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Icom M802 HF Marine Radio WITH DSC IC-M802 (DSC Version) 1 Year Warranty

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Icom M802 HF Marine Radio WITH DSC IC-M802 (DSC Version) 1 Year Warranty

Product Information

The latest ICOM Digital Signal Processor technology with a compact remote head

Standard 4×8 remote controller

The IC-M802 offers an industry-standard 4-inch tall (10.16 cm) remote controller. When set up with the IC-M502 VHF radio, Icom offers you a complete communications station.

Large LCD with dot matrix characters

You can easily read the alphanumeric name of any of the 1355 ITU channels at a glance with the large LCD display. Nighttime operation is no problem with 10 levels (plus OFF) adjustable backlit display and keypad.

Easy to use in all conditions

The IC-M802 offers two large dials – bank and channel – for easy channel selection. Up to 16 banks of 20 (max.) each for user channels, and 17 banks for ITU channels are available.

Built-in digital selective calling

For added safety at sea, the IC-M802 offers the latest in one-touch DSC emergency communications technology. (ITU Class E standard.) The emergency button is covered by a red, spring loaded hatch to avoid accidental DSC activation.

Digital signal processor advantage

The speech compressor, utilizing DSP, increases average talk power. Flexible filter settings provide for narrow band signals like e-mail, SITOR, FSK and other operation without an optional filter.

150W (PEP) of powerful output

150 Watts of power offers superior worldwide communications. A one piece, die cast aluminum chassis and a large cooling fan allow continuous transmission at full output power– very important for data communications, like e-mail.

One-touch e-mail access

An SSB first! The IC-M802 can be set to memorize your HF e-mail access frequency, mode and bandwidth settings. At sea e-mail has never been easier.
* Please consult with an HF e-mail provider for details.

Automatic antenna tuner, AT-140

An optional automatic antenna tuner, AT-140, easily connects to the IC-M802. When the tuner cannot tune the antenna, the IC-M802 bypasses the tuner and displays a warning indicator on the LCD.

Other features

  • Wide band receive coverage (0.5 – 29.9999MHz)
  • Remote control mic allows you to select channels directly
  • Accessory RS-232C port allows connection of modem, etc.
  • GPS input, NMEA 0183 version 3.01
  • A headphone jack in front of the controller


The Icom M802 comes preprogrammed with both Marine SSB and Ham/amateur Radio frequencies. The M802's flexible three-piece design makes it easy to install: mount the separate control head & speaker at your nav/helm station where space is scarce, and squirrel-away the main radio unit in a more seldom used locker or cubby hole up to 16-feet (5 metres) away. Both the control head and speaker have a generously wide bezel, making a professional-looking "flush mount" installation a snap, even for skippers who aren't expert wood workers (requires optional MB-75 flush Mount Kit). 

  Available for Export






Programming the Icom-M802, & the Open Ham/Dial Mode

The Icom M802 has two modes of operation - "Marine" which is the default and "Open".

The radio is much easier to program in "Open" mode and thus it is recommended that the radio be put into "open" mode before programming is comenced.

"Open" mode is also advantageous as it also enables the radio to operate on lower side band (SSB), on other HF frequencies such as ham radio and also makes for easier manual tuning - ie like your AM / FM radio that you probably have in your car.

The CLAR/RX key toggles the radio back-and-forth between the Marine Mode and the Open Mode.

To determine if the Open Mode on your M802 is enabled press the CLAR/RX key on the keypad. If enabled, the LCD display will change, displaying frequency information with a cursor beneath the rightmost digit.  If the display does not change or there's no cursor beneath the displayed frequency, the Open Mode is not enabled.

Here's how to put the radio into the Open Mode and set frequencies:



Dial Display Change


Put the radio into the OPEN mode.

With the radio turned off hold down the 2, mode, and TX keys at the same time, and turn the radio on.

Normal dial display. The M802 doesn't indicate if its in the open/Dial mode or closed mode.


