RF Ground - Marine Mobile Installation

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Marc Gorelnik:
I have canvassed the internet for guidance on installing an HF rig on a boat, in this case a power boat. There are as many different opinions as there are installations, it seems. Moreover, the marine SSB community has a different take from the amateur community.

For hams, this is just a random length vertical antenna on a floating platform. The consensus is to lay out wire radials as one would in a fixed application. Of course, there isn't much real estate on a 25 ft. fiberglass boat.

Marine SSB mavens recoil at the thought of using wire. No less an expert than Gorden West has writen "running wire — even battery cable —
is not effective as an RF ground (counterpoise) at radio frequencies. Although, wire looks like a good DC ground, it looks invisible at most radio frequencies." Copper foil (or a ground strap) is the only effective conductor sayeth the sailors.

The ham in me says "if one can use wire as the radiating element, then why not as the counterpoise." True, we're dealing with the skin effect, but how much current are we dealing with here? Or is it the inductance that matters?

Quite a separate question from whether wire conducts RF energy is using the sea's surface as part of your counterpoise. Here, it makes sense to use large surface areas of foil or screen to capacitively couple the RF ground to the sea.

In my application, which remains under construction, I have had 150 sq. ft. of copper mesh laid into the hull. Large (8 ga) wire was then soldered to the mesh. I expect about an 8 ft. run to the antenna tuner.

Except . . . that Gorden West now has me concerned that I've blown it. My signal will never reach that beautiful counterpoise in the hull because the heavy gause wire "looks invisible" at RF frequencies. Could this be true?

The copper screen is soldered to the wire and now lies under a layer of resin. No more soldering to the screen. If this is truly a problem, can this be salvaged by minimizing the run of wire (say 6") and then running a ground strap from there to the tuner?

It seems that no one would question this in a fixed application. (I run a random length vertical at home with a few wire radials.) I just don't understand why wire would be blessed on land but useless at sea. There must be something I am missing.

I am pleading for some reliable information, preferably from someone who has gone through a marine mobile installation. Thanks.

73s

Marc

Charles P. Cohen:
I have a 36' sailboat -- IC-706 and SG-230 tuner.

The antenna is an insulated backstay.

The counterpoise is a few 12-gauge wires (two 16', two 36') running forward from the stern, along the toerails, on top of the deck.  There is no connection between the counterpoise and the sea.

My logic was similar to yours -- if it works on land, it should work on the water.   And it did.

Other boats can hear me fine -- I was sailing, and working the ham and marine nets down the Pacific Coast from San Francisco to El Salvador, over the past 18 months.

I originally tried using 16' counterpoise wires, and a 16' antenna hanging beside the backstay.  Results were OK on 20m, but very poor on 40m.  And I had lots of RF showing up in the boat's DC system -- my switch panel lit up nicely when I talked.  It quieted down almost completely with the longer counterpoise wires.

I know one other boat using a counterpoise.  It has two _bundles_ of counterpoise wires, each wire cut to 1/4 wave at a mid-band frequency.   His signal is fine.  

I think you'll be OK with the copper screen and 8-gauge wire if you can get a decent length of antenna wire into the air -- e.g., a 20' marine SSB whip.  I would _guess_ that you'd have a stronger signal if you added some counterpoise wires, instead of using just the copper grid.

Sea water offers a nearly perfect (no-loss) ground.  I think that means that ground losses, associated with "imperfect" radial systems in land-based antennas, don't have such importance on a boat.

25' is a little smaller than most SSB-carrying boats.  One proven antenna for "space-challenged" boats is a loaded dipole -- e.g., a pair of Hamsticks, or a Buddipole.  On 20m, those work quite well, and they completely eliminate all ground/counterpoise issues.

Don't fret too much.  Most boat grounding systems are built iteratively -- you keep adding stuff to the ground/counterpoise until you're happy with your signal.

Tom Rauch:
Marc,

At radio frequencies a wide copper strap simply looks like two thick conductors spaced some small distance apart in parallel. Current tends to bunch up at the outer edges of the wide flashing with a minimum in the very middle area. The fact the magnetic field is distributed over the width reduces inductance.

A second effect is distributed capacitance is increased.

A wide flashing has less impedance than a single round conductor even though it has more loss resistance than a round conductor of the same surface area and materials.

