Antennas for small boats need to be of reasonable size and to be easily elevated above their mounting points to increase antenna height. Good electrical performance, durability, and reasonable cost are all desired attributes. Here I look closely at the MORAD VHF-156HD or "Hot Rod" antenna and its mounts.
The MORAD VHF-156HD antenna is a commercial grade, rugged antenna with a number of mounting systems. It is an all-metal antenna and compared to consumer-grade lower-tier fiberglass antennas is significantly more expensive but also significantly more durable. The antenna is very well known in the Pacific Northwest and has always had a strong presence in the commercial, government, and military boat markets where antennas tend to be installed by professional radio technicians. As you move toward the East Coast of the USA and into recreational boats with antennas installed by the boat owner, the MORAD antenna is perhaps less known and less utilized. Its distribution into big marine retailers is limited. MORAD does sell directly to retail customers for individual order quantities.
The MORAD VHF-156HD antenna is a commercial grade VHF Marine Band antenna. The antenna is constructed of anodized aluminum, stainless steel, and nylon. The overall length of a MORAD VHF-156HD (i.e. tuned for 156-MHz) antenna is about 50.25-inches and maximum diameter is 1.8125-inches. The upper radiating element (the "hot rod") is stainless steel. The antenna is terminated in a SO-239-type jack which will mate with the common PL-259 cable-mounted plug. The mechanical base of the antenna is designed to fit over a 1-inch diameter stanchion or pipe and secure to it with three stainless-steel set screws. The antenna is rated to survive winds speeds of 87-knots (100-MPH). The assembled weight is 1.5-lbs. The MSRP is $164. No coaxial transmission line is supplied with the antenna; it must be purchased separately.
The MORAD VHF-156HD antenna has linear vertical polarization with an omnidirectional azimuthal pattern. The radiation characteristic is assumed to generally have one main lobe, and the vertical pattern is described as "low angle", i.e., presumably at the horizon. The antenna input impedance is nominally 50-Ohm with a rather impressive bandwidth of 10-MHz with less than 1.5:1 VSWR. The antenna is described as having 6 dB gain but no reference for gain is provided. This is typical for manufacturers of marine antennas. Marine antenna "gain" is a rather loosely-defined quantity.
The overall length of the antenna is about 50.25-inches. In terms of wavelength at 156.8-MHz (75.7-inches) that represents 0.66-wavelength. The radiator is short of a half-wave, and the sleeve is about a quarter-wavelength. Exactly what is happening with the radiating element (the "hot rod"), the cylindrical sleeve element (perhaps a counterpoise or balun or some crafty method of feeding the radiator), and the impedance matching to the 50-Ohm antenna feed point is hard to know.
The construction of the MORAD VHF-156HD can properly be called rugged. It should have a long useful life on small and fast boats. At $164, the VHF-156HD is out of the realm of consumers who seek the lowest possible price. If the anticipated performance is obtained and the antenna lasts ten years or more, the value is certainly there. The moment when you really need a VHF Marine Band antenna to work well is usually a situation with high winds and rough seas—the worst time for your boat's antenna to break.
All antennas work better when elevated. Putting the antenna above and clear of other conducting surfaces allows it to work as intended and for its signal to propagate farther and stronger. Increasing antenna height is the principal means to improve signal strength when starting at a low mounting height—height trumps gain. To increase the height of a MORAD VHF-156HD antenna I now look at the details of its mounting and extension masts.
In contrast to many recreational-grade VHF Marine Band antennas, the MORAD VHF-156HD antenna is unusual: its mounting is not already tailored for a 1x14-threaded base. Instead the antenna is designed to fit over a 1-inch outside diameter tubing (or a similar diameter nipple) and bind to it with set screws.
There are three common methods of installing a MORAD HD antenna, and often an adaptor is needed:
Each of these mounting options will use a different method of fixing the MORAD HD antenna to the mount or stanchion.
Using the HD antenna with the common 1 x 14 threaded ratchet mount will require a M91 Ratchet Mount Adaptor. This is a 4-inch-long adaptor with a 1-inch nipple to which the antenna will fit over and be secured by the three set screws in the antenna base. On the other end is a 1x14 threaded coupling for threading onto the typical ratchet mount. A large oval hole in one side allows for the transmission line to exit.
There are three variations of the M91 Ratchet Mount Adaptor:
In this mounting the HD antenna will be mounted directly to a 1-inch diameter stanchion or extension pipe; MORAD offers stanchions in four length and in either white or gold anodized aluminum:
The lower end of the extension pole or stanchion will then be fitted with an adaptor that has a socket that accepts the 1-inch stanchion pipe at its upper end and secures the stanchion in place with set screws. The other end of the adaptor has a 1 x 14 threaded female coupling to thread onto the ratchet mount. This adaptor is the M87; gold finish $40; white finish $41. It is also available without the side hole as the M87-No Side Hole model.
Without an added support, the 5-foot extension may be the maximum feasible. The strength of the ratchet mount, the rigidity of the mounting surface, the sea state, the boat speed, and the wind speed should all be considered when assessing the maximum height for an unsupported extension mast above its base.
