VHF Installation

By Frank Lanier

 

Reliable VHF communications are an integral part of any safe, enjoyable day on the water.  Hand-held VHF radios are popular choice with boaters due to convenience and portability (a handy option for small boat or dingy use), however with a maximum output of six watts range for even the best hand-held is limited to around five miles.  Compared to the 25 watts and approximately 25 miles a fixed mount unit provides, the choice is clear as to which you’ll want for primary communications should the feces hit the rotary oscillator.

            Installing a fixed mount VHF radio is fairly straightforward and well within the ability of most do-it yourselfers, however if you have doubts concerning an installation, always seek the advice of a competent electronics technician.

            The first step is selecting a VHF radio and antenna that meets you needs.  There are numerous choices available when it comes to radios – the best approach is to list the models that offer the features and price you want, then narrow it down from there.   Factors to consider when selecting a radio range from location (waterproof models or those with remote mikes for exposed installations for example) to the unit’s warranty, which can range from one year to three or more.

            Antenna selection is one of those areas where you really do get what you pay for.  Regardless the VHF radio selected, performance will only be as good as the antenna you pair it with.  Considerations for purchasing a VHF antenna include price, construction (type and size of the element, quality of components, finish, etc), and the antenna’s gain, which we’ll discuss in a moment.  Less expensive fiberglass models often utilize thin copper wire for the “element” (the part that actually radiates and receives signals) rather than the more substantial brass or copper tubes found in higher end antennas.  The nylon ferrule (mounting base) of lower end antennas are also more prone to failure than the chromed brass ones found in better quality units.

            As to material selection wire antennas provide less windage (making them ideal for sailboat masts) but are “whippy” in longer lengths.  Fiberglass antennas are more beefy and ridged, meaning they can be made longer without excessive movement, providing both height and strength for deck mounted installations.

            Higher end antennas also typically utilize better coax, the cable that conducts the signal from your radio to your antenna – some antennas come with a length of coax cable (which may or may not be long enough), while others provide a short lead and require purchase of additional cable, connectors, etc.  As with any wire run the primary concern here is signal loss, a factor of both cable length, quality of construction, and the number of connectors or cable slices in the run (each of which increases signal loss).

            There are three common types of coax: RG-58 (the least expensive), RG-8X and RG-8U (the best, providing the least amount of signal loss).  Signal loss for cable runs on smaller vessels (typically less than 20 feet) is not generally a huge concern, however even in such a short run signal loss can be double when using RG-58 vice RG-8U.

            One critical element of antenna selection is gain, the increase (or decrease) of an antenna’s effective radiated power.  Gain essentially describes how an antenna amplifies and shapes (or refocuses) the signal it transmits, channeling more of it towards the horizon for example (where it does the most good) rather than skyward or into the water.  Gain is measured in decibels (dBs) and VHF antennas typically fall within three common ratings: 3dB, 6dB, and 9dB.  In a nutshell, antennas with a higher dB rating provides a sharper, more concentrated radiation pattern (and greater theoretical distance) than those with lower dB ratings (think spotlight as compared to a floodlight).

            That being said, the best choice is not always simply to select the antenna with the highest dB.  In the case of a sailboat mast installation for example, the more focused “beam” of a 9dB antenna will often be shooting skyward or down into the water as the vessel pitches and rolls, in which case the broader pattern of a 3dB antenna will give better performance.  The best choice for a smaller power boat is typically a 6dB antenna, which provides maximum range with minimal signal loss (due to rolling while underway).  Larger power vessels with dual VHF radios may opt for the belt and suspenders approach by installing a 9dB antenna at the upper helm (which will typically be used in calmer seas) and a 6 or 3 dB antenna at the lower helm for rougher conditions.

