Still holding its own - HF Radio
Still holding its own - HF Radioby Jeff Williams A backstay makes an excellent antenna with an antenna tuner and insulators to keep it electrically isolated from the rest of the rig. If you’re thinking about that first offshore passage, you have to face the need for long-range communications equipment on board. Life is easy along the U.S. coast: VHF radios can talk to other boats and hear National Oceanic and Atmospheric Administration (NOAA) weather broadcasts, cell phones and smartphones keep you in shoreside contact and allow you to surf the Web, and most marinas offer Wi-Fi. But once out of sight of land, everything changes.
Offshore communications equipment can be classed as satellite-based or terrestrial-based. A fundamental truth is that compared to most terrestrial systems, satellite communications systems are more expensive to operate. With satellite communications — whether voice or data — you will pay by the minute or by the byte, on the order of $1.00 per minute or more. Additionally, satellite communications systems operate like telephones — they are used for point-to-point communications only.
In contrast, high frequency single-sideband (HF SSB) radios cost nothing to operate and they can be used for both station-to-station operations and for broadcast transmissions and reception. That means you can listen to local or regional “nets” of boats and weather situations as well as broadcasts of weather forecasts and radiofax charts. They are essential for distress situations, allowing contact with nearby ships and regional rescue centers. HF radios can — with additional equipment — also be used for sending and receiving e-mail.
Satellite communications offer certain advantages with their telephone-like operation, but they cannot deliver the casual boat-to-boat communications that are pervasive in the cruising community. Nor can they provide weather information as cost-effectively as HF radio.
HF radio continues to enjoy a dominant position in offshore communications within the cruising community. Cruisers that I’ve spoken with that have satellite but not HF radio equipment on board have lamented that decision. A good quality HF receiver should be considered the bare minimum for offshore work. A transceiver and antenna tuner are the preferred equipment. Adding an e-mail modem completes the communications suite.
| HF SSB units from Icom (top) and Furuno. |
Choosing the right equipment
Choosing the right HF radio is important for ensuring reliability and ease of use. Generally, radios used by cruisers are either commercial marine radios or ham radios. Looking at ham radios, you’ll find a broader range of manufacturers, features, cost, and capabilities, but unless you’re a licensed ham operator and really love fiddling with knobs and pushing buttons, it’s better to look at the commercial marine radios. Also, ham radios do not support digital selective calling (DSC), a growing requirement for marine applications. Hams, this doesn’t mean you can’t still operate on the ham bands. Most marine radios offer options that open the radios up to include the ham frequencies for licensed operators.
Within the recreational segment, the commercial marine radio market has been dominated by Icom and Furuno. Their radios have respected performance specifications and support e-mail operation. Lower quality radios may perform adequately for voice communications, but will not stand up to the higher demands of data communications.
You must also install a separate antenna tuner. Unlike VHF radios which operate over a narrow range of frequencies and thus can operate with an antenna permanently “tuned” to the VHF band, HF radios operate over wide frequencies and numerous bands requiring the antenna to be retuned with each frequency or channel change. The commercial marine radios mentioned above all have companion automatic antenna tuners available.
Most problems with HF radio operations can be traced to poor installation practices. With a good installation, however, HF radios will operate reliably and effectively; consistent, robust contacts at distances of 3,000 miles and more are routine for this equipment.
When installing the transceiver, it is important to have sufficiently sized power and return wires from your 12-volt distribution point. I emphasize return because many people forget that the negative side of the DC power connection carries just as much current as the positive side. And notice the use of the word return, not ground; do not use your ship’s bonding ground for negative return.
To choose the right wire size, use charts like those found in the West Marine Advisor on Marine Wire or Marinco’s technical information on Ancor wire. These are based on requirements set by the U.S. Coast Guard, ABYC, and associated national standards.
As an example, if you measure the distance from your power point to the transceiver as 10 feet, then you must use two times 10 feet (20 feet) as the length of the circuit (remember, power plus return). Refer to your owners manual and find the maximum current draw for the radio at full power. The Icom-802, for example, requires 30 amps. Using the West Marine table for 3 percent drop (not 10 percent drop), enter the table from the bottom on the 20-foot line. Go up the line until you read across to 30 amps. You will find you need AWG 6 wire size for this installation. Marinco provides the same information in a tabulated format.