Now think about what we are doing with multiple wires. When we use multiple wires spaced some distance apart, we have essentially the same thing at radio frequencies. We have distributed the magnetic field over a larger area and reduced inductance, we have increased distributed capacitance. We have paralleled two (or more) wires increasing capacitance.

The only real difference is at very low frequencies where the lesser amount of copper might have increased resistance.

There isn't any electrical reason in the world a single copper flashing would work better as a ground than parallel wires in an HF antenna system. The copper flashing is probably better mechanically, but that won't make the signal change. Two wires spaced a foot or more apart would probably be better than a single copper flashing four inches wide for that radio ground. It's all a matter of spreading the current out.

73 Tom

Alan Applegate:
I have installed an Icom IC-706 and an AH-4 in a 45 foot cat (I'd like to say I owned it, but I don't). Each hull has its own keel plate. Every metal object on the boat is grounded to these keel plates in one fashion or another. They are connected together by a flat copper strap about 2 inches wide.

The AH-4 is in the left hull and feeds the port mainstay (about 60 feet in length) with a short jumper, about 12 inches or so. The ground side is connected to the keel plate with about 18 inches of copper strap similar to the one connecting the plates together. With the combination, it will easily tune 80 thru 10.

This combination works better than the trapped vertical which failed less than 30 days after it was installed (aluminum and salt water just don't get along).

Alan, KØBG
www.k0bg.com

John:
Marc,
I've not only done many HF Marine installs (on my own boats, as well as others), I regularly operate HF Maritime Mobile.....(both Ham and Marine HF)

I'll try to answer your question in as simple way as possible, and if you wish further info / explaination, PLEASE get in touch with me via e-mail or phone.....
I'd be glad to help.....

First off, I'd say give your set-up a try.....if it works fine for you, with no ill effects (no RF into anything on board, and no RF feedback into your rig), then you're home free.....
Attaching the copper strap to a short piece (6") of the 8ga wire (that you've already got glassed-in) and running that to the AH-4's ground lug, would be what I'd recommend......



Most of the confusion you're having here can be traced to the "multiple meanings" of different words, depending on who is speaking them......

And, a secondary factor to the decrepancies you note, are the widely different users / applications....
(Hams may want/need to work only on 20 meters, or maybe only 40m and 20m.....and will put up with inefficiencies and other problems that would be verbotten in the world of commercial Marine  radio....... While those needing HF Marine communications for Safety, etc. on many HF bands 2, 4, 6, 8, 12, 16, 18, 22, and 25 mhz, all with NO problems, and near instant access, will in essence NEED a different system design, that the hams find more than adequate......}


The electrons flow the same way they've always flowed, and whether you're on 40m CW or on an 8Mhz Maritime frequency, whether you're on land or on the water, your antenna and grounding set-up can be optimized in similar ways.....



"counterpoise"
"RF Ground"
"radial"
"ground wire"
"ground radial"
"ground screen"
"low inductance RF Ground connection"
plus some other words.....

All of the above might seem to be words desribing the same thing, and many people do use them interchangably, BUT they are NOT all synominous.....
They ALL have different meanings.....

Point of fact:
When someone (Gordon West, etc.) mentions that wire is no good as an RF ground, they are NOT speaking of using that wire AS the counterpoise (such as you'd do in a landlocked installation), but rather they are speaking of NOT using wire as a low inductance (low RF loss) CONNECTION to your counterpoise......
The counterpoise, in these cases IS the WATER.....(most noteably, sea-water.....as known as the next best RF counerpoise behind a copper-plated Earth....Hi, hi...)

When you, (or anyone) builds an antenna needing a counterpoise (such as a end-fed vertical, etc.) on LAND, you'd use some wire.....either, "tuned" to 1/4 wavelengths on each band, and placed/mounted ABOVE the ground (above the grass/earth/dirt) by 1'- 6' high....(known as an "elevated" radial system or "tuned-elevated" radials)
or you'd use some "non-resonant" radials, laid ON the ground / buried a few inches.......

Marc, please note that, "tuned, elevated" radials, make a VERY good counterpoise for the specific frequencies they're made/tuned for, whether they are used on land, or on a boat......
BUT, a few things to consider are:
1)  Why not take advantage of that infinatly large, wideband counterpoise right around you.....the sea water????
2)  Do you want the added complexity of mounting, rigging, installing  "tuned" "radilas"????(or the possible safety hazard of laying out radials on a deck???)
3)  What about use on frequencies other than one or two ham bands????

