Antenna size

[All U Get]

Hi all,

I have an antenna mounted on the spreader that needs replacing. It is 32” long and I believe it is for our cell phone booster or am/fm radio. Would any antenna suffice for the replacement or do I have to get a specific marine antenna? I’m thinking about the local car shop.

 

[Mark Maulden]

You need to find out what it’s for.

 

[Don S/V ILLusion]

Many whip antennas have a loading coil in their base which can vary in size and length to account for a resonant antenna. You need to either replace it with an antenna designed for a specific frequency range or find out what frequency it is resonant on.

 

[Project_Mayhem]

Generally speaking, the higher the frequency, the smaller the antenna. I'd guess at 32" it's for your radio and not cell

 

[Brian D]

Show us a photo of what you presently have, Tom. Also try and find out where it is terminated inside the boat. That should help.

Now, as for length, if there IS a loading coil then it is part of the entire antenna. Most "dual" band antennas have a coil somewhere in the middle of the "whip". But sounds like that is not your case. And as mentioned, cell frequencies are short in wavelength, so the antenna will also be "short", although there have been some manufactures who have made multi "wavelength" cell phone antenna to try and increase the EIRP (effective isotropic radiated power) of the antenna, or its gain in dBi. But at least find out where the connector is located in the boat.

Finally, if you can find someone with a VNA, they can tell you exactly what frequency the antenna is tuned for and, therefore, what its intended use is.

 

[All U Get]

You need to find out what it’s for.

I have been working on this for twelve years, my important antenna are on the masthead. Everyone I’ve hired over the years have ignored checking it for me. It’s now crumbling away and I was able to break off the whip by taping two boat hooks together.

Show us a photo of what you presently have, Tom. Also try and find out where it is terminated inside the boat. That should help.

Now, as for length, if there IS a loading coil then it is part of the entire antenna. Most "dual" band antennas have a coil somewhere in the middle of the "whip". But sounds like that is not your case. And as mentioned, cell frequencies are short in wavelength, so the antenna will also be "short", although there have been some manufactures who have made multi "wavelength" cell phone antenna to try and increase the EIRP (effective isotropic radiated power) of the antenna, or its gain in dBi. But at least find out where the connector is located in the boat.

Finally, if you can find someone with a VNA, they can tell you exactly what frequency the antenna is tuned for and, therefore, what its intended use is.

If I can get a bosuns chair and a couple of drunken sailors to crank me to the spreader I’ll unscrew the base. Just tired waiting since last spring for my repairs to be done. The service yard had people leave for various reasons and they got behind on their list.