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ELECTRONIC COMMUNICATIONS SYSTEMS

ELECTRONIC COMMUNICATIONS SYSTEMS. PART 4-1. AMPLITUDE MODULATION RECEPTION. AM DEMODULATION. REVERSE PROCESS OF AM MODULATION AM RECEIVER RE-CREATES THE ORIGINAL INFORMATION RECEIVER MUST BE ABLE TO BANDLIMIT THE TOTAL RADIO-FREQUENCY SPECTRUM TO A

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ELECTRONIC COMMUNICATIONS SYSTEMS

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  1. ELECTRONIC COMMUNICATIONS SYSTEMS PART 4-1 ENZO PATERNO

  2. AMPLITUDE MODULATION RECEPTION ENZO PATERNO

  3. AM DEMODULATION • REVERSE PROCESS OF AM MODULATION • AM RECEIVER RE-CREATES THE ORIGINAL • INFORMATION • RECEIVER MUST BE ABLE TO BANDLIMIT THE • TOTAL RADIO-FREQUENCY SPECTRUM TO A • DESIRED BAND OF FREQUENCIES (i.e. TUNING • THE RECEIVER) ENZO PATERNO

  4. AM RECEIVER 1st STAGE LAST STAGE ENZO PATERNO

  5. AM RECEIVER • RF SECTION: DETECTS, BANDLIMITS AND • AMPLIFIES RF SIGNALS • MIXER/CONVERTER: DOWN-CONVERTS THE RECEIVED • RF FREQUENCIES TO INTERMEDIATE FREQUENCIES • (IFs) • IF SECTION: AMPLIFICATION AND SELECTIVITY • (TUNING) • AM DETECTOR: DEMODULATES THE AM WAVE AND • CONVERTS IT BACK TO THE ORIGINAL SIGNAL • AUDIO SECTION: AMPLIFIES THE RECOVERED • INFORMATION ENZO PATERNO

  6. AM RECEIVER - SELECTIVITY • SELECTIVITY: RECEIVER PARAMETER TO MEASURE • THE ABILITY OF THE RECEIVER TO ACCEPT A GIVEN • BAND OF FREQUENCIES AND REJECT ALL OTHERS • (FOR EXAMPLE IN AM BROADCASTING - EACH CHANNEL • IS ALLOCATED A 10 kHz BANDWITH - BP FILTER IS OF • 10 kHz BW TO PASS ONLY THE SPECIFIC CHANNEL) • SHAPE FACTOR (SF): USED TO MEASURE SELECTIVITY • (IDEAL SF = 1) BW 60 dB BELOW MAXIMUM SIGNAL LEVEL EXAMPLE: BW 3 dB BELOW MAXIMUM SIGNAL LEVEL ENZO PATERNO

  7. AM RECEIVER - SENSITIVITY • SENSITIVITY: RECEIVER PARAMETER TO MEASURE • THE MINIMUM RF SIGNAL LEVEL THAT CAN BE • DETECTED AT THE INPUT TO THE RECEIVER AND STILL • PRODUCE A USABLE DEMODULATED INFORMATION • SIGNAL (ALSO CALLED RECEIVER THRESHOLD) • SENSITIVITY IS USUALLY STATED IN MICROVOLTS OF • RECEIVED SIGNAL (i.e. COMMERCIAL BROADCAST AM • RECEIVER IS 50 uV, TWO-WAY MOBILE RADIO IS • BETWEEN 0.1 uV and 10 uV) • SENSITIVITY OF AN AM RECEIVER DEPENDS ON THE • NOISE POWER PRESENT AT THE INPUT TO THE • RECEIVER (LOWER NOISE, LOWER SENSITIVITY LEVELS) ENZO PATERNO

