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Old 17-05-2011, 22:41   #1
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411 Earthing Wire

on my bene 411 i found a earthing wire connected to the keel bolt running to the house batters and not connected to anything so ive connected it to the neg. terminal(mush the same as to the engine block)any one got anything simerlar.bill
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Old 24-05-2011, 12:29   #2
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Re: 411 Earthing Wire

Connecting that wire can give you better lightning and radio grounds, but it can also lead to more electrolysis--that's probably why it was disconnected. If you want to use it for a radio ground, a capacitor will allow RF current to flow, but not DC.
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Old 24-05-2011, 12:32   #3
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Re: 411 Earthing Wire

Useless for a radio ground. HF radio waves are attenuated to ZERO in just a few inches of seawater. Anyway, you don't want to attach your radio (RF) ground to any other ground on the boat (DC ground, lightning ground, bonding system).

Bill
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Old 25-05-2011, 06:39   #4
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Re: 411 Earthing Wire

Quote:
Originally Posted by btrayfors View Post
Useless for a radio ground. HF radio waves are attenuated to ZERO in just a few inches of seawater. Anyway, you don't want to attach your radio (RF) ground to any other ground on the boat (DC ground, lightning ground, bonding system).

Bill
could it be an earth for the motor as theres no zingks on the yanmar(just the shaft one)
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Old 25-05-2011, 07:29   #5
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Re: 411 Earthing Wire

Hi bigpuff,

On my bene 393 the only wires I remember connected to the keel bolts were the ones tied to the shrouds for lightning protection.

Frank
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Old 25-05-2011, 11:59   #6
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Re: 411 Earthing Wire

The zincs on the shaft are connected to the motor. Tying the keel to the motor sets up an electrolysis battery, as the potential for the keel material is different than for the bronze prop and SS shaft.

I don't know what Bill has been smoking--a metal keel will make an excellent RF ground, for exactly the reason he stated.
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Old 25-05-2011, 12:26   #7
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Re: 411 Earthing Wire

Quote:
Originally Posted by donradcliffe View Post
.....

I don't know what Bill has been smoking--a metal keel will make an excellent RF ground, for exactly the reason he stated.
Well, Don, it must have been some pretty strong stuff :-)

But, I stand by my statement: RF is attenuated to near ZERO in just a few inches of water.

The purpose of an RF ground -- as contrasted with all other types of grounds on a boat -- is

1. to provide "the other half of the dipole" to generate the electro-magnetic radio waves; and

2. to collect RF energy to be channeled back to the feedpoint of the antenna where it can be retransmitted in a slightly different phase. The sea SURFACE, not depth, is very useful for this purpose.

The sea surface is also very good for bouncing RF energy up to the ionosphere.

All you do when you feed RF to any depth below an inch or two of seawater is heat the water!

Bill
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Old 25-05-2011, 12:42   #8
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Re: 411 Earthing Wire

Bill, I'm still not comfortable with your RF ground theory. You could be right, but I'm not sure.

How would you analyze this case:

Replace the ocean with a massive chunk of copper. Carve out a little hole for your boat and keel. Connect your RF ground wire to the copper under the keel. Is this a bad ground at (say) 14 MHz?

Or, instead of the boat, just drill a six-foot deep, one-inch diameter hole in the copper and attach the (insulated) ground wire to the bottom of the hole. Is this a bad ground? How bad is it?

My fields and waves theory isn't good enough to be able to visualize this.
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Old 25-05-2011, 12:54   #9
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Re: 411 Earthing Wire

Paul,

Basic point is that there's no need for external ground plates or for connecting to something deep down in the bilge.

When you connect to the keel, for example, the beneficial part of that connection isn't the keel itself, but the long copper foil or wire run to the keel.

Consider the "100 sq ft of copper" recommendation. This is about the most persistent myth found in most of the SSB literature, including many instruction manuals. It's demonstrably garbage.

Radials -- including radial WIRES -- work very, very well. This fact, not claim, belies another myth repeated over and over in the SSB "literature", i.e., that you can't use wires for a ground system because RF travels only on the surface and you must, therefore, use only wide copper strips. Garbage! Total, unadulterated garbage. And, again, demonstrably so.

Gordon West himself, after making the "100 sq ft" recommendation for years, actually did some tests with a colleague and found that a simple connection from the tuner to the nearest bronze thru-hull worked just fine.

Many hams know the benefits of radials. The KISS-SSB radial ground system, for example, works like gangbusters. It consists of a bunch of small wires of carefully worked out length stuffed into a 10' length of rubber hose.

There is no real need to connect to seawater, either directly or "capacitatively". Radials on deck or in the bilge work just fine. In fact, there's good evidence that elevated radials work better than grounded radials.

I've installed many RF grounds on boats which consisted of using s/s rub rails, pushpit/lifelines, pulpit complex, rudder housings, big aluminum swim platforms, resonant and non-resonant radial systems, etc., etc. All of them work very, very well. No need to connect to seawater.

Folks can do what they want -- and they will, because everyone has their own beliefs -- but I'm here to tell you from my long experience as a ham and as a sailor and as a professional SSB installer and as a Net Controller on several HF maritime nets (having talked to literally hundreds of boats on thousands of occasions) that you should be wary of many things published re: SSB RF ground installations.

Bill
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Old 25-05-2011, 13:05   #10
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Re: 411 Earthing Wire

Bill, thanks for the overview. I do understand that there are many ways to build an effective ground system (I'm a ham, and an electronics engineer with RF product design experience).

