Volume 32 No 1 Feb-Mar 1981.pdf - Lakes Gliding Club

Fig 1 THE TRANSMITTERGLIDERRADIOCRYSTALOSCILLATORMULTIPLIERDRIVERMODULATORPOWERAMPLIFIER\J-3KHz +3KHz 1ICENTRE IFREQUENCY II6KHzBANDWIDTH [/COLlN DEWS, Chai'rman of the BGA Radio CommitteeFig 2With the introduction of 25Khz channel spacing in theaeronautical band and the almost certain probability thatduring 198 I the gliding movement will be assigned an additionalchannel (within the band 130.4-129.9Mhz) it willbecome increasingly important for us t~ use our radios efficienllyand responsibly.We shall need to consider very carefully how to make thehest use of the assigned radio channels and also make surethat our radio equipment is performing correctly.Perhaps the best place to start ,is at the beginning with somevery hasic radio principles before considering installations,licences. ccIII signs and procedures. This first al1ide hastherefnre been written for the reader with little or no knowledgeof radio.A Human Analogy. When we speak to each other as we sit inour living rooms oi· offices we use a system which is a'lmostanalogous to radio; wc create sound waves through our mouthswhich are modulated by the vocal cor,ds and the actions of thetongue (llld lips. These sound waves are transmitted through theair and a portion of this energy is collected by the ears of ourlistener. The ear drums detect the sound waves as vibration~and transmit these impulses .\0 the brain. The greater the distancebetween the speaker and the I'istener the smaller theenergy received by the ears of the listener.THE RADIO EQUIPMENTTile Transmitter. The radio transmi\ler is basical')y agenerator of h,igh frequency alternating current. This current isfed into aA aerial system eO:lbling the current to oscillate up anddown the aerial. The energy in the aerial produces an electromagneticfield which leaves lhe aerial in the forf,n of electromagneticwaves. We refer to this energy as the carrier waveand it can be likened (0 the flow of the air through the throat andmouth of a person speaking. In order to make the radio carrierwave carry intelligence, we need to modulate it with an electricalequivalent to our vocal cords. Sound waves used for telephoniccommunication cover 11 frequency range of approximately300 to 3000Hz and later we shal'l see the signiticance ofkeeping within this frequency range.(Hz is an