Select tuning capabilities

Press the CLAR/RX button. If the radio is in the Open/Dial Mode an arrow pointing right will appear next to the RX on the top line of the LCD display. The channel label will be replaced with the stored frequency and mode, and a cursor (underline) will be under one of the numbers. If the sideways arrow to the right of RX does not appear the radio is in the "closed" mode. Repeat step 1 above.



Dialing-in the Frequency

Turn the left knob until the cursor is under the number in the column you want to change (ie we have moved the cursor from the far right column to the far left column in our example)



Dialing-in the Frequency

Turn the right knob left or right until the desired number in the selected column is displayed (ie - we have changed the 8 now to a 14 in our example)



Dialing-in the Frequency

Turn the left knob clockwise to move the cursor to the next column you want to change (in this example the 100KHz column).



Dialing-in the Frequency

Turn the right knob left or right until the desired number in the selected column displayed in the 100 KHz column (in this example 3).



Dialing-in the Frequency

Turn the left knob clockwise to move the cursor to the next column you want to change (in this example the 10KHz column).



Dialing-in the Frequency

Turn the right knob left or right until the desired number in the selected column displayed in the 10 KHz column (in this example 1).



Dialing-in the Frequency

Turn the left knob clockwise to move the cursor to the next column you want to change (in this example the 1KHz column).



Dialing-in the Frequency

Turn the right knob left or right until the desired number in the selected column is displayed in the 1 KHz column (in this example 3).



Store the new Transmit & receive  frequency

Press and hold the ENT key. When the little right pointing arrow  disappears, the LCD display reverts back to showing the channel label, and SIMP is displayed on the top line, the new frequency and mode has been set. In this example the radio will transmit and receive on 14.313 MHz.

The "SIMP" displayed on the first line of the LCD indicates the transmit and receive frequencies are the same.



Press the FREQ/CH key to toggle between the channel and frequency mode.



Note: It is not necessary to set each column individually. Put the cursor under any of the columns and rotate the right-hand knob, tuning the radio as you would a regular AM / FM radio. Remember, the farther to the right a column is located, the finer the tuning increment.


Programming Simplex Frequencies into the User Channel Group



What's  Happening


Press the Freq/CH button to put the M-802 into the Channel Mode if necessary.

With each press of the CH/Freq button the LCD display will toggle back and forth, displaying the selected radio channel, and with the next press displaying the frequency stored in that radio channel.


Select the channel you wish to program by turning the large right-hand knob (channel selector knob)

The channel selector knob selects channels within a Channel Group.


Press the CLAR/RX button

The small right pointing will appear next to the RX on the top line of the LCD display. The channel label will be replaced with the stored frequency and mode, and a cursor (underline) will be under one of the numbers


Enter the desired frequency using the keypad, or dial it in using the two large front panel knobs.

You are entering a new receive & transmit frequency.


Press and hold the ENT key. When the small right pointing arrow disappears, the LCD display reverts back to showing the channel label, and SIMP is displayed on the top line, the new frequency and mode has been set.

Stores the new RX & TX frequency and mode for this radio channel into the M-802's permanent memory.


Programming Duplex Frequencies into the User Channel Group



What's  Happening


Store the receive frequency following the instructions for programming a simplex frequency described above.

Writes the receive frequency into memory.


Press the TX key

LCD displays changes to the frequency mode and TX flashes.


Enter the new transmit frequency using the keypad, or knobs.



Press and hold the ENT key.

Writes the new transmit frequency into memory. The LCD display reverts back to showing the channel label and DUP replaces SMIP.

Adding Names/Labels to Your Channels



What's  Happening


Press the Freq/CH button to put the M-802 into the Channel Mode if necessary.

Put the M-802 into the Channel Mode.


Press the "F" (Function button)

Enable the function mode.


Press the Freq/CH

The LCD dial display will show a line of character positions.


