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VHF Basics- A Primer

Very High Frequency (VHF) radios have been around for many years and remain the primary means of communication in aviation, marine, manufacturing and heavy industries. VHF  radios operate on line-of sight, meaning the signal is sent and received in a straight line.  In practice, however, VHF radio waves can be slightly "bent" by the atmosphere, adding as much as 20% to a radio's range. Range is primarily a function of the antenna to which the radio is connected.  As a general rule, VHF's(25 watt RF output)  have a range of up to 20 miles, depending on the height of the antenna and its "gain" or ability to amplify the transmit and receive signals. If you need to communicate over a greater distance consider installing a Single Side Band (SSB) radio - which has the capability to transmit over hundreds of miles. 

The Federal Communications Commission limits VHF radios to 25 watts maximum power and most units have a one-watt standby setting.  Higher wattage does not necessarily mean greater broadcast range.   Rather, the wattage boost you get at the high-power transmit setting pushes your signal through interference, usually nearby heavy VHF traffic. It should be noted that a VHF radio's capability is only as good as the entire system - the power supply, cabling and antenna, all properly installed, shielded, grounded and weather proof. We also should point out that while all the radios came fuse protected, it is better to have a  fuse close to the power source(outside), rather than close to the radio.

Fixed-mount or hand-held?

Modern hand-held VHF radios are full featured and extremely convenient, and they have the significant advantage in an emergency of being independent of the electrical system. Where maximum range and/or continuous use are more important, you will want a fixed-mount unit.

Not a telephone

Though the VHF can be used  much like a telephone to call others and relay information, to make appointments, or sometimes just to chat. Before you join in, however, you should recognize the differences between VHF radio and telephone communication:

• Radio conversations are not private. When you talk on the VHF, everyone within range tuned to that channel is listening.

• A radio conversation ties up the channel you are using. No one else within a 25-30 mile radius can use it until you sign off. Think of this situation as an airport terminal with a single bank of five pay phones. If callers are lined up three-deep while some blockhead drones on and on about the size of the mosquitoes in India, you can be sure he won't be the only unhappy tourist. In high- traffic areas, keep calls short.

Use low power

All fixed-mount VHF radios can transmit at either 25 watts or 1 watt. The maximum power from a handheld is typically 5 watts. With either type, if your radio contact is nearby, set the power setting to low (1 watt) to reduce the distance the signal carries beyond your target. Also watch your language; not only is profanity over the air against the law, it will be particularly offensive to other boaters with children aboard.

Making telephone calls

You can place telephone calls over the VHF radio. For this you have to use a trunked radio with a DTMF telephone keypad. The system uses a radio trunking controller connected to a PSTN telephone line and you should be in range of the controller, typically 25 km(20 miles) for making the call.

Channels

Most VHF radios on the market today have in excess of twenty twenty-five usable channels. All channels can be tuned within a frequency range of 146-175 MHz with a channel spacing of 25 kHz\12.5 kHz.

Using a Radio

Using a VHF radio is as easy as announcing yourself on an apartment intercom. Turn the power on, set to the desired channel and listen for a few seconds. If Channel isn't in use, key the microphone-meaning squeeze the button on its side, called PTT(press-to- talk) and speak. 

Using a VHF radio is one of the easier things to do , but there are things you need to do to operate a VHF properly. Most VHF radios have some or all of the following:

 * Volume knob

* "Squelch" knob.  Adjusting the squelch is similar to tuning your radio--it will make the signal sound much more clear.

* Channel knob or up/down buttons.  This lets you change the channel you are using.

* Channel display screen.  This tells you what channel you are on, and also any other feature that you may be using.

* Scan Button.  This will automatically change your radio channel to one that is currently being used by other boaters.  You may also be able to "Priority scan" which will allow you to program specific channels that you frequently use.  

* 1/25 or hi/lo button.  This allows you to raise or lower the power with which you broadcast your signal.  For boats close to you, use low power.  For boats farther away, use high. 

* Transmit button.  This is usually on the mike.  Simply push it down, and your radio will transmit a signal.

Prices:

 * VHF radios come in many shapes, sizes and colors to meet anyone's needs today. Prices start at about $119.00 for a basic model and can go as high as $1100.00 for the full - featured units. The main factor governing prices of the VHF radios are the features available. When choosing a VHF radio you should first make a list of the features you feel you want and need .

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