Domes and Dish Antenna
	Domes come in all sizes
	The biggest is to receive TV signals, the larger one fitted on the right mast is Inmarsat-A, the smaller one fitted also on the middle mast is Inmarsat-M, and the smallest one on the left mast is Inmarsat Mini-M. Some satellite communication systems operate at very low power, and they need a very directional antenna to focus the signal into a beam. Such a system uses a dish antenna. The dish itself is not unlike the receiving dish for domestic satellite television, and indeed, if the ship was fixed firmly in one position, virtually the same antenna could be used. However, as we all know, ships move around, all to keep the dish pointed at the satellite while the boat moves. To protect the mechanism and to prevent the wind moving the dish, the antenna is encased in plastic dome -- the ubiquitous mushroom that we see on commercial ships. The glass fibre dome is transparent to the radio frequencies. However, a layer of salt, perhaps mixed with bit of dirt, will act as a fairly effective shield, stopping the radio signals from reaching the dish antenna inside. The dome must not be painted, except with a special paint, because normal paint is opaque to radio signals. Care must be taken not to transmit while anybody is working on or near the dome. The frequencies used for satellite communication are extremely high, and the effect off being close to the dome when the set is transmitting would be akin to putting your head in a microwave cooker -- an experience to be avoided.
	Ends