  8. AM RECEIVER - FIDELITY • FIDELITY: IS A MEASURE OF THE ABILITY OF A • COMMUNICATIONS SYSTEM TO PRODUCE AT THE • OUTPUT OF THE RECEIVER, AN EXACT REPLICA OF • THE ORIGINAL SOURCE INFORMATION • ANY FREQUENCY, PHASE, OR AMPLITUDE VARIATIONS • THAT ARE PRESENT IN THE DEMODULATED • WAVEFORM THAT WERE NOT IN THE ORIGINAL • INFORMATION SIGNAL ARE CONSIDERED • DISTORTION. THE THREE DISTORTIONS ARE: • AMPLITUDE, FREQUENCY AND PHASE ENZO PATERNO

  9. COHERENT RECEIVERS • COHERENT RECEIVERS: SYNCHRONOUS RECEIVER • WHERE THE FREQUENCIES GENERATED IN THE • RECEIVER AND USED FOR DEMODULATION ARE • SYNCHRONIZED TO OSCILLATOR FREQUENCIES • GENERATED IN THE TRANSMITTER (THE RECEIVER • MUST HAVE SOME MEANS OF RECOVERING THE • RECEIVED CARRIER AND SYNCHRONIZING TO IT) • COHERENT DEMODULATION IS WHERE A LOCALLY • GENERATED CARRIER IS SYNCHRONIZED TO THE • TRANSMITTER’S CARRIER FREQUENCY. • THIS TECHNIQUE IS RARELY USED IN PRACTICE. ENZO PATERNO

  10. NONCOHERENT RECEIVERS • NONCOHERENT RECEIVERS: ASYNCHRONOUS • RECEIVERS WHERE EITHER NO FREQUENCIES ARE • GENERATED IN THE RECEIVER OR FREQUENCIES • USED IN THE DEMODULATION ARE COMPLETELY • INDEPENDENT FROM THE TRANSMITTER’S CARRIER • FREQUENCY • THREE NONCOHERENT METHODS OF AM MODULATION • ARE: • RECTIFIER DEMODULATION • ENVELOPE DETECTION • SQUARE-LAW DETECTION ENZO PATERNO

  11. NONCOHERENT RECEIVERS • NONCOHERENT DETECTION: ALSO CALLED • ENVELOPE DETECTION BECAUSE THE • INFORMATION IS RECOVERED FROM THE RECEIVED WAVEFORM BY DETECTING THE SHAPE OF THE • MODULATED ENVELOPE ENZO PATERNO

  12. SUPERHETERODYNE RECEIVER NONCOHERENT RECEIVER ENZO PATERNO

  13. SUPERHETERODYNE RECEIVER • HETERODYNE: TO MIX TWO FREQUENCIES • TOGETHER IN A NONLINEAR DEVICE OR TO • TRANSLATE ONE FREQUENCY INTO ANOTHER USING • NONLINEAR MIXING • RF SECTION: THE PRESELECTOR IS A BROAD-TUNED • BANDPASS FILTER WITH AN ADJUSTABLE CENTER • FREQUENCY THAT IS TUNED TO THE DESIRED CARRIER • FREQUENCY. MAIN PURPOSE OF THE PRESELECTOR • IS TO PREVENT UNWANTED RADIO FREQUENCY • (IMAGE FREQUENCY) FROM ENTERING THE RECEIVER. • RF FOR COMMERCIAL AM BROADCAST IS: 535 kHz TO • 1605 kHz ENZO PATERNO

  14. SUPERHETERODYNE RECEIVER • MIXER/CONVERTER: THIS SECTION INCLUDES A • RADIO-FREQUENCY OSCILLATOR STAGE (LOCAL • OSCILLATOR) AND A MIXER/CONVERTER STAGE • (THE FIRST DETECTOR) WHICH IS A NONLINEAR • DEVICE USED TO CONVERT RF’S TO IF’S (RF-TO-IF • FREQUENCY TRANSLATION). IF SIGNALS IN • COMMECIAL AM BROADCAST ARE BETWEEN 450 kHz • AND 460 kHz. THE MOST COMMON IF USED IS 455 kHz • IF SECTION: A SERIES OF IF AMPLIFIERS AND BP • FILTERS (CALLED IF STRIP). MOST OF THE RECEIVER • GAIN AND SELECTIVITY IS ACHIEVED IN THE • IF SECTION ENZO PATERNO

