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
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...
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I hope this helps!
Fair winds...
John