Page 14 - How to Go Boating Flip 1
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es of VHF them all. A repeater is a radio receiver/transmitter mounted on a high
point with clear visibility around it. The tops of hills and mountains
There are two basic styles of VHF: the handheld and the fixed mount. are where they are usually found. The repeater picks up the VHF
There are distinct differences between them in performance, which all
comes down to repeaters, aerials and power. Let me demystify some transmission, then resends it. The line
of this for you. of sight to a repeater is high and clear,
likely several thousand feet above the
1) VHF range is restricted to line of sight. This means that the two water, and is way more than your boat
communicating radios need to be able to ‘see’ each other. aerial, which could be as little as three
metres above the water.
2) The range is improved in several ways. The first is by having a You now need to know a little bit
longer or better-quality aerial. Because of the curvature of the earth, about the differences of the various
the higher the aerial is mounted, the better the range. channels.
3) The power of the VHF is also a component in the performance. A VHF Channels
fixed mount VHF has a maximum power of 25 watts and a handheld
has a maximum of 5 watts. This doesn’t make a fixed mount There are two types of channels on a
provide five times the range of a handheld. Other factors affect the VHF: simplex and semi-duplex.
performance. The best comparison I was ever given was to think of it
like a balloon. Add five times the air into a partially inflated balloon and Simplex channels use the same
it won’t increase in diameter by a factor of five. frequency to transmit and receive.
They are designed for short-range
4) This brings us to repeaters, the single biggest range extender of use: boat to boat, or boat to nearby
shore facilities (for example, port
authorities).
Semi-duplex channels use a separate
transmit-and-receive frequency
because a repeater has to resend the
transmission and can’t do it on the
frequency you are already transmitting
on.
Repeater channels can boost the
range by huge amounts. Seventy
86 How to Go Boating and Where
point with clear visibility around it. The tops of hills and mountains
There are two basic styles of VHF: the handheld and the fixed mount. are where they are usually found. The repeater picks up the VHF
There are distinct differences between them in performance, which all
comes down to repeaters, aerials and power. Let me demystify some transmission, then resends it. The line
of this for you. of sight to a repeater is high and clear,
likely several thousand feet above the
1) VHF range is restricted to line of sight. This means that the two water, and is way more than your boat
communicating radios need to be able to ‘see’ each other. aerial, which could be as little as three
metres above the water.
2) The range is improved in several ways. The first is by having a You now need to know a little bit
longer or better-quality aerial. Because of the curvature of the earth, about the differences of the various
the higher the aerial is mounted, the better the range. channels.
3) The power of the VHF is also a component in the performance. A VHF Channels
fixed mount VHF has a maximum power of 25 watts and a handheld
has a maximum of 5 watts. This doesn’t make a fixed mount There are two types of channels on a
provide five times the range of a handheld. Other factors affect the VHF: simplex and semi-duplex.
performance. The best comparison I was ever given was to think of it
like a balloon. Add five times the air into a partially inflated balloon and Simplex channels use the same
it won’t increase in diameter by a factor of five. frequency to transmit and receive.
They are designed for short-range
4) This brings us to repeaters, the single biggest range extender of use: boat to boat, or boat to nearby
shore facilities (for example, port
authorities).
Semi-duplex channels use a separate
transmit-and-receive frequency
because a repeater has to resend the
transmission and can’t do it on the
frequency you are already transmitting
on.
Repeater channels can boost the
range by huge amounts. Seventy
86 How to Go Boating and Where
