Features February 2007 Issue

3dB VHF Antenna Test

3 dB sticks run neck-and-neck in performance.

Buy a good VHF radio and an even better VHF antenna. That’s advice that we have all heard at one time or another. But what constitutes a good VHF antenna?

Recreational marine VHF antennas are usually broken down into three categories, and grouped by overall length and also by gain rating, which is expressed in decibels (dB). The three types are 3- and 4-foot sailboat antennas (3 dB gain); 8-foot powerboat antennas (6 dB gain); and 16-plus-foot, long-stick antennas (9+ dB gain), which are popular on larger, long-range craft. Antenna gain is a ratio related to an antenna’s effective radiated power (ERP) instead of a fixed quantitative value.

Marine VHF Antenna
The L-bracket is the most common mount for a 36-inch, 3 dB antenna. If you want to see a noticeable improvement in the range of your VHF, upgrade to RG-8X (5/16-inch) tinned copper coaxial cable.
An antenna’s decibel rating can be thought of as the design of the antenna’s transmit-and-receive footprint or its radiation pattern (see "
What is there to gain from gain," page 18). A 3 dB-gain antenna has a nice, circular transmit-and-receive pattern, whereas a 6 dB-gain antenna operates in more of an oval vertical plane.

All of the antennas in our 3 dB test group have a radiating element (the part of the antenna that transmits and receives the radio waves) that is half of a wavelength long. At a nominal VHF frequency of 165 MHz, one wavelength is 71.65 inches, or 1.99 meters (300 divided by frequency in megacycles = wavelength in meters) Dividing 71.65 inches in half gives us the average whip length of 36 inches that most 3 dB sailboat-style antennas are fitted with.

Because height is the single most important factor in determining the operational range of a VHF antenna, and sailboats have to contend with heeling angle, an antenna with a broad radiation pattern that keeps the signal pattern in line with the horizon is preferred. The horizontal signal pattern of a 3 dB antenna is a nice, broad 80 degrees, whereas the horizontal angle for a standard 8-foot, 6 dB powerboat-style antenna is a much sharper 35 degrees.

What we tested

We contacted the three most popular manufacturers of marine recreational antennas (Comrod, Digital Antenna, and Shakespeare) and requested their participation in an "at-sea" VHF antenna performance test. We asked the manufacturers to send us two of each of their best 36-inch, 3 dB antennas; 8-foot, 6 dB antennas; their long-stick, 9 to 10 dB antennas in the 16-foot range; and any other entry-level, 8-foot VHF antenna they would like to submit for our sea trial/ field evaluation. A total of 17 antenna models were entered in our test. This article focuses on the 3 dB antenna comparison. We’ll cover the results of the other antennas in a future issue.

Shakespeare 5215

The Shakespeare 5215 3 dB-gain sail antenna is the most popular 3 dB wire whip antenna on the market. This antenna has a nice balance between light weight and simple, durable construction. Shakespeare’s 5247 and 5215 antennas are similar in appearance and share the same antenna coil design. The difference between these two models is that the 5247 has a mechanism that allows you to lift the antenna and lay it down while it is still mounted (a handy feature if you’re the sort that likes to play chicken with a local fixed bridge). The 5215 is permanently mounted and is the only antenna in our test group with a non-removable whip.

The Shakespeare website and brochure state that the 5215 "squatty body" antenna features a hermetically sealed, tin-plated copper wire coil and a stainless steel body and whip. When we cut open this antenna, however, we found that the stainless steel was actually brass. The material is fine for this application, but we think Shakespeare’s specs should be corrected.

An area that concerns us with this antenna is the use of un-tinned copper wire for the coil of the antenna. The coil of any end-fed, half-wavelength 3 dB antenna is the heart of the device. Although the copper wire that Shakespeare uses for its antenna coil is substantial in comparison to the Metz or GAM coil, we feel an un-tinned copper coil will be less resistant to corrosion, which in turn will reduce the performance of this antenna.

