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vhf antenna question

Old 10-10-2008, 08:45 AM
  #1  
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Default vhf antenna question

I currently have a 8ft 8db gain Shakespeare. It is mounted on my radar arch. The top 1ft has been chopped off due to forgetting to fold it down when trailering. This is the second time in 5 years and I'm kind of getting pissed. What would be the real world disadvantage of replacing it with a 5ft 3db gain? Downsizing would also prevent me from having to fold it going under local bridges.

Any real world experience of my estimated calling range 8ft vs 5ft? I have an icom VHF.
Thanks in advance.
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Old 10-10-2008, 10:12 AM
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Default Re: vhf antenna question

Here's some info.

http://members.toast.net/boatguy/vhfant.htm


Ken
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Old 10-10-2008, 10:17 AM
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Default Re: vhf antenna question

I think the real difference that you would experience would be a drop in extreme range when transmitting from far offshore to a Coast Guard or Marina shore mounted tower. The longer antenna is a full wave antenna and is more efficient on transmit that the 5' although the difference in real life situations is probably not dramatic. In receive mode, the fact that your antenna is mounted high on your boat probably gives you enough height that you would be working at the effective range of the average radio anyway when out on the water. A broken antenna is not effective in transmit or receive so a good condition 5' is better than a broken 8' antenna.
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Old 10-10-2008, 10:47 AM
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Default Re: vhf antenna question

The big difference will be on transmit: 6db is twice the power of 3db - it doesn't mean twice the range though. Unless you regularly run more than 15 miles offshore, I think a 4' - 3db will be fine.
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Old 10-10-2008, 11:29 AM
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Default Re: vhf antenna question

Your VHF works on line of sight. I would have it as high as possible, especially if you run offshore.
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Old 10-11-2008, 04:18 AM
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Default Re: vhf antenna question

I do not think you will notice much difference really.

That 5 foot antenna may have the same gain as your broken 8 footer did. I broke an 8 foot antenna. The second time this happened (long story - but it involves the installation of a new t-top and my failure to update my "before you tow home" checklist) I decided to dissect the antenna.

What I found was that the actual antenna element was nowhere near 8 feet. In fact, it was less than 4 feet. Most of the "8 foot antenna" is actually feedline. A 5/8 wave antenna (marketed as 6 db gain) is only 3 feet 9 inches if cut for channel 16.

I soldered a connector onto a 5 foot antenna for a friend of mine. After it was put on I was able to talk to another friend of mine on channel 71 (yea yea I know...laws and land and all.....send the FCC to arrest me). The other friend was on a hand held radio, at least 15 miles away. The hand held radio happened to be on the 30something floor of a tall condo building with a back porch facing inland, but still it was a good haul for a hand held to fixed mount simplex communication.

The 5 foot antenna also claimed "6 db" gain by the way.

The only thing you would be losing is about 3 feet of height, as the 8 foot antennas do place the antenna element at the tip of the fiberglass shell.
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Old 10-11-2008, 05:12 AM
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Default Re: vhf antenna question

Read this:

http://www.pyacht.com/shakespeare-antenna-selection.htm
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