cbradio



	CB, Radio, Antennas and transitter page. This page is all about my interest in radio and RF devices. This page will allow you to make your own antennas with simple maths.



By far the best antenna for most radio equipment is the dipole or long wire antenna. This simple antenna offers good reception and a very small ammount of directivity as emmited RF is weakest end on the antenna ie: on its axis. Another good point about the classic dipole is that it produces an equal currant and voltage field. where the current is maximum at the feed point and less at the ends, and the voltage is max at the ends and less at the feedpoint. The constructon of a dipole is very straightforward, you must have some wire handy, 0.5 or 1mm squared is best prefered and the following sum...... 300 / f in MHz = wire length in Meters. eg: 300 / 27Mhz = 11.1111111 meters of wire. now that we know the full wavelength of our antenna, we can now decide if we want it to be a long wire antenna, or a dipole. if you wish to have a quick antenna, then go for the long wire type, as it is simply the full wavelength wire suspended between two trees or towers. make sure you use some insulating wire to hold the antenna to the tower or tree. then simply run a lenght of coax to one end of the antenna and back to the radio. If the antenna is for transmitting i recomend using an ATU or AMU for reducing the swr of the antenna. The dipole can be made into various types ranging from 3/8 wave, 1/2 wave and 1/4 wave. simply calculate the full wavelength of the antenna to begin with and then decide if you want a 1/2 wave or a 1/4 wave antenna. we will use the 1/2 wave antenna for this page. divide the full wavelength value by 2 and now with the figure you have cut the lenght of wire required. now, to make a dipole, you must find the middle of the wire and make a cut at that point. strip back the insulation and now connect the feedline to the antenna. Hoist the antenna up somwhere high and listen on the radio. Thats all there is to it.



		latest project, recieving both E fields and H fields with prototype antenna. more soon. 21/12/03

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