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Fun Projects 07 Chapter

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       FREE-POWER RECEIVER
                AM        (RE)
                                                      "extracted"
           usesa strange to get lts power. usespower
This project             way               lt
                     to                 transistor. a reasonably
fromthe tunedstation giveto the amplifier        With
strongapplied modulation                         produces strong
                               thistypeof detector
                        envelope,                       a
demodulated  output.
                               station, more
Naturally, closer areto a strong
        the      you                  the         yourradio
                                            current
willbeableto supply.
               you
Forbestresults, must everything
                        do          possible deliver strong
                                             to      a      signalto
thetransistordetector. recommend
                    We              a goodantenna ground, lat-
                                                   and       the
ter preferably
             beingmade a water
                       to        pipeor solid       ground
                                             external     composed
of a pipedriven least feetintomoist
               at    5                                  for
                                          Thisis important ensuring
                                     earth.
maximum   signalpickup.        I
lf youhave     of                            (up      100
                     available, longer antenna to about
          plenty space       the     the
feet), better results.
      the    the
Figure I shows schematic
             the                                         Ob-
                          diagram the Free-Power receiver.
                                 of             AM
serve the heartof the circuit a germanium
     that                   is           transistor works a
                                                 that    as
detector audio
        and    amplifier.
Gomponents placement a terminal
                    on                             is
                               stripusedas a chassis shownin
Figurc2.Theterminal canbefixed an experiment
                  strip         on                  that
                                               board canbe
constructed somecommon
          using           toolsandmaterials.

Ql is anygermanium  transistor, asGE-2 2N107.You findgerma-
                            such     or          can
nium                                               Nonworking
     transistors oldnonworking transistor receivers.
              in               AM      radio
AM radios alsosupply variable
          can            the                            (ferrite
                                  capacitor the loopstick
                                          and
rod).
Earphone bea high-impedance
         must                                   earphones
                                     Low-impedance
                           crystaltype.
            in
don'tfunction thiscircuit.



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Figure I




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Figurc 2



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                   PartsList - Free-Power Receiver
                                        AM
              Q1                              -
                                      transistorseetext
                   - NPNor PNPgermanium

              XTAL - Crystal
                           earPhone
              L1             -
                   - LooPstickseetext

              CV   - 365pFvariable       -
                                 capacitor seetext

              Rl   - 12,000         resistor
                          ohm,114W,57"
              C1   - 1 uF,25WVDC          capacitor
                                electrolytic


                               ldeasto ExPlore
     Tolearnmore    the
                about circuit:
              o Replace by 15turnsof No.28 wire,wound a ferrite to
                        Ll                           on        rod,
                           stations.
              tuneshort'wave
                            Ql            diode removing andC1
              o Byreplacing witha germanium    and     R1
                                                 set'
                                           crystal
              you'litransform radio a simple
                            this   into
              o AlterR1in a range      4,7}Oand
                                 between             ohms getbetter
                                                47,000   to
                                               used'
                         depending thetransistor
              performance,        on
                       the                                  What
                                               such the8C548'
                                           type,
              o Replace transistor a silicon
                                with               as
                       with
              willhaPPen sensivitY?
         science                               uses:
                                     and,uncommon
                     involving circuit
               project       the
              o Explain crystal function tellabout
                        how     sets        and         radiohistory. you
                                                                   lf
              areinterested moreradio
                          in         history      textscanbe found the
                                            several                in
              public
                   librarY.
              o lf youwantto learnmore    radio
                                      about    receivers, to findinforma-
                                                       try
              tionaboutheterodyne super-hereterodyne
                                 and                types'
                      -
         tl