Principles & Applications Electronics Principles & Applications Eighth Edition Charles A. Schuler Chapter 12 Communications (student version) ©2013

INTRODUCTION Modulation and Demodulation Simple Receivers Superheterodyne Receivers Frequency Modulation Single Sideband Wireless Data Troubleshooting

Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to.

Concept Preview Modulation is the process of adding information to an RF signal. The information signal controls the amplitude of the RF signal when amplitude modulation is used. The envelope of an AM signal has the same shape as the information signal (oscilloscope display). AM produces upper and lower sidebands. A spectrum analyzer displays an AM signal’s carrier and sidebands.

Oscillator A high-frequency oscillator can launch a radio wave. High frequencies are often called radio frequencies. Learning Outcome 1: Define modulation and demodulation. Page 369 - 374. Oscillator The process of adding information to the radio signal is called modulation.

Amplitude Modulation Modulator Radio Frequency (RF) AM = RF x AF + RF Learning Outcome 1: Define modulation and demodulation. Page 369 - 374. Also, Learning Outcome 2: Describe AM, FM and SSB. Audio Frequency (AF)

On a spectrum analyzer, AM looks like this: Since the RF carrier frequency is much higher than the modulating frequency, an actual oscilloscope display of AM looks like this: Learning Outcome 1: Define modulation and demodulation. Page 369 - 374. Also, Learning Outcome 2: Describe AM, FM and SSB. On a spectrum analyzer, AM looks like this:

Oscilloscope fC = carrier frequency Spectrum Analyzer amplitude time fC = carrier frequency amplitude frequency Spectrum Analyzer Learning Outcome 1: Define modulation and demodulation. Page 369 - 374. Also, Learning Outcome 4: Predict the bandwidth of AM. LSB = fC - fAUDIO USB = fC + fAUDIO AM produces sum and difference frequencies called sidebands.

An amplitude modulator AF +VCC 2p LC 1 fC = L C RF Learning Outcome 1: Define modulation and demodulation. Page 369 - 374. Also, Learning Outcome 2: Describe AM, FM and SSB. (fC) An amplitude modulator

The process of placing information on a carrier wave is _________. AM quiz The process of placing information on a carrier wave is _________. modulation With AM, the _________ of the carrier wave is controlled or varied. amplitude The oscilloscope displays a graph of ________ versus time. amplitude Learning Outcome 1: Define modulation and demodulation. Page 369 - 374. Also, Learning Outcome 2: Describe AM, FM and SSB. The spectrum analyzer displays a graph of _________ versus time. frequency A spectrum analyzer display of AM shows a carrier plus two ________. sidebands

Concept Review Modulation is the process of adding information to an RF signal. The information signal controls the amplitude of the RF signal when amplitude modulation is used. The envelope of an AM signal has the same shape as the information signal (oscilloscope display). AM produces upper and lower sidebands. A spectrum analyzer displays an AM signal’s carrier and sidebands. Repeat Segment

Concept Preview Information signal recovery is called detection. AM receivers often use a diode detector. Tuned amplifiers provide selectivity so that only the desired station will be received. Superheterodyne receivers use an intermediate frequency (IF) before detection. A local oscillator is mixed with the desired station to convert it to the intermediate frequency. An image frequency will also mix with the oscillator and produce the intermediate frequency. Selectivity before the mixer eliminates the image.

An AM detector AM in Diode Audio out This capacitor approaches a short Learning Outcome 1: Define modulation and demodulation. Page 372 This capacitor approaches a short circuit at the carrier frequency. An AM detector

A very basic AM receiver Antenna A very basic AM receiver Learning Outcome 3: Explain receiver operation. Page 376 - 377. Transmitter Diode Headphones

A practical receiver needs tuned amplifiers to provide selectivity and sensitivity. Learning Outcome 3: Explain receiver operation. Page 376 - 377. gain frequency

It’s too difficult to simultaneously tune several circuits. The IF amplifier is permanently tuned to one frequency. Antenna Audio Mixer IF amplifier Detector The desired station frequency is mixed to the IF frequency. Oscillator Carrier and sidebands IF passband Learning Outcome 5: Calculate the oscillator frequency for superheterodyne receivers. Page 378 - 380.

Frequency mixing is also called converting or heterodyning. Receivers like this are known as superheterodyne types. Antenna Mixer IF amplifier Detector Learning Outcome 5: Calculate the oscillator frequency for superheterodyne receivers. Page 378 - 380. This is called the local oscillator and it is tuned above the station frequency by an amount equal to the IF frequency. Oscillator

Some typical frequencies: fSTATION = 1020 kHz Some typical frequencies: fIF = 455 kHz Mixer IF amplifier Detector Learning Outcome 5: Calculate the oscillator frequency for superheterodyne receivers. Page 378 - 380. Oscillator fLO = 1475 kHz Note: the two inputs to the mixer have a difference of 455 kHz.

