A Marine VHF radio is installed on all large ships and most motorized small craft. It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours and marinas, and operates in the VHF frequency range, between 156 to 174 MHz. Although it is widely used for collision avoidance, its use for this purpose is contentious and is strongly discouraged by some countries, including the UK. [1]
A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as channels. Channel 16 (156.8 MHz) is the international calling and distress channel. Channel 9 can also be used in some places as a secondary call and distress channel. Transmission power ranges between 1 and 25 watts, giving a maximum range of up to about 60 nautical miles (111 km) between aerials mounted on tall ships and hills, and 5 nautical miles (9 km) between aerials mounted on small boats at sea-level. [2] Frequency modulation is used.
Marine VHF radios mostly uses "simplex" transmission, where communication can only take place in one direction at a time. A transmit button on the set or microphone determines whether it is operating as a transmitter or a receiver. The majority of channels, however, are set aside for "duplex" transmissions channels where communication can take place in both directions simultaneously [3]. Each duplex channel has two frequency assignments. This is mainly because, in the days before mobile phones and satcomms became widespread, the duplex channels could be used to place calls on the public telephone system for a fee via a marine operator. This facility is still available in some areas, though its use has largely died out. In US waters, Marine VHF radios can also receive weather radio broadcasts, where they are available, on receive-only channels wx1, wx2, etc.
Marine radios can be "voice-only" or can include "Digital Selective Calling".
Voice-only equipment is the traditional type, which relies totally on the human voice for calling and communicating. A VHF set and a VHF channel 70 DSC set, the DSC on top, both produced by Sailor A VHF set and a VHF channel 70 DSC set, the DSC on top, both produced by Sailor
Digital Selective Calling equipment, a part of GMDSS, provides all the functionality of voice-only equipment and, additionally, allows several other features:
* a transmitter can call a receiver automatically using Digital Selective Calling on Channel 70, using a telephone-type number known as a Maritime Mobile Service Identity or MMSI * a distress button, which automatically sends a digital distress signal identifying the calling vessel and the nature of the emergency * a connection to a GPS receiver allowing the digital distress message to contain the distressed vessel's position
The MMSI is a nine digit number identifying a VHF set or group of sets. The left hand digits of MMSI indicate the country and type of station. For example, here are MMSI prefixes of four station types:
* Ship : 23 is the United Kingdom – e.g. a UK ship : 232003556 * Coast : 00 – e.g. Solent Coastguard : 002320011 * Group of stations : 0 – e.g. 023207823 * Portable DSC equipment : for UK 2359 - e.g. 235900498
The accepted conventions for use of marine radio are collectively termed "proper operating procedure." These conventions include:
* Listening for 2 minutes before transmitting * Using Channel 16 only to establish communication (if necessary) and then switch to a different channel * using a set of international "calling" procedures such as the "Mayday" distress call, the "Pan-pan" urgency call and Securité navigational hazard call. * using "pro-words" based on the English language such as Acknowledge, All after, All before, All stations, Confirm, Correct, Correction, In figures, In letters, Over, Out, Radio check, Read back, Received, Repeat, Say again, Spell, Standby, Station calling, This is, Wait, Word after, Word before, Wrong * using the NATO phonetic alphabet: Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliet, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu * using a phonetic numbering system based on the English language: Wun, Too, Tree, Fow-er, Fife, Six, Sev-en, Ait, Nin-er, Zero, Decimal
Marine VHF radio is sometimes illegally operated inland. Since enforcement is often the job of the local coast guard, enforcement away from the water is sometimes difficult.
What do you mean when you say a Xantrex inverter produces modified sine wave output?
The AC output waveform for many Xantrex Technology Inc. inverters is called a quasi-sine wave or a modified sine wave (MSW). It is a stepped waveform that is designed to have characteristics similar to the sine wave shape of utility power. A waveform of this type is suitable for most AC loads, including linear and switching power supplies used in electronic equipment, transformers, and motors. The modified sine wave produced by the inverter is designed to have RMS (root mean square) voltage of 115 volts, the same as standard household power.
What are the practical differences between modified sine wave (MSW) and true sine wave (TSW) output?
Most AC products run fine on MSW inverters. TSW inverters are about two to three times as expensive per watt due to having more sophisticated design and manufacturing requirements, and more expensive components. As a result, most people prefer to use MSW inverters if their applications allow it. Xantrex Technology Inc. does not guarantee that your AC application will work with an MSW inverter, and they advise our customers to check with the manufacturer of your AC device as to whether or not it will run with a Xantrex MSW inverter or whether you should purchase a Xantrex TSW product for your application.
Can I turn an MSW inverter into a TSW inverter?
If you have an MSW inverter and suspect you need a TSW inverter, please note there is no ‘filter’ or ‘retrofit’ you can apply to the output of an MSW inverter to ‘clean up the output’ or ‘turn it into TSW’.
Here are a few pointers about which kind of inverter to use:
In general, any device that senses either voltage peaks or zero crossings could have problems when running from MSW. Devices such as these should be run from TSW inverters. Ham radio and CB radio operators may notice RF noise from MSW inverters; in that case do not run the radio and the inverter at the same time. Electronics that modulate RF (radio frequency) signals on the AC line will not work and may be damaged. You may notice hum or buzz in the audio of TV’s, radios and satellite systems used with MSW inverters. Audiophiles or professionals using sophisticated audio, remote measurement, surveillance or telemetry equipment should use TSW.
Examples of problem devices are motor speed controllers employing triacs, and some small battery rechargers that do not incorporate a transformer between the utility power and the load. To help you visualize this, if there isn’t a ‘wall wart’ between the battery charger (or the battery in the device) and the AC plug, don’t use MSW.
