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Old 13-08-2008, 23:48   #1
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An unusual SSB install

I have read heaps on SSB installs but can't decide on the best route for me.

As I have no stays I will most likely run a whip off of somewhere but I am probably not going to have a targa bar so the location is rather open. Don't really like the idea of any stayed poles at the rear and I doubt the carbon masts will make a good arial

I was tending towards a set of radials or a mesh glassed on under the bridge deck but wonder about the implications of lightning with it only being 1" under my feet. This leaves the saildrive legs, don't like, or a dedicated penetration for the earth, say a 3" diameter bronze disk through bolted.

As construction is getting more advanced I will need to make some decisions soon to build it in. Any ideas will be gratefully considered

Mike
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Old 14-08-2008, 08:18   #2
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Hi, Mike.

I have an SSB, but am not a techie. I should probably just wait for Bill Trayfors to chime in, but since your post scrolled of the "Portal" page, maybe he won't see it.

Your idea of installing copper radials or mesh in the bridge deck is intriguing, but my understanding from what I've read is that the counterpoise needs to be close to the water (e.g. up against, or embedded in, the hull below the waterline) so that inductive coupling can take place.

OK, Bill, your turn!
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Old 14-08-2008, 09:23   #3
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please see private message i sent you.
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Old 14-08-2008, 10:50   #4
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Have you considered an external copper tape glassed on one of the masts?
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Old 14-08-2008, 12:48   #5
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Mike, my understanding is that if you put radials under the bridge deck they will form a "counterpoise" to the other half of the antenna, but if you put tape down in the hull, under the waterline, it becomes capacitively coupled to the ocean--effectively becoming an RF "ground" and performing better.

The Dynamplates (sintered bronze--not plain solid bronze) have a good reputation for making RF ground to the water, but they are also not lightning grounds. They're apparently problematic because a strike can superheat the wate rin them and blow them up. (Ooopsie.)

You might very well be able to use the CF mast as an antenna, because it is an electrical conductor, albeit not a great one. I've never heard of someone doing it that way--but you might be able to clamp your antenna wire to the mast at some elevation and tune it to resonance. (Emphasis on "might", experiment, and SWR meter all required.<G>) Putting a stick on the stern quarter and running tapes down under the waterline is probably going to be the fastest, cheapest, most reliable, highest performance, all in one shot.

Bear in mind that every marine SSB installation varies--even on "identical" boats, so the question is how much are you willing to experiment, versus trying to get the best compromise the first time around.
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Old 14-08-2008, 14:49   #6
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I don't know much about multihulls. But, I do know a thing or three about radios, so I'm told :-)

RF grounds come in various flavors. HelloSailor is correct in saying that each boat is different, even "identical" designs.

Hud3 is correct in saying that (many "authoritative" sources) recommend building a counterpoise which is coupled to seawater, either directly or via "capacitative coupling".

The problem with many "authoritative sources", including manufacturers of HF radios, is that they're wrong. Dead wrong. And, they're very slow to admit it.

Forget the now infamous "100 square feet of copper"; that's pure bunk!

Forget the "round wires won't work....you must use wide copper strips, because RF travels on the outside". Partial truth, but the implication is that wires won't work and that's pure bunk.

Forget the admonition that Dynaplates or external grounding plates are required, or are the "best" grounding. That's nonsense.

Forget the notion that you "must" build a RF ground which couples to seawater. That's pure bunk.

Forget the notion that radials must be buried deep in the bowels of the vessel, so that they can "couple" to seawater. Nonsense. Any experienced ham can tell you that elevated radials work better than buried radials.

Forget the notion that you must couple to seawater far under the surface. Nonsense! RF energy is greatly attenuated by just a few inches of seawater. Ever hear of submarines using HF to communicate with one another? Of course not. All you're doing by coupling deep down to seawater is heating the ocean...a miniscule amount.

There are lots of ways to build an effective RF ground system. See my "RF Grounds in the Marine Environment" discussion on the SSCA website and elsewhere.

Want to do something simple and effective (Gordon West and I agree on this)? Just run a 3-4" copper strip from your tuner ground lug to the nearest bronze thru-hull (which is NOT otherwise bonded). Presto...you have an effective RF ground!

Can you improve on it? Yes, of course. Radials help. More copper helps. Other metals in the hull help (NOT keels, for reasons cited above). But how much? Probably not enough for you to notice.

