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Old 08-01-2009, 10:48   #16
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Will it work? Yes, absolutely. Mine has worked flawlessly for 19 years now, as have those I've installed on customer's boats :-)

Install the tuner as close as you can underdeck, and run a length of GTO-15 wire from the tuner to the "alternate backstay". You can just put loops in each end of the s/s wire, using Nicopress sleeves w/thimbles if you wish, and use 2' or more of poly line at each end to support it. This line serves as insulators.

One healthy wide heavy copper strap from the tuner to the nearest bronze thru-hull is sufficient. The thru-hull should not be otherwise bonded to the boat's grounding system. If you're worried about corrosion potential, follow Stan Honey's advice and make up a capacitive blocking device to install in the ground strap (or purchase a commercial equivalent). This allows AC currents to pass unimpeded (RF is AC), while blocking potentially damaging DC current.

Later, if you wish to improve transmitting performance a bit -- or, if you're having trouble tuning on a particular band -- install some 1/4-wave radials underdeck (consisting of any type insulated wire, 1/4-wavelength long at the desired frequency).

Bill
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Old 08-01-2009, 11:10   #17
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Bill is the man when it comes to this stuff!

Hey Bill, I have not be able to access your excellent pictorial on Dipole antennas. Any chance you could get it back up? I can provide web/gallery space if that is what you need.

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Old 08-01-2009, 14:42   #18
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Many thanks to Bill, everyone on this thread and on this forum for that matter. This has been an immense help.
Kirk
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Old 08-01-2009, 19:23   #19
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Originally Posted by btrayfors View Post
<snip>...
1. Forget the ground plate...you don't need it. If you've already bought it, sell it or give it away......<snip>
Bill, I am aware that you don't suggest the use of the dynaplate from other threads and I don't have any problem with that; however could you explain why you feel that the nearest bronze thru hull is essentially better than the dynaplate.

Apart from say the additional cost, I can't see any real difference between using one or the other. What am I missing here?
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Old 09-01-2009, 00:30   #20
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Hi Bill, many thanks for the advice - I have a cat with a Dyna plate already installed, as well as the tuner directly under the whip antenna and amabout to complete the installation of the ICOM 802. Boat is in the water - is there a valid reason why I should not use the Dyna Plate or do you just consider it not so necessary from the get go ??
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Old 09-01-2009, 05:11   #21
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Chris,

Thanks much for the server offer. Actually, we have the new gallery software up on a new server, and are awaiting the return of our technical person from Europe to migrate the database of photos into the new software.

Hopefully, it won't be much longer.

If you need a specific pic, let me know and I can email it to you. Just shoot me an email: bill at wdsg dot com

Sorry for the inconvenience.

Bill
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Old 09-01-2009, 05:43   #22
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Groundplate or Not?

Wotname and Paul,

It's not that external ground plates are a bad thing so much as they are, IMHO, completely unnecessary in many installations. I know I'm swimming upstream in this belief, given the preponderance of advice given in most texts and by many techies and satisfied users.

Let me try to explain my reasoning.

1. Since RF is heavily attenuated when travelling thru only a few inches of seawater, it makes little sense to me to try to "couple to seawater" by connecting to a fitting which is a few feet below the surface of seawater. All you're doing is creating a decent DC ground -- not a bad thing in itself -- and helping to warm seawater as RF energy gets routed to the groundplate.

2. Actual in-water tests were done some years ago by Gordon West. He and his colleagues found that a ground strap from the tuner to a nearby bronze thru-hull did the job just fine -- and as well as other alternatives they tried.

3. I believe that the reason both solutions work just fine is that the copper strapping leading from the tuner to the thru-hull or ground plate is what is doing the actual work, not the fact that it's connected to a fitting deep underwater. It's serving as a radial or, if you will, the "other half" of a dipole antenna.

