Can a VHF Marine Antenna be Used on Land?

thinbluebbq

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Hi all. Looking to see if the Shakespeare 5101 Marine VHF antenna can be used effectively in a base station at home? Thanks in advance for the guidance.
 

wowologist

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And most marine antennas that are made to mount over water don't have physical ground plane elements and are using the water as a giant ground plane, so you may actually need to create a ground plane for it.
 

dave3825

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if you want to transmit within the marine band from home you would need a shore station license.
Does home mean in the house or at the property? Lol Last year I regularly did radio checks from my boat while it was on the trailer using my marine radio before heading out. I was surprised at the range considering I was 17 miles from the water in densely populated area with lots of trees.
 

PACNWDude

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While maintaining radios for a fleet of vessels on the west coast, it was common to see the same antennas commonly mounted to vessels used at ports and marina's for shore stations. These were mostly Shakespeare fiberglass antennas. If they are not good enough for marine grade outdoor antennas, I think their factory seconds become fishing rods......joking. Then there are those that stream the feed to Automatic Identification System (AIS) use to track vessels, which seem to go high dollar and buy Morad fishing boat antennas and use them on land. They work, but beware the legal side as some have noted. They are still 25/1 watt radios in VHF, so you will get decent range, even in the evergreen forests of the West coast.
 

prcguy

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Not really. All marine antennas I know of are self sufficient and ground independent. If anything, a closer proximity to flat earth or seawater as in below a few wavelengths above ground will push the radiation pattern upwards and loose gain at the horizon. All vertical antennas regardless of ground plane or ground independent and at any frequency will act the same.

And most marine antennas that are made to mount over water don't have physical ground plane elements and are using the water as a giant ground plane, so you may actually need to create a ground plane for it.
 

wowologist

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"
Not really. All marine antennas I know of are self sufficient and ground independent. If anything, a closer proximity to flat earth or seawater as in below a few wavelengths above ground will push the radiation pattern upwards and loose gain at the horizon. All vertical antennas regardless of ground plane or ground independent and at any frequency will act the same.


wowologist said:


And most marine antennas that are made to mount over water don't have physical ground plane elements and are using the water as a giant ground plane, so you may actually need to create a ground plane for it. "
Since this antenna has one element straight up from the connection at the base, and is "usually" 1/2 wl ....where do you think the other pole of the di-pole is?
 

mmckenna

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Since this antenna has one element straight up from the connection at the base, and is "usually" 1/2 wl ....where do you think the other pole of the di-pole is?
Often the cheap marine VHF antennas are just stripped back coaxial cable. The other pole is the outer braid pulled back over the coax, or dangling down inside the tube. The shorter sail boat antennas that they run at the top of the mast is 1/2 wave and uses the coax shield on the feedline. Again, no ground plane.
Better fiberglass antennas use actual metal elements.

Keep in mind that most recreational boats are fiberglass, so no ground plane under the antenna.
 

PACNWDude

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Great info on Shakespeare antennas.

That strip of foam does not help there either, as many times the top cap falls off, breaks off, and then water get inside the fiberglass rod, corroding the entire length of wire "antenna" until it fails. Had an entire batch of Shakespeare antennas do this on a small fleet of ships in Puget Sound a few years ago. I switched to Morad antennas at that point.
 

prcguy

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If its a dipole element then it has everything it needs and no ground required. Many smaller VHF marine sticks are the equivalent of a J-pole with a matching circuit at the base of a 1/2 wavelength element. Its self sufficient and no ground or ground plane required. Some larger versions are stacked elements, 1/2 or 5/8 wavelength with 1/4 wave phase inverting stubs between elements and a bazooka balun or equivalent in the base so no ground plane is required.

A ground plane for an antenna must be right at the feedpoint to be considered a ground plane or counterpoise. I have never seen a marine antenna mounted so its base is touching the water to make use of it as a ground plane.

Since this antenna has one element straight up from the connection at the base, and is "usually" 1/2 wl ....where do you think the other pole of the di-pole is?
 

prcguy

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And I'll add to this just because I like to stir sh*t up. In general, with equivalent radios and antennas at each end, you will probably get less range or varying range across sea water on VHF/UHF compared to flat earth due to the better conductivity and reflection of sea water vs dirt. The problem arises from ground bounce, or water bounce where the direct path signal is interfered with by the signal bounced at an angle off the ground or water and when the phase of the reflected signal is near 180deg out of phase with the direct signal you get signal cancelation and degraded reception. Ground bounce happens over earth or water but sea water would be a worse scenario.

With a typical land based antenna on a roof you have much less of a ground bounce problem because the ground is broken up by houses, buildings, trees, etc, leaving mostly the direct path.



If its a dipole element then it has everything it needs and no ground required. Many smaller VHF marine sticks are the equivalent of a J-pole with a matching circuit at the base of a 1/2 wavelength element. Its self sufficient and no ground or ground plane required. Some larger versions are stacked elements, 1/2 or 5/8 wavelength with 1/4 wave phase inverting stubs between elements and a bazooka balun or equivalent in the base so no ground plane is required.

A ground plane for an antenna must be right at the feedpoint to be considered a ground plane or counterpoise. I have never seen a marine antenna mounted so its base is touching the water to make use of it as a ground plane.
 
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