Rotate the right-hand Channel Selector knob to select the first character position.

Rotating the channel selector knob selects the character position where you want to enter a letter or number.


Using the keypad, enter the desired character.

Use the "1" key for Q, Z, q, z, and space, the "0" key for 0, and symbols + - = / ( ) * < > and @


Rotate the right-hand Channel Selector knob to select the next character position.


Using the keypad, enter the next character.



Continue with steps 6 - 7 until you have either completed the channel label, or all eight positions are filled.

The maximum channel label size is eight characters.


Press ENT when finished.

Stores the newly entered channel label into the radio's permanent memory.

ICOM IC-M802 - What is Digital Selective Calling (DSC)

By Chuck Husick
Published: December, 2002

ICOM's new IC—M802 is one of the first examples of a new generation of single sideband radio using Digital Selective Calling technology. It combines a DSC controller and a dedicated scanning DSC distress watch receiver with the company's well-regarded transceiver technology in a package designed for yachts and small commercial vessels. The superior range of a DSC SSB radio over a VHF to summon aid in an emergency makes it a must-have on any well-equipped ocean-going yacht.

DSC is an integral part of the Global Maritime Distress and Safety System. It automates the emergency calling process and ensures that all DSC-equipped radios within range will announce the receipt of an emergency or urgency call. DSC calling also facilitates routine communication with other vessels.

During an emergency, depressing the radio's Distress button for five seconds sends a call for assistance. This transmission contains the vessel's unique maritime mobile service identification number, the nature of the distress (undesignated, fire/explosion, flooding, collision, grounding, capsizing, sinking, disabled/adrift, abandoning ship, piracy attack, man overboard or epirb emission), the vessel's position (from a GPS interface) and the time of transmission.

Under the provisions of the GMDSS, coast stations, large ships and most commercial vessels on the high seas are equipped with DSC-capable VHF and SSB radios. Your chances of communicating with another vessel in an emergency or for routine business will be greatly enhanced if your vessel can send a DSC call that will "ring their bell by triggering the ship's DSC-watch receiver.

The basic technical specifications of the IC-M802 are typical for a radio of this class. The digitally tuned receiver covers the frequency range from 0.5 to 29.999 MHz for AM and SSB signals. The transmitter operates on all of the marine bands from 1.6 to 27.5 MHz at your choice of 150, 60 or 20 watts peak envelope power. The radio's extensive memory greatly simplifies the process of selecting frequencies/channels, e-mail operations and direct calls to stations identified by their MMSI numbers or names. The memory stores 242 SSB duplex channels, 72 SSB simplex, 662 FSK duplex, plus 160 user-programmable channel memory locations. In the set we tested, 134 of the 160 channels had been previously programmed for public correspondence, ship-to-ship frequencies, a number of ham nets and other services.

In addition to storing the main frequencies, the radio stores a maximum of 100 vessel/station names, MMSIs, plus transmit and receive frequencies. It can store as Call Frequency, Traffic Frequency or Scan Frequency a maximum of 50 frequency pairs. You may select for automatic continuous scanning up to six of the stored Scan frequencies. The radio's intermediate frequency amplifier passband and the FSK mark and shift frequencies and FSK polarity are easily set from the display screen.

A modem (compatible with the user's e-mail service) and a computer plug into the main receive/transmit unit. The user selects e-mail frequencies stored in the 160-capacity user memory by pressing the front panel e-mail button followed by use of the radio's group and channel selector knobs. The IC-M802 offers a narrow-band direct printing or fax system as an alternative to e-mail.

Unlike a VHF with DSC, which employs a single receiver for channel 70 DSC watch and regular communication channels, an SSB with DSC must have two separate receivers. One receiver is used for normal communication. The other, connected to its own antenna, is dedicated to monitoring the DSC distress frequencies. The receive-only antenna can be a relatively short vertical whip and does not require an antenna coupler or tuner.