4. There are many ways to create a good RF ground, as noted in the piece on RF grounds referenced above. Wire radials, lifelines/pulpits/pushpits, copper straps, aluminum toerails, aluminum swim platforms, stainless rub rails, aluminum hull-to-deck beams, radar arches, etc., etc. have all been used successfully. Often, in my experience, these solutions work better than the traditionally-prescribed groundplate or keel solutions.

That said, I've come to believe that a "belt-and-suspenders" solution may be optimum for many situations. That is, by all means connect a copper strap or heavy wire from the tuner to the nearest bronze thru-hull or other underwater fitting which is not otherwise grounded to the boat's DC ground system. The purpose is twofold: (1) to serve as a ground to bleed off static electricity and other spurious signals on the antenna system and thereby help reduce noise; and (2) to provide -- via the copper foil or wire itself -- a radial. This, alone, will work OK. That is, the tuner will tune up on most or all bands.

However, the "suspenders" part is to improve the RF ground by tying in additional radials or metals which can serve as RF collection devices to route emitted RF back to the transceiver to strengthen the overall radiated signal. These need not be "coupled" to the seawater. In fact, they are often more effective when they are located above the seawater to serve as "elevated radials". Hams who have experimented with radials know that they work very well, and that elevated radials work better than those buried underground.

Every boat installation is different. Even those with the same make and model boat. That's why it's important to experiment a bit, and not be rigorously tied to a single approach.

One final thought. Nothing substitutes for actual experience in communications. You can take a newbie to radio and an experienced operator -- give them a shot at exactly the same radio setup to play with and make contacts. The experienced operator will be able not only to make contacts, but to have a pretty good idea of how well the installation is working.

The newbie, through no fault of his own other than being inexperienced, will not be able to tell whether the installation is a good one or not. He/she may be inclined to say it's a good installation if some contact is made with another boat, and this may not be the case at all. After all, in the ham world there's the guy in hospital with a transceiver coupled to his bedsprings and happily talking away on the air. Yeah, it can be (and has been) done, but no one is gonna say that the setup was a particularly good one :-)

On a bet once when I was stationed in Morocco in the late seventies, I hooked an Atlas 215X thru a tuner to an 8' long aluminum curtain rod on the wall, called a station stateside, and got an immediate, "Yeah, CN8CW, you're five nine" (a strong signal report). Terrific as a stunt, but no one there was prepared to argue that the 8' curtain rod would outperform the 5-element monoband beam on a 70' tower outside :-)

Bill
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Old 09-01-2009, 07:06   #23
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Bill, not to keep re-hashing the dyna plate, but if it is already installed on my boat before the radio installation would it be wise to abandon it or would it be fine to go ahead and use it?
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Old 09-01-2009, 08:04   #24
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If it's in good shape, go ahead and use it. Just be sure that connections are good between the plate and the copper strap, and between the strap and the tuner.

See how it works. You can always add radials later if needed/desired.

B.
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Old 10-01-2009, 11:05   #25
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I read a long time ago, taht if you use a galvanic isolation system, and you connect the counterpoise system to the thru hulls and fuel tanks that taht is much better than trying to come up with 150 sf of copper sheeting in the bilge for counter poise.
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Old 12-01-2009, 07:34   #26
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I don't think this has been mentioned already, so remember that the antenna starts at the output terminal of the antenna tuner. If using a simple backstay antenna the length of GTO-15 needs to be added to the length of the insulated part of the backstay when calculating antenna length. See AT-140 installation manual page 1 regarding undesirable antenna lengths.

If adding a Pactor set-up, its well worth fitting a coax line isolator, located just before the antenna tuner to reduce stray RF interference. Also fitting of clip on ferrites to data cables can help if you have interference problems, particularly with autopilots as the M-802 can put out 150 watts. See Jim Corenmans excellent advice on this subject at SailMail Primer

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Old 14-01-2009, 01:06   #27
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Quote:
Originally Posted by btrayfors View Post
Wotname and Paul,

It's not that external ground plates are a bad thing so much as they are, IMHO, completely unnecessary in many installations. I know I'm swimming upstream in this belief, given the preponderance of advice given in most texts and by many techies and satisfied users.

