Maritime mobile amateur radio
Encyclopedia
Most countries' amateur radio
licences 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.
Maritime mobile operation is defined as operating a transmitter that is located on any vessel at sea. This means any manned structure afloat outside of the high water mark. Operating on vessels on inland waterways is defined as mobile working, and so requires /M to be added to the callsign, not /MM as for maritime mobile operation.
There is a requirement that the amateur radio equipment must only be installed with the written permission of the vessel's master. This does not affect those who intend to install a transceiver on their own boat, but is relevant to anyone who intends to make transmissions from a ferry or other passenger ship. In such cases, the master of the ship has the right to demand radio silence from the amateur operator. There is no requirement to keep a log of calls, but a written record of information about frequencies, times, operators and their callsigns is in fact usually very valuable.
It is not a requirement that the station transmits its location, but of course this is advisable, and easy to do with on-board GPS location. UK amateurs have a system of regional secondary locators that they must use within UK territorial waters (e.g. adding D for Isle of Man, M for Scotland etc in the second position in their callsign). In international waters, this is not necessary. When in the territorial waters of other countries, CEPT
rules apply and these can get complex. The normal procedure is to prepend the national locator of the host country to the normal callsign, separated with another slash. So, amateur station A0AA, operating from a vessel within the territorial tidal waters of a country identified by the prefix B would identify itself as B/A0AA/MM when transmitting.
In international waters, amateur licensees must only use frequency bands allocated internationally by the ITU
. In any country's territorial waters, they should abide by the frequency allocations and bandplan
s applicable to the host country.
) with other electronic equipment aboard.
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 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 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 transceivers will not need an ATU and will not suffer unduly from a poor (high) SWR
.
antenna, a good electrical earth 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 earthing. 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 earthing plate, or the hull earth-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 earthing 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.
receiver and an AIS
system. Many of these items are computerised and many of them are networked together with data, RF and power connections. All of this is crammed into a very compact, three-dimensional space and that space is shared by not only the radio operator, but perhaps several other crew and/or family members. Safety and EMC
issues have never been so important.
One important fact to bear in mind is that the antenna lead, from the point where it leaves the relevant terminal on the HF ATU is a transmitting antenna. There is nothing that can or should be done to prevent RF radiation from this lead. It should be a specialist, high-voltage insulated, single-core wire and it should be rigidly mounted, well away from any other wiring, outside of any conducting faraday cage
, in the shortest, straightest possible route to the point where it will connect to the external antenna, be that a whip or an insulated part of the standing rigging. If it has to cross other wiring, crossing should be at right-angles and with the maximum possible spacing or separation, preferably with earthed copper tape between the two cables and perhaps with ferrite chokes added to the other lead both sides of the crossing point. The purpose of any cable or lead so crossed should be noted and consideration given to de-powering whatever equipment it serves before any transmissions are ever made. Whatever it is will probably misbehave due to the RF interference it will receive, and it may permanently be damaged by the RF currents that are induced in it by a 100 - 200 W transmission coupled in this way.
With regard to the transmitting antenna above decks, it is essential that all aboard are aware when the transceiver is in use and transmissions are likely to be made. Anybody holding on to the relevant stay
and/or touching its antenna feed wire could suffer severe HF burns
if the transmitter is keyed.
As discussed above, good earthing is essential in the installation of transmitting equipment, and good RF management will also pay dividends in terms of the ability to use other electronic equipment while transmitting, without damage to the other gear, or debilitating interference in the other gear during transmissions. In extremis, it may be possible to disengage electronic steering and switch off or do without navigation instruments while the radio operator aboard makes a scheduled call, but others aboard will be much more grateful if this is not necessary and life aboard can continue as normal while people gather around the transceiver to hear news from ashore and from other boats, as well as weather or other important routing information.
Other equipment aboard may also interfere
with the reception of low-power SSB
or digital signals. Usual candidates include anything with a badly suppressed electric motor
, such as a fridge, fans, or an electronic self-steering system, as well as many depth sounders and some radar systems. Better suppression
of DC motors may be retrofitted and RF chokes
can be made by winding some turns of the power and transducer leads through a suitable ferrite ring
(see Toroidal inductors and transformers
). Failing this, it may be necessary to de-power some of these other items during important radio reception times. One radio receiver that may be overlooked is the Navtex, if fitted. By tuning the HF rig down to its relevant frequencies (e.g. 518 kHz) it may be possible to identify sources of interference that are limiting its range, and switch them off or improve their EMC characteristics. Once this is done and these frequencies are quiet, far from land it is surprising what range Navtex can achieve, especially at night.
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
licences allow licensed operators to install and use radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
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.
Licensing
The following notes are made with regard to the UK 'Full' amateur radio licence terms, provisions and limitations, and so may vary slightly from other amateur licences.Maritime mobile operation is defined as operating a transmitter that is located on any vessel at sea. This means any manned structure afloat outside of the high water mark. Operating on vessels on inland waterways is defined as mobile working, and so requires /M to be added to the callsign, not /MM as for maritime mobile operation.