Although yachts and other voluntarily equipped vessels are not legally required to maintain a constant listening watch on their SSB radios, doing so is part of good seamanship. Maintaining a watch with a DSC-equipped radio does not require listening to the radio's speaker. Any DSC emergency, urgency, all-ships call or call addressed to your vessel's MMSI will be announced by an alarm or alert tone. Information about the incoming call will appear on the radio's display screen, and all of the information contained in the distress call will be logged. Receipt of a distress call will automatically tune the communication receiver and the transmitter to the international voice-distress communication frequency, 2182.0 kHz.

Digital encoding for all distress calls provides advantages beyond eliminating the need to monitor the sound from the radio's speaker. When signal conditions are poor, the digital message is more likely to be received than a voice call. Incoming call information is placed in memory, simplifying the process of establishing voice contact with the calling station. Call categories, in addition to distress, include urgency calls ("Pan Pan), safety calls ("Securite), calls to stations within a geographic area you designate, calls to any station in listening range (all-ships calls), and routine calls to individual ships or shore stations addressed by their MMSI number.

Routine DSC calls to other vessels are sent using simplex frequencies agreed to beforehand by the vessels involved. Vessels traveling together can use group calling to exchange information throughout the flotilla. Send a position request call to a cooperating vessel, and its DSC radio will automatically and silently send you its position information.

You may transmit on any one of six DSC distress frequencies or in sequence on all of them, and the call automatically repeats at intervals of 31/2 to 41/2 minutes until another vessel answers or the vessel in distress cancels. An easily accessed on-screen menu is used to program the content of the distress call.

Operating an SSB DSC radio transceiver to the full extent of its capabilities can be challenging. Vessels required to have such equipment must carry crew who have undergone special training. In the face of the IC-M802's necessary complexity, ICOM has done a commendable job of making it easy to use, especially in an emergency when a person unfamiliar with the equipment may have to send a distress message.

The radio is controlled with three rotary controls: volume, frequency group and frequency channel selection; a 15-button keypad; and eight push buttons. Making optimum use of the radio's many functions requires considerable study of the instruction manual, followed by some hours of practice.

All DSC transceivers, including the IC-M802, must always be connected to a GPS receiver to ensure that your vessel's position information is sent as a part of any distress call. (Position information can be entered manually in the event the GPS fails.) Position information is also used in routine communications, including position reporting and when making or responding to a geographic call.

Connecting a headset to the jack on the control unit's front panel cuts off the speaker. Anyone accustomed to using a combination headset/boom mike when piloting an aircraft will quickly figure out how to make one work with this radio. Keeping both hands free while communicating can be a real plus when taking notes or when the sea gets up.

Every yachtsman doesn't need an SSB with or without DSC, but anyone who ventures offshore would be wise to consider the IC-M802 as a supplement to a DSC VHF—for safety's sake. Price: $3,200, radio only.


What Antenna should I use for my M802 DSC receiver???

In order to receive DSC signals with the M-802, you must have the DSC-receive antenna connected. This is the only way that the radio will be able to receive DSC signals since it is a class D DSC radio.

As the DSC antenna is only used for receive its performance / set-up is nowhere near as critical as your primary HF transmitting  antenna (ie a tuner or coupler is not required).

You can use a Metz weatherfax antenna or any HF whip antenna to connect to the receive port. You cannot use your VHF receiving DSC antenna

Without the DSC receiving antenna, you will still be able to transmit a distress call (this is transmitted via your primary backstay or whip antenna), however, the radio will never hear an acknowledgement nor would you be able to hear someone else in distress and come to their aid.



