North Carolina Fishing Reports

g8tr74 · 1st Mate Joined: Apr 18, 2007 Posts: 98

I need to replace a broken vhf attena on my center console that is t-top mounted, the one I have been using is a Shakespeare 8' 6db galaxy series and it has worked fine but i was just wondering if there is anything better available, and where in Wilmington can they be purchased. I mainly fish offshore in the 20-60 mile range.

feeshnfinatic · Posted: Sun Jun 29, 2008 5:17 pm Post subject:

boaters world on college rd
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Offshore Bob · Posted: Sun Jun 29, 2008 6:40 pm Post subject:

Digital antennas are by far the best, you can get them on ebay

http://www.digitalantenna.com/vhfantennas.html
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Back-Lash · Ol'Salt Joined: Dec 15, 2004 Posts: 693 Location: MT.Olive

Selecting a VHF Antenna

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What they do
VHF antennas are a crucial part of your VHF installation, and understanding how they work and how to select the correct antenna can greatly improve your ability to communicate with other boaters and shore stations. The main purpose of a VHF antenna is to provide a radiator for the power that the transmitter in the radio produces, and to radiate this energy in the correct direction. Antennas also have to be enclosed in a weather-protected enclosure (or be made of a corrosion resistant metal) and must be able to withstand the substantial forces generated by a boat pounding in heavy seas.

Selection criteria:

dB Rating
An antenna’s dB rating (or antenna gain) indicates the apparent increase in transmitting power due to its ability to focus energy. Antennas with a high dB rating concentrate energy perpendicular to the antenna shaft in a field that is shaped like a disk. This makes your radio signal appear stronger to receiving stations around you. It also reduces the amount of energy transmitted above or below the antenna, which can be a problem if your boat is pitching or rolling in seas. A concentrated signal can actually fade in and fade out as the boat rolls and pitches.

As the dB rating of the antenna increases, so does the height of the antenna, but the horizontal angle diminishes.

The broad radiation pattern from a low dB antenna allows a sailboat to heel over and still send signals toward the horizon. Sailboats should use a 3dB antenna mounted at the top of the mast whenever possible.

Gains and losses
Customers have asked us if it’s necessary to match the antenna gain in dB to the loss (in dB) caused by the coaxial cable inside the antenna. While the concepts are related, you can’t trade one for another. Here’s how we explain it:
A gain increase of 3dB means a doubling of signal strength: 6dB is a fourfold increase, and 9dB is an eightfold increase. The actual watts transmitted doesn’t increase; it’s just that the power is concentrated, much like a reflector on a flashlight, in a more concentrated beam. Therefore, a radio with a 6dB antenna will sound like it has a larger transmitter than the same radio with a 3dB antenna. Coaxial cable, while efficient, loses some energy with every foot. In the West Advisor on Selecting Coax Cable (see www.westmarine.com) we’ve noted that RG-58 coax (the small stuff) loses 3dB for every 49’ of run. That’s roughly the same as saying that if you have a 49’ run of cable, your radio will sound like it’s transmitting with 12.5 watts instead of 25. If you run the same cable 98’, you’ll sound like you’ve got a 6 watt radio. Note that by putting your antenna at the top of an 80’ mast, even using small coax, you’ll still get very good range, but your coax will have reduced your effective power. Therefore, it is prudent to use the largest coax you can, especially on long runs. The trade-off is more weight aloft, which increases heel and diminishes sailing performance, so you will have to compromise.

Construction
VHF antennas are made of stainless steel or fiberglass. For masthead mounting, short stainless “whip” antennas create less windage and provide the appropriate wide radiation pattern required by a heeling sailboat. Small powerboats may also use stainless whip antennas because they are rugged.
Fiberglass tube antennas vary in quality. For high-end applications we recommend Shakespeare Mariner Series and Galaxy antennas, which are coated with smooth, polyurethane and will last 5-10 years. They use stainless-steel ferrules as well as brass and copper elements for maximum range and efficiency.

Standard fiberglass antennas last a few years, longer perhaps when used on covered boats. When the fiberglass begins to discolor and sliver, it should be replaced. One major difference in antenna construction is in the used to attach an antenna to its mount. Less expensive antennas use nylon, which is not as strong as the chromed-brass or stainless steel found on quality antennas.

