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1. True. Inverted conical Monopoles are used where a wide variety of closely spaced frequencies are required (e.g. spread spectrum over 1-2 MHz). Spread Spectrum was developed during the World Wars for secure data and voice transmission. Link to more info: http://en.wikipedia.org/wiki/Spread_spectrum At 3.0 MHz and above a quarter wave length would be around 80 feet tall, and could be less due to distributed capacitance in the antenna.
2. Angle of departure of radio waves from a propagating antenna is determined by near-field and far-field ground resistance/conductivity. Current and radiation of signal does occur on the radial system. The shape of the propagated wave is determined by the current distribution along the length of the antenna. For monopole antennas, current distribution is the determining factor as to where the most or least signal leave the radiator. Little current equals higher impedance versus more current equals lower impedance (Ohms Law). Lobes and nulls of the signal pattern are dependent on the mutual impedance of the radiator.
3. BCB inverted conical monopoles are used for SHORTWAVE broadcasting world wide. The broadcast service in most countries outside the United States, Canada and Mexico are on HF frequencies (>2.0 MHz), not MW frequencies. The primary reason for the lack of use in the U.S. is the vertical space, real estate and money required to construct a working antenna system. Even though the antenna can be shorter than the normal vertical BCB monopole, accepted efficiency standards set by the FCC necessarily dictate a minimum height and field strength. An acceptable BCB AM inverted conical monopole would be huge. One quarter wavelength at 1600 KHz is 146 feet; longer at lower frequencies. The investment required for construction and subsequent engineering filings would be prohibitive in respect to any possibility of economic recovery.
As a final note: The AM broadcast service is fading into history, just as Morse code has as an accepted consumer method of communication. The service continues to persist purely because of the millions invested already and regulations and licensing. News/Talk on Am was supposed to save the band, but at last glance, less than 15 percent of people in the U.S. get their news and information from radio. The leading sources are the internet and television. Print and radio come in dead last. Even, the Yellow Pages are ceasing to be printed because of the use of their internet service. It’s a changing world, like it or not.
And just for Rich…3X’s, 3X’s, 3X’s (adjust speed as needed).