Frequency coverage



(unit: MHz)
0.5– 29.9999 (continuous)

1.6– 2.9999, 4.0– 4.9999, 6.0– 6.9999

8.0– 8.9999, 12.0– 13.9999, 16.0– 17.9999

18.0– 19.9999, 22.0– 22.9999, 25.0– 27.5000

Type of emission

J3E (SSB), J2B (AFSK), F1B
(FSK), A1A (CW), H3E (AM*)

*Rx only

Number of channels 1355 (max.)
(160 programmable channels; 249 ITU SSB duplex; 72 ITU
SSB simplex; 662 ITU FSK duplex; 160 e-mail; 21 ITU
4MHz simplex; 31 ITU 8MHz simplex)
Antenna impedance 50Ω (SO-239)
Power supply requirement 13.6V DC ±15%

Max. current drain

(at 13.6V DC)

Tx (Max. power) 30A (typ.)

Rx (Max. audio) 3.0A

Operating temp. range
Guaranteed range

–30°C to +60°C; –22°F to +140°F

–20°C to +55°C; –4°F to +131°F

Frequency stability ±10Hz (at –20°C to +55°C)


Main unit

240×94×238.4mm; 9716×31116×938in
220×110×84.4mm; 82132×41132×3516in
110×110×84.4mm; 41132×41132×3516in

Main unit

4.7kg; 10.36lb
570g; 1.26lb
370g; 0.81lb
Output power 150, 60, 20W PEP (Selectable)
Spurious emissions –62dB
Unwanted sideband 55dB
Carrier suppression 40dB
Microphone impedance 2.4kΩ

Sensitivity (at 10dB S/N)

  J3E, A1A J2B, F1B H3E DSC (J2B)
0.5 – 1.5999MHz 6.3µV 32µV 0.5µV
(at 1% error rate)
1.6 – 1.7999MHz 0.89µV 0.89µV 6.3µV
1.8 – 3.9999MHz 0.5µV 0.5µV 3.2µV
4.0 –29.9999MHz  

Spurious response

rejection ratio

Tx/Rx (1.5-29.9999MHz) More than 70dB
DSC (Except 1st IF image) More than 50dB
DSC (1st IF image) More than 60dB
Audio output power 4.0W at 10% distortion with a 4Ω load
Audio output impedance: 4–8Ω
Clarity variable range ±150Hz
GPS interface NMEA 0183 version 3.01

All stated specifications are subject to change without notice or obligation.

Supplied accessories

  • Separation cable, OPC-1106 (5m; 16.4ft)
  • Hand microphone, HM-135
  • External speaker, SP-24
  • Mounting bracket kits
  • Microphone hanger
  • DC power cables
  • ACC plugs
  • Spare fuse

System Overview

System Overview


Solving RF Interference Problems


Radio transmitters have a great fondness for causing interference. This is not surprising, since their primary job is to pump 100 watts or more of radio energy into the sky. Ideally all of this energy would be sent off towards the distant receiver, but this is not the case. Antennas, particularly small ones, radiate in all directions, and worse yet, any imbalance in the antenna system causes the coax cable, power wires, and every other interconnection to becme part of the antenna system and radiate also. In the days before digital communications this was a nuisance at worse, but when modems and computers get interconnected with transmitters and radios the potential for chaos is great. This is especially problematic for small installations such as boats and RV's where the antenna and ground system literally wrap around the radio and other components.

With respect to HF email, there are two primary symptoms that can be traced to wayward RF energy: distortion of the transmitted audio signal, and data errors between the computer and modem. The distortion problem is subtle because you will rarely hear it yourself. But if your transmitted signal gets back into the audio connection between the modem and transmitter, then it can be rectified and produce its own audio signal, which will be transmitted and produce more interference, etc.. It is very much like the "howl" that emits from a public-address system when the gain is turned up too high, noise feeding upon itself.

Data errors can occur in the modem's serial-port connection. These will usually be detected by the error checking associated with binary modes but it will not be at all obvious that RF is to blame. And if ASCII mode is used then the errors may simply be missed. Errors can happen either sending or receiving messages. If sending, then errors are likely at the beginning of the message transmission, as the computer is busy sending data to the controller's buffer memory at the same time that the controller is sending the beginning of the message over the radio. When receiving a message, the incoming data is usually being transferred to the computer at the same time that the controller is transmitting the "Ack" (Acknowledge) burst back to the sending station. In either case there are serial data transfers happening at the same time that the radio is transmitting digital data.