  15. SUPERHETERODYNE RECEIVER • DETECTOR SECTION: CONVERTS THE IF SIGNALS BACK • TO THE ORIGINAL SOURCE INFORMATION (ALSO • CALLED THE AUDIO DETECTOR OR THE SECOND • DETECTOR). IT CAN BE AS SIMPLE AS A DIODE OR AS • COMPLEX AS A PLL OR BALANCED MODULATOR • AUDIO AMPLIFIER SECTION: COMPRISES SEVERAL • CASCADED AUDIO AMPLIFIERS AND ONE OR MORE • SPEAKERS. ENZO PATERNO

  16. LOCAL OSCILLATOR RF SIGNALS ARE COMBINED WITH THE LOCAL OSCILLATOR FREQUENCY IN A NONLINEAR DEVICE THE LOCAL OSCILLATOR IS DESIGNED SUCH THAT ITSFREQUENCY OF OSCILLATION IS ALWAYS ABOVE OR BELOW THE DESIRED RF CARRIER BY AN AMOUNT EQUAL TO THE IF CENTER FREQUENCY. THUS: PRESELECTOR AND LOCAL OSCILLATOR CENTER FREQUENCIES ARE GANG TUNED SO TO ALWAYS SATISFY THE CONDITION SHOWN ABOVE ENZO PATERNO

  17. LOCAL OSCILLATOR • WHEN THE LOCAL OSCILLATOR FREQUENCY IS • TUNED ABOVE THE RF, IT IS CALLED HIGH-SIDE • INJECTION (HIGH BEAT INJECTION) • WHEN THE LOCAL OSCILLATOR FREQUENCY IS TUNED • BELOW THE RF, IT IS CALLED LOW-SIDE INJECTION • (LOW BEAT INJECTION) • IN AM BROADCAST_BAND RECEIVERS, HIGH-SIDE • INJECTION IS ALWAYS USED ENZO PATERNO

  18. LOCAL OSCILLATOR TRACKING TRACKING IS THE ABILITY OF THE LOCAL OSC. IN A RECEIVER TO OSCILLATE EITHER ABOVE OR BELOW THE SELECTED RF CARRIER BY AN AMOUNT EQUAL TO THE INTERMEDIATE FREQUENCY THROUGHOUT THE ENTIRE RADIO FREQUENCY BAND FOR HIGH-SIDE INJECTION: LOCAL OSCILLATOR TRACKS ABOVE THE INCOMING RF CARRIER BY THE AMOUNT: FOR LOW-SIDE INJECTION: LOCAL OSCILLATOR TRACKS BELOW THE INCOMING RF CARRIER BY THE AMOUNT: ENZO PATERNO

  19. EXAMPLE AM SUPERHETERODYNE RECEIVER USING HIGH-SIDE INJECTION, WITH LOCAL OSCILLATOR OF 1355 kHz. INCOMING RF WAVE CONSISTS OF A CARRIER (900 kHz) AND USF (905 kHz) & LSF (895 kHz). ENZO PATERNO

  20. EXAMPLE ENZO PATERNO

  21. IMAGE FREQUENCY AN IMAGE FREQUENCY IS ANY FREQUENCY OTHER THAN THE SELECTED RADIO FREQUENCY CARRIER THAT IF ALLOWED TO ENTER A RECEIVER AND MIX WITH THE LOCAL OSCILLATOR, WILL PRODUCE A CROSS-PRODUCT FREQUENCY THAT IS EQUAL TO THE IF. AN IMAGE FREQUENCY IS EQUIVALENT TO A SECOND RADIO FREQUENCY THAT WILL PRODUCE AN IF THAT WILL INTERFERE WITH THE IF FROM THE DESIREDRADIO FREQUENCY. ONCE AN IMAGE FREQUENCY HAS BEEN MIXED DOWN TO IF, IT CANNOT BE FILTERED OUT OR SUPPRESSED. ENZO PATERNO

