327
Chapter 7 Tutorial
Modulation
4
7
The amount of amplitude modulation is called the modulation depth which
refers to the portion of the amplitude range that will be used by the
modulation. For example, a depth setting of 80% causes the amplitude to
vary from 10% to 90% of the amplitude setting (90% – 10% = 80%) with
either an internal or a full-scale (±5V) external modulating signal.
Frequency Modulation (FM)
For FM, the function generator uses modulation samples to modify the
output frequency of the instrument by changing the content of the PIR
(see “Direct Digital Synthesis” on page 311). Note that since the rear-
panel Modulation In connector is dc-coupled, you can use the 33210A to
emulate a voltage-controlled oscillator (VCO).
The variation in frequency of the modulated waveform from the carrier
frequency is called the frequency deviation. Waveforms with frequency
deviations less than 1% of the modulating signal’s bandwidth are
referred to as narrowband FM. Waveforms with larger deviations are
referred to as wideband FM. The bandwidth of the modulated signal can
be approximated by the following equations.
BW
≅
2
x
(Modulating Signal Bandwidth)
For narrowband FM
BW
≅
2
x
(Dev Modulating Signal Bandwidth)
For wideband FM
In the United States, commercial FM stations usually have a modulation
bandwidth of 15 kHz and deviation of 75 kHz, making them “wideband”.
Therefore, the modulated bandwidth is: 2
x
(75 kHz + 15 kHz) = 180 kHz.
Channel spacing is 200 kHz.
Frequency Modulation
Modulating Signal
Modulated Carrier
33210A users guide.book Page 327 Wednesday, July 16, 2008 11:16 AM
Summary of Contents for 33210A
Page 1: ...Keysight 33210A 10 MHz Function Arbitrary Waveform Generator User s Guide ...
Page 2: ......
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Page 14: ...12 Contents Contents 33210A users guide book Page 12 Wednesday July 16 2008 11 16 AM ...
Page 15: ...1 1 Quick Start 33210A users guide book Page 13 Wednesday July 16 2008 11 16 AM ...
Page 53: ...3 3 Features and Functions 33210A users guide book Page 51 Wednesday July 16 2008 11 16 AM ...
Page 273: ...5 5 Error Messages 33210A users guide book Page 271 Wednesday July 16 2008 11 16 AM ...
Page 301: ...6 6 Application Programs 33210A users guide book Page 299 Wednesday July 16 2008 11 16 AM ...
Page 311: ...7 7 Tutorial 33210A users guide book Page 309 Wednesday July 16 2008 11 16 AM ...
Page 335: ...8 8 Specifications 33210A users guide book Page 333 Wednesday July 16 2008 11 16 AM ...