Page 2 - Table of Contents
2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Analog Carriers and Modulation 1 Basic Sine Wave Amplitude Modulation (AM) . . . . . . . . . . . . . . . 3 2 AM with Adjacent Carriers . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Multi-Tone Testing . . ....
Page 3 - Introduction
3 One of the most challenging tasks in designingwireless communications products is the develop-ment of a rational approach to characterizing andtesting components, assemblies, and sub-systems.Baseband modulation and RF signal characteristicsare becoming increasingly complex as standardsand common s...
Page 5 - Basic Sine Wave Amplitude Modulation (AM); Analog Carriers and Modulation
5 The best introduction to theAWG is to parallel the procedureof generating a carrier with aconventional signal generator.With a signal generator, onesimply enters the carrierfrequency and the output ampli-tude, such as 1000 kHz at0 dBm. With an AWG, onecreates a sequence of points torepresent the w...
Page 7 - AM with Adjacent Carriers
7 A simple addition to the AMsignal demonstrates the flexibilityof equation-based waveformdescriptions. A common task inevaluating receiver performanceis to evaluate the effect of adja-cent carriers. For the basic AMsignal, one can easily add modu-lated carriers 10 kHz above andbelow the original si...
Page 11 - Frequency Modulation
11 Frequency modulation introducescontrol of the phase argument, Φ , in the basic carrier equation: A sin ( ω ct + Φ ). FM is implemented by varying Φ in direct proportion to the integral of the modulatingsignal. Thus, for a modulatingsignal m(t), the FM signal can bewritten: A sin ( ω ct + k ∫ m(x)...
Page 12 - FM with Dual-Tone Modulation
12 While basic single-tone FM is abuilt-in function of virtually allconventional signal generators,dual-tone FM modulation clearlycontrasts the flexibility of theAWG approach. Dual-tonemodulation tests can be used tomeasure intermodulation prod-ucts in a noise reductioncompandor (compressor-expander...
Page 14 - FM Stereo
14 A final example of conventionalanalog modulation combinesmost of the above techniques tosimulate the stereo modulationused in broadcast FM. Themodulating signal consists ofthree components, 1) thecomposite audio which is thesum of the left and right (L+R)channels, 2) the stereo pilotsignal which ...
Page 16 - Adding Noise to a Carrier Signal — AWG Noise Characteristics
16 Although the removal of noise isa common design goal, a noisesource can be an extremelyuseful test stimulus or signalimpairment. The AWG 2041provides a built-in noise func-tion, but its characteristics arequite different than traditionalsources such as noise diodes. AnAWG 1 noise waveform is actu...
Page 19 - Digital Phase Modulation — PSK; Digital Modulation
19 Digital Phase Modulation — PSK 8 The modulating signals in theforegoing examples have beensinusoidal or continuous wave-forms. A simple step to digitalmodulation is made with a slightvariation to sinusoidal modula-tion. Figure 21 shows one cycleof a sinewave that has beenquantized into steps betw...
Page 21 - Baseband Digital Patterns
21 Baseband Digital Patterns 9 Before continuing with exam-ples of digital modulation, it isimportant to establish a methodof creating arbitrary test datapatterns. Figure 24 shows directentry of a 28-bit binary pattern.In this case, the 0 or 1 value ofeach data bit is repeated for 1000points in the ...
Page 22 - Digital AM — OOK and BPSK
22 The simplest example of digitalmodulation is to turn the carrieron or off, depending on the stateof the modulation data. On-offkeying (OOK) can be directlyimplemented by multiplying acarrier by the 1 or 0 value of thedata pattern. This example uses a10.7 MHz carrier created in a28,000 point recor...
Page 23 - Digital FM — FSK
23 The modulating data alters thecarrier frequency infrequency-shift keying (FSK). Adigital modulation index of 0.5is used in this example; that is,the frequency shift will be 1 ⁄ 2 the 40 kbaud data rate or 20 kHz. Ifthe carrier remains centered at10.7 MHz, this results in the twodata frequencies o...
Page 25 - Quadrature Modulation
25 Multi-level data modulationsplits the amplitude, frequency,or phase of the carrier into morethan two discrete states. 8-PSKpreviously demonstrated directcontrol of the phase Φ in the equation A cos( ω ct + Φ ); A was constant. The eight symbolswere equally spaced pointsaround the polar axes.Alter...
Page 26 - DUT
26 Figure 32. Quadrature amplitude modulated(QAM) signal generated by combining anamplitude modulated cosine carrier (upper) andan amplitude modulated sine carrier. There are16 symbols, so this is 16-QAM. I In I/Q Modulated RF Out Discrete Q Signal Discrete I Signal Ch. 2 Out Ch. 1 Out AWG RF Genera...
Page 27 - Filtering Out Unwanted Sidebands
27 One effect of the edge transitionsin digital modulation patterns isa wider than desired occupiedspectrum of the transmittedsignal. The solution is to filterthe baseband digital signalbefore it modulates the carrier.The two most common filtertypes for this application areGaussian and Nyquist filte...
Page 30 - Direct Sequence Spread Spectrum
30 The final example of digitalmodulation spreads the energyin a BPSK signal by amplitudemodulating the carrier with aspreading pattern. In the sameway that the baseband datapattern spreads the energy of anunmodulated carrier, a spread-ing pattern further spreads theenergy of a modulated carrier.Pse...
Page 31 - For More Information on Tektronix Instrumentation
31 For More Information on Tektronix Instrumentation Tektronix offers a broad line of signal sources and electronic measurement products for engineering,service, and evaluation requirements in virtually every industry. For detailed information about the Tektronix tools used in developing this bookle...
Page 32 - AWG 2000 Series Arbitrary Waveform Generators
32 Tektronix AWG ArbitraryWaveform Generators give themost extensive capabilities forediting waveforms, with 8 or 12bits of vertical resolution andwaveform frequencies to500 MHz. AWGs contain a highspeed, high resolution digital toanalog convertor with sophisti-cated triggering and modesettings, plu...
Page 33 - TDS 744A Digitizing Oscilloscope
33 The TDS 744A represents thenext generation of digitizingscope performance. This versa-tile general-purpose instrumentintroduces Tek’s new InstaVu ™ acquisition feature and sets abenchmark in waveform capturerate for DSOs. The TDS 744Acan display more than 400,000 acquisitions per second—a rate2,5...