AND, on land, if you'd use a "random length wire" for the antenna, and also for the counterpoise.....you need to remember that all the RF energy that goes into your counterpoise, goes 3 places....
1) some may get radiated, 2) some is disapated in the ground (earth), and 3) some can run back into your shack, or get "choked" off by a balun, isolator, etc....
On a small boat, that RF energy that flows through the counterpoise / ground system NEEDS to be kept out of the various sensitive electronic equipment on board, and therefore, you should look for a way that it can be radiated (either by the sea water or "tuned radials"), or shunted to ground (attached to the water, etc.).....
This simple problem (RFI) is why many hams on boats swear by resonant antennas (dipoles or verticals with "tuned" radials), as they do not suffer nearly as much from the dreaded RFI problems of end-fed random length antennas.....
BUT, resonant antennas are just that, "resonant"....
and are therefore NOT multiband / multi-frequency antennas that are needed for other HF applications on board (such as Offshore use of HF Marine Frequencies from 2 mhz thru 25 mhz....)




Again, back to my original point.....confusion....
What many (Gordon West, etc) recommend is in FACT, using a low inductive "RF Ground Connection" to your counterpoise.....
Whatever that counterpoise may be......
1) A couple of Giant DynaPlates (such as I use on my 47' sloop)
2) A copper screen, capacitively coupled to the sea water (such as you've done)
3) Connecting all the bronze thru-hulls together, along with keel bolts, metal tanks, etc. all with copper strap/foil (as many others do)
4)  Attaching "tuned" radial wire directly to the tuner/coupler ground connection (as others do, also)

They are NOT saying that wire cannot be a counterpoise.....but that if you want a very wideband installation,  which IS the primary reason for using a random length wire/backstay antenna fed by a remote automatic antenna coupler (AH-4, AT-140, etc), in the first place, use a wideband low loss counterpoise (the sea water) and connect to it with a low inductance (low loss) connection (3" - 6" wide copper strap / foil)


An HF antenna (and whatever counterpoise may be needed), on a small boat is a COMPROMISE.......
That's an agreeable fact that you'll get little arguement on......

But, your application, whether an occassionaly rag-chew with friends on 40m or use as a piece of safety gear on offshore passages, will be a factor in deciding what antenna / counterpoise set-up will work best.....
(this is also a fairly agreeable fact..)

Marc, I do hope this helps clear up a few things....

To sum up:
 Offshore Marine HF (primarily for safety / weather) applications, actually REQUIRE a different set-up, than a "sailing" ham who just wants to rag-chew with some friends on only 1 or 2 bands......
 This combines with a casual use of words / terminology, and the blurring of those word's meaning, and ends up with many thinking that "hams" say one thing, and "sailors" say the opposite.......
Which, of course, is NOT the case......it's just confusion based on the misunderstanding of the words/terminology, and a slightly different take on the preceived application.....
  Remember, what I wrote above...electrons flow the same way for all of us....whether on an HF ham band, or an HF Marine band....whether on land or at sea....


One last thought.....
There isn't a lack of technical knowledge / expertise on this subject, just a lack of understanding of the basics.....and that's what frustrates those of us who've been doing this for so long....

73,
John,   KA4WJA


P.S.  
I assisted in my first HF SSB Marine install in 1975, and I've installed / troubleshooted / repaired many since then as well as operating on both Marine HF and ham HF from sea for more than 25 years......

My present HF set-up, on board, is an Icom M-802 Marine HF Transceiver with an AT-140 remote antenna coupler, an insulated backstay (approx 60'), fed with GTO-15 wire fron At-140 to backstay, and 8' of 6" wide copper strap (4 times thicker than the "foil") running to 2 Giant Dynaplates (each 12" x 18") mounted about 2' - 2.5' below the waterline, along the boat's centerline, for my RF counterpoise.......
It works GREAT 1.8mhz - 29mhz.....(Marine and Ham), with constant reports of "can't believe that's only a 100 watts!..." and "loudest Maritime Mobile on the air..."

73,
John,  KA4WJA


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