I am in the initial stages of planning a part 15 station. (I'm very much a novice so bear with me.) I live on the 2nd floor of an apt building. I was thinking my balcony might be a good place for my antenna but I've read that the length of the antenna, ground line and transmission line cannot exceed 3 meters. Since I live on the 2nd floor, it is of course more than 3 meters to the earth below. Does this mean that I must somehow ground to the building ... is that feasible?
I am in the initial stages of planning a part 15 station. (I'm very much a novice so bear with me.) I live on the 2nd floor of an apt building. I was thinking my balcony might be a good place for my antenna but I've read that the length of the antenna, ground line and transmission line cannot exceed 3 meters. Since I live on the 2nd floor, it is of course more than 3 meters to the earth below. Does this mean that I must somehow ground to the building ... is that feasible?
Also, I'm wondering about royalties. Do I have to contact BMI & ASCAP individually? How does that process work? Any idea on their fees? I'm trying to budget.
Lot's of info here on BMI/ASCAP:
The ground issue is a puzzler. Probably best not to use any structural component of the building, and definitly best to aviod using cable TV or power grounds - you really don't know what's on the other end of those. Same thing with cold water pipes.
When I operated from a second floor balcony I put a ground rod in the landscape area directly below my deck and drove it quite a distance below the beauty bark, and ran insulated solid core copper behind the plastic siding to my deck, when no one was looking, of course. Just temporarily, you understand, for testing purposes. Operating the station with that ground would, of course, be in excess of the regulations, obviously, and is something no one should do, most certainly.
Experimental broadcasting for a better tomorrow!
...I've read that the length of the antenna, ground line and transmission line cannot exceed 3 meters. Since I live on the 2nd floor, it is of course more than 3 meters to the earth below. Does this mean that I must somehow ground to the building ... is that feasible?
From an engineering point of view, you could connect the antenna output of your tx to the loading coil input of a ~3 meter vertical radiator, and connect the ground terminal of the tx directly to the center of a straight, horizontal wire of ~ 6 meters or so that is insulated from ground. The total, radiating length of this system will include the ~3-meter vertical and coil length plus the length of the conductor from the tx to the center of the horizontal wire. There must be no conducting path from any of this system to a "building" or earth ground.
This installation may cause some controversy to those who believe that the horizontal wire is radiating, and should be counted in the 3-meter radiating length. This may include FCC inspectors, so be careful. But the radiation from each half of the horizontal wire cancels the radiation from the other half, so the net, useful radiation from it theoretically is zero.
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Rich,
If the ground that you propose does not radiate then what is the purpose of building it? I anticipate you will answer that it returns ground current, but again for what purpose. Does it increase the radiated field in a way that cannot be achieved in another manner?
Thanks in advance,
Neil
An antenna cannot radiate if there is no path for current to flow in it. The horizontal wire I described provides that, by collecting current from the fields of the driven radiator, and returning that current to the transmitter/antenna system to complete the path.
An analogy here is that a battery cannot deliver power to a load connected to just one of its terminals.
A straight, horizontal wire used as I described will not radiate because the instantaneous r-f current in the two halves is flowing in opposite directions, and the net radiation from this condition is zero.
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Rich, thanks for the explanation. I had in mind VHF antennas which function without radials such as the "Ringo Ranger". I suppose the feed line for end fed antennas such as this acts as a ground by returning the current from the field.
If the original poster tries your suggested ground, I would be interested in the results. It sounds like a nice solution for folks with limited outdoor space or roof mounted systems.
Neil
If the original poster tries your suggested ground, I would be interested in the results. It sounds like a nice solution for folks with limited outdoor space or roof mounted systems.
One consideration with this is that the loading coil inductance needed will be rather unpredictable, because the input capacitance (and radiation pattern) of the antenna will be affected by the building steel, AC wiring, other nearby conductors, and how far it is above the earth.
A 3-meter Part 15 AM antenna system with its base at ground level gives more predictable performance, but for those who can't do that -- the extra work needed to find system resonance, and any odd radiation patterns that result may be an acceptable choice.
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Good points Rich. I would add that for those who are inclined to experimenting that the addition of a variable capacitor in series with the coil and antenna may provide a way around the unknowns since it is much easier to adjust a variable cap than to fuss with coil taps. The inductance of the loading coil will need to be made larger (more turns) than usual and the extra inductance can be tuned out with the variable cap.
Neil