Does imbedded copper (at the time of hull layup) help? Yes, of course. If you've got the chance, do it. Pay attention to connections, so that surface corrosion won't spoil a good ground.

Do radial wires work? You betcha, they do! Especially 1/4 wave radials.

Do they need to be made of copper strips? No. Any insulated wire will work. Be careful to insulate the ends...they're hot!

Do they need to be close to seawater? NO, not at all. Elevated radials work very, very well.

Aluminum toerails work very well. Pushpits, lifelines, pulpits work very well. S/S rub rails work quite well.

Aluminum angle iron used for hull-to-deck bonding in some boats work very well.

Interior "RF grounding paint" works quite well, I'm told (but have not direct experience).

Don't be afraid to experiment. This ain't pure science. It's an admixture of physical science and art, due to the fact that -- as HelloSailor said -- each boat is different.

Bill
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Old 14-08-2008, 21:14   #7
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Quote:
Originally Posted by sandy daugherty View Post
Have you considered an external copper tape glassed on one of the masts?
Sandy
Thats a **** hot idea, hadn't crossed my mind. Even without a good connection to the mast I would think it would couple into the carbon and make it part of the element. Only problem may be that the masts will be folding, have a local 7 meter bridge to contend with, so I will need straps to bridge the hinge. Being able to rotate 360 degrees means the connection will need to be below the bottom bearing which may be difficult. Will have a talk with Rob Denney to see what he thinks of his creation being radiated This would put the tuner up forard which shifts the ground question around considerably


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Originally Posted by btrayfors View Post
Want to do something simple and effective (Gordon West and I agree on this)? Just run a 3-4" copper strip from your tuner ground lug to the nearest bronze thru-hull (which is NOT otherwise bonded). Presto...you have an effective RF ground!

Can you improve on it? Yes, of course. Radials help. More copper helps. Other metals in the hull help (NOT keels, for reasons cited above). But how much? Probably not enough for you to notice.

Bill
Bill I have read most of your stuff over at SSCA and it is your comments along the line of the above that makes me wonder if I , and many others, stress too much and overcomplicate the issue. I have worked in many areas of electronics but unfortunately never in radio comms equipment so have no experience to draw on.

There is nearly no sizable metal on board apart from motors, pushpit and galley equipment. No metal thru hulls which is why I was thinking of a dedicated bronze disk, although if the tuner is forward this will be difficult as the entire subfloor area is a network of sealed chambers. I could always put in a sealed port to access one however.

Radials, to me seem a good option but at 1/4 wavelength I don't know where I would put them. Under the bridge deck is only 7 meters and anywhere else is either very visable or would run close and parrallel to all the other electrical/electonic wiring.

Then there is a mesh imbeded in either the bridge deck or the cabin roof. How many square feet would be appropriate. In your estimation does this style of ground compare well to radials or a single direct water connection.

Due to the shape of a cat and my situation there would be quite a significant distance between the tuner and one of the ground planes if I opt for a combined system. With 2 six meter booms free to rotate the only place I could put a whip would be the very outer aft quarters or on top of the dingy davits.

I think I am tending towards a whip on the port stern quarter with just a bronze disk imediately below in the head with the tuner in a cocpit locker which gives runs of about 2 meters for the earth and 3 meters for the GTO cable. None of which is anywhere near other wiring, although this gives a long run from the ssb to the tuner which will need to follow other wiring. Hate power rf near anything, don't ask why or I may have a rant about comms guys who have caused me much grief in the past

Thanks for all contributions everybody
Mike
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Old 15-08-2008, 18:10   #8
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Another option to think about. Iv'e seen several high tech racing boats, kevlar, foam, carbon fiber mast, that use just a 14 gauge wire inserted into the braided line used for the topping lift. When removed from the boom it is attached to a fitting at the stern and the wire is long enough to reach the stud on a thru-deck insulator that is connected to the tuner below deck. Very simple, works great. You wouldn't really need the tru-deck insulator as you could just have a short section of wire coming out thru a normal thru-deck watertight fitting.

Eric
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Old 15-08-2008, 18:23   #9
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Mike,

You don't necessarily need 1/4 wave radials. Radials of any length will work, and they can be folded, bent around corners, etc. More shorter ones is better than fewer longer ones.

The bronze plate under the tuner could work. But, you could also just use some wide copper stripping. Not the thin stuff normally sold by radio stores (because it degrades over time, physically). The thicker stuff isn't any better electrically (at HF frequencies), but it will last much longer in the marine environment.

