Maritime mobile amateur radio
Most countries' amateur radio licences allow licensed operators to install and use radio transmission equipment while at sea. Such operation is known a 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.
Maritime Mobile Nets
Many long-standing and sophisticated radio nets are regularly operated by shore-based amateur volunteers for seafaring operators.
| Frequency (MHz) | Time(s) (UTC) | Operator(s) | Notes | ||
|---|---|---|---|---|---|
| Transatlantic maritime mobile net | 21.400 | 1300 | Trudi (8P6QM) | Based in Barbados, Atlantic crossing | |
| Worldwide weather net | 21.303 | 1300 | Neville (G3LMO), Richard (KT4UW), Don (6Y5DA) | ||
| UK maritime mobile net | 14.303 | 0800 1800 | Bill (G4FRN), Bruce (G4YZH), Tony (G0IAD) and others | ||
| Mississauga maritime net | 14.121 | 1145 | Doug (VE3NBL), Ernie (VE3EGM) | Based in Canada, Atlantic crossing | |
| Caribbean maritime mobile net | 7.241 | 1100 | Lou (KV4JH) | Caribbean cruising | |
| Caribbean weather net | 7.086 | 1120 | George (KP2G) | Caribbean weather information | |
| INTERMAR German maritime mobile service net | 14.313 | 1630 | Rolf (DL0IMA) | daily all Oceans | |
| The Maritime Mobile Service Network | 14.300 | 1700-0200 (winter) 1600-0200 (summer) | Net Manager is Rene (K4EDX) with over 70 net controllers | Atlantic, Caribbean and E. Pacific with hourly WX report. Position reports posted upon request. See our web page[1] | |
| Note: Information dated 2000 - Mistweb entries South, East-west, West-east; and www.intermar-ev.de | |||||
Technical considerations
There are some special considerations when installing and using amateur radio transmitters and receivers afloat. These include power supply, RF earthing, antenna design and EMC (Electro-Magnetic Compatibility) with other electronic equipment aboard.
Antenna design and installation
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 earthing plate, bolted to the outside of the hull, well under the waterline, as an earth. On metal hulled boats the earthing plate can be dispensed with, and the whole hull used as a ground. 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 mastead, 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 supporing 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 2 m band, the masthead vertical whip that is normally installed for marine VHF operation will provide good omni-directional vertically polarised signals. The frequency of operation around 145 MHz is close enough to the antenna's design frequency of 156 MHz that most amateur tranceivers will not need an ATU and will not suffer unduly from the SWR.