Discussions of antennas often stirs some controversy, so I will preface this with the statement that ... this works for me. If you don't like it, don't use it.
I have been employed for 40 years as a communications
tech and antenna
. When I bought my diminutive 26 foot sloop
, I wanted HF coverage from 160 meters on up with no gaps
, covering the entire HF spectrum of both Ham and Maritime bands. Conventional wisdom in the sailing community is to use an insulated backstay antenna
; but I vowed to avoid chopping up my rigging
with insulators, dealing with the lightning
suppression issues of an insulated stay, and juggling the antenna length to avoid exact 1/2 wave multiples at any operating frequency -- which creates untuneable gaps. So I chose instead a Delta
Insulated backstay antennas work very well on vessels that are large enough to offer a ground plane that is a substantial portion of a quarter wave length at the lowest expected operating frequency. The ground plane is usually accomplished either by connecting to a conductive hull
- or in the case of fiberglass
hulls - with a wire mesh laid inside the hull
below the waterline that establishes capacitive coupling through the fiberglass
to the sea.
But with smaller vessels, as is the case with my 26 foot Pearson
Ariel, the length of the vessel is insufficient to provide a good counterpoise
at longer wavelengths - since the Ariel is only 18.5 feet long at the water
line – just slightly longer than a quarter wave at 20 meters. To operate efficiently at 30, 40, 80 and 160 meters, I needed another solution.
There are also some serious disadvantages to the conventional insulated backstay antenna: 1) it requires the installation
of insulators in the backstay, which operates at high mechanical tension. If an insulator fails, you can lose the mast
(a very inconvenient experience at sea). Using "Johnny Ball" insulators (the type you see on utility pole guy wires) will prevent complete loss of the backstay (it'll slack the backstay instead) because they interlock the lines, but a failed Johnny Ball insulator still results in a short-circuited and therefore failed antenna. Insulators require at least four (usually swaged) mechanical connections, which are also vulnerable to failure. 2) The insulated backstay has no DC continuity to the rest of the vessel, making anything connected to the antenna vulnerable to static buildup and lightning
damage. Connecting lightning suppressors at the output of an antenna tuner is a tricky compromise since the legitimate RF voltages can be over 1,000 volts when the antenna length approaches a half wave or multiples. Electrically bonding everything on the vessel is the most effective lightning countermeasure - and an insulated backstay is unbonded from the rest of the boat by its very nature of being insulated. 3) The antenna “tuner” (correctly called a coupler) may not be able to tune the antenna when its length approximates a half wave, or multiples of half waves, because an end-fed half wave antenna presents infinite impedance at its feed point. If the objective is to operate on ALL of the Ham bands, and on ALL of the maritime bands (which are interspersed between the Ham bands), then choosing the correct length of an insulated backstay antenna presents a daunting problem of avoiding half wavelengths. A loop antenna, on the other hand, presents much more moderate excursions in its impedance up and down the bands.
I’ve been operating a Delta
Loop antenna as illustrated (see attachment) for over two years with very good success. It is tunable from 1.7 to 30 MHz, with no gaps. There is complete DC continuity between all of the antenna elements, negating the need for lightning suppression (I trail a zinc plate at the backstay chain plate
during thunderstorm activity and whenever at the dock). And the biggest advantage, in my estimation, is the fact that no modifications whatsoever need to be made to the sailing rig. I chose a feedpoint at the forestay because when the forestay is energized with RF, it's less of a hazard of giving the crew (me) an RF burn (I've had a few - they're nasty and take forever to heal). The feed connection is made on the inside at one of the three large through-hull bolts attaching the stem. The ground line is 2 inch tin-plated flat copper braid (you may want to use flat stainless steel
braid instead) that runs through the bilge
and connects at the backstay chainplate with one of the three chainplate bolts. The antenna "tuner" (coupler) is located in the space previously used by the water
tank. I used an SGC model SG-230 tuner, but others should work as well. I used inexpensive snap-on ferrite RF suppressors on all of the wires that exit the mast
base, installed at the mast base. Note that the ground wire also connects to the mast base (don't use an RF suppressor on that wire) and is bonded to the wire that runs through the bilge
. That wire is very important: without it, the boom is "hot" when transmitting (burn risk). The shroud
wire chainplates are not connected to anything, and the shrouds act as resonators at shorter wavelengths. And the shroud
lines attached to the mast smooth out impedance excursions.
The lightning discharge path is a straight shot down the backstay to the submerged zinc plate, providing a "zone of protection" under the backstay (protecting the cockpit). The ground to seawater is only needed for lightning suppression - it is completely unnecessary for RF propagation. Caution: don't use any metal but zinc - anything else will cause rapid corrosion
of an aluminum propeller
. I used bronze at first, and practically dissolved my prop after 6 weeks of immersion.
I've had some great "QSOs" (conversations) with other vessels in New Zealand
, all over Europe
, and Brasil, and solid email
coverage with Sailmail stations in Hawaii
with 50 watts. Conversations with other distant Hams are often met with incredulous comments when I tell them I'm not using an enormous directional antenna with a high power amplifier.