Elements Inside the Antenna
There are three main styles of electrical elements: those using cut lengths of coax cable, those using a simple brass radiator, and those using a more complicated copper and brass radiator. While all provide acceptable performance, better antennas use brass or copper inside the fiberglass for maximum strength and durability.

So what kind of range can I expect?
VHF radios are one of the most cost-effective pieces of safety gear that you can put on your boat. Using relatively inexpensive transceivers and one of many styles of antennas, a VHF radio enables you to contact the Coast Guard or other vessels when you’re in trouble. Of course, most VHF use is for more enjoyable pursuits, like chatting about the day’s fishing, or letting a bridge tender know that you would like to pass.

To maximize the range of your VHF, there are a few rules that you should know:

Marine VHF radios for recreational boats are limited to 25 watts of output so, unlike Single Sideband or Ham radios, you cannot boost your range with a more powerful transmitter. A quality installation always helps, though. That includes a good 12V DC power connection, and quality coax connections.

Even if you increase your power, it wouldn’t help much. VHF radios operate on a line of sight principle between stations, meaning that the signals do not bend around obstructions or over the horizon (Okay, they do a little, but think of them as traveling about as straight as a beam of light.)

This means that antenna height, more than any other factor, determines how far you can transmit. An antenna mounted up high can “see” farther over the horizon.

Under the right conditions, a very small transmitter can communicate over vast distances. For example, the signal from an EPIRB (emergency beacon) is less than one tenth of a watt, yet it is picked up by satellites orbiting 528 miles above the earth.

So, the wattage of the radio is much less important than antenna height in determining range. Antenna gain is important, however. This is a measure of how much the antenna focuses the radio’s energy in the horizontal direction. If several otherwise equal radios try to contact a single receiving radio, the higher gain antenna is the one the receiving radio will hear.

So how far can one VHF installation talk to another VHF installation? There are an infinite number of radio-to-radio distances and heights that we could examine, so we’ve simplified by using the examples shown below. They were taken from a special section on VHF radios in Motorboating & Sailing. The antenna heights are given for a handheld in a small boat, a typical powerboat antenna height of 10', and sailboat installations with 30 ft. and 60 ft. heights. Distances are in nautical miles. Coast Guard shore stations are often located on the highest mountains along the coast or mounted on tall towers, which gives them tremendous range. They also maintain a network of repeaters, which are now providing complete coverage of the East and West Coasts of the U.S. with the new Rescue 21 system in place, so that even if a station or vessel is not located nearby, they can still communicate with you.

Bottom line: You should concentrate on having a good VHF installation, with clean antenna connections and a good power supply to the radio, and maximize the height of your antenna to maximize the range of your radio.

Conclusion
Selecting the right type of VHF antenna for your boat is important for making your radio perform properly. But so is getting the kind of antenna mount that will hold up to the demands of your boat's performance. A fast powerboat, traveling offshore in big seas requires the heaviest stainless steel mount, as well as a rugged top-quality antenna, for example.

Pay careful attention to the possibility of corrosion in all the connections in your system. Many sailboats have a coax fitting located at the base of the mast, which are a common source of signal loss. Good quality coax fittings are a must, and they should be inspected each season.

Your VHF radio is one of the most important pieces of onboard safety gear, and the right antenna, mount and coax are all important for maximizing its range and reliability.

Antenna Gain Height Horizontal Angle
3dB 5' ±80º
6dB 6' ±35º
9dB 18-23' ±20º
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rhartjr · Posted: Mon Jun 30, 2008 7:03 am Post subject:

Kind of like the Ford or Chevy debate, pick your poison. Shakespeare Galaxy 5225 or a Digital 529. Both are about the same in performance.

Ray

Curmudgeon · Ol'Salt Joined: Mar 03, 2006 Posts: 115

Why change from something you've been satisfied with to something you have no experience with? 60 miles is a long way out to discover someone's definition of "by far the best" isn't the same as yours ... Shocked

g8tr74 · 1st Mate Joined: Apr 18, 2007 Posts: 98

thanks to everyone that posted a reply. great site with great advice!

robby · Posted: Tue Jul 01, 2008 7:34 pm Post subject:

i thought i knew a little info but after that thread i am very lost and confused
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