There is a requirement that the amateur radio equipment must only be installed with the written permission of the vessel's master. This does not affect those who intend to install a transceiver on their own boat, but is relevant to anyone who intends to make transmissions from a ferry or other passenger ship. In such cases, the master of the ship has the right to demand radio silence from the amateur operator. There is no requirement to keep a log of calls, but a written record of information about frequencies, times, operators and their callsigns is in fact usually very valuable.
It is not a requirement that the station transmits its location, but of course this is advisable, and easy to do with on-board GPS location. UK amateurs have a system of regional secondary locators that they must use within UK territorial waters (e.g. adding D for Isle of Man, M for Scotland etc in the second position in their callsign). In international waters, this is not necessary. When in the territorial waters of other countries, CEPT
CEPT
CEPT may refer to:* The European Conference of Postal and Telecommunications Administrations* The CEPT, Ahmedabad* The Committee of European Pharmacy Technicians * Common Effective Preferential Tariff...
rules apply and these can get complex. The normal procedure is to prepend the national locator of the host country to the normal callsign, separated with another slash. So, amateur station A0AA, operating from a vessel within the territorial tidal waters of a country identified by the prefix B would identify itself as B/A0AA/MM when transmitting.
In international waters, amateur licensees must only use frequency bands allocated internationally by the ITU
Itu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
. In any country's territorial waters, they should abide by the frequency allocations and bandplan
Bandplan
A bandplan or band plan is a plan for using a particular band of radio frequencies, that are a portion of the electromagnetic spectrum . Each bandplan defines the frequency range to be included, how channels are to be defined, and what will be carried on those channels...
s applicable to the host country.
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 Barbados Barbados is an island country in the Lesser Antilles. It is in length and as much as in width, amounting to . It is situated in the western area of the North Atlantic and 100 kilometres east of the Windward Islands and the Caribbean Sea; therein, it is about east of the islands of Saint... , 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 | 0745 local time, i.e. 1145 (Canadian summer time) or 1245 GMT | Doug (VE3NBL), Ernie (VE3EGM) | Based in Canada, Atlantic crossing |
| Caribbean maritime mobile net | 7.241 | 1100 | Lou (KV4JC) | 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. |
| ANAVRE Spanish maritime mobile service net | 14.323 | 1630 2230 | Ignacio (EA4FZZ), Manel (EA3CBQ) | daily Med. & Northeast Atlantic |
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 (Electromagnetic compatibilityElectromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
) with other electronic equipment aboard.
Antenna design and installation
For MFMedium frequency
Medium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...
and HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
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
Negligible
Negligible refers to the quantities so small that they can be ignored when studying the larger effect. Although related to the more mathematical concepts of infinitesimal, the idea of negligibility is particularly useful in practical disciplines like physics, chemistry, mechanical and electronic...
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
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
. 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
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
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
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
operation on the 2 m band, the masthead vertical whip that is normally installed for marine VHF operation
Marine VHF radio
Marine VHF radio is installed on all large ships and most seagoing small craft. It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours, locks, bridges and marinas, and operates in the VHF frequency range, between 156 to 174 MHz...
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 transceivers will not need an ATU and will not suffer unduly from a poor (high) SWR
Standing wave ratio
In telecommunications, standing wave ratio is the ratio of the amplitude of a partial standing wave at an antinode to the amplitude at an adjacent node , in an electrical transmission line....
.
Earthing
For a single-ended HFHigh frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
antenna, a good electrical earth 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
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
that presents very little electrical impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
to the RF currents. For fibreglass and wooden hulls and HF transmission, the usual solution is to attach a sintered
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...
bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
plate to the outside of the hull for RF earthing. 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
Antenna tuner
An antenna tuner, transmatch or antenna tuning unit is a device connected between a radio transmitter or receiver and its antenna to improve the efficiency of the power transfer between them by matching the impedance of the equipment to the antenna...
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
Skin effect
Skin effect is the tendency of an alternating electric current to distribute itself within a conductor with the current density being largest near the surface of the conductor, decreasing at greater depths. In other words, the electric current flows mainly at the "skin" of the conductor, at an...
. The key pathway from the ATU of a single-ended antenna system to the earthing plate, or the hull earth-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 earthing 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
Ground plane
In electrical engineering, a ground plane is an electrically conductive surface.-Radio antenna theory :In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to...
, and effort put into achieving a good connection to it will be handsomely repaid.
