Vertical On Dock - Towertalk Forum at eHam.net

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eHam.net Forum : Towertalk : Vertical On Dock

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Vertical On Dock	Reply
by HAARON on October 17, 2005	Mail this to a friend!
Hello. I recently passed my general exam, and was wondering if it would be possible (or practical) to install a multi-band vertical on my pier, and use the water as a substitute for radials. Not enough power to bake fish, but appreciate any recommendations or comments.

RE: Vertical On Dock	Reply
by WW5AA on October 17, 2005	Mail this to a friend!
Harold, It would work great if it's salt water. Fresh water is a poor ground and the actual ground potential is the key factor. Is it a 1/4 wave vertical, vetical dipole...homebrew or commercial...need more info to really help. de Lindy

RE: Vertical On Dock	Reply
by WB6BYU on October 17, 2005	Mail this to a friend!
Salt water makes a great ground plane, but you probably will still want some radials. Here's why: Trying to ground a vertical to salt water is a real problem. If you drop a wire down into the water, then the length from the base of the antenna to the water is, effectively, added to the length of the antenna. So if you have any tidal action (or even large waves) the effective length of the antenna (and thus the resonant frequency and SWR) will vary over time. And if the wire length to the waterline happens to be a quarter wavelength, that isn't going to work very well at all. Besides, the ground wire is going to corrode pretty quickly, and you will have difficulty keeping good electrical contact with the water. What is better is to install the antenna on the pier with 2 or 4 quarter wave radials per band, which may be run along the sides of the pier rather than in a radial pattern. (You can also use tuned, shortened radials.) This makes the antenna installation self- contained. The salt water underneath will still provide an excellent conducting plane for low angle radiation. Or, there are some vertical antennas that are advertised as "no-radial" or "half-wave" designs. Since a pier is generally a pretty exposed location and subject to storms, choose one that is very well made and without lots of fussy bits, joints, and appurtences that may get damaged in a strong blow.

RE: Vertical On Dock	Reply
by HAARON on October 17, 2005	Mail this to a friend!
Thanks very much for the information. The water is brackish, so sounds like nothing to be gained. The ground extending the length of the antenna makes perfectly good sense as well. May well play with the idea of multiple radials, as I could place the antenna where I could run the radials actually under the pier in multiple directions. With the water, I hope that the vertical will function well enough to preclude a beam, at least for the time being. Again, thanks much, your information helped a lot. 73s

RE: Vertical On Dock	Reply
by K5LXP on October 19, 2005	Mail this to a friend!
The only real advantage of saltwater occurs in the far field anyway. Yes, it's a better counterpoise than dry sand would be, but not nearly as good as metal radials. If you're trying to get away from using radials, consider a half wave antenna like a ringo ranger or j-pole. Mark K5LXP Albuquerque, NM

RE: Vertical On Dock	Reply
by N3JBH on October 19, 2005	Mail this to a friend!
just for interest sake where are you going to do this. like florida? or even in USA kinda maybe offer us some details where as the ground(earth) surfaces around the globe are not all the same. you could maybe be in great place. and really dont need to be out on the dock. thanks jeff/n3jbh

RE: Vertical On Dock	Reply
by HAARON on October 19, 2005	Mail this to a friend!
I am on Dawson Creek along the Pamlico Sound in North Carolina. The dock goes out over the water for approx. 50 feet. There are a lot of tall trees in the yard, and the dock is about as obstruction free as I can get. North, East and West clear. The water is brackish, so I would not approach the conductivity of ocean water, probably closer to fresh. The dock does occupy a pretty large area, so I could run radials under the dock, just could not get correct lengths for each band around the entire 360 degrees. Was looking to put up a multi-band, ideally 80-10, and thought I could capitalize on the low radiation angle. This is a stop-gap until I can afford and have time to put up a good rotor and multi-band beam, and would continue to be the primary antenna for 40 and 80.

RE: Vertical On Dock	Reply
by WB6BYU on October 21, 2005	Mail this to a friend!
It doesn't take a lot of salt in the water to make it conductive. Sticking a pair of ohmeter probes into the water a foot or two apart should give you a good indication of how conductive it is. And you can always try a horizontal antenna strung over the tops of your trees - even a simple dipole would give a good comparison of the performance of the two antennas. You'll have a far better real-world indication of which works best in your situation than the rest of us can give you!

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