If an ASCII transmission is in progress then the usual symptom is that characters are lost from the message. Given the general lack of attention paid to spelling these days, such errors usually go unnoticed. If a binary transfer is in progress then a format or checksum error generally occurs because the binary protocol includes error checking. If an error is detected then an error message is sent and a disconnect occurs. Errors of this type are almost always related to RF interference related to ground system problems.

Airmail logs incoming serial-port errors in its Logfile.txt file, located in the c:\program files\airmail\ folder. Open this file and look for something resembling "comm: Error reported to input: 2", this indicates a framing error detected by airmail's serial-input driver. This may also correlate to a disconnect due to a binary format or checksum error. Note that errors in outgoing data would be detected by the controller and not by Airmail, and usually result in lost characters with no other indication of trouble. For the PTC-II controller, Airmail now uses CRC-Host mode which was developed for precisely this reason and which detects and corrects serial-port data errors. (There will be a "retry" entry in Airmail's log file).

Ground systems:

The usual marine antenna/ground system consists of an automatic tuner at the base of the backstay or stern-mounted vertical antenna, a grounding strap from the tuner to a ground system, and a coax cable to the transceiver which itself is usually grounded. Ideally all of the antenna current flows between the antenna wire and the seawater ground system through the tuner, and with a perfect ground system at the tuner then that is what would happen (see Fig. 1).

But grounds are never perfect, and even a ground connected to a large external metal keel has a ground strap of some length which can develop some resistance (impedance) at certain frequencies. If there were no other path then the impedance of the ground system wouldn't matter, but the radio itself is always grounded, either directly or via the DC power wiring, and the nice fat shield on the coax cable provides a good ground conductor. Note that the transmitted signal is balanced between the inner conductor and shield, this can be considered "inside" the coax caable and will not radiate. The stray ground path is on the shield alone, an unbalanced current, and will radiate. This is called a ground loop (see Fig. 2). Other loops are formed by the cables that connect the controller and computer, and their 12V power connections (which themselves are always grounded somewhere).

These ground loops have impedance just like any other wire, and DC wiring in particular makes a pretty poor ground conductor. RF antenna currents using these ground loops as alternative ground paths will radiate interference signals into other cables (just like an antenna) as well as by simple voltage drops due to the impedance of the ground loops themselves. These interference signals will raise havoc with everything.

It would seem attractive to simply beef up the ground system, i.e. reduce its impedance and make that path more attractive. This will certainly help and is a good first step, but it is equally important to make the unwanted paths less attractive.

The solution:

Changing frequencies will typically change the problem, making it better or worse depending on how the impedance of the various ground paths change with frequency. Reducing the output power will always reduce the interference, and is a definitive test to verify that the problem is RF-related (as long as there is enough power to maintain a good link). A permanent solution has three parts:

Make the primary ground system as good as possible;
Make the tuner-to-radio-to-ground path via the coax shield less attractive by using a ferrite "line isolator" add impedance to that loop;
and break up any additional ground loops between radio, controller and computer with clip-on ferrite chokes.

Task 1.

The first task is a careful review of the ground system connected to the tuner. The backstay or vertical antenna is only half of the antenna system, the other half being the ground system. Different frequencies will "see" the ground differently, so what works on one frequency band may not work well on another. Higher frequency signals (21-28 MHz) have a shorter wavelength and need a few square meters (tens of square feet) of metal surface located close to the tuner. Because the square-footage requirement is lower, a direct seawater connection is less important. Lower frequencies (7 to 10 MHz) have a longer wavelength and need more square footage of ground plane than can easily be provided, so a good seawater connection is required. This requires a few square feet of seawater contact but does not need to be as close as it would in order to be effective at high frequencies.