              Finally, combination antennas (VHF/cell phone or VHF/AM/FM for example) are available for installations where you have limited mounting area.  The cost however, is reduced performance on the VHF side – dedicated antennas provide better performance and should always be the first choice if space is available.  Regardless the type of antenna you choose, keep in mind VHF is “line of sight,” meaning it should be mounted as high as possible for best performance,

Before you fire up that drill or hole saw

            Before beginning any project, take a moment to step back and visualize the installation as a whole.  Draw out the entire installation and mentally walk though it in efforts to head off any potential problems.  You’ve chosen a location for the radio, but is there a path to run power and antenna wires?  Can you actually access the mounting nuts and bolts for the antenna mount?  Hopefully you’ve verified you can prior to drilling.

Doing the deed

            Once you’ve chosen a VHF radio, selected an antenna, planned out the installation, and assembled all of the necessary tools and required installation items (wiring, connectors, etc) it’s time to get down to business.  Here’s some guidance and tips to help you along.  It’s not all inclusive and won’t cover every circumstance, but it will help you along the path to VHF installation nirvana.

  1. Once you’ve selected a location for radio, use the gimbled mount as a template to mark and drill holes for the mounting hardware (using through bolts rather than screws if at all possible).  If it looks like space will be an issue, do a dry run by inserting the radio in the mount and placing both in the new location (to assure adequate clearance) prior to drilling.  You’ll also want to be doubly sure of what’s on the other side of the mount location prior to drilling – putting holes in hoses or electrical cables are never conducive to a good install.
  2. Drill the holes and mount the bracket.  For console mounts in exposed locations, place a small amount of marine grade silicone at each hole to prevent water entry.  Now’s also a good time to install the microphone holder, so it won’t be bouncing around later on.
  3. Next up is power, which involves installation of a wire run from a suitable circuit breaker in your DC distribution panel to the radio.  Use a dedicated circuit breaker in the panel if possible and avoid direct battery connections (which can mean longer runs and increased engine noise).  Most units will come with an in-line fuse holder as part of the wiring harness.  Be sure to keep this in place and ensure that the properly sized fuse is used – the circuit breaker protects the wire run, but it’s the fuse that protects the radio.
  4. You’ll need two conductors for the wire run, a red (positive) wire and black (negative) one.  You can run two separate wires and save few pennies, but an easier, neater way is to use dual conductor wiring.  Regardless, always use good quality marine grade wire. Size-wise, 16 or 14 AWG will usually work well in most installations (radio manufacturers will typically include table of wire size recommendations based on length in their manuals).  Route the wiring such that it is protected as much as possible and provide support and chafe protection (grommets, etc) where necessary.
  5. Purchase good quality, marine grade connectors for all power connections.  Use heat-shrink or heat-shrink type crimp on connectors to prevent corrosion.  As with most modern electronics, when connecting power to the radio be sure to observe the proper polarity.  Inadvertently crossing positive and negative leads (even for a second) can easily damage your new radio.
  6. Next up is mounting the antenna and running the coax.  Typical mounting options  include flat base mounts (for use on decks, cabin sides, or other such flat surfaces) and rail mount types, which can be clamped on to any appropriately sized tubing.  Both types come in fixed or ratcheting styles, the benefit of the latter being you can lower the antenna should the need arise (high winds, low bridges, etc).
  7. Make sure the coax run between radio and antenna is as short and straight as possible (no 90-degree bends or kinks), is properly supported and protected against chafe or other such damage.  Unlike CB coax, you can cut VHF coax to shorten it, but don’t go crazy – leave at least three feet, the minimum distance you want between the radio and antenna anyway (to avoid transmit related feedback into the radio’s receiver).
  8. Soldered antenna connectors are considered the best for coax, but they can be a bear to install properly.  Good-quality crimp-on (no-solder) connectors are now available that provide excellent service.

            Finally, with the antenna and power leads properly connected turn the radio on and test your installation to confirm all is well.  If you can listen to the WX station or hear the chatter of other VHF users, you’re half way there, however you’ll want to conduct a radio check to confirm both transmit and receive is working – a good practice anytime you’re preparing to get underway.