Superheterodyne receivers can also respond to the image frequency. fSTATION = 1020 kHz fIMAGE = 1930 kHz (1930 - 1475 = 455) A tuned circuit before the mixer is required. fIF = 455 kHz Mixer IF amplifier Detector Learning Outcome 6: Calculate the image frequency for superheterodyne receivers. Page 378 - 380. Oscillator fLO = 1475 kHz

Receiver quiz Recovering the information from a modulated signal is called __________. detection AM detection is often accomplished with a _________ rectifier. diode Radio receivers employ tuned amplifiers to provide sensitivity and ______. selectivity Superheterodyne receivers convert each signal to an _______ frequency. intermediate A superhet can respond to one additional frequency called the _______. image

Concept Review Information signal recovery is called detection. AM receivers often use a diode detector. Tuned amplifiers provide selectivity so that only the desired station will be received. Superheterodyne receivers use an intermediate frequency (IF) before detection. A local oscillator is mixed with the desired station to convert it to the intermediate frequency. An image frequency will also mix with the oscillator and produce the intermediate frequency. Selectivity before the mixer eliminates the image. Repeat Segment

Concept Preview With frequency modulation (FM), the information signal controls the frequency of the carrier. FM produces more sidebands than AM and thus has greater bandwidth. Noise and static can be removed from an FM signal by clipping. The carrier in an AM signal can be eliminated by using a balanced modulator. Single sideband AM also eliminates one of the sidebands.

Frequency Modulation One way to accomplish this is to use a varicap diode in the oscillator tank circuit. RF Oscillator Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. The audio signal changes the varicap bias and the resonant frequency of the tank circuit. Audio Frequency (AF)

On a spectrum analyzer, FM shows more sidebands than AM. Lower sidebands Upper sidebands Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. fC FM usually requires more bandwidth than AM.

An FM receiver can use an amplitude limiter Noise is always a problem in any communication system. FM has an advantage over AM since it offers better noise rejection. FM signal plus noise Noise removed LIMITER Modulation preserved Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. An FM receiver can use an amplitude limiter to remove noise. An AM receiver cannot since the modulation would be defeated.

DSBSC Modulation Balanced modulator Radio Frequency (RF) DSBSC = RF x AF Balanced modulator Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. Audio Frequency (AF)

DSBSC Modulation Balanced modulator LSB No carrier USB Radio Frequency (RF) DSBSC Modulation Spectrum analyzer Balanced modulator Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. LSB No carrier USB Audio Frequency (AF)

Since the sidebands are redundant, one can be filtered out to decrease bandwidth. Balanced modulator Bandpass filter SSBSC The lower sideband is not in the passband. Only the upper sideband is transmitted. Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. frequency

A superheterodyne SSB receiver requires a second oscillator to replace the missing carrier. Mixer IF amplifier Detector Oscillator Oscillator Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387.

With FM, amplitude noise can be removed with a ___________. limiter FM and SSB quiz With FM, amplitude noise can be removed with a ___________. limiter FM needs more bandwidth than AM since there are more _________. sidebands A balanced modulator produces sidebands but no ___________. carrier Learning Outcome 2: List the characteristics of FM and SSB. Page 381 - 387. In SSB, one of the sidebands can be eliminated by using a ____________. filter SSB demodulation requires an oscillator to replace the missing _________. carrier

Concept Review With frequency modulation (FM), the information signal controls the frequency of the carrier. FM produces more sidebands than AM and thus has greater bandwidth. Noise and static can be removed from an FM signal by clipping. The carrier in an AM signal can be eliminated by using a balanced modulator. Single sideband AM also eliminates one of the sidebands. Repeat Segment

Wireless data devices are providing faster and more convenient communication and operation in several key areas. Here, the discussion is limited to WiFi, Bluetooth, and RFID technology. Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

3 Direct-sequence spread spectrum 4 Frequency-hopping spread spectrum Learning Outcome 7: Describe wireless data systems. Page 388 – 393. 1 Multiple input and multiple output antennas at both transmitter and receiver (smart antenna technology) 2 The original specification was released as IEEE 802.11 in 1997 followed by 802.11a and 802.11b in 1999. 3 Direct-sequence spread spectrum 4 Frequency-hopping spread spectrum 5 Orthogonal frequency-division multiplexing 6 IEEE 802.11y is licensed by the FCC in the United States.

Bluetooth (IEEE 802.15) Range: 10 to 100 meters Power: 1 to 100 mW Sensitivity: 0.1 nW (-70 dBm) Data rate: 1 Mbps Bluetooth II: 3 Mbps Frequency: 2.4 GHz (same as 802.11b and 802.11g) Learning Outcome 7: Describe wireless data systems. Page 388 – 393. Bluetooth technology is designed for personal area networks (PANs) and for appliances that don't require large data flows (printers, keyboards, mice, personal computers, and mobile phones). Bluetooth enable automobiles allow hands-free phone operation.

Radio Frequency Identification Devices (RFID) extend barcode technology into many new application areas. Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

Inductive Reader and Tag Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

Backscatter Reader and Tag Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

Receiver troubleshooting Signal injection is standard practice. Both AF and RF signal generators may be required. Some receivers may require adjustments of their tuned circuits. This is called alignment. Learning Outcome 8: Troubleshoot receivers. Page 394 – 395.

Wireless troubleshooting Software problems include: Adapters are disabled Adapters are not authenticated Adapters are not configured properly Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

Wireless network troubleshooting Hardware problems include: Adapters are physically turned off or missing Interference Distance and obstructions to the signal Multipath signal distortion Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

A field-strength meter can be used to determine if transmitters are working at all. However, this type of go/no-go test will only identify a limited range of possible problems. Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

More advanced wireless network troubleshooting can be accomplished with dedicated test equipment or with special software running on general purpose equipment such as notebook computers and some portable devices. Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

REVIEW Modulation and Demodulation Simple Receivers Superheterodyne Receivers Frequency Modulation Single Sideband Wireless Data Troubleshooting