Please note two other common problem loads, electric shavers and emergency flashlights. Both of these items have batteries in them but connect directly into the wall to charge, without an external transformer. Don’t use items like these with an MSW inverter. If you do use an MSW inverter with a transformer-less charger, your product will likely be damaged. Garage door openers, laser printers and large strobes used in photography have all been reported as trouble loads for MSW inverters; they either don’t work at all or stop working entirely, so don’t take a chance – use TSW.
As a general rule, products operating through an AC adapter will work fine from an MSW inverter. These include laptops and cell phone chargers, video games, camcorder and digital camera chargers. Televisions generally work well; some VCR’s with inexpensive power supplies run poorly. Consider switching to another brand of VCR in that case. A potential solution for RV’ers or off-grid cottagers is to purchase our smallest TSW inverter (such as the RS400) to run TV, VCR and audio equipment, and a larger MSW inverter (such as the XPower 1750 Plus) for the coffee maker, hair dryer and microwave.
Xantrex Technology Inc. customers frequently ask about the use of inverters for medical equipment. Unless specifically noted in the regulatory approvals for the product, assume that no Xantrex inverter has regulatory approval for use with medical devices or life support equipment. If you use a Xantrex Technology Inc. inverter with a medical device it’s at your own risk; this is also stated in the warranty for the products.
A: Sonar works much like marine radar, only in water rather than air. The transducer emits a pulse of sound energy in a direction which the operator sets, and then waits for a return of sound energy bounced off objects in its path. The electronics convert these signals into images which are then viewed by the operator. Various factors affect signal propagation through the water and the shape and density of the targets dictate how well the signals are reflected back. The harder the target, and the more nearly vertical it is, the better it reflects energy. The converse is also true. So targets which are angled away from you produce poor returns. Just like with marine radar there is a learning curve with sonar. What we know now, after just a few hours of practice, is that the basic system is quite user friendly. It looks like we are already operating at a level which gives us good functionality maybe 75% of the time. Getting to where we can efficiently use the system in difficult conditions is going to take some real world practice - just as with marine radar.
Question: I would like to set up my ICOM M604 VHFmarine radio as a land base station. Which radios can set this way and how do I code the MMSI number?
Answer: The ICOM M604 VHF Marine radio can be set as a land base station. You can set the MMSI number to recognize this by coding the prefix of the number with "00".
In the November issue of QST, a reviewer commented, there was one minor issue operating the IC-2820H. This was an issue with the UHF in DV not being repeated 100% of the time. While there are a few people who have reported having this issue, it is not a wide spread problem. This is more of an idiosyncrasy of the radio and most operators would never notice if they operate the radio in a more traditional VHF on the left and UHF on the right. As announced further in the article, there is a modification available to the radio.
In addition to the issue listed above, there have been some reports of dropped communications where the radio will not transmit when the PTT is pressed on the microphone. From what we have seen, this is an intermittent issue which not everyone has or will experience. We have a firmware update that fixes this issue as well.
As these are not field installable updates, your IC-2820H’s will need to come back to the ICOM America Service department located in Bellevue, WA. These will be handled on a first come, first served basis.
Upgrade Procedure:
This will be handled as a warranty repair. Send your IC-2820H to the following: (RMA not required)
ICOM America, Inc. Attn: Service Department (2820H upgrade) 2380 116th Ave NE Bellevue, WA 98004
Icom does not recommend a specific manufacturer of GPS equipment. However, most GPS equipment that meets the NMEA 0183 standard, Version 2.0 or better, will work with ICOM VHF radios. This NMEA standard uses the following 3-letter sentences:
GGA= Essential fix data with 3D location and accuracy (preferred sentence) This includes Lat / Long, fix quality, number of satellites, horizontal dilution of position, altitude above sea level, height of geoid (mean sea level), time in seconds since last DGPS update, DGPS ID, and checksum data.
GLL= Geographic position, Lat / Long This includes Lat / Long position, time of fix, data active or V (void) and checksum data.
RMC= NMEA recommended minimum This includes time of fix, active or void, Lat / Long, speed over ground, track angle, date, magnetic variation, and checksum data.
Q-Why do cell antennas need to be installed vertically or horizontally? Does it make a difference in performance if an antenna is not installed properly?
A-There are three types of polarization for all transmitted RF energy (cell signals) - vertical, horizontal and circular.
The type of polarization is dictated by the transmitting antenna; virtually all cell towers use vertical dipoles. This is why we specify that all Digital Antenna omni-directional antennas must be vertically positioned.
All cellular signals are vertically polarized. However, over distance they do rotate in space, at least theoretically.
The cell tower sends the cell signal in a vertical pattern. Because the actual path of the signal from the cell tower to the outside antenna can vary, including multiple bounces and reflections between the tower and the antenna, it would be impossible to know the exact relation of the polarization being received.
An antenna should be installed with the proper polarization according to the instructions. In general, the signal should improve with proper polarization since microwave (cell) signals are very sensitive to it.
Q-How do I know which size trim tabs to purchase for my boat?
A-Many factors affect the choice of properly sized trim tabs, and the ultimate responsibility for selection is up to the boat owner. These sizing recommendations are based on average performance. Your choice may vary based on power, engine configuration, weight distribution, type of boat, and use. When making a choice between trim tab sizes, remember that the largest trim tabs that will comfortably fit on the transom will be the most efficient. For complete information see article on trim tab sizing.
Q- I work on an oil platform and I am being required to use an intrinsically safe VHF radio. Can you provide more information?
A- Intrinsically safe radios are VHF radios that use use low capacitance components, special board layout and encapsulation techniques to prevent sparks in hazardous environments. The main uses of this special type of VHF radio are in industries such as oil and gas, chemical production, ignitable fibers such as insulation or filters, and even in ares that the air may be saturated with dust particles such as coal mines or a flour factory. Read more
