Agilent Spectrum Analysis Basics - Agilent Technologies

More documents

Recommendations

Info

Why measure spectra? The frequency domain also has its measurement strengths. We have already seen in Figures 1-1 and 1-2 that the frequency domain is better for determining the harmonic content of a signal. People involved in wireless communications are extremely interested in out-of-band and spurious emissions. For example, cellular radio systems must be checked for harmonics of the carrier signal that might interfere with other systems operating at the same frequencies as the harmonics. Engineers and technicians are also very concerned about distortion of the message modulated onto a carrier. Third-order intermodulation (two tones of a complex signal modulating each other) can be particularly troublesome because the distortion components can fall within the band of interest and so will not be filtered away. <strong>Spectrum</strong> monitoring is another important frequency-domain measurement activity. Government regulatory agencies allocate different frequencies for various radio services, such as broadcast television and radio, mobile phone systems, police and emergency communications, and a host of other applications. It is critical that each of these services operates at the assigned frequency and stays within the allocated channel bandwidth. Transmitters and other intentional radiators can often be required to operate at closely spaced adjacent frequencies. A key performance measure for the power amplifiers and other components used in these systems is the amount of signal energy that spills over into adjacent channels and causes interference. Electromagnetic interference (EMI) is a term applied to unwanted emissions from both intentional and unintentional radiators. Here, the concern is that these unwanted emissions, either radiated or conducted (through the power lines or other interconnecting wires), might impair the operation of other systems. Almost anyone designing or manufacturing electrical or electronic products must test for emission levels versus frequency according to regulations set by various government agencies or industry-standard bodies. Figures 1-3 through 1-6 illustrate some of these measurements. 6
Figure 1-3. Harmonic distortion test of a transmitter Figure 1-4. GSM radio signal and spectral mask showing limits of unwanted emissions Figure 1- 5. Two-tone test on an RF power amplifier Figure 1-6. Radiated emissions plotted against CISPR11 limits as part of an EMI test 7
Page 1 and 2: Agilent Spectrum Analysis Basics Ap
Page 3 and 4: Table of Contents — continued Cha
Page 5: Some measurements require that we p
Page 9 and 10: While we have defined spectrum anal
Page 11 and 12: Since the output of a spectrum anal
Page 13 and 14: We need to pick an LO frequency and
Page 15 and 16: To separate closely spaced signals
Page 17 and 18: Agilent data sheets describe the ab
Page 19 and 20: This allows us to calculate the fil
Page 21 and 22: Some modern spectrum analyzers allo
Page 23 and 24: On the other hand, the rise time of
Page 25 and 26: The width of the resolution (IF) fi
Page 27 and 28: The “bucket” concept is importa
Page 29 and 30: Peak (positive) detection One way t
Page 31 and 32: The normal detection algorithm: If
Page 33 and 34: EMI detectors: average and quasi-pe
Page 35 and 36: The effect is most noticeable in me
Page 37 and 38: Thus, the display gradually converg
Page 39 and 40: In some cases, time-gating capabili
Page 41 and 42: Timeslots 0 1 2 3 4 5 6 7 Timeslots
Page 43 and 44: Gated sweep Gated sweep, sometimes
Page 45 and 46: In Chapter 2, we did a filter skirt
Page 47 and 48: Custom signal processing IC Turning
Page 49 and 50: Chapter 4 Amplitude and Frequency A
Page 51 and 52: Following the input filter are the
Page 53 and 54: Improving overall uncertainty When
Page 55 and 56: Examples Let’s look at some ampli
Page 57 and 58:
In a factory setting, there is ofte
Page 59 and 60:
Because the input attenuator has no
Page 61 and 62:
Noise figure Many receiver manufact
Page 63 and 64:
Using these expressions, we’ll se
Page 65 and 66:
Let’s first test the two previous
Page 67 and 68:
This is the 2.5 dB factor that we a
Page 69 and 70:
When we add a preamplifier to our a
Page 71 and 72:
2D dB 3D dB 3D dB 3D dB With a cons
Page 73 and 74:
We can construct a similar line for
Page 75 and 76:
Figure 6-2 shows the dynamic range
Page 77 and 78:
Dynamic range versus measurement un
Page 79 and 80:
Let’s see what happened to our dy
Page 81 and 82:
The range of the log amplifier can
Page 83 and 84:
Chapter 7 Extending the Frequency R
Page 85 and 86:
Next let’s see to what extent har
Page 87 and 88:
In examining Figure 7-5, we find so
Page 89 and 90:
Can we conclude from this discussio
Page 91 and 92:
Amplitude calibration So far, we ha
Page 93 and 94:
From the graph, we see that a -10 d
Page 95 and 96:
Pluses and minuses of preselection
Page 97 and 98:
Table 7-1 shows the harmonic mixing
Page 99 and 100:
Figure 7-15. Which ones are the rea
Page 101 and 102:
Figure 7-18. The image suppress fun
Page 103 and 104:
Other examples of built-in measurem
Page 105 and 106:
Digital modulation analysis The com
Page 107 and 108:
Data transfer and remote instrument
Page 109 and 110:
Summary The objective of this appli
Page 111 and 112:
Delta marker: A mode in which a fix
Page 113 and 114:
Frequency stability: A general phra
Page 115 and 116:
LO feedthrough: The response on the
Page 117 and 118:
Residual responses: Discrete respon
Page 119 and 120:
Video: In a spectrum analyzer, a te
show all

Agilent Spectrum Analysis Basics - Agilent Technologies

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?