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  #61  
Old 03-16-2008
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Bill, then what's all the hullabaloo about needing to be in the water to transmit because of the counterpoise? Urban legend or is my understanding of the ground situation even worse than I had assumed?
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  #62  
Old 03-16-2008
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Maybe a bit of both :-)

Most "authorities" love to tout the "perfect ground" characteristics of seawater, and most references attempt to "couple" the ground side of a marine antenna system to that "perfect ground".

The truth is, there are several ways to create a good RF ground. One of them has little to do with the water. It is to use a system of "radials" or other things acting essentially as "radials" to provide the return path for RF.

In your case, you said you have "copper strapping all around the interior of the hull". That should serve as an effective counterpoise, quite independent of seawater.

Try it on one band to see how your tuner achieves a tune. Should work with no problem.

Bill

Last edited by btrayfors; 03-16-2008 at 07:49 PM.
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  #63  
Old 03-16-2008
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The unit definitely indicates that we're "tuned." I know that cause it says "TUNED" right across the screen once it locks in on a frequency. My powers of deductive reasoning know no bounds.

I'm occupied with Sunday evening kid stuff, so I can't get to the boat tonight, but I'm going to shoot you a message at some point to schedule a time to talk via SSB, if you're willing. Just curious to check it out. Likely to be one night during the week, or next weekend, if any of that works for you (not sure if you're on your boat, near your boat, or whether you have a home-based station, which is what I suspect).
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  #64  
Old 03-16-2008
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I've got a question for the experts who are hanging out in this thread -- it may be somewhat 'off thread' in which case I beg forgiveness, but here goes.

Billy Ruff'n is a steel boat. I bought her from a guy who was both a EE PhD and a HAM. He had an IC 707 installed using an insulated back stay as the antenna. He had installed a big dynaplate and had the radio grounded to it via a large round battery cable.

Because I wanted to assure my wife that 'help was always at hand' I replaced the 707 with an IC 802 linked to the GPS, so that with a push of the big red button she (alone) could tell the world we needed help. While installing the 802 w/ AT 140 tuner I decided, based on my reading, that neither the round ground wire nor dynaplate were optimal. Because everyone says a steel boat is a great ground plane, I grounded the tuner to the hull by sanding paint off a nearby frame and bolting a 8" cable from turner to the frame. It worked OK, but not great. Other boats told me my signal was not very good. (As I wan't a ham at that point, my only signal reports came from boats that were within a few hundred miles.)

Later I someone convince me that grounding the radio to the hull was inappropriate. His logic --- and this gets to the question I have --- his logic was the following: the antenna (backstay) is 'insulated' from the rest of the boat. Why then did I have the ground electrically connected to the rest of the boat up to and including the parts of the backstay that were not 'insulated'. His point seemed correct -- grounding the radio to a steel hull that is electrically connected to the rig is the same thing as grounding to everything but the antenna itself. Being too dumb to argue, I rewired the tuner ground to the dynaplate, but this time I used a 3" wide copper ribbon (wrapped in tape to prevent it from grounding to the hull on its way to the dynaplate). Voila, I instantaneously got much clearer transmissions and very good (4000 nm plus) DX comms.

So, what happened? Why was grounding to the hull of a steel boat a bad idea?
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Old 03-17-2008
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Billyruffn-

You may have a case of coincidence here. If you used a 8" cable for the first connection, that may have been the cause of the bad signal. SSB radio antenna connection really should be made using copper ribbon, as you did in the second case, and that may be the reason for the improvement. You changed TWO variables... the counter poise itself and the method of connection to the counter poise. My guess is that the hull of your steel beastie would be an even better counterpoise than the dynaplate, but needed to be connected via ribbon rather than cable.
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  #66  
Old 03-17-2008
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Gremlins at work :-)

Could be several explanations. One which does NOT explain this is that somehow the dynaplate is a better RF ground than the steel hull of the boat!

I'd suspect first the connection between the tuner and the hull. The correct way to connect to a steel hull is to use a wide copper strap, clean the protective covering off a small portion of the hull, and bolt the ground strap securely to the hull, then cover it with a protective coating.

It is important to clean the hull section first, since virtually all steel hulls -- mild steel, corten steel, etc. -- have (or should have) protective coverings on both sides.

Another thing to consider is poor connections and surface corrosion. When you changed the ground, you could very well have replaced bad connections with better ones.

I don't really understand your "friend's" logic. Surely the ground plate is attached to the hull which is attached to everything else except the insulated backstay? Even if the ground plate were to be isolated from the hull...which would seem to be impossibly convoluted...they're both sitting in the same medium...saltwater, so the "isolation" wouldn't account for much, would it?

Next, I'd suspect the propagation conditions. They have been pretty horrible lately as we're near the bottom of the sunspot cycle. Occasionally, even in these conditions, there are days or hours during the day when propagation is pretty good -- even excellent. Without a side-by-side simultaneous comparison, it would be impossible to conclude that one is necessarily better than the other.

