VOLTCRAFT FG 8210 Bedienungsanleitung Seite 33

8.4 FM SIGNAL GENERATOR
Frequency modulation (FM) is the change of the output frequency depending on the progress of a second infeed
control frequency.
Proