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Author Topic: Vertical over Saltwater  (Read 717 times)
WB6IFA
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Posts: 3




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« on: August 04, 2008, 06:14:56 PM »

I have always read that the best place to mount a vertical is over saltwater.  How is this done?  I have a situation where my QTH has a dock out into a saltwater lagoon feed by the Bay.  How do I effectively create a ground for the vertical with the saltwater.  My dock is 14ft by 14ft and I will be mounting the vertical on the side of the dock about 12 feet from the land.

Any suggestions would be appreciated.

Howard - K6SID
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W5FYI
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« Reply #1 on: August 04, 2008, 06:22:50 PM »

Gordon West of West Radio School has experience. His tips for boats (www.kp44.org/ftp/SeawaterGroundingFor_HF_Radios_byGordonWest.pdf) should also be useful for docks.
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K4TMC
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« Reply #2 on: August 04, 2008, 06:28:22 PM »

Check the information on this web page - http://www.k2kw.com/verticals/verticalinfo.htm

It should help you understand the effect of a saltwater envirnoment.

I envy your situation!

73,
Henry - K4TMC
Raleigh, NC (100+ miles from the coast)
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K5LXP
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« Reply #3 on: August 04, 2008, 07:23:58 PM »

Keep in mind the best saltwater doesn't conduct as well as copper wire.  Not even close.  The article referred to by K4TMC is a good one.

Mark K5LXP
Albuquerque, NM
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WB6IFA
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« Reply #4 on: August 04, 2008, 08:09:35 PM »


Both articles are good. But I am not sure about how to effectively take advantage of the situation. One article says that you do need an effective radial system. The other basically says to dangle a 3" copper strip into the water...

I have also been given advice independent of this forum that I should take copper foil and put it around the dock in a loop fashion. Please keep in mind that I only have a dock and could possibly extend some radials into the yard.

Howard - still confused
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K2KW
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« Reply #5 on: August 04, 2008, 11:52:07 PM »

I happened to be working late, and saw your question.  The issue here is current return for the antenna.  Plunking a radial/copper sheet etc into the water is old wives tale.  It does not provide proper current return for the antenna.  In a dipole, the current return is each 1/4 side of the dipole.  For a vertical, the only way you get proper current return is through radials.  A piece of wire in the water might be good for lightening ground, it's not good enough for current return of an antenna.

radials can be resonant or non-resonant.  Non-resonant are radials laid on the ground.  Resonant are elevated radials that are tuned to the frequency.  On a dock, I would suggest resonant radials, preferably on standoffs on the side or below the dock, as long as they are above the water.  You will need at least one for each band, if you are using a multiband antenna.

There really is a difference when you do it right!  

As other noted, there's info on my website, though one of these days I will need to better organize it.

I've installed hundreds of verticals ove the years...

73, Kenny K2KW
www.k2kw.com
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W8JI
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« Reply #6 on: August 05, 2008, 04:07:01 AM »

Howard,

If you try to use the water as the exclusive ground or the direct ground you will have tuning issues if the water changes height in relation to the antenna.

You also will have significant loss if you only dangle a conductor into the water.

The ground requires surface area of a very good conductor like metallic wire above the saltwater, not just salty water. You need a plate or screen of wires on the dock or just below the dock to form the direct ground connection. You actually don't need to connect to the water at all.

The water has a big positive effect in the Fresnel zone of the antenna where current is not too dense. That's where the primary advantage is.

73 Tom
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WA3SKN
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« Reply #7 on: August 05, 2008, 04:13:45 AM »

Well, Howard... why don't you try both ways?  Experiment!
Mount a vertical on a piling, then try it with a piece of wire (or copper pipe) in the water.  Then, replace the wire with a regular radial system.
Then you will KNOW how well it works!  This is part of the "fun" of ham radio.
(Its a cheap experiment!)
73s.

-Mike.
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DIPOLE
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« Reply #8 on: August 05, 2008, 04:26:41 AM »

With a vertical's RF ground, there are two "almost" separate issues.  There is 1) the necessary current return, and 2) ground reflections affecting pattern.

For the current return part, I'd still go for getting as much copper wire down as possible.  Current flow happens in the vertical's near field.  Like previously mentioned, salt water is a good conductor, but not nearly as good as copper.  You will still need radials just like someone living in a desert, either ground radials or elevated tuned radials.  The second issue is ground reflection.  This is where your salt water QTH blows everyone else away.  But it's also the thing you can do least about.  Ground reflections occur for great distances from the antenna and interact with non-reflected waves in complicated ways.  The net/net of this is that the better the far field ground conductivity, the lower will be your pseudo-Brewster angle and the better your DX.  A "perfect ground" will have an angle of 0-degrees.

A basketball analogy... A basketball (your signal) will bounce much better of a hardwood (salt water) floor than it will off a thick carpeted floor (ground at my QTH).  In the first case, there is virtually no velocity reduction.  In the second, the velocity will be severely retarded by the floor.  But this is happening for many wavelengths away, much farther than a reasonably dense copper radial field can be extended.  In addition, the radial field is what determines the inflation on your basketball.  A vertical antenna with no radials over poor ground is like trying to bounce a flat basketball on carpet.  Most of your bounce force (power) is simply lost.
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WB6IFA
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« Reply #9 on: August 05, 2008, 08:03:33 AM »

I would first like to thank all of you who have responded. This is my first time on this forum and the response has been fantastic.  I now have a lot better idea regarding the issues dealing my situation.  

The water level fluctuation is not an issue for the city keeps the lagoon at a level that is fairly constant, maybe changing by 6" a couple of times a day.  The flow is enough to change all the water once every 4 days or so. Also, they lower the lagoon about 4 times a year for a week for dock maintenance. It will be interesting to see what effect this has on the vertical's performance when the lowering occurs.

I can now see that I have confused the two main issues before me: 1) the current return; and 2) the ground reflection.  Just putting these two issues into perspective has helped me get a handle around the problem.

Again, I would like to thank everyone for their response and if there are any other thoughts out there please keep them coming.

Howard - K6SID
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N4UM
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« Reply #10 on: August 05, 2008, 08:45:15 AM »

Howard:

I've been running verticals mounted on my dock over salt water for a number of years.  The system I use is relatively simple and seems to work pretty well.  

I use a sheet of copper about 2 by 10 feet down in the water under each of my verticals.  This may be unnecessary according to a number of other posts on this subject - but it makes me feel better anyway!

I run two radials in opposite directions stapled to the underside of my dock.  My verticals are monobanders so I run a set out from the base of each vertical.  I use this kind of system on 40 and 30 meters.

My son (K4RUM) also lives on salt water and uses a SteppIR vertical for 40 thru 6 meters.  In his case, the dock is fairly high off of the water - about 5 feet.  (His last dock got trashed in a hurricane so he replaced it with a higher one.)  He also uses a big sheet of copper down in the water directly below the SteppIR.  When initially installed without radials, the SteppIR exhibited a decent SWR on 40 but matching on 30 and higher was difficult.  To rectify this, we installed a pair of radials for each band stapled to the underside of the dock.  We actually made each pair of radials slightly shorter than a quarter wave...more like .2375 wavelengths.  We ran the radials in straight lines where possible but a number of them had bends in them etc. This dramatically improved the SWR on thie higher frequency bands but I have no way of knowing whether or not the antenna actually radiated any better.  Since we had a coax run of about 250 feet any decrease in the SWR would be expected to have a significant improvment.

I run a sloped base fed, base loaded wire on 80 with the feed point out on my dock.  I have no radials on this antenna (only the ubiquitous copper sheet in the water beneath it).  It works very well.  I use a similar antenna on 60 meters with good results.

On 160 I use a bent Marconi.  The vertical section is 40 feet long and mounted on a piling on my dock - again with only the copper sheet beneath it.  The horizontal section is 95 feet long.  It also works quite well with no radials.

My experience has been that radials don't seem to be necessary on the lower frequencies where the height of the vertical above the water is relatively small in terms of wavelengths but that they are of some benefit on the higher frequencies where the height of the vertical above the water is substanial in terms of wavelengths.  I suspect my obervations may not jibe with predictions made by those who are more knowledgeable in antenna theory but they seem to work anyway!

BTW I've had very good luck using Davis RF's Buryflex coax around and under saltwater.  At a previous location I had about several pieces of it about 50 feet in length submerged to a depth of about 8 feet for several years with no apparent degradation in its proprties.  They make good stuff.

In any case, play around with things and see what happens!
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WB4TJH
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« Reply #11 on: August 05, 2008, 11:38:52 AM »

I have a friend who lives here on Sarasota Bay, and I tried to get him to mount his HF vertical on his small dock for months. Well, recently, he did so, and now he is raving about the improvement in both receive and transmitted signal strength. He just took a coil of heavy copper wire connected to the ground side of his vertical, and dropped it into the water below the dock. Apparently, it did the job. I know he's really pleased with the results. There's nothing like a perfectly conducting ground under a vertical.
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K7KBN
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« Reply #12 on: August 05, 2008, 03:28:15 PM »

If you really want to try various antenna configurations over sea water, pay a visit to your friendly Navy recruiter.  He'll fix you right up!

Worked for me.

73
Pat K7KBN
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73
Pat K7KBN
CWO4 USNR Ret.
K5END
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« Reply #13 on: August 05, 2008, 03:45:42 PM »

I think Tom (W8JI) pointed out the best of all worlds for you.

FWIW, I'd second his method.

It would probably make the most efficient use of your assets, if done properly. The dock is already built.

Try it out first with something cheap, like chicken wire and do as he suggests. See how well it works. If you like it, then make something more permanent (resistant to corrosion.)

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K5PEW
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« Reply #14 on: August 06, 2008, 11:47:14 PM »

I looked at your place on Google Earth. I doubt that grounding into the salt water in your inland waterway will give you any real advantage at all.

My personal opinion is you would benefit the most from a tri-band beam up 45ft or so. You are close enough to the bay and the ocean that once that signal gets out headed West, it's going to go a long, long way.

With a vertical, I think the difference between setting radials in the back lawn and grounding it into the lagoon would be negligible. Either way, you're going to have a strong signal to the West.

If you can't get a beam past the HOA, try a couple of low profile SVDA arrays, say for 10 and 15 meters. You could set those up cheap and easy in the back yard, about 5ft off the ground, and no worries about radials. You could hit the Pacific hard and be able to switch them East as well.

Good luck!

Graham Welch - K5PEW
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