So the ideal ground system is a combination of a ground plane laid against the hull near the tuner, plus a connection to the engine, metal tanks, and any other large metal, and a connection to an external keel or other large underwater metal. These should all be interconnected with a network of 3-4" copper strap which will have a low impedance at all frequencies.

Consider electrolysis when connecting external metal parts (such as a through-hull or prop strut) to the ground system. You will never create a new problem by connecting underwater metal that are already connected to the green-wire DC bonding system, but connecting metal that was previously isolated can create a new electrolysis problem. If in doubt then provide a DC block. Stan Honey's method is simple and effective: cut a quarter-inch gap in the copper foil, and bridge that gap with a dozen ceramic disc capacitors (.01uF line-bypass caps would be a suitable choice). This blocks DC electrolysis currents while providing a low-impedance RF path for antenna currents.

Henry VE0ME, a Canadian ham of some considerable experience, favors an separate antenna ground with no connection to the rest of a vessel's ground system. In other words, run a ground strap from the tuner ground to a large underwater plate (such as the largest-sized Dynaplate), but do not connect this plate to the rest of the ship's ground system. Splitting the ground system this way would break up the major ground loop shown in fig. 2. The key to making this method work is providing a large enough ground plate for the isolated tuner ground, the smaller Dynaplates are not adequate. The disadvantages are those associated with grounding plates in general, drag unless the plate is set flush, and concerns about electrolysis.

For more information on grounding and electrolysis, see Stan Honey's excellent article in Practical Sailor, October 15, 1996 issue.

Task 2.

After we've done what we can with the ground, the second job is to make the alternative ground paths less attractive to the antenna currents. That is done by adding RF impedance to the coax, in the form of a Line Isolator (a large ferrite choke) or multiple clip-on ferrites. This adds impedance to unbalanced common-mode currents such as the ground currents using the shield as an RF path. The transmitter output to the tuner is a balanced signal, i.e. there are equal and opposite currents flowing in the shield and inner conductor). The net current from a balanced signal through the ferrite is zero, so there is no attenuation at all, i.e. zero impedance. But antenna currents using the shield as a ground path flow in one direction only and see the ferrite as an impedance (see Fig 3).

A typical line isolator is about 20 turns of RG-8X around a ferrite rod inside a plastic housing with a female coax connector on each end. Our favorite is the Radio Works model T-4 (ungrounded), about $30 from Radio Works ( which also has a good discussion of grounding techniques), or also available for a few extra dollars from Farallon Electronics ( or HF Radio in Alameda ( You will also need a male-male coax jumper to connect the line isolator to the tuner, as the line isolator comes with two female connectors. Clip-on ferrites will do the same job, but it would take a dozen or more to have the same effectiveness.

The best place to locate a line isolator is close to the tuner itself. In terms of ground currents it doesn't matter where it is located, but if the coax is long then it will still be able to radiate some signal if the line isolator is located at the radio end of the coax.

In addition to the line isolator on the tuner coax, one or more clip-on ferrites should also be added to the tuner control wires. These control signals are usually grounded to the tuner ground, and provide an alternative ground path if not blocked. An alternative to multiple ferrites is to use the large size and loop the wire through it a few times.

Adding a line isolator (and ferrites to the tuner control cable) should stop most of the ground currents from taking the detour through the "radio shack", but will not substitute for an adequate ground system. And of course never add any sort of ferrite choke to the ground connection itself. Many users have also reported that adding a line isolator also cleans up other problems such as autopilot interference, but that will depend on how the other equipment is configured.

Task 3.

Providing a good tuner ground and isolating the alternative coax path are the most important tasks, but while we are cleaning things up we should also break up the ground loops between the radio, controller and computer.

