Don't forget to put your boat agroundJan 1, 2003
The recent article by Gordon Wyatt on antennas ("Homemade antenna," Issue No. 90) was very interesting and practical. However, no mention was made of the fact that a proper grounding or counterpoise system must be included with all HF long-wire or insulated backstay installations. In fact, a proper seawater ground is the key to good performance. As mentioned in the article, the antenna coupler will match the 50-ohm output impedance of the transceiver to the long wire, but only if a ground is attached to the coupler. I have experimented with such antennas for the past 20 years and have the following comments:
Although one may be lucky with a relatively simple grounding scheme on a particular installation such as a steel or aluminum hull, it may not work at all on another boat. Here are some of the methods that I have tried myself or have seen others try on fiberglass hulls, all with poor results: 1. Simply grounding to the keel bolts on a sailboat with a lead keel. If the keel is encased in epoxy or fiberglass, it will not couple the radio frequency (RF) to seawater ground. 2. Simply grounding the engine and propeller prop shaft with propeller in contact with the sea water will not provide enough surface contact with the sea for RF grounding. 3. Use of stainless steel lifelines as a counterpoise. Again, RF coupling to the sea water is insufficient, and the conductivity of stainless steel is less than that of copper. 4. Use of a copper ground plate that is too small. At least 10 square feet is necessary for salt water and 20 square feet for fresh water.5. Use of a single Dynaplate in fresh water. Use several Dynaplates to obtain the equivalent of 20 square feet of copper plate. 6. Incorrect use of round wire such as #8 copper instead of the proper copper foil for bonding and grounding at RF frequencies. In general, use at least 10 square feet of copper plate or its equivalent in Dynaplates for saltwater and 20 square feet for fresh water ground exterior of the hull on a fiberglass boat.
Bond the engine block, and copper ground plates/Dynaplates/lead keel together with copper foil tape. Always use a standing wave ratio (SWR) meter or a forward-power vs. reflected-power meter to verify a low SWR on all marine HF bands.
Given a properly functioning antenna coupler, a low SWR on one HF band and a high SWR on another HF band indicates a poor RF ground system.
Last, carefully read and study manufacturers' instructions when installing any HF transceiver or tuner. Also check out the many publications devoted to marine radio installations such as: The Guide for the Maritime Ham, by the Seven Seas Cruising Association.