In order to observe the frequency change clearly, the offset of frequency modulation can be set much larger
in the demonstration. But in practice, the offset value of frequency modulation is under 5% in order to limit
the bandwidth taken by the carrier signal.
7.2.4 Setting of modulation waveform:
Since the signal of channel B is taken as the modulation signal, the modulation waveform is, in fact, the
waveform of channel B. Pressing the key “AM/FM” and selecting “Mod Shape”, the serial number of channel
B will be changed to green. The setting of modulation waveform can be carried by entering the serial
number by the number keys or adjusting of knob.
7.3 Frequency modulation (FM)
PeakTech
®
4050
In Frequency modulation, the frequency of the carrier is varied by the instantaneous voltage of modulating
waveform, the carrier shape is sine usually, but square, ramp or arbitrary waveform can also be used. Of
course, using DC or noise as carrier wave is useless.
7.3.1 Carrier setting:
Press
【
CarrFreq
〗
softkey to select “carrier frequency” or “carrier amplitude”. It is able to set carrier
frequency and amplitude at any moment while the FM signal is outputted.
7.3.2 Modulating waveform frequency:
In frequency modulation, the modulating frequency is always much lower than the carrier frequency. If
internal modulating signal is used, you can set the modulating frequency within the range of 2mHz
～
20 kHz.
If external modulating signal is used, the modulating frequency setting is ignored.
7.3.3 Frequency deviation:
It represents the maximum variation in frequency of the modulated signal from the carrier frequency. For
sine modulating waveform with no DC offset, when the amplitude of the modulating waveform is at positive
peak value, the frequency of the modulated signal is equal to the frequency of the carrier plus the frequency
deviation, and when it is at the negative peak value, the frequency is equal to the carrier frequency minus
the frequency deviation. Therefore, the frequency deviation setting must conform to the following two
conditions:
Frequency deviation
≤
carrier frequency
Frequency decarrier frequency
≤
maximum frequency of the selected signal
7.3.4
Modulating waveform shape:
It is able to set modulating waveform shape if internal modulating signal is used. Press
〖
SineModu
〗
softkey
to select “sine modulation”, “square modulation”, “triangle modulation” or “ramp modulation”. Modulating
waveform shape setting would be ignored if external modulating signal is used.
7.3.5 Modulating source:
The function generator will accept an internal or external modulation source for FM. Press
〖
Int Modu
〗
softkey to select “external source”. The modulating signal is inputted from the rear panel “Modulation In”
connector for FM. If the amplitude of the external modulating signal is ± 5V, the frequency deviation setting
and the display value accord with the real frequency offset. Otherwise, the frequency deviation setting and
display value are not accurate.
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