I know there have been part 15 broadcasters who have used bodies of water as ground, Tiny Harbor Radio immeadiatly comes to mind. But per the rules and regulations I'm unaware of any reference to specifically determine the actual legality of such - neither for or against.
Now this is all in regard to my sailboat installation experimentations..
I assume/suspect that providing the antenna system above water does not exceed the 3 meter limit, then such an istallation would be legal.. but, again, that's assumption on my part, because I'm unaware of any legal stipulation which might conclude otherwise..
There are also other factors I ponder over; for example, if from the surface of the water (ie: ocean) as well as all below the surface is considered ground, in a legal standpoint - in the very same respect as a soil is ground, then that would conclude it is compleately legal for the ground lead (posistioned just above the water line), to be attached to a wire which runs all the way down - however many feet - to the bottom, weighted with an anchor or whatever..
Or so it seems to me; such an installation would be legal.. but if.. let us suppose, that were not the case, and for whatever reason, it somehow violated the 3 meter rule - then that problem could easily be remedied by connecting the ground lead to a copper plate attached to the underside of the boat.
But.., I wonder further.. Water is a conductor, expecially salt water.. so in essence a radiating ground????
Now to be honest, I'm kind of retarded when it comes to radio theory.. I've never been more than an old kid playing with my part 15 toys. I am only, in this case, making armchair speculations which I hope is seriously misconstruded, and would like to hear the actual facts..
And so, I ask here.. from anyone who knows, but particularly directed at the individual of whom I have a tendency of being irritated by, but nevertheless respect his knowledge...
Rich, you know who you are.
Perfectly legal. Seawater does not radiate but reduces ground losses. Reduced ground loss = more range.
From the Wikipedia webpage "Ground (electricity):"
Radio communications: An electrical connection to earth can be used as a reference potential for radio frequency signals for certain kinds of antennas. ... An ideal signal ground maintains a fixed potential (zero) regardless of how much electric current flows into ground or out of ground.
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- Maintaining a fixed, zero potential at every point on the surface of an r-f ground reference would require that surface to have zero resistance at that radio frequency
- Sea water doesn't have zero r-f resistance, but in the medium-wave band it is >160X better than the best conductivity of dry earth
- Any conductor of any size/shape/length essentially would achieve the r-f characteristics of sea water where that conductor first enters/contacts the seawater which would continue for such conductors below its surface, but NOT for any of those conductors NOT immersed in sea water.
- A "Part 15" AM transmitter+3m whip mounted atop a mast on a boat faces the same §15.219(b) scenario for a "long radiating ground lead" as if it was mounted over dry land atop a home TV tower, or similar
(Hope this was not too irritating.)
My take on the technology of a sea water ground is if one considers that the intent of the 3 meter rule is to limit field strength by restricting radiators then the question is does the sea water radiate the RF signal?
It can be shown that if the returning currents are equal and opposite throughout the water that there is no net far field radiation which is the same result as the returning currents in the soil. Since the soil ground is not considered part of the ground lead length then it follows that neither should the sea.
This is how I would explain it to the jury.
Neil
A "Part 15" AM transmitter+3m whip mounted atop a mast on a boat faces the same §15.219(b) scenario for a "long radiating ground lead" as if it was mounted over dry land atop a home TV tower, or similar
Not atop the mast. The transmitter was situated low in the aft of the cockpit by where the outbooard engine is located, with the ground wire fed through one of the scupper holes (it allows any water which may splash into the cockpit to drain right back out again), and the scuppers are only a few inches above the water line... therefore the 3 meter rule is maintained.
By the way, my experimentation on the boat has been discontinued for a while thanks to Hurricane Matthew.. My boat was not damaged at all, but it's 300 foot in on dry land on an islanis accessable only by water . You can check it out if you want: http://grampian26sailboat.blogspot.com/ (scroll past the first post, and se the next two)
We used to have a kids book here called The Sailor Dog, and his name was Scuppers. 🙂 I never knew where the name had come from, now I do.
Maybe you don't even need a boat, just a simple platform with a metal plate on the bottom, and the transmitter in a waterproof box above. How about a bouy with a ten foot antenna on it and a flag with the station's call letters on the flag. Every dock could have one.
Well, I didn't buy the boat for the sake of a place to install the transmitter, having the boat just happened to create the oportunity of a great place to put it.
I actually intended to use it as a live aboard in the wintertime to cut cost, because my budget is usually very tight this time of year.. I was just getting ready to move aboard when the hurricane came.. It really sucks that I had spent money for the boat all summer to prepare her with all the little luxeries and comforts.. whereas usually that money would have been put aside to cover expenses during winter when I have no paychecks.
So now, no work, no money, no boat... Merry Christmas.
But I'm glad you know your dog is a drain hole..
Commercial broadcasters commonly use seawater as a ground. KKMO (1360 kHz, Tacoma) has its tower out in Puget Sound and its radials in the water. They have very good coverage. At least one Coos Bay, OR station uses seawater for its ground.
I would think maintenance would be high due to electrolisys disolving the radials.
The now-silent WHEB (750) in Portsmouth, NH was built on a tidal marsh...it used to boast that its 1 KW coverage was better than MOST of the 5 KW's in the area!! Having worked there a short time in the early '70s, I can vouch for this!! It was a daytimer (sharing the channel with WSB, Atlanta).....the story goes that, had they been granted their license 2 months earlier (in 1932, IIRC.....) WHEB would have been NH's ONLY 50 kW AM station!!
FWIW..... WBZ (1030) Boston's transmitter in Hull, MA os surrounded by seawater....THEIR covereage is legendary (OK.....some apparent IBOC issues recently have kept them from the usual stellar performance....!)...
Yes, I recall discussions in the past about these stations... But those are licensed stations. I guess I asked my question wrong, I knew that saltwater ground itself was legal, but wondered in the case of part 15 if saltwater could possibly be classified as a radiating ground - which has been answered above that it is not.
Also, want to mention something that occured to me later when Rich specified that a transmitter at the top of a sailboats mast would not be legal.. Even if it were, it would not be a good place to put one -- It's best to have it low on the boat. I learned this from sailboat forums in relation to using long range wifi anttenna boosters (which apparently work somehow by not only receiving, but sending signals as well). The higher the antenna, the greater the swaying, and thus the more unstable the signal. For best performance the antennas should be located low on the boat -- I assume the same principle would apply to part 15 transmitters.
... The higher the antenna, the greater the swaying, and thus the more unstable the signal. For best performance the antennas should be located low on the boat -- I assume the same principle would apply to part 15 transmitters.
True, but the radiation pattern of a short monopole such as used in Part 15 AM setups (even with a long, radiating ground lead) changes very slowly at low elevation angles.
The fields radiated in the horizontal plane in some directions from such a system would be reduced by about 50% when the vertical axis of its antenna system swayed to about +/-30° from the vertical plane.
The fields radiated in the horizontal plane in some directions from such a system would be reduced by about 50% when the vertical axis of its antenna system swayed to about +/-30° from the vertical plane.
That was exactly my point.. The wifi also is monophone (5ft), and they perform better if positioned lower on the boat so the sway is not as pronounced. - My point was I the same pricincple applies to a part 15 xmtr.
I'm don't see what your countering.