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The Marconi Antenna
  The Marconi Antenna is one of the more popular antenna types.   It's general form is a ground mounted quarter wave radiator.
It is the antenna used by most broadcast radio stations.  (frequently it is not an exact 1/4 wave length for other reasons)   It can be grounded at the base and shunt fed, or it can be isolated from ground (the tower sits on an insulator)  This antenna depends on an effective counterpoise system to radiate efficiently.  The counterpoise can be radial wires, a screen (radial wires with connecting concentric wire rings, or a evenly spaced connected cross hatch), sheet metal strips or a body of water, highly conductive salt water have been used.  The wires can be buried, lay on the ground or they could be elevated, even overhead.  The base (bottom of the vertical radiator) needs to be above the counterpoise if it is elevated.  A isolated radiator on a good counterpoise has an impedance just under 40 ohms without reactance.  Poor conductivity in the counterpoise causes increased "ground losses" which increases the base impedance, making it a good match for 50 ohm cable.  At reduced efficiency.
Ron KA4INM [email protected]