Another shortcoming in the Shakespeare 5215 is the use of a thin plastic cap for the top cover of the antenna coil. In our opinion, the plastic coil cap, which is glued to the brass antenna body, will probably never fail during normal use. But for vessels that winter in northern boatyards, have their mast removed, and are rack stored for the winter, it wouldn’t take a very large bump during the demasting process especially in cold weather to crack the top plastic cap and create an entry point for water and corrosion.

Bottom Line: The 5215 performs well and represents a decent value from a well-respected manufacturer. It is also readily available at most retailers.

Metz Manta 6

Metz Communication Co., based in Laconia, N.H., is a relatively small "boutique" antenna manufacturer. The 3 dB Metz Manta 6 antenna has had a loyal following among seasoned mariners for many years. Our first impressions of this antenna were quite good. The antenna’s exterior body is rolled stainless steel, with a layer of protective coating applied to the inside of the coil chamber. The coil of the Manta 6 is constructed of tinned copper wire wrapped around a Lexan dowel that integrates the antenna whip’s base into the antenna cable attachment point. The stainless steel whip on the Metz is easily removed by loosening the compression nut with a small, adjustable wrench.

It wasn’t until we disassembled the Metz that we discovered some specific issues that could complicate matters if you had to change the whip or whole antenna aloft. First, Metz uses a compression sleeve to hold the whip onto its antenna. Technically, tightening a compression sleeve is not much different than tightening an Allen set screw, but if you drop the Allen wrench, you can go and get another one. If you drop the 1/16-inch diameter Metz compression sleeve, your 10-minute job just got a whole lot more complicated. And speaking of complications, Metz is the only antenna in our 3 dB group that doesn’t use a permanently mounted coax fitting on the base of the antenna.

Embedded inside the coil body of the Manta 6 antenna is a male UHF/PL-259 connector, which necessitates the use of the Metz-supplied female UHF/PL-259 adapter. Our problem with this adapter is that it is not permanently secured at the factory with Loctite thread sealant. If you overtighten the PL-259 a bit too much onto the Metz adapter, you could end up unthreading the adapter right out of the bottom of the antenna when removing the coax from the antenna. While it is not a big deal to thread the adapter back into the antenna, be aware of the hidden spacer inside the coil base, which keeps the adapter from threading up inside the coil too far. Twice during our handling of this antenna we found ourselves bent over on the deck looking for a part (the spacer) that fell out of the antenna.

According to Metz, customers requested the design so that they could mount the antenna not only with a Metz bracket, but with other mounts (like magnetic mounts found on some autos, flush-deck mounts seen on some powerboats, and conversion brackets).

Bottom Line: The Manta 6 held its ground well in the performance test, but there are some installation issues to be aware of. It may not be as readily available as a Shakespeare, but it’s worth special ordering if the time allows.

Digital 222-VW

Digital Antenna Co.’s model 222 wire whip antenna is a big, heavy antenna that weighs about 10 ounces. The 36-inch stainless steel antenna whip is triple the diameter of any other antenna that we tested in the group. Taking into account the weight and windage of this antenna in comparison, the GAM SS-2 antenna weighs a scant 3.7 ounces the Digital 222 is probably not the right antenna choice for a toothbrush-chopping performance racer. But where this antenna shines is in its overall range performance and its indestructibility. If you expect icicles in your rigging, here’s an antenna to hang your wool cap on.

The Digital 222 finished first in our range performance test, closely shadowed by the Metz Manta 6. But when we took the 222 to the band saw, we discovered that this antenna had no equal in construction design. The body of the 222’s coil housing is made of aluminum. The coil of the 222 is constructed of tinned copper wire and is protected with a plastic top cap that is much thicker than the Shakespeare 5215. But what is unique to Digital’s 222 is that the entire body of the antenna’s coil is filled with a firm, silicone-type sealant that locks everything inside of the coil into one impenetrable, waterproof mass.