A white aluminum stanchion is fitted to a white M87 adaptor with side hole, and threaded onto a 1 x 14 ratchet mount. With this mounting the VHF-156HD antenna mounts directly onto the 1-inch stanchion.
MORAD also makes a heavy-duty M99 ratchet mount with 1 x 14 threads ($66). This mount is shown above in the two illustrations.
Typically the HD antenna will be mounted directly to the 1-inch stanchion or pole. The pole will be held in place by two M6 bulkhead mounts (sold in pairs for $43) separated a few feet apart, creating a fixed installation. There is also a lay-down version M600 ($85 for a set) which has a swivel base, an upper locking latch to permit the antenna to be laid down for storage, and a storage rest hook to retain it when lowered. With either mount, the transmission line will exit at the bottom of the stanchion. Because a through-bolt mount is used to fix the stanchion to the M600 swivel base, in the M600 mount the transmission line cannot be the usual 0.5-inch diameter RG-213/U as there will be insufficient clearance around the through-bolt. A smaller transmission line must be used with the M600.
An M600 lay-down mount is used for mounting to a pilot house or bulkhead. For a 10-foot stanchion the spacing between upper and lower mount should be 30-inches.
MORAD sells some pre-assembled RG-8X coaxial cable transmission line with suitable connectors. At the antenna end they provide a PL-259 plug; at the radio end they provide an FME female connector and an FME-female-to-PL259 adaptor. A 15-foot cable with connectors sells for $30. For self-installers this cable kit is a good choice. There are also versions with 25-foot and 35-foot cable lengths. Or the installer can choose their own transmission line and assemble the connectors.
Pre-assembled RG-8X transmission line with a PL-259 connector for the antenna and an FME connector and adaptor for the radio end.
I particularly like the use of the FME ("For Mobile Equipment") connector in this application. (A separate article about FME connectors illustrates them and gives some sources for buying them.) The FME female plug is barely larger than the transmission line itself, which will make passing the transmission line and FME connector through bulkheads or piping much easier. A pre-installed connector also removes one the most common problems for the boater-owner self-installer: fitting a PL-259 to a coaxial cable seems to be a problem for a majority of boaters.
Because many boats have existing ratchet mounting bases with the 1 x 14 thread, this mounting is likely to be the most common for MORAD HD antennas. If mounting directly to the ratchet mount or to an existing extension mast with 1 x 14 threaded couplers, installation of a MORAD HD will require the antenna ($164), an M91 RACHET MOUNT ADAPTOR ($40), and transmission line. That will run $204 for antenna and adaptor, with the transmission line cost adding $30, for a total of $234. If a ratchet mount is needed, the M99 ($66) should be used. This raises the total cost to $300.
To elevate a MORAD HD above a ratchet mount using a 1-inch stanchion, the antenna ($164), a M87 adaptor ($40), a two-foot section of 1-inch stanchion V2 ($29), and transmission line ($30) are needed. The total cost would be $263. If a five-foot V5 ($48) extension is used, the cost increases to $282. Again, if a ratched mount is needed, the M99 ($66) should be used, and the costs are then $329 (2-foot) and $348 (5-foot). These costs are certainly well above many other commonly used antennas for recreational boats.
I am not writing this from a perspective of a first-hand user. Years ago when I was looking for a new antenna for my boat, the MORAD was not in my search, probably because I am a Great Lakes boater and the antenna was just not very common around here or elsewhere in the eastern USA. I am reviewing it primarily to help myself understand its unusual mounting system. Until I really dug into the MORAD website and explored all its documentation in detail, I was quite confused about the mounting system.
I like the antenna for its rugged construction and wide use in commercial, government, and military applications. Yes, the cost is high, but the value seems to be there. I have been considering adding a second VHF Marine Band radio to my boat, and that would require another antenna. I've been curious about the MORAD, and that curiosity really prompted this article. The VHF-156HD is on my list to consider for my next antenna.
MORAD Antenna Company is an American company located in Bellingham, Washington. It manufactures antennas there using modern CNC machines and a skilled staff of local people. A brief glimpse of the MORAD factory can be seen in their short promotional video. All antennas are assembled, tuned, and tested by hand.
MORAD also makes a number of other HD-type antennas. For marine use they stock the VHF-159HD, tuned to have decent VSWR on both the low end of the VHF Marine Band for voice and at the high end of the band for AIS, for users who want to share one antenna between a ship radio and an AIS transpoder. MORAD also makes a VHF-162HD for dedicated use with AIS transponders. They build HD-style for antennas for the Aviation Band (122-MHz) and Amateur Radio 2-Meter Band (146-MHz). They can build HD-style antennas for any custom frequency from 122-MHz to 850-Mhz. In addition, they make other antennas for the VHF Marine Band with greater length and higher gain, and also antennas for Medium Frequency and High Frequency bands. Their line of antennas, mounts, and accessories is comprehensive.
Readers with a question or comment can post them to a thread in the VHF MARINE RADIO forum reserved for that purpose.
Photos courtesy of MORAD Antenna Company.
Portions copyright © 2018 by James W. Hebert.
Author: James W. Hebert
This article first appeared February 21, 2018.
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