Isolating the ground loops is again done by adding common-mode impedance, in this case in the form of clip-on ferrites (see Fig 3 again). These are small split ferrite cylinders, about 3/4" in diameter, 1-1/4" long, with a 1/4" hole through the middle for a cable. Clip-on ferrites are sold by Radio Shack, but better ones are made by Fair-Rite, their part number for type-43 material in a 1/4" hole size is P/N 04-43-164-251 and available from Newark Electronics ( Fair-Rite's type-31 material performs a little better at HF radio frequencies, their part number is 04-31-164-281 for the 1/4" hole size, and 04-31-164-181 for the 1/2" hole size. The type-31 parts are not sold by Newark but are available with a $50 minimum from Amidon and stocked by many dealers.

Use one ferrite to each end of the computer-to-controller cable, and one at each end of the controller-to-radio cable. And don't forget the tuner cable as noted above. The signals inside the cable will not be effected, only the ground currents trying to use the cable shield as an "sneak" path.


Important: The ferrite halves must meet perfectly in order to be effective. If in doubt, remove the ferrite halves from their plastic housing and secure with tape and/or tie-wraps.

And also make sure that the cables are properly shielded, with the shield connected to the connector shell (and equipment chassis) at both ends. This can be verified with an ohmmeter, and if the metal shells of the DIN or DB-style rectangular connector at each end are connected, then the shield is terminated correctly.

Metal boats:

Steel or aluminum boats don't have a problem with the ground system, but aluminum boats in particular usually have isolated 12V neutral wiring to protect against electrolysis and are subject to significant interference problems. In some cases the problem seems to be much worse than with a fiberglass or wood boat, probably because any stray RF energy is trapped inside a shielded box (the hull), analogous to the proverbial "fox in the henhouse".

The steps outlined above should be equally effective with metal boats. The line isolator in particular should eliminate the stray RF at the source and would be the logical first step. If additional help is needed, the 12V negative connections to the computer, controller and radio can be RF-grounded using capacitors to provide a RF ground with DC blocking. Also provide a similar capacitively-coupled RF ground for the radio chassis. Ceramic-disc capacitors are a good choice for this duty, and a dozen 0.01 line-voltage type capacitors wired in parallel will provide an inexpensive and low-impedance path for HF frequencies.





Accessing weather information at sea

A range of services provide current weather information for mariners at sea. VHF radio is accessible from in-shore waters, HF radio for much greater distances off-shore, and the satellite 'Inmarsat C SafetyNET' services provide global access.

VHF voice radio

  • Where: In-shore.
  • What: Weather and maritime safety information.
  • Schedules: See providers.
  • Provider: State/territory government marine transport and safety agencies for most. Bureau, some QLD and WA
  • Details: VHF marine radio weather services 

HF voice radio & radiofax

  • Where: Off-shore
  • Details: HF marine radio weather services
  • Provider: Bureau for weather. Other agencies for distress and safety services
  • Voice
    • What: Warnings and forecasts
    • Schedules: Marine warnings are broadcast every hour, on the hour UTC. Forecasts and reports are broadcast on a fixed schedule repeated every four hours.
  • Fax
    • What: Warning summaries and charts
    • Schedules
    • How: Reception requires a marine fax unit attached to your HF radio such as our SCS pactor modem product (ask us for information)

Fax frequencies

VMC Fax frequencies (kHz):   Fax schedule
Fax broadcasts run on a 24 hour cycle. or by faxing 1902 93 5046 (call costs $1.38 per minute including GST, higher from mobile phones).
Fax schedule

Fax Schedule
Times are the local time (EST) at the transmitter.
Daytime (5am-7pm) 20469
Night-time (7pm-5am) 2628
Anytime 5100, 11030 and 13920
VMW Fax frequencies (kHz):
Times are the local time (WST) at the transmitter.
Daytime (5am-7pm) 18060
Night-time (7pm-5am) 5755
Anytime 7535, 10555 and 15615
Shipping Weight:  7.01

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