, the hull can be considered to be in contact with the water, as the insulating properties of the paint layer against the water is a capacitance that presents very little electrical impedance to the RF currents. For fibreglass and wooden hulls and HF transmission, the usual solution is to attach a sintered bronze plate to the outside of the hull for RF ground. The construction of a sintered bronze plate is porous to water so that although the plate may be only a square foot or two and an inch thick, the actual surface area of metal in electrical contact with the water is very many times that.

Once a good connection to the sea water has been established, it is necessary to make a good RF connection from the transceiver and/or the ATU to the grounding system. While it might seem that a good, thick wire is all that is needed, for large RF currents it is usually recommended that copper grounding tape is used. This is not because thick wires will not be able to support the currents involved, but because it is more likely that RF currents will remain flowing along something that has a wide surface area without re-transmitting themselves along the way due to skin effect. The key pathway from the ATU of a single-ended antenna system to the ground plate, or the hull ground-point, should be as short and as straight as possible. This should be considered from the start when deciding where to mount the various components within the hull. There is not much that the installer can do about the losses in, and the efficiencies of, the transceiver, the ATU, the antenna or its feed, but extra effort put into the efficiency of the ground paths will pay much bigger dividends, in terms of radiated power and freedom from EMC problems later, than any other single aspect of the installation. The salty sea makes an exceptionally good ground plane, and effort put into achieving a good connection to it will be handsomely repaid.


Going on a cruise?

You will first need the permission of the cruise ship company itself to even have an Amateur Radio transmitter in your possession while on board (whether in use or not).  So your first step is to make sure you have written authorization to have your radio with you.
Next, besides the company itself you will need to have permission of the ship's captain in order to use the radio.  Do not assume you can simply throw up a vertical outside of your stateroom and operate!

Once you have authorization to operate ship board, you still have to worry about reciprocal operating privileges with the country where your ship is, including territorial waters.

Canadian and US licensees need no special permit or authorization other than their own Industry Canada or FCC license and they stay within Canadian, US or International waters.  When an FCC licensed amateur is operating an amateur rig aboard a US-registered vessel in international waters, he or she must follow Part 97 of the FCC rules, particularly Section 97.11. 

If the ship is of foreign registry, you must obtain a reciprocal operating authorization from the country of registry in addition to being in compliance with Section 97.11. When amateurs enter the territorial waters of a country, they fall under their communications jurisdiction. This means that they must obtain the required reciprocal operating authorization. There are three such authorizations: CEPT which applies to most European countries and certain overseas territories; IARP which applies to certain countries in the America's; Reciprocal Permit which is available from most countries, but application must be made to the country and a fee paid.

In Canada, these permits may be obtained from Radio Amateurs of Canada (RAC) for a modest fee.






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