Marine VHF Antenna
Our test featured several short whip antennas, from left, the Shakespeare 5215, the Comrod AV53BI-3, the Digital 222-VW, the Shakespeare 5415 (a 24-inch boat/dinghy antenna to be featured in a future article), the Metz Manta 6, and the GAM SS-2. Not pictured is the foldable Shakespeare 5247.
Even the attachment of the stainless steel whip to the coil body is very different on the 222. Digital uses a push-and-twist connection on its whip. Although it requires considerable force to push and twist the whip on and off of its base, we found that when we shook the base coil by hand, we could see and hear the whip slightly rocking back and forth on the flange receptacle. We would have preferred that the whip was more solidly mounted to the coil, particularly considering the weight and extra windage of the heavy-duty whip.

We were also a little surprised that the Digital’s stainless steel whip was as soft as it was, taking into consideration the whip’s sizeable diameter. We were easily able to set a into this whip, while all of the other antennas that we tested easily sprang back to shape after a considerable flex. We do see an advantage to the Digital’s triple-diameter stiff whip, on installations where the flexible whip of a more conventional 3 dB antenna might bang into adjacent rigging or equipment.

Bottom Line: This rugged antenna has superior performance, and superior construction. If the extra weight is not a concern, this antenna should outlast the boat.

GAM Model SS-2

GAM Electronics is a small antenna manufacturing company based in Manchester, N.H. GAM’s SS-2 36-inch, stainless-steel whip, sailboat VHF antenna has the smallest diameter coil of any VHF antenna on the market. The coil on the SS-2 is clad in a stainless steel housing that measures only 1 inch in diameter.

The interior inspection of the GAM revealed tinned copper wire wrapped around a plastic dowel and soldered at both ends. The antenna whip can be removed/replaced using an Allen key, and the performance of this antenna was equal to the Shakespeare 5215.

Bottom Line: This antenna is a good choice when small size and less wind resistance are important.

Comrod AV53BI-3 / Norway

The AV53 by Comrod is an expensive antenna that the manufacturer claims will outlast any antenna on the market. The whip is fitted to a brass 1x14 marine ferrule at the base. The antenna connection is a female BNC twist connector tucked way up inside the ferrule. We are guessing that Comrod was anticipating this antenna would be pole-mounted on a commercial vessel via a male pipe flange, or on a very large sailboat mast that had enough room on the top plate of the mast to install a 1 x 14 deck flange.

If the AV53 was mounted in these ways, the antenna cable would be completely concealed and protected by the antenna’s coil. This would make for a very clean and secure installation. Unfortunately for Comrod, most of the 3 dB wire whip antennas that we use here in the U.S. are bracket-mounted to the side of a mast. In order to side-mount the AV53, you would have to order a special accessory mount.

Bottom Line: We have no reason to doubt that the Comrod, whose antennas are widely used by commercial vessels, would hold up well in the marine environment. High price, limited dealer support here in the U.S., and installation hurdles hold back widespread acceptance among recreational sailboats.

Conclusion

The designs of all of the 3 dB-gain, sailboat-style antennas that we tested are similar (end-fed, 1/2 wavelength), and as such, the performance differential between the different models was minimal. And so the final determining factors for our testers were price and the construction differences between the models.

The Digital 222 3 dB was our distance champ by a narrow margin and was, hands down, the most substantial antenna in our test group. Some, however, might be reluctant to add an extra half-pound aloft. The Metz Manta 6, GAM SS-2, and Shakespeare’s 5215 are all well-made, closely-priced antennas that each placed high on our performance and quality rank; the longer warranty for the Metz, our Budget Buy, and the GAM give them a slight edge.

Ultimately, we didn’t find a huge difference in operational range between quality 3 dB gain sailboat VHF antennas. VHF communication is all about height. The tallest mast wins, provided that a good quality coax is used between the VHF and its antenna. RG-58 (1/4-inch) coax is outdated. If you want to see a noticeable improvement with the range on your VHF (both transmitting and receiving), upgrade to RG-8X (5/16-inch) coax. Also, use a coax that has both a tinned (corrosion resistant) center conductor and shield. A tinned coax will not signal degrade over the years, like un-tinned copper will when subjected to salt air.

Comments (0)

Be the first to comment on this post using the section below.

New to Practical Sailor?
Register for Free!

Already Registered?
Log In