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Old 15-06-2017, 17:28   #16
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Re: Welding cable as counterpoise

Toddster,
Paul gave you some good info...perhaps I can add some detail...

1) Despite what some in on-line discussions might want to say, the design / construction of antenna ground systems and counterpoises (for end-fed "Marconi-type" antennas / base-fed verticals) is well understood and effects have been scientifically proven (both by the "math" and real-world test results)...
The research into this started in the 1920's and 30's, and continues, even today, but not much new has been discovered since the 50's/60's....with a great deal of practical real-world results from the 50's and 60's, as well....
(the radio broadcasters and universities did a lot of this, with the US federal gov't adding to this as well...but, please understand that a surprising amount of research and real-world testing has been done by my fellow ham operators!! And, we hams did all of this for fun, not for profit, nor for climbing the corporate/academic/gov't ladder!!)

2) Due to the limitations of vertical antennas, versus horizontally-polarized antennas, on HF frequencies above 5mhz to 8mhz, much of the "professional" research is concentrated on MF and lower-HF freqs....and most of the "amateur" research is for 1.8mhz thru 10mhz, and some thru 14mhz...
This isn't to say that the designs change much for the higher HF freqs, just that most discussions concentrate on the lower half of the HF spectrum...
{and with the solar-cycle falling, and in the doldrums for the next 3 - 5 years, our use of bands above 14mhz will be less and less, so this is actually a moot point for us here and now.... }

3) In general, fresh water is worse than almost all land masses when it comes of conductivity, especially at RF!
It is about the same (or slightly worse than) as flat dry sand...
So, any/all recommendations for antenna grounds in "poor" and "very poor" soil conditions holds true for fresh water...
{BTW, sea water is so close to the theoretical "perfect ground", that pseudo-Brewster angle is less than 1 degree at 14mhz, versus 0 degrees for "perfect ground"....and about 14 degrees for "good"/"very good"....and > 20 degrees for "poor"....not to mention the 5 to 7db difference between "perfect" and "good"....
Now you know why antennas over sea water work so well... }

So, for a fresh water situation, follow the recommendations for vertical antennas over "poor" ground...(actually that would be to use a horizontal antenna!! so, don't go that far!! Just follow the vertical antenna ground recommendations!!)

In general, get as much RF conductor connected to the ground terminal of the tuner, as close to the tuner as possible....and, while it might sound contradictory to what I wrote earlier, use of wide copper strapping here is actually good! (this is NOT about the old spec / "myth" that you need "100 sq ft" of copper in the bilge...this is about getting as low of resistance as possible for the antenna return currents as possible, when you don't have much of an antenna ground....)
Remember this is for a boat in FRESH WATER...
Running from the ground lug of your tuner, you can lay out a few (4 to 8)short (5' to 10' long) pieces of 3" wide copper strap, in the bilges as short radials....and also connect any metal tanks, keel bolts, etc., with copper strapping from the tuner ground lug....
Connecting to a close-by, underwater, bronze thru-hull is also good, so that when you do venture into salt water, you're all set!!!
You can also connect your alum toe rails (attach using a threaded bolt, below the anodizing), lifelines, pushpits, etc....(but since these are usually a far distance away from the tuner, copper strapping here is not needed, just use some tinned copper wire...)
You can also run as many as wire radials as you can fit...maybe another half-dozen...

BTW, once you get beyond the number of 16 - 24 radials (symmetrically-spaced, which is impossible to do here!), you start to run into diminishing further returns....so, if you could get half that many, you'd be doing well!!

{Again, please take precise note that the recommendation here to use copper strapping AS the actual radial / counterpoise is specific to this exact example ("poor" / "very poor" ground conductivity, and/or fresh water) and is NOT necessary for most other radial systems....where plain ordinary wire works fine!
The use of wide copper strapping to connect the tuner to the sea water, when using the sea water as your antenna ground / counterpoise, IS recommended always, and is completely different than this specific query... }

Now, I don't know anyone that is going to go to all that effort / expense....but, you did ask!!
So, that's what I'd recommend, if you really wanted to get the most out of a vertical HF antenna over fresh water!!
(but, if you can rig even a horiz dipole or inverted-v, up about 1/2-wave, you'll be better off by at least 6db, and probably as much as 10+db on many paths....so, if you'll not be in an ocean for a while, save the effort! )



4) You'll notice I didn't really mention how you measure all of this....
Well, that's because the results are well-known and if design/build to the recommendations, you'll not need to do any metered measurements/testing....
{BTW, I use my Delta TCT-N and a scope....as my rf current metering (measuring antenna current directly)....works great!!
But, a fluorescent light tube, taped near the bottom of the backstay works just as well!!!
Just FYI, using SSB there are way too many variables....so use CW or a constant-carrier FSK, or unmodulated AM...

