For anyone looking to try an experiment, put a 1/8 wavelength slinky inside a 3M PVC pipe with a cap on top, and several taps at the bottom. Lay the pvc tube horizontally and spray the inside with insulating foam to get the coils even and stop it from jiggling. Those of you in tall buildings, just hang a slinky out the window and use a fishing reel with the line running down the center, reel it back in when your finished broadcasting. Slinky's also would work well horizontally laying in plastic rain gutters. From Wikipedia:
The length of a Slinky spring if stretched out strait, or flat, would be the circumference of one turn of the Slinky times the number of turns in the Slinky.
The circumference of a circle (shape of a slinky) is calculated as:
C = 2 x PI x R
Where: C is Circumference, R is the Radius, and PI = 3.1415...
The final equation would be as follows.
slinky_length = 2 x PI x R x
Each Slinky contains 67 feet of flat steel wire, and weighs approximately 1/2 pound.
Slinky size varies, so if you can't find the right length, try the dollar stores for slinky knockoffs, sometimes they are longer. Ground systems do not have to be in the ground, but out of sight is out of mind. Fences, metal roofed buildings, water pipes, concrete rebar, clotheslines, and powerline neutral should all be used to your advantage. Take a long look at your location, write down everything you see from the list above, break out the tape measure, and go to work.
Tommy Johnson
http://cat-am.com
They make great Isotron antennas too!
RFB
Ground systems do not have to be in the ground, but out of sight is out of mind.
This may be true concerning the station operator and neighbors but an FCC inspector will know better. This has been discussed thoroughly on this board. Any ground system which radiates needs to be included in the 3 meter length restriction to comply with the intent of this rule which is to limit all radiating elements to total of 3 meter length. A non radiating ground system can be achieved above ground but random lengths and directions of conductors won't suffice.
Neil
Neil is correct with regard to a permanent installation, but Ultanium (which sounds wonderfully like "ultimatum") did preface his remark with the key word "experiment," and, often times on this website, it has been allowed that doing experiments is a fair part of the game so long as you end up with a compliant system.
Once upon a time I was involved in experimentation with RF devices used for medical purposes. The FCC rules only allowed operation outside the part 15 limits if permission was obtained from the the FCC Field Office Engineer in Charge. Doing so required providing a description of the experiment and permission, if granted, was for specified short time intervals.
The need for seeking permission to depart from the rules for experimentation makes it clear that just because a device or system is operated "as an experiment" operation outside the rules is not permissible.
Neil
"The FCC rules only allowed operation outside the part 15 limits if permission was obtained from the the FCC Field Office Engineer in Charge. Doing so required providing a description of the experiment and permission, if granted, was for specified short time intervals."
Indeed. And this special permission is not any easier to obtain than a regular CP for that matter!
In the long run its not really worth the trouble for Part 15 operators/owners. The costs to obtain that special permission, plus all the requirements that usually get placed upon experimental licenses is kin to an actual license and the requirements the licensee must meet on a regular basis.
Not sure any of the Part 15'ers out there are ready to throw down several thousand dollars if not more, and keep up with endless paperwork and reporting and logging and measuring etc etc etc.
RFB
Only going by imprecise memory, but I think 30-seconds of on time is allowed for a laboratory experiment without paperwork.
In any case, a Part 15 operator, being completely above board, would have to first "TRY" his setup to determine if it met the rules. This would be an "experimentation."
Remember "burning the carbon out"? Don't know why I thought of that.
Neil