[ Reply | Next | Previous | Up ]
From: Alan G3NOQ
Date: 05 Dec 2002
Time: 03:04:05
Remote Name: 20.138.254.2
Peter - it just means a symmetrical structure like a centre-fed dipole. If it is fed with a balanced feeder (2 parallel wires close together) the feeder remains electrically neutral and balanced, with equal and opposite currents on the two wires. The opposite is an unbalanced system like a monopole on a conducting sheet, fed by coax from underneath. . . . Problems come if you feed a balanced antenna with an unbalanced line, like a centre-fed dipole connected straight on to a coax feeder, because the outer conductor of the coax, being connected to one side of the dipole, sees a voltage between it and the "live" side of the dipole, and this induces currents in the outer surface of the coax and it then radiates and becomes part of the antenna, spoiling the nice pattern . . . So if there is a need to use a coax feeder with a dipole, there is a special transformer, a balun, placed at the antenna end of the feeder, to convert balanced to unbalanced, so that the feeder does not pick up and radiate . . . . best regards, Alan