You can buy wide copper rolls, usually 10' or so in length and up to a couple of feet wide, at any good roofing store (it's used for flashing on rooftops). I've found that 16 guage works very well. Buy some tin shears also, if you don't already have them on hand. Cut the copper to fit whatever area you have, keeping it as wide as possible. You can solder pieces together to make them longer if needed. This will work very well.

If it turns out that there's a problem band, i.e., one that the tuner has trouble with, just cut a 1/4 wave radial made of any kind of insulated wire and string it in the bilge or under decks or wherever. The tuner then will be happy. But if you do the copper thing well, you probably won't need radials.

Bill
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Old 15-08-2008, 21:52   #10
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Eric
The boom is rigid so I won't have a topping lift. The only string going aloft will be the main halyard which will be internal. As the main has a huge headboard and large roach any line even to the most aft corner will be impossible.

Bill
What do you think of the idea to utilise the carbon mast as the radiating element. It is 15.5 meters. This would work very well from a connections point of view. The bronze disk would be imediately below and a cabinet right next to it to house the tuner would give connections less than half a meter to both. The run to the ssb would be short and not be near anything.

Why sheet and not bronze mesh. The mesh would be totaly encapsulated in epoxy so reasonably free of corrosion. Under the cabin top I would end up with very long connetions to the tuner regardless of where the aerial is. I could glass it up under the bridgedeck to give a lot shorter run.

Radials are difficult as I do not have bilges at all and I feel the only practical place to put them is under the bridge deck. Being able to fold them helps considerably. This would dictate a connection length of at least 4 meters in the case of using the mast. If using a whip at the aft corner it would be a lot shorter but then I would have long connections to the whip and bronze disk.

I see now why people call it art rather than science.

Mike
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Old 16-08-2008, 02:04   #11
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Mike,
FWIW, once you decide on a course of action, I would be happy to drop by and carry out any testing for you (by way of SWR) etc. I have a boot full of RF gear (as well as shop full that I can access). You might have to have a coldy ready to open .
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Old 16-08-2008, 04:48   #12
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Mike,
FWIW, once you decide on a course of action, I would be happy to drop by and carry out any testing for you (by way of SWR) etc. I have a boot full of RF gear (as well as shop full that I can access). You might have to have a coldy ready to open .
Thanks for the offer, I am probably just over a year away from splashing. I am sure I will take you up on it, assuming I ever decide.
I used to be very indecisive, but now I am not sure.

Mike
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Old 16-08-2008, 05:07   #13
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If you don't go for a seawater ground, the testing can be done whenever you antenna system is complete. If necessary, we can put a signal generator (HF freqs) onto the antenna via a manual tuner (got a couple of them) and see how the antenna system is going to perform. Not a guarantee but a good pointer
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Old 16-08-2008, 05:18   #14
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Mike,

While sipping my morning coffee and reflecting on your last post -- I feel your pain :-) -- I was thinking the same thing as wotname. Great minds and all that!

You don't have to make all the decisions now. The embedded bronze mesh should work fine. The more the merrier.

I don't know about the carbon mast, since I've never had occasion to experiment with them. It might work OK. However, if it doesn't there are still other options, including a stern-mounted whip.

Wotname's offer to help is very generous, and he's right: you could put a good antenna analyzer to work after the boat is built and get a pretty good indication of what's gonna work and what's not.

One further thought about RF grounds: I know very little about multihulls, but if you are planning to install rubrails on the outside of the hulls, they can work very well if they're metal. I've had good success in using aluminum toerails, lifelines/pulpits/pushpits, and s/s rub rails in the past. If you were going to a vertical antenna on the stern solution, it could be that a single s/s rub rail on the nearest hull would work fairly well.

You're right...it's an admixture of art and science, with a healthy measure of luck and insanity tossed in!

Bill
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Old 16-08-2008, 07:23   #15
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Testing would be good but the boat is under a roof that would prevent the masts being stepped. It wont come out untill it is nearly time to splash.

I will do some measuring of the various possabilities. All possabilities being equal I tend to favour the most closely coupled solutions.

I had forgotten about the rub rail, I have been thinking of having one despite the destruction of the clean look.

Wotname
How about if I find a carbon tube could we set that up just to do a comparison between it and a verticle wire. Maybe try a direct ground connection then a set of radials. Would at least give some confidence in using the mast

Mike
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