GRF-1300 User Manual and Teaching Materials
Experiment 6: FM signal measurement
Relevant
information
Since frequency modulation is a common type of modulation,
it is important to learn the principles and characteristics of FM
waves. Compared to AM waves, the amplitude of an FM wave
doesn’t carry the modulating signal information. This allows an
amplitude limiter to be used to eliminate the magnitude
interference before demodulation. The noise power spectral density
in an FM wave band is evenly distributed at the input terminal. But
due to frequency modulation, it is affected by frequency at the
output terminal. Because the bandwidth of a modulated signal is
far less than the FM wave bandwidth, it can pass through a low-
pass filter to attenuate noise and increase the output signal to noise
ratio during demodulation. FM waveforms are advantageous as
they utilize power efficiently and have a high degree of fidelity as
they rely on the phase of the modulated signal and not the
amplitude to carry the baseband signal. The FM circuit in this
experiment uses a phase-locked loop. The phase-locked loop circuit
principles described earlier can be used to study the application of
a phase-locked loop circuit for this section.
Item
Equipment
Quantity Note
1
Spectrum analyzer
1
GSP-730
2
RF & Communication Trainer
1
GRF-1300
3
RF wire
2
100mm
4
RF wire
1
800mm
Experiment
equipment
5
Adapter
1
N-SMA
Experiment
goals
1.
Understand the working principals of frequency modulation.
2.
Use a spectrum analyzer to measure the FM characteristics of an
FM wave.
3.
Master phase-locked loop principals that are used in FM.
Experiment
principles
1.
Time domain analysis.
Frequency modulation is a type of modulation in which the
instantaneous frequency deviation of the modulated signal with
respect to the frequency of the carrier signal is directly
proportional to the instantaneous amplitude of the modulating
signal.
Assume that the modulating signal is
u
Ω
(
t
) =
U
Ω
m
cos
Ω
t
68
Summary of Contents for GRF-1300
Page 15: ...Introduction to the GRF 1300 Figure A 10 Operation interface for HyperTerminal 13 ...
Page 19: ...Overview of the Time and Frequency Domain Time domain Frequency domain 17 ...
Page 20: ...GRF 1300 User Manual and Teaching Materials NOTES 18 ...
Page 21: ...Overview of the Time and Frequency Domain NOTES 19 ...
Page 22: ...GRF 1300 User Manual and Teaching Materials NOTES 20 ...
Page 23: ...Overview of the Time and Frequency Domain NOTES 21 ...
Page 24: ...GRF 1300 User Manual and Teaching Materials 22 NOTES ...
Page 30: ...GRF 1300 User Manual and Teaching Materials NOTES 28 ...
Page 31: ...An Introduction to Spectrum Analyzers NOTES 29 ...
Page 56: ...GRF 1300 User Manual and Teaching Materials NOTES 54 ...
Page 57: ...RF Communication and Signals Experiments NOTES 55 ...
Page 58: ...GRF 1300 User Manual and Teaching Materials NOTES 56 ...
Page 59: ...RF Communication and Signals Experiments NOTES 57 ...
Page 95: ...RF Communication and Signals Experiments 10MHz frequency deviation test results 93 ...
Page 101: ...Test for Learning Outcomes NOTES 99 ...
Page 102: ...GRF 1300 User Manual and Teaching Materials NOTES 100 ...
Page 103: ...Test for Learning Outcomes NOTES 101 ...
Page 104: ...GRF 1300 User Manual and Teaching Materials 102 NOTES ...
Page 109: ...Appendix Modulation Index and Sideband Amplitude Comparison Table 107 ...