Make sure that you have a sufficiently-sized circuit breaker for your transceiver as well. In this case, it must be at least 30 amps. Forty or 50 amps would be better to avoid unwanted trips when the radio is operating at its maximum output power. Keep in mind that circuit breakers are sized to the wire runs they are protecting based on the wires’ ampacity. From the Marinco information, the ampacity of AWG 6 wire is 102 amps, thus a 40- or 50-amp breaker is safe.
Use a high-grade marine wire — pre-tinned copper stranded wire is best. The tinned conductors resist corrosion much better than bare copper. In general, only stranded wire should be used on boats to resist stress fatigue due to vibration. It is much easier to work with as well. (For more good tips on wiring, see Harry Hungate’s Practical wiring in issue 200, March/April 2012.)
Terminals should be crimped and may be soldered as well. Crimping is preferred as it produces a solid mechanical bond. I prefer to both crimp and solder — the crimp provides the mechanical strength and the solder prevents moisture intrusion into the bond. Residue solder flux should be cleaned from the connector with alcohol. The crimp and insulation end should then be covered with a section of adhesive-lined heat shrink tubing. The heat shrink inhibits moisture, acts as a strain relief, and reduces flexing at the bonding point. It’s expensive, I know, but the alternative is less reliable electrical connections that you’ll have to diagnose at night in heavy seas during a gale.
While you’re in the neighborhood, check to be sure that the wiring from your batteries to your power distribution point is adequate to the task as well. If you’re working on a refit of an older boat, you may find that the wiring to the fuse or switch panel isn’t big enough to support the addition of an HF radio. You may need to make your connection closer to the batteries themselves.
The transceiver will also require a ground bond. We’ll come back to this later.
Antenna tuner installation
| The use of short pieces of PVC tubing to hold the antenna feed wire off the lower part of the backstay (just above Jeff and Raine Wiliams’ ship’s cat Carib). |
The antenna tuner is an essential part of your HF radio installation. Its function is to match the electrical properties of your antenna to the output of the radio at every frequency that you choose to operate on. Think of it like a camera lens — if it isn’t in focus, it’s not going to work. Without a tuner, you could easily damage your nice, new transceiver and other electronics on your boat. Regardless of its catalog descriptor, it is not an “option.”
Your HF antenna actually starts at the antenna tuner. Remember this: the wire connected to the antenna terminal on the tuner is part of the antenna. For this reason, correct location of the tuner is very important. You want to minimize the length of the wire and any bends in the run from the top of the tuner to your antenna proper. The tuner should be out of the weather, but close to any overhead through which the antenna wire will run.
To complicate things a bit more, coming out of the opposite end of the tuner is the connection to the counterpoise or RF ground. The length of these connections into the RF ground system also need to be minimized. It’s a balancing act to pick a good location, but give preference to optimizing the antenna lead run from the tuner to the antenna proper.
An antenna tuner basically has four connections: power and control from the transceiver, a coaxial connection carrying the radio signal to/from the transceiver, an antenna connection, and an RF ground (or counterpoise) connection.
The first two are relatively easy. The transceiver manufacturer will supply or sell a recommended cable for the power and control. They may also specify a maximum length for this.
The coaxial cable must be low loss, 50-ohm cable. Typically recommended cables are RG-8X and RG-8U, and these should be marine-grade with pre-tinned conductors. It’s a little tricky soldering coaxial connectors, so you may just want to purchase a good marine-grade cable of the length you need with connectors already installed. Don’t use multiple cables with additional connectors — each connector contributes to losses in both transmission and reception. Again, I would recommend adding adhesive-lined heat shrink or self-vulcanizing tape to the exposed end of the connector to reduce moisture intrusion.
Your HF radio antenna will probably be either a long fiberglass whip or an insulated section of standing rigging. If you are using a whip, you may have some flexibility in placing the antenna. Try to keep it several feet away from all other antennae. Remember your HF radio can put out 150 watts of power.
