Homemade antenna

There are two ways to acquire a good high frequency (HF) antenna. Most mariners buy a commercial model off the shelf; the other option is to build one yourself. Building your own is a lot easier than it sounds. This type of antenna can be used for both marine SSB and Ham radios in the frequency range from two to 30 MHz.

First, let’s take a quick look at what are considered standard options for sailboats. The most overlooked option is a whip-style antenna mounted to the aft rail of the boat. With you doing the installation, the cost will be between $400 and $600.

The other standard option and the one most chosen is the insulated back stay. Probably 80% to 90% of sailboats with Ham and SSB radios select this style of antenna.

There is an alternative antenna that works in exactly the same manner as an insulated backstay that you can install for $27.73 in parts, plus tax and shipping. (See the accompanying sidebar for purchasing information for parts.) I have had this type of antenna on my Pearson 303 Comfort Zone for seven years without a failure. The first radio contact I made with it was from the U.S. East Coast to Denmark, and I have regularly talked across the Caribbean. This is all accomplished with less than 100 watts of output power.

The antenna is very simple to install. It requires one trip to the top of the mast and the drilling of one hole in your boat. The parts required are two porcelain insulators known as egg insulators, one porcelain feed-through, and 100 feet of insulated antenna wire. The only variable in this is, of course, the length of the antenna wire, which will vary depending on rig height and boat size.

There are several ways to calculate the distance from the top of your mast to the aft rail. The simplest is to securely attach a line to your main halyard and raise it to the top of the mast. Then stretch the line to your aft rail in the center of the stern and mark the line. After retrieving the line, measure the section from the end tied to the halyard to the mark and add at least 10 feet. This is the minimum amount of antenna wire to purchase.

The egg insulators are really self-explanatory once you have one in your hand. The nylon line and the insulated antenna wire loop around each other, separated by the insulator. Before going up the mast, attach the insulated antenna wire to the insulator by passing the wire twice through one of the holes in the insulator, leaving about six or seven inches of bitter end. Then wrap the bitter end around the standing part of the antenna, making half hitches with the last couple of wraps. If you have any worries about this wrap coming loose, you can tape it or apply heat-shrink tubing over the wrap.

Now it is time to go up the mast. Using an 18-inch length of 1/8-inch nylon line, attach the insulator to your bosun’s chair or whatever mast-climbing method you use. At the top of the mast make two loops with the line around the bail at the masthead and through the remaining hole in the insulator. I have had a square knot holding this line for years. If attached properly, the holes in the insulator that the line passes through will be the farthest from the bail, and the holes the antenna passes through will be the closest. The egg insulator is just one of many types any insulator will work if you can put an antenna wire through one end and a nylon line through the other end to tie off with. Tying off to the stern rail, back on deck at the aft rail, tie off the other insulator at least three feet from the backstay. The insulator can be tied off anywhere it doesn’t interfere with the bimini or any of the many other devices we hang off our aft rails. While you are deciding where to tie it off, keep in mind that the antenna will continue on down to the deck and attach to a deck feed-through. On my boat, the through-deck fitting is right below where the insulator is tied off. Leave six to eight inches of line between the rail and the insulator to adjust tension on the antenna. With the insulator in place, run the remaining end of the antenna wire through the other hole in the insulator and pull the antenna tight.

Holding the antenna taut, run the wire through the insulator hole again. Make a couple of wraps around the antenna with the last one being a half hitch.

To install the feed-through, drill a one-inch hole through the deck just below where the insulator is tied off. When installing the through-deck fitting be sure to use a high-quality sealant such as Life Caulk. After the feed-through is in place, bring down the antenna wire to measure for final cutting. Keep the wire as short as possible without putting tension on the connection at the top of the feed-through. After cutting the wire to length, strip off a quarter inch of insulation and install a circular crimp connector. Place this over the feed-through post and secure.

Now that the antenna is installed, it’s time to position the antenna coupler belowdecks. To many mariners the antenna coupler is the least understood part of the system. The coupler is described as an impedance-matching device (impedance can be thought as a complex type of resistance). An HF radio has a constant output impedance of 50 ohms. However, our antenna varies in impedance depending on the frequency selected. The antenna coupler, with its special sensing circuits, senses the impedance of the antenna at the selected frequency. It then changes its circuits so that the antenna always appears to have a 50 ohms impedance.

It is important to remember that everything downstream of the antenna coupler is part of the antenna and radiates radio frequency (RF) energy when you transmit. For the best use of this energy the antenna coupler should be mounted as close to the abovedecks antenna as possible. The farther it is mounted away from the deck feed-through, the more RF will be radiated belowdecks and could interfere with other electronics. The antenna just described works exactly like an insulated backstay antenna at a fraction of the cost, and the backstay doesn’t have to be broken.

By Ocean Navigator