  22. IMAGE FREQUENCY FOR A RADIO FREQUENCY TO PRODUCE A CROSS PRODUCT EQUAL TO THE IF, IT MUST BE DISPLACED FROM THE LOCAL OSCILLATOR FREQUENCY BY A VALUE EQUAL TO THE IF: FOR HIGH-SIDE INJECTION: GIVING: ENZO PATERNO

  23. IMAGE FREQUENCY RELATIVE FREQUENCY SPECTRUM FOR THE RF, IF, LOCAL OSCILLATOR, AND IMAGE FREQUENCIES FOR A SUPERHETERODYNE RECEIVER USING HIGH-SIDE INJECTION FOR BETTER IMAGE-FREQUENCY REJECTION, A HIGH INTERMEDIATE FREQUENCY IS PREFERRED ENZO PATERNO

  24. RECTIFIER DETECTOR C LOW- PASS FILTER RECTIFIER + + R R B THE NEGATIVE PART OF THE AM WAVE IS SUPPRESSED AT THE OUTPUT OF THEDIODE. THUS, THE OUTPUT ACROSS THE RESISTOR IS A RECTIFIED VERSION OFTHE AM WAVE. IN ESSENCE, THE AM SIGNAL IS MULTIPLIED BY K(t) [TRAIN OF PULSE] ENZO PATERNO

  25. RECTIFIER DETECTOR ENZO PATERNO

  26. DSB-SC / DSB-FC DISADVANTAGES • DSB-FC (AM): CARRIER POWER IS 2/3 TOTAL POWER • DSB-FC (AM): CARRIER CONTAINS NO INFORMATION • DSB: USES TWICE AS MUCH FREQUENCY AS USED IN • SSB • ONLY SIDEBANDS CONTAIN THE INFORMATION • USB INFORMATION = LSB INFORMATION • TRANSMITTING BOTH SIDEBANDS IS REDUNDANT • DSB-FC: IS BOTH POWER AND BW INEFFICIENT • DSB-SC: BW INEFFICIENT ENZO PATERNO

  27. SSB TECHNIQUES • AM SSBFC: CARRIER @ FULL POWER & 1 SIDEBAND • AM SSBSC: NO CARRIER & 1 SIDEBAND (NO ENVELOPE) • AM SSBRC: 10% CARRIER (PILOT) & 1 SIDEBAND • AM ISB: SINGLE CARRIER MODULATED BY TWO • INDEPENDENT MODULATING SIGNALS. TRANSMITTER • CONSISTS OF TWO SSB-SC MODULATORS (DSB SIGNAL • WITH TWO INDEPENDENT SSBs). FINALLY CARRIER IS • REINSERTED AS IN SSBRC. • USED FOR STEREO AM: LEFT CHANNEL = LSB • RIGHT CHANNEL = USB • AM VSB: CARRIER & FULL 1st SB & PART OF 2d SB ENZO PATERNO

  28. DSB/SSB POWER DISTRIBUTION DSBFC: SSBFC: DSBSC: SSBSC: SSBRC: ENZO PATERNO

  29. AMPLITUDE MODULATION SYSTEMS DSBFC AM SSBFC AM SSBSC AM SSBRC AM ISB AM VSB AM ENZO PATERNO

  30. DSBFC WAVE ENZO PATERNO

  31. SSBFC WAVE PEAK CHANGE IN THE ENVELOPE IS HALF THAT OF THE DSB WAVE (ONLY ONE SIDEBAND) 100% MODULATED SSBFC WAVE WITH A SINGLE FREQUENCY MODULATING WAVE ENZO PATERNO

  32. SSBSC WAVE THE WAVEFORM IS NOT AN ENVELOPE; IT IS A SINE WAVE AT A SINGLE FREQUENCY EQUAL TO THE CARRIER FREQUENCY PLUS/MINUS THE MODULATING SIGNAL FREQUENCY ENZO PATERNO

  33. ISB WAVE WAVE IS SIMILAR TO A DSBSC WAVE BUT WITH A REPETITION RATE TWICE THAT OF THE MODULATING SIGNAL FREQUENCY . ENZO PATERNO

  34. VARIOUS AM WAVES DSBFC DSBSC SSBSC ENZO PATERNO

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