FORMZ:SWRTHYPHASCISPELPRGHDOC h PICP69LINP6Z BOXP6Z dOVLP6Z dSWCL@BlackWhiteRedGreenBlueCyanYellowMagentafSalmonwPeachUBrownellowLight GreenwwwGrey DarkOrangeݙVanillalowGrey LightIDXHIDXDSoftSansdTitleepz,IDXDSoftSansdBlank LinefIDXDSoftSansdLetter HeadergIDXDSoftSans dIndex EntryhTOCH TOCDSoftSansdTitlenz%TOCDSoftSans dBlank LineoTOCDSoftSansdZLevel 1pTOCDSoftSans dZLevel 2qTOCDSoftSerif dLevel 3rTOCDSoftSerif dhLevel 4sTOCDSoftSerif dvLevel 5tTOCDSoftSerif d*Level 6uTOCDSoftSerif dLevel 7vTOCDSoftSerif d8Level 8wIDXPSEC1 PTPAG3pA PRN3KBVtils:APPLICATIONS/FinalWriter/FWFonts/SWOLFonts/Serif/WŬWW~WW { dELX.FormulaText{WPASDSoftSansdDocument TitlePASDSoftSansdSection Namepz??PASDSoftSansdTopic Nameq{??PASDSoftSansdSub Topic 1r|??PASDSoftSansdSub Topic 2s}??PASDSoftSans dBodyPASDSoftSans dIndented BodyTOCP!rOUTPBIBPTOIPENDPDSP2PHHFDASoftSans dSoftSans dPNDASoftSans dSHPP6Z dGRMRStrictly.For Business Writing.For Casual Writing.Custom 1.Custom 2.Custom 3.IDXLConductorsTDINFFCOP3 W1TWRFDTAWorchester Utils:APPLICATIONS/FinalWriter/FWFonts/SWOLFonts/Serif/FDTASoftSansW8W%YW$PWwLWW$oW$WtW_W$PW# W$WtW~GINF jGINFUtils:GRAPHICS/PPaint/Brushes/FWriter5/Line2.bshMXRMXRz7j9BlackFORMTILBMBMHD& D,CMAP0f"@@CAMGBODY<U߻TU߻TU߻Twww<GINF SHD1PW/W/lW/PTMainTBDYRULEOATTR dCHRSElectronic Servicing yr.1 pt.1ATTR dCHRS ATTR hdCHRS ATTR hdCHRS ATTR dCHRSLecture: 025 - tATTR [dCHRS ATTR hdCHRS ATTR hdCHRS ATTR hdCHRS ATTR hdCHRS Thursday - 17ATTR hdCHRS - AprATTR hdCHRS ATTR hdCHRS-1997RULEATTR hdCHRSRULEATTR hxCHRSSUPERHETERODYNE RECEIVERRULEATTR hxCHRSRULE)ATTR) hdCHRS)A simple radio is called a tuned radio frequency reciever (trf reciever), which had a disadvantage that the demodulation is done at different frequencies depending on the station frequency tuned on. So the super heterodyne am/fm reciever was constructed in 1913, and is shown in figure 7.3 / 7.5. RULEATTR hdCHRSRULEATTR hdCHRSBlock A, B and G (R.F. amplifier, Mixer, and Local Oscillator) forms the radio's tuner. The mixer can be also called the first demodulator or the frequency changer. It gets the selected tuned frequency from the R.F. amplifier, and a frequency of 470kHz + the carrier frequency of the station from the local oscillator. The local oscillator produces a steady frequency of 470kHz larger from the selected carrier frequency. The mixer, or first demodulator produces a frequency which is the difference between the two frequencies, which hence it is always 470kHz + the info carried on the carrier. In simpler words, what happens is that the info is first demodulated from the original station carrier, and modulated back on a constant carrier frequency of 470kHz.RULEATTR hdCHRSRULEuATTRu hdCHRSuAmplifying the 470kHz modulated wave will increase the selectivity and sensitivity of the reciever without any feedback, as it happend in the trf reciever. To bring local and distant stations to the same level of gain, the IF amplifying gain is controlled aoutomatically by the a.g.c (automatic gain control) d.c. voltage that each station produces at the demodulation (D).RULEATTR hdCHRSRULEATTR hdCHRSAfter block (D), the signal is amplified by an Audio Frequency Amplifier, which it's gain is controlled by the volume control knob/slider. The A.F. voltage amplifier can be considered as a driver stage amplifier because it drives the power amplifier (F) and the load speaker. RULEATTR hdCHRSRULEATTR hdCHRSThe F.M. superheterodyne reciever differs only in that it's frequency range is 88-108 Mhz instead of 540 - 1600Hz and the other difference is the the local oscillator produces a wave at a frequency of 10.7Mhz more from the carrier frequency instead of 470kHz as in the Am reciever. Also since tuning to difficult to be done manually, modern and good FM recievers possess an automatic frequency control.RULEATTR hdCHRSRULEATTR dCHRSRMSTRULEATTR dCHRSLMSTRULEATTR dCHRS