Safety and EMC
A modern sailing boat, or any other modern sea-going craft, is a much more complex electronic environment than ever in the past, and even more so than a normal home-based amateur radio 'shack'. The vessel will probably have electronic navigation instruments, one or more GPS receivers, electronic automatic steering, domestic radio and perhaps television receivers as well as probably radar and VHF transmitters and receivers too. It may have various GMDSS devices too, such as a NavtexNavtex
NAVTEX is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships...
receiver and an AIS
Automatic Identification System
The Automatic Identification System is an automatic tracking system used on ships and by Vessel traffic services for identifying and locating vessels by electronically exchanging data with other nearby ships and AIS Base stations...
system. Many of these items are computerised and many of them are networked together with data, RF and power connections. All of this is crammed into a very compact, three-dimensional space and that space is shared by not only the radio operator, but perhaps several other crew and/or family members. Safety and EMC
Electromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
issues have never been so important.
One important fact to bear in mind is that the antenna lead, from the point where it leaves the relevant terminal on the HF ATU is a transmitting antenna. There is nothing that can or should be done to prevent RF radiation from this lead. It should be a specialist, high-voltage insulated, single-core wire and it should be rigidly mounted, well away from any other wiring, outside of any conducting faraday cage
Faraday cage
A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields...
, in the shortest, straightest possible route to the point where it will connect to the external antenna, be that a whip or an insulated part of the standing rigging. If it has to cross other wiring, crossing should be at right-angles and with the maximum possible spacing or separation, preferably with earthed copper tape between the two cables and perhaps with ferrite chokes added to the other lead both sides of the crossing point. The purpose of any cable or lead so crossed should be noted and consideration given to de-powering whatever equipment it serves before any transmissions are ever made. Whatever it is will probably misbehave due to the RF interference it will receive, and it may permanently be damaged by the RF currents that are induced in it by a 100 - 200 W transmission coupled in this way.
With regard to the transmitting antenna above decks, it is essential that all aboard are aware when the transceiver is in use and transmissions are likely to be made. Anybody holding on to the relevant stay
Stays (nautical)
Stays are the heavy ropes, wires, or rods on sailing vessels that run from the masts to the hull, usually fore-and-aft along the centerline of the vessel...
and/or touching its antenna feed wire could suffer severe HF burns
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
if the transmitter is keyed.
As discussed above, good earthing is essential in the installation of transmitting equipment, and good RF management will also pay dividends in terms of the ability to use other electronic equipment while transmitting, without damage to the other gear, or debilitating interference in the other gear during transmissions. In extremis, it may be possible to disengage electronic steering and switch off or do without navigation instruments while the radio operator aboard makes a scheduled call, but others aboard will be much more grateful if this is not necessary and life aboard can continue as normal while people gather around the transceiver to hear news from ashore and from other boats, as well as weather or other important routing information.
Other equipment aboard may also interfere
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
with the reception of low-power SSB
Single-sideband modulation
Single-sideband modulation or Single-sideband suppressed-carrier is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth....
or digital signals. Usual candidates include anything with a badly suppressed electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
, such as a fridge, fans, or an electronic self-steering system, as well as many depth sounders and some radar systems. Better suppression
Filter capacitor
Filter capacitors are any capacitors used for filtering. Filter capacitors are common in electrical and electronic work, and cover a number of applications, such as:* Glitch removal on Direct current power rails...
of DC motors may be retrofitted and RF chokes
Choke (electronics)
A choke is a coil of insulated wire, often wound on a magnetic core, used as a passive inductor which blocks higher-frequency alternating current in an electrical circuit while passing signals of much lower frequency and direct current by having an impedance largely determined by reactance, which...
can be made by winding some turns of the power and transducer leads through a suitable ferrite ring
Ferrite bead
A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits. It is a specific type of electronic choke. Ferrite beads employ the mechanism of high dissipation of high frequency currents in a ferrite to build high frequency noise suppression devices...
(see Toroidal inductors and transformers
Toroidal inductors and transformers
Toroidal inductors and transformers are electronic components, typically consisting of a circular ring-shaped magnetic core of iron powder, ferrite, or other material around which wire is coiled to make an inductor. Toroidal coils are used in a broad range of applications, such as high-frequency...
). Failing this, it may be necessary to de-power some of these other items during important radio reception times. One radio receiver that may be overlooked is the Navtex, if fitted. By tuning the HF rig down to its relevant frequencies (e.g. 518 kHz) it may be possible to identify sources of interference that are limiting its range, and switch them off or improve their EMC characteristics. Once this is done and these frequencies are quiet, far from land it is surprising what range Navtex can achieve, especially at night.
See also
- Amateur radioAmateur radioAmateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
- Marine and mobile radio telephonyMarine and mobile radio telephonyThe Marine Radiotelephone Service or HF ship-to-shore operates on shortwave radio frequencies, using single-sideband modulation. The usual method is that a ship calls a shore station, and the shore station's marine operator connects the caller to the public switched telephone network...
- Satellite Internet accessSatellite Internet accessSatellite Internet access is Internet access provided through satellites. The service can be provided to users world-wide through low Earth orbit satellites. Geostationary satellites can offer higher data speeds, but their signals can not reach some polar regions of the world...