Let me try to explain my reasoning.

1. Since RF is heavily attenuated when travelling thru only a few inches of seawater, it makes little sense to me to try to "couple to seawater" by connecting to a fitting which is a few feet below the surface of seawater. All you're doing is creating a decent DC ground -- not a bad thing in itself -- and helping to warm seawater as RF energy gets routed to the groundplate...............<snip>
Bill
Bill,

Thanks for the long and detailed reply. It's you first point that I find most interesting - I am not doubtimg your opinion but I have never really considered the RF attentuation of seawater. I just sort of considered it to be reasonable. In say, comparing last based masts where we try to ensure the ground is marshy or at least damp, then I figured sea water would have to a lot better.

Your point about using whatever metal is availble for the ground plane is totally accepted.

Thanks again.
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Old 14-01-2009, 04:12   #28
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There are some leaps of faith here that are just plain incorrect physics.

First, the fact that the rf field only penetrates a few inches (at MF and HF) actually indicates seawater is a very good "conductor" not a poor one. The depth of penetration into the ground or water of the rf field is due to skin effect and is not to do with how deep it can "conduct" itself to. This can easily be seen by considering if we have our antenna mounted over a thick copper plate the depth of penetration of the field into the plate will be only small fractions of an inch (I think we most all know that). That even though the copper plate is a far better conductor of rf than seawater is. And if we have our antenna mounted over very poor ground the penetration may be 10 meters or more - any check of the literature will show that to be so.

Second, as to metal fittings, copper plates or whatever is used as the "interface" to the sea for the ground then if one thinks about it they are not several feet under the sea as has been said, they are on the surface of the sea as the sea surface which the skin effect is on is the surface of the sea that wraps around the outside of the hull. The fact that the sea surface bends down around the hull is of little concern. Again that can be seen by considering a copper plate in air as the ground. Just because the copper plate is bent in some way it does not mean that the rf propagating through the surface of the plate by skin effect has to short circuit the bend by suddenly propagating through the air just because it finds the plate bent - the rf will follow the bent plate propagating by skin effect.

This is a touchy subject on marine forums and which I tend to avoid. So I will leave it at the above plain physics level and not get into grounding practices.
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Old 14-01-2009, 08:28   #29
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MidLandOne makes some good points. As often happens when we try to make very complex subjects simple-to-understand, we tend sometimes to trip over, skirt, or ignore the underlying scientific truths.

Yes, seawater (not freshwater) is a very good conductor of RF. On the surface.

Yes, just a few inches of seawater and freshwater both tend to greatly attenuate RF signals -- at the HF frequencies generally used for marine and ham communications.

Yes, it's true, submarines generally don't use HF for communications. However, they HAVE used VLF communications for many years over long distances, and at very slow "data rates". Recent advances and experiments in data communications have shown that RF communications underwater may be useful for niche applications, generally over relatively short distances. But, for our purposes, these facts are irrelevant.

Yes, the skin effect MidLandOne speaks of is real and important in HF/RF communications. The "bent conductor" phenomenon may be important as well when we think of "coupling to seawater". One thoughtful individual has toyed with the thought that bottom paint containing heavy concentrations of copper may serve as an excellent medium to couple HF/RF to seawater.

One test I have read about claimed that direct coupling to seawater is far more effective than is the famed "capacitive coupling" we often read about.

What we're dealing with here is the interface between the physics of RF propagation at HF frequencies (which we understand only imperfectly) and the art and practice thereof (which is frought with even more uncertainties) -- all as applied to operations in the small boat environment (which has it's own significant variations and permutations).

It's a true wonder that any of this works at all :-)

Bill
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Old 14-01-2009, 10:05   #30
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does anyone really need to understand any of that when installing a ssb? because if I do then I'm screwed.
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