Experiment 4: measurement of the rf carrier – GW Instek GRF-1300A User Manual
Page 49
RF Communication and Signals Experiments
Experiment 4: Measurement of the RF Carrier
Relevant
information
In communication systems, RF signals generally use carrier
signals. As a low frequency signal cannot be easily transmitted
very far over air, the low frequency message (such as voice) must
be placed into a higher frequency signal so it can be being
transmitted over a distance using an antenna. This high-
frequency signal carries the message, and is thus called the
carrier. In this experiment we will perform basic measurements
on RF signals and measure important parameters such as phase
noise and harmonic distortion.
The carrier of this experimental system is generated by a
PLL. Phase locked loops are widely used as phase-locked
receivers, or for phase-locked frequency modulation and
demodulation. They are also often used as a local oscillator for
transmitters and receivers. We must learn in detail the working
principles of PLL circuits when we study RF circuits. This
experiment allows students to comprehend high frequency
signals by measuring the carrier frequency spectrum. It also
makes students recognize the basic structure of a PLL circuit. In
the following experiments, we will further study the locked and
unlocked conditions of a phase-locked loop.
Item Equipment
Quantity Note
1
Spectrum analyzer
1
GSP-730
2
RF & Communication Trainer
1
GRF-1300A
3
RF wire
1
800mm
Experiment
equipment
4
Adapter
1
N-SMA
Experiment
goals
Measure an RF signal from the GRF-1300A RF &
Communication Trainer. Also perform measurements on more
important parameters such as phase noise and harmonic
distortion.
Experiment
principles
A Phase locked loop (PLL) is a phase error control system. It
compares the phase between a reference signal and an output
signal to generate a phase error voltage for adjusting the
frequency output of the voltage-controlled oscillator – for the
purpose of synchronizing the output frequency with the
reference signal. Its basic circuit structure is shown in Figure 4-1.
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