If you are using an insulated stay, a backstay is best — shrouds tend to be complicated to insulate because of their connections to spreaders and their radiating properties are compromised by being parallel to other shrouds and the mast itself. The upper insulator for the backstay should be four or five feet from the top of the stay; the lower insulator should be at or above eye level for safety. In any event, the length of the insulated wire should be at least 20 feet.
Use a good quality high-voltage wire, such as GTO-15, to run from the antenna to the tuner. Keep in mind this wire is part of your antenna: keep it away from other wires and antennae, run it as straight as possible, and don’t put any unnecessary kinks, bends, or loops in it.
Attach the wire to the upper wire terminal of the backstay insulator using a stainless steel hose clamp. Before you do this, strip back an inch of insulation from the GTO-15 and use a soldering iron to pre-tin the wire with additional solder. Clean the flux from the connection with alcohol, then use adhesive-lined heat shrink to seal the insulation end from water intrusion. This end is going to be out in the weather and pointing upward, so seal it well. Take a small piece of copper foil and fold it over the wire end to make a wire sandwich. Clamp this sandwich to the terminal and then wrap all with self-vulcanizing tape.
If you run the wire lead along the lower (uninsulated) section of the backstay, use short pieces of PVC pipe to make plastic standoffs about three inches long to hold the wire away from the stay. Loop cable ties through the PVC and around both wires to hold them in place.
Also, check your backstay’s lower end for a connection to ship’s ground. If there is such a connection, remove it. You do not want several feet of grounded wire running parallel to your antenna wire.
Attach the lower end of the GTO-15 wire to the antenna terminal on the tuner. Once again, it’s a good idea to pre-tin that bare wire and seal the insulation.
The RF ground serves several purposes in the antenna system. In one respect, it’s a mirror to reflect signals radiated downward by the antenna. In another, it balances the antenna system, reducing power losses from the transmitter. Without it, the signals from the antenna will try to reflect off of everything metallic in the boat and unwanted power will be absorbed by equipment, causing all sorts of interference to instruments, radios, autopilots, etc.
Conceptually, imagine yourself on your antenna looking downward: you need to see as big a reflective plane as possible. Obviously, the seawater would make the perfect reflector. Unfortunately, filling your boat with water violates boating rule number one about keeping the water on the outside.
Some good examples of metal that can form a counterpoise are metal toe rails and stanchion bases (and lifelines). You can also use metallic tanks, an external ground plate (such as a Dynaplate), and a lead or iron keel. You create the ground plane by interconnecting these and tying them to the antenna tuner.
Radio frequency energy behaves a bit different from the DC that you’re accustomed to from the ship’s batteries. RF travels on the surface of conductors and not so much inside a wire; a phenomenon known as skin effect. Copper foil is an excellent conductor of radio frequencies; it should be used to tie your RF ground components together. You can fold over the corners of the foil to form a thick layer, drill a hole through the layers, and attach the foil to bolts in this manner.
An excellent ground plane can also be established in fiberglass boats by incorporating a square yard or so of copper screen in the layup of the hull below the waterline. The radio frequency energy actually couples from the screen to the seawater through the hull. You can add the screen onto the inside surface of the hull and cover it with epoxy to create the same effect. Solder a copper tab at some convenient place to make the foil connection.
In summary, run copper foil from your tuner to toe rail bolts on both sides if possible, to any nearby metal tanks, to copper screening laid up in the hull, to a keel bolt, and to the HF radio’s metal case (the previously deferred transceiver ground). Your RF ground should be tied to ship’s ground at just one point if possible.
On our J/40 Gryphon, our HF radio installation evolved during the first two years of cruising. We ended up with an Icom M-710, automatic antenna tuner, copper foil to toe rails and Dynaplate, and an insulated backstay antenna. Once these systems were in place, we consistently succeeded with 3,000-mile contacts for weather information and e-mail communications across the Indian and Atlantic Oceans. And we still do.
Jeff & Raine Williams sailed their J/40 Gryphon around the world from 1998 to 2004. They sailed Gryphon again to New Zealand in 2010 where they are now based.
Last edited by administrator; 08-21-2012 at 02:58 PM.