The importance of this factor (propagation) cannot be overestimated. I'm on the radio everyday, and listening on the HF bands almost all day. For many years. I participate in several nets, including the WaterWay net in the mornings. One day I might be able to hear a station in Charleston with an extremely strong signal. Ten minutes earlier, however, that same station was not copyable. Propagation changes. Chuck, ND7K, runs a LOT of power from his land-based station in the Florida Keys. He has an excellent antenna setup as well. Usually, he's VERY strong. However, sometimes even during the course of the 45-minute net his signal fades to the point of being almost gone completely. Propagation changes. I run 500 watts into an excellent antenna system from my home QTH. Usually I receive very strong signal reports from stations on the Net. But, occasionally, I don't. Propagation changes, from minute-to-minute, hour-to-hour, and day-to-day.

Finally, the 802 is known to be quirky and to have relatively low average power output or "talk power". Gordon West and others have commented on this. The radio usually ships from the factory with the speech compression turned off, and only a technician can turn it on. Thus a combination of propagation conditions, relatively low power output, and timing could well have given the impression that somehow the ground plate is better.

Not!

:-)

Bill

Last edited by btrayfors; 03-17-2008 at 10:52 AM.
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I've stated my position on the use of Dynaplates in this thread before. I'm an advocate for them and that position hasn't changed...grows stronger every day in fact, and so I'm not surprised that good results were realized... that's the way it should be. I would have expected better from the steel hull though, although it would be wrong to conclude that the Dynaplate was 'better', or the steel 'worse'...just 'different' on that particular day, that particular hour. That's just the way it is.
I should say that it's not particularly the performance of the Dynaplate that grabs me, but the relative ease of achieving a predictably good result compared to that of a poorly installed copper sheathing, which is usually the case....but I digress...
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  #68  
Old 03-17-2008
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Hmmm....let's see.

The attenuation of RF signals in seawater at the HF frequencies used for marine radio is on the order of 70-80db per foot.

Most dynaplates are installed on sailboats some 3' or more underwater.

Perhaps someone can explain to me what they do?

Because if they are able to "couple to seawater" at that depth, what happens to the RF energy injected so far underwater?

Maybe submarines should reconsider the use of RF communications underwater, since obviously the dynaplate folks have discovered an anomalous physical science phenomenon :-)

Guess it's just magical ....

Bill

Last edited by btrayfors; 03-17-2008 at 02:42 PM.
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Old 03-17-2008
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Given the shape of the hull and the location of the Dynaplate, my guess is that it's no more than 8-10 inches underwater -- but you guys are way beyond me here. I'll let this sleeping dog lie -- the radio works great, which in the end is all that matters.

Another perhaps slightly afield question -- but one related to the earlier discussion of Marine HF vs Ham radios as modern means of communications.

When I was in the process of deciding to replace the POs IC 707, I spoke with Icom tech people and they said one reason to replace it was that (let me see if I can explain this correctly) -- that the 707 wasn't really designed as a email compatible radio. Apparently, email modem transmissions are off and on, no power and full power with nothing in between. The ham radios ae built for voice and CW, but apparently the CW signal doesn't stress the system the way an email transmission would. The Icom guys indicated that using the 707 for heavy duty email correspondence might shorten it's useful life. (I hope I represented their perspective correctly, but that's basically what I took away from the conversation).

Any thoughts on this? Are Ham radios of pre-email vintage engineered to handle the full power burst of data transmissions? Same for Marine SSBs of the same vintage? If not, does this mean that people using the HF radio for email need to use only the more modern models??
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Old 03-17-2008
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The 707 is one of the most beautiful ham radios ever designed but, unfortunately, it also was plagued with problems. IMO, you're lucky to be rid of it. OOPS....MY BAD. I thought you were referring to the older Yaesu 707. The Icom 707 is a different animal completely. Forget this paragraph!

One problem is switching speed....some of the older marine and ham rigs have problems switching from transmit to receive fast enough to accommodate the higher packet data speeds, esp. Pactor III. Sometimes there are work-arounds, sometimes not.

Another problem is the higher AVERAGE power output required of, e.g., Pactor transmissions. Voice transmission over SSB has peaks and valleys. On voice peaks you put out near full power, while at other times you put out much less than that and sometimes near nothing. On CW, there are breaks as well. But some modern data protocols place a higher demand on the transmitter to put out near constant power during exchanges.

Some ham rigs will take it just fine; others require setting their output power back a bit. Ditto for some older marine rigs. And, like in most things, there's a fair amount of erroneous lore out there. For example, you can see on the SAILMAIL site the statement that the Kenwood TKM-707 marine rig must be run at reduced power, but some have found that's not true at all.

Either way, power output isn't likely to be a problem, since you can make excellent data connections with very low power anyway. And the new protocols are so good they can make connections even when you can't tell there's a station at the other end! Quite amazing, really.

And, yes, if you're gonna have a dynaplate it's probably best to have it installed near the waterline. But why anyone would do this on a steel or aluminum boat escapes me completely :-)

Bill

Last edited by btrayfors; 03-17-2008 at 06:14 PM.
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