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Boat antenna?

Old 02-23-2015, 01:35 PM
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Default Boat antenna?

Can someone explain to me the different antennae's on a boat?

My 26 foot currently has 1, for the VHF. it looks like there used to be another one, with a cable similar to the VHF one. Is there a need for 2 VHF antenna's?

I cant seem to find manyarticles about this.
Old 02-23-2015, 02:35 PM
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If you have 2 vhf radios (for redundancy) then having 2 antennas (for redundancy) makes sense. There are also am/fm antennas that look very similar to vhf antennas.
Old 02-23-2015, 03:00 PM
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Originally Posted by flyhigh123 View Post
Can someone explain to me the different antennae's on a boat?
Yes, I can explain this. The ANTENNAE on boats are found on the insects on the boat. The aerials attached to radios are called ANTENNAS.

An antenna cannot be used simultaneously by more than one transmitter (in any sort of practical manner), so each transmitter needs its own dedicated antenna.

Last edited by jhebert; 02-23-2015 at 04:43 PM.
Old 02-23-2015, 05:12 PM
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Originally Posted by jhebert View Post
Yes, I can explain this. The ANTENNAE on boats are found on the insects on the boat. The aerials attached to radios are called ANTENNAS.

An antenna cannot be used simultaneously by more than one transmitter (in any sort of practical manner), so each transmitter needs its own dedicated antenna.
Jim,

What happens to VHF signal when using one of those AM/FM/VHF splitters that are used to share an antenna between vhf and Fm Radio?

Is the VHF transmit/receive ability Compromised??
Old 02-23-2015, 09:45 PM
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Originally Posted by Lima Bravo View Post
...What happens to VHF signal when using one of those AM/FM/VHF splitters that are used to share an antenna between vhf and Fm Radio? Is the VHF transmit/receive ability Compromised?
A splitter cannot do what you ask. You need a diplexer. See

http://en.wikipedia.org/wiki/Diplexer

The VHF Marine Band is at 156 to 162-MHz. The FM Broadcast Band is 88 to 108-MHz. There is enough separation in frequency that it is possible to connect a receiver for the FM Broadcast Band and a VHF Marine Band transmitter to the same antenna and keep the transmitter emission out of the other receiver with a diplexer. Whether or not a particular device being sold for this function into the recreational marine market works in the optimum manner is impossible to say.

Typically any diplexer used for transmission must have low insertion loss, otherwise the lost transmitter power would be dissipated in the diplexer, and unless the diplexer were built with sufficiently large components to be able to tolerate the power loss occurring in them, there would be a lot of heating.

Since VHF Marine Band transmitters are relatively low power, 25-watts, if a diplexer had a 1-dB loss it would have to absorb about 5-watts of power, which is not an enormous amount.

The diplexer must keep almost all of the transmitter power out of the second receiver port, otherwise the second receiver would be damaged.

This can be done. Can it be done with a $45 marine device? That's hard to say.
Old 02-23-2015, 09:49 PM
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Originally Posted by flyhigh123 View Post
Can someone explain to me the different antennae's on a boat?

My 26 foot currently has 1, for the VHF. it looks like there used to be another one, with a cable similar to the VHF one. Is there a need for 2 VHF antenna's?

I cant seem to find manyarticles about this.
I have 2 VHF's, so I have two antennas. However, it's possible the second antenna on your boat was for a CB radio -- the cabling and connectors are the same. ;?

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