As Paul mentioned, SWR measurement here will be of no use....
{also, please take note of Paul's comment on tuner losses....'cause they can be quite large, especially on the lower bands, with shorter antennas!!!}

Quote:
Originally Posted by toddster8 View Post
Hah, I was going to ask you experts about the (my) situation of being in a freshwater home port with occasional escape to saltwater. Perhaps eventually permanent. Of course, one doesn't really need long-range radio in fresh water, but that is where all the rigging and testing is happening.

Also, what dependent variable could be used for testing different counterpoise options? I think in previous discussion some of you said that SWR is not a good indicator of function? Assuming that we do not have an electronics lab at hand...
I hope this helps!

Fair winds...

John
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Old 15-06-2017, 18:07   #17
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Re: Welding cable as counterpoise

Thanks Paul and John. Thinking about how I might accomplish the above advice, considering the complex topology of the boat spaces. Any thoughts on adhesive backed copper foil tape? It's very thin, but looks as if one might be able to make relatively neat (and inexpensive) runs of it along the underside of decks, inside portions of hulls, etc. Passing through bulkheads might be a bit tricky. I'd need to go through at least one bulkhead to reach a through-hull. The end effect might be a sort of distorted cone shape with the apex being the tuner.

Well, topologically, the strut through-bolts are in the same compartment as the tuner. Not sure if they're bonze or stainless. They ought to be isolated from the engine ground. Guess I can check. That would count as my weekly yoga attempt.
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Old 15-06-2017, 18:34   #18
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Re: Welding cable as counterpoise

Todd,
Oh boy!
Please do not take these things so seriously, nor too literally....

This is a fairly esoteric subject (antenna grounds for verticals over fresh water), and way in the weds of what most here will be interested in....so if you want more details, you will be better served by "ON4UN's Low-Band DX'ing" and the "ARRL Antenna Book", and "Radio Engineering Handbook", etc...and think "poor" ground conductivity rather than fresh water...



And, BTW....since we don't know what boat you have, what radio/tuner you have, what HF antenna you have, where you are located, where you desire to communicate to, what band/freq, what time-of-day, what type of comms (Voice, CW, digital....ham and/or marine), etc. etc. etc...
There is nothing else I can offer you in specifics...
Usually, someone asking for this specific of advice/recommendation would've shared at least all of the above first, and then ask....



But, in brief...
Read what I wrote above again...
It is not about running long lengths of strapping all over the boat...
It is about getting as much RF conducting material (copper, etc.) as close to the tuner as possible...meaning using more/short radials, not longer ones!!

If you can't make a half-dozen copper strap radials of 5' to 10' work, then make 'em as long as you can....(3' to 6', is short...but put in as many as you can, and you'll be much better off than if you have none!!)
If you can't make 3" wide strapping work, then use 2" wide, or 1" wide...

If you cannot make any of this work...
Then just tie in all you can....toe rails, lifelines, pushpits, rub rails, tanks, etc...
And, then toss in some wire radials!!

If you cannot do any of that??
Well, then....either accept that the antenna will work without any ground at all (although not that well), or go with a horizontal antenna...


As for copper foil???
No...
You will regret any money spent on it, and any time installing it...
(yes, in a fresh water environ, you wont have the same problems with corrosion that the rest of us salt water sailors have...but, it's just a matter of time before you get into the ocean!! )

Running radials under the decks / inside cabin headliners, and under cabin sole, is actually quite normal....(and I think I mentioned these earlier??)...use wire and it will be a lot easier....


I'm afraid my mention of using copper strapping is confusing the issue....and I regret even mentioning this...
As I write above, this is a very esoteric subject (although one I have a great deal of experience with)....

So, please ignore my mention of copper strapping...
If you must use a vertical antenna in this application, of poor ground conductivity (not what I'd recommend!), then tie in what you can, toss in some radials, etc..and be happy!


Quote:
Originally Posted by toddster8 View Post
Thanks Paul and John. Thinking about how I might accomplish the above advice, considering the complex topology of the boat spaces. Any thoughts on adhesive backed copper foil tape? It's very thin, but looks as if one might be able to make relatively neat (and inexpensive) runs of it along the underside of decks, inside portions of hulls, etc. Passing through bulkheads might be a bit tricky. I'd need to go through at least one bulkhead to reach a through-hull. The end effect might be a sort of distorted cone shape with the apex being the tuner.

Well, topologically, the strut through-bolts are in the same compartment as the tuner. Not sure if they're bonze or stainless. They ought to be isolated from the engine ground. Guess I can check. That would count as my weekly yoga attempt.
It's not about what compartment the things are in...
Nor, whether you need to roll up the strap to get it thru a hole (perfectly fine!!)

Using your strut (SS or bronze) is fine....but they're usually painted with antifouling, so might not be great (???), you'd just have to see...
Also, running to a thru-hull is good....and as long as it's less than 10' away, it will work well...


Honestly, you're over-thinking all of this...

Fair winds..

John
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Old 15-06-2017, 20:37   #19
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Re: Welding cable as counterpoise

We have ours bolted to a Bronze thruhull. Been that way since 1978
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