What I don't understand is the concept that a seawater connection at the bottom of the keel is significantly worse than a connection at the surface, especially at HF frequencies.

By the way, it is very well known that a good elevated radial system is superior to a buried radial system when there is a lossy ground substrate. I don't think that seawater is lossy enough to make a difference when used with anything we can install on a boat.
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Old 25-05-2011, 13:14   #11
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Re: 411 Earthing Wire

Paul,

The surface of seawater is a great conductor, as you know. But RF at HF frequencies does not travel thru seawater beneath the surface....at least not in any amount to be useful.

Arguably, then, you'd want to put any RF in contact with the surface of seawater, not it's depths, in order to derive any beneficial effect of return to the feedpoint of the antenna.

As an EE and experienced ham, you also know that even without such return, antenna systems can work very well...they just might not have that little boost from re-radiated RF. And, in all practical setups aboard, there will be considerable return anyway thru the connected wires, copper foil, etc.

I'm certainly not one to claim that connection to the keel won't work or is necessarily less effective than some other RF grounding schemes, but it ain't necessary and could, e.g., introduce problems (such as the keel bolts also being used for the DC system ground or lightning ground or bonding system ground, etc.).

If I may draw a rough analogy from practices common in the ham world:

It used to be claimed that radials should be buried, or that a good RF ground consisted of a long iron bar driven deep into the ground. Consider that analogous to pumping RF deep into seawater. Ground is lossy, even damp ground. Seawater, at any depth below a few inches, is very lossy.

Contrast that with elevated radials. They're more effective than buried ones, or ones lying on the ground. Why? Because, presumably, they are not then coupled to a lossy ground, but are free to return all "captured" RF to the feedpoint, and to work their magic in creating a strong electro-magnetic field.

Or, so methinks, anyway :-)

73,

Bill
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Old 25-05-2011, 13:45   #12
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Re: 411 Earthing Wire

(bigpuff, sorry for the hijack. I think you've already got your answer though.)
Quote:
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Ground is lossy, even damp ground. Seawater, at any depth below a few inches, is very lossy.
And this is where I have questions. Soil is lossy -- it is a poor conductor. It has high resistance and the much of the RF power traveling through it is converted into heat rather than being radiated.

Copper is not (very) lossy. It conducts well, has low resistance, and makes a good radiator.

Seawater falls somewhere in between. You seem to be talking about loss due to shielding geometry, rather than loss due to poor conductivity.

As for the geometry, we do have a surface contact to the seawater, at the interface between the hull/keel and the water. This interface runs along the outside of the hull up to the surface of the ocean.

If it is a conductivity problem, then a properly-dimensioned elevated counterpoise should be superior to any seawater connection, at the surface or below.

So is this a geometry problem? A conductivity problem? Both? Something else?

I might just have to bring some test gear down to the boat and make some measurements. This could be interesting. Or, I might go sailing instead, it depends on the weather and wind.

73,
Paul - wb6cxc
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Old 25-05-2011, 15:06   #13
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Re: 411 Earthing Wire

Hah...that's always been my problem! Much rather sail than do antenna tests :-)

But, I've spent a lot of hours puzzling things myself, and in deep -- and sometimes boozy -- debates with other knowledgeable and experienced ham/cruisers.

One thing I've always wanted to do is to set up tests which could be revealing and reasonably reliable. However, when I and my colleagues with boats have actually tried to work out the protocols for the testing, we found that it is no small matter to design a series of tests which could conceivably come up with reasonably definitive answers.

The variables are many -- astonishingly so. While we have all the platforms and the radios and much of the test equipment which would be required, and we have lots of friends who would love to work the "other end" or "other ends" from their boats in different locations, the time and effort required would just be excessive. Worthy of a substantial Federal grant :-)

In the absence of such testing results, what we are left with is dealing with real-world installations -- good and bad. And, mediocre. As a Net Controller and a participant in maritime nets from many parts of the world over the past forty years or so, I have had contact with many boats in all three categories, on several bands (mostly 40, 20, and 15 meters), over short and long distances (e.g., trans-Atlantic), and all sorts of propagation conditions affected by all phases of several sunspot cycles.

What have I gathered from this experience?

1. Antenna systems are extremely important, and vary in effectiveness from boat-to-boat. "Antenna systems" means the antenna itself, the feedline, the tuner, the coax to the transceiver, and the entire RF ground system.

2. Transmitter power is relatively unimportant.

3. User experience and operating skill is extremely important.

4. The ubiquitous end-fed backstay antenna is pretty good on many bands, but not really good on any band.

5. The most effective seagoing DX antenna you can rig on a sailboat is a single-band vertical dipole, rigged with the lower insulator near the deck and trimmed for resonance on the intended band. 20m and 15m vertical dipoles are particularly good; 40m vertical dipoles are less good and approx. the same as a good backstay installation.

6. Power connections to the radio are important, to provide good voltage to the radio when transmitting, and to reduce RFI.

7. There are many ways to skin the "RF ground" cat. Tuned radials are especially good, but there are many other good solutions as well (some mentioned in an earlier post).

8. There's a lot of misinformation out there, from books, instruction manuals, and from users who think their installation is the best (often, because they've spent a lot of time and effort setting it up, and they've made a "1,000 mile contact").

Talk about thread drift....I may win the prize on this one.

Sorry!

Bill
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Old 31-05-2011, 09:08   #14
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Re: 411 Earthing Wire

i got lost 5 threads ago.thanks for all the info though
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