To fully explain the principals and operation of medium and high frequency radio (MF/HF-SSB) would take hundreds of pages and would go well beyond what the average maritime user is likely to need. However, a basic understanding of Medium Frequency (MF) and High Frequency (HF) Single Sideband (MF/HF-SSB) is an absolute must if you plan to communicate effectively. So here we will try to provide you with some of those basics and caution you that we are not providing answers to every possible factor or situation.
The Marine MF/HF-SSB radio is a combined transmitter and receiver much like your VHF. The primary difference between the two is the frequency ranges that they operate in. Typically Marine MF/HF-SSB radios operate in the frequency range of 1.6 MHz to 30 MHz. Probably, the most important concept here is that: "They allow the operator to select a frequency based on atmospheric conditions to establish communications over varying distances."
Unlike VHF which is typically a line of sight radio, MF/HF radios are able to refract their signals within the atmosphere providing increased range. This plays an important role in long distance ship to ship or ship to shore communications.
The #1 reason of course is SAFETY, but even routine long distance communications is still an important consideration. When your cruising ambitions or your job begin to take you further offshore, when you begin fishing the canyons, or making your first jump from the mainland to an offshore island; you will quickly realize that your tried and true VHF radio is no longer up to the job.
When the distances involved get out beyond 30 NM’s or so (depending on antenna heights,) the VHF marine radio is no longer adequate to provide either normal or emergency communications. In order to maintain this communications lifeline will now require the use of MF/HF radio or a satellite communications system.
The rapid advances in electronics that we have witnessed over the past 20 to 30 years, such as the changes we have seen in the personal computer, have also provided benefits in the manufacturing of radio communications equipment. Today the average boat owner can make use of HF world-wide communications systems that would be the envy of even the largest ships of yesteryear.
Along with the long range communications abilities of HF-SSB radio, these sets can be easily adapted to provide the user with a number of other services. Email, teletype, NAVTEX, and weather facsimile are among the many things that can be easily accessed. These services are easily set up by making use of a computer, some software, and a modem. Also many of the newer marine HF-SSB radios can be "Unlocked" allowing access to the amateur radio frequencies for those boaters who are also licensed amateur radio operators.
Unlike the marine VHF radio operating at frequencies between 150 and 160 MHz, (MF) and (HF) radios use lower frequencies (1.6 to 30 MHz.) These lower frequencies are a major factor in allowing HF radios to communicate over much longer distances. In fact, given the right conditions, worldwide communications are possible. Because of this and the relatively low cost, HF SSB is extremely popular for the blue water passagemaker and long distance or world cruiser.
The distance that one can reliably communicate depends on many factors. We are only going to mention a few of the most common:
As you will learn, many of these factors are tied directly to the sun and its effect on our planet’s atmosphere. This one thing alone, is probably the single most important factor in HF communication and that leads us into our next topic "Propagation."
To be able to communicate effectively and to achieve the full benefit from your HF radio, the MF/HF radio operator must have at least a basic understanding of radio wave propagation.
"Propagation" is the reason that HF radios can communicate at longer distances. Simply put, propagation is the refraction/reflection of radio waves by the different layers of the ionosphere. There are 3 types of propagation by HF radio and all are propagated simultaneously. They are Ground Waves, Direct Waves, and Sky Waves. We will take a closer look at 2 of these types of propagation that are of major importance to the mariner:
Radio wave propagation is probably the cause of most headaches for the new HF radio operator. Many do not understand when using a frequency that is capable of communicating at 4000 NM, why they can’t talk to the Coast Guard only 250 NM away. The simple answer: with the higher frequencies needed for long range communications, the ground wave may not reach the station and the sky wave may pass right over it.
The illustration below may help in visualizing this. Any station within the skip zone will likely never hear your broadcast.
The basic rule when using HF radio, is to know how far (approximately) you are trying to communicate. Once that distance is known then it is a simply a matter of selecting an appropriate frequency.
Some rules of thumb on frequency selection:
While these are useful to keep in mind, you must remember that these are only general guidelines.
There are a number of computer programs and applications on the market to assist you in selecting the right frequency to use for communications. Some are even able to account for current solar phenomena in their calculations to improve their accuracy. The question is - are these necessary for the average marine HF radio user? Probably not.
There are also many tables, like the one below, available that can provide you with a starting point for selecting the proper frequency for communications. These tables should provide an acceptable starting point in selecting the correct frequency for any given communications distance.
|Marine MF/HF-SSB Sky Wave Propogation
|MF/HF Frequency Band
|Often Unpredictable or Unusable
|* 2 MHz is Ground Wave Coverage Only.
Remember, the sky wave ranges shown above are approximate only. They may vary considerably due to atmospheric conditions. Unlike VHF, the HF ranges listed do not mean that you can communicate to anyone out to that range, instead;
It indicates the approximate ranges that you can communicate AT!
If you are trying to communicate with someone 400 NM's away on a 16 MHz frequency it is highly unlikely that you will succeed. Your ground wave signal will never reach them and your sky wave will likely skip right over them.
Simply multiply the Frequency Band (2, 4, 6, 8 MHz, etc.) times 100 to arrive at the average range for that frequency band.
If trying to contact either a shore station or ship station that is about 1500 NM away at 1400 LT. A good frequency to start for initial contact might be in the 16 MHz Band. (16)MHz * (100) = 1600 NM. You could then try the next frequency band below or above that to check for improved communications.
Finally a short explanation of some of the nomenclature you will be dealing with when using a marine HF-SSB.
"ITU Channels:" The International Telecommunications Union, has established a standardized list of paired frequencies for transmit and receive and assigned them channel designators. These ITU Channels use the same frequencies worldwide much like your VHF.
"Simplex:" Simplex is when the frequency you transmit and receive on are the same. An example would be when you transmit and receive on 2182.0 kHz.
"Duplex:" Is when you transmit on one frequency (say 8195.0 kHz) and you receive on a completely different frequency (say 8719.0 kHz.) This particular pairing of frequencies by the way is known as "ITU Channel 801."
As a general rule, ship to ship communications are carried out on simplex frequencies where both transmit and receive frequencies are the same. Duplex frequencies on the other hand are intended for use as ship to shore frequencies although simplex frequencies can also be used for this purpose.
A quick note about Upper Sideband (USB), Lower Sideband (LSB), and Amplitude Modulation (AM) as well as the A3J / A3A / A3H emission settings on your HF radio. As a practical matter with voice communications using Marine HF-SSB these settings can be left at "USB" and "A3J."
Most Marine HF-SSB radios come with a large selection of channels programmed into the radio so that it is ready to use out of the box. While many of these channels can be re-programmed, generally speaking the distress frequencies both voice and DSC are not re-programmable.
HF/SSB radios typically being more complex to operate than the typical VHF marine radio, most countries including the U.S. require that vessels operating MF/HF SSB radios must have a station license and the radio operator must also be licensed to operate them. See our Ship Station Licensing and Radio Operator Licensing pages for more details.
Training of some variety is highly recommended for the operator of HF-SSB radios. Whether you choose some type of formal training or self-instruction you will need a good grasp of HF radio procedures to be able to operate your MF/HF-Single Sideband Radio efficiently.