250
Chapter 5 Tutorial
Modulation
5
Phase Modulation (PM) PM is similar to FM, but the phase of the
carrier waveform is varied, rather than the frequency:
y(t)=sin[ω
c
t+d·m(t) ]
where m(t) is the modulating signal and d is the phase deviation.
Frequency-Shift Keying (FSK) FSK is similar to FM, except the
carrier frequency alternates between two preset values, the carrier
frequency and the hop frequency. Sometimes the hop and carrier
frequencies are called “Mark” and “Space,” respectively. The rate at
which the frequency switches values is determined by an internal timer
or the signal on the rear panel Ext Trig connector. Frequency changes
are instantaneous and phase-continuous.
The internal modulating signal is a square wave with 50% duty cycle.
Binary Phase Shift Keying (BPSK) BPSK is similar to FSK, except it
is the carrier’s phase, rather than its frequency, that switches between
two values. The rate at which the phase switches values is determined by
an internal timer or the signal on the rear panel Ext Trig connector.
Phase changes are instantaneous.
The internal modulating signal is a square wave with 50% duty cycle.
Pulse Width Modulation (PWM) PWM is only available for the Pulse
waveform, and as its name suggests, the pulse width varies according to
the modulating signal. The amount by which the pulse width varies is
called the width deviation, and it can be specified as a percentage of the
waveform period (that is, duty cycle) or in units of time. For example, if
you specify a pulse with 20% duty cycle and then enable PWM with a 5%
deviation, the duty cycle will vary from 15% to 25% under control of the
modulating signal.
To Next Page
Loading...
Need help?
General
