VHF Antenna Height

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sydngoose

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Ive only installed Digital 529's for the past 8 years: not a single failure.
Off shore fishing this past week off of NE Florida I was hearing USCG Charleston, SC broadcasts. I just like the Digital brand and the 529 model.
 

Swatski

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VHF radio transmission distance is based upon 1) curvature of the Earth, 2) height of the receiving antenna, and 3) height of the transmission antenna.

The additional range offered by an 8ft antenna is about 1mile (or less) than a 4ft antenna) assuming both are mounted to a cabin or T-Top 8ft above the water.

Here is the calculator ...... CEPD Tools - Transmission Calculators
Okay, let's be real. Your original "60 mile range" comment is off. Max transmission w/25 watts has a theoretical maximum range of up to about 60 nautical miles - BUT that is ONLY for idealized conditions, and could only be approached in perfect weather by tall ships and/or beaming off the hills. The range drops to a effective range of only about 5 (five) nautical miles in real world conditions for small boats at sea level. Those emergency DSC calls can actually travel further, but voice calls will generally not, and what Pelagic said is right on - and I could just repeat here.

Importantly, in this context, even a few miles of extra range can represent a multi-fold difference.
There is zero question an 8ft VHF antenna has potential for more effective range than a 4ft, in general; but there is also not question a good 4ft setup will beat a crappy one no matter how long the antenna.

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GoodChance

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Okay, let's be real. Your original "60 mile range" comment is off. Max transmission w/25 watts has a theoretical maximum range of up to about 60 nautical miles - BUT that is ONLY for idealized conditions, and could only be approached in perfect weather by tall ships and/or beaming off the hills. The range drops to a effective range of only about 5 (five) nautical miles in real world conditions for small boats at sea level. Those emergency DSC calls can actually travel further, but voice calls will generally not, and what Pelagic said is right on - and I could just repeat here.

Importantly, in this context, even a few miles of extra range can represent a multi-fold difference.
There is zero question an 8ft VHF antenna has potential for more effective range than a 4ft, in general; but there is also not question a good 4ft setup will beat a crappy one no matter how long the antenna.

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Let's be real ....

On my old 23 Parker and now my 26 Southport I am regularly 50-150 miles offshore in the Florida Gulf of Mexico. At 50-60 miles, I can communicate with the USCG station in Clearwater FL. That's with a 4ft antenna. Not sure how that happens but it does. Maybe the USCG has a "relay" station in the open sea.

At 100+ miles I can hear the USCG in Alabama and in Ft Myers.

That's the real world

Furuno 3.jpg
Furuno 5.jpgFuruno 5.jpg
 

Swatski

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Let's be real ....

On my old 23 Parker and now my 26 Southport I am regularly 50-150 miles offshore in the Florida Gulf of Mexico. At 50-60 miles, I can communicate with the USCG station in Clearwater FL. That's with a 4ft antenna. Not sure how that happens but it does. Maybe the USCG has a "relay" station in the open sea.

At 100+ miles I can hear the USCG in Alabama and in Ft Myers.

That's the real world

View attachment 27924
View attachment 27925View attachment 27925
Dammm, that just proves the sea in the Gulf of Mexico is pretty flat !! lol.

On a more serious note, thank you for this comment. I can't say I routinely go our 50-150 mile out, and my VHFs have not been most stellar aside from their antennas, so I'll defer to your judgment and experience.

Great pics, man!

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Swatski

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The CG has maybe a 300 foot tower and they are not using just 25 watts
Well, yes. That's kind of the point I was trying to make about the transmission part of the equation.
Which is what really matters, sometimes.

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GoodChance

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8' Vhf Ver 3' Vhf. You won't believe who won. - The Hull Truth - Boating and Fishing Forum

FYI - If if you must hold-your-nose to visit THT, they occasionally have some good, real-world information. This post from THT is one of these and the results posted here mimic the real-world results that I've seen with VHF antennas.

While in theory an 8ft antenna should be be better performing than a 3 or 4ft antenna....... in the real world, this isn't always the case. For example, 2 weeks back I was 115 miles due west of Tampa and with a "short" 4ft Digital antenna mounted on a standard T-top, I could hear transmission from the Bay pilots in Tampa.

Take this FWIW.
 

Andy

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8' Vhf Ver 3' Vhf. You won't believe who won. - The Hull Truth - Boating and Fishing Forum

FYI - If if you must hold-your-nose to visit THT, they occasionally have some good, real-world information. This post from THT is one of these and the results posted here mimic the real-world results that I've seen with VHF antennas.

While in theory an 8ft antenna should be be better performing than a 3 or 4ft antenna....... in the real world, this isn't always the case. For example, 2 weeks back I was 115 miles due west of Tampa and with a "short" 4ft Digital antenna mounted on a standard T-top, I could hear transmission from the Bay pilots in Tampa.

Take this FWIW.
Others here have mentioned this. "What you are 'receiving' has a lot to do with who's sending. How high and how powerful is their equipment?" And, the person from THT didn't say he could transmit that far; just receive, which would not be useful in an emergency situation. Atmospheric conditions also play a role; there are many days I can 'hear' transmissions from the Chesapeake Bay area (also from Pilot base stations). I'm 116 miles south of Norfolk (the way the crow flies). They would not be able to hear me. I mentioned once before how, with similar, tall 9db antennas, on two boats 48 miles apart, we could communicate; both send and receive. We could not, even if one of us switched to our 8' antennas (we both, had both on the boats)... Plus, what the person from THT assumed is that since he could hear the transmission from 115 miles, with a 4 ft antenna, that would be the same with an 8'. Well, it was likely, that same day, someone with an 8' antenna, or a 28' antenna would have heard the same transmission, much farther out. (But they too, would still not be able to 'communicate').... Marine VHF radios transmit 25w on the high setting. For a variety of reasons, a lot of those radio are not 'producing' 25w of broadcast power... One last thought; One persons single-episode experience does not constitute a 'study'... Have you heard of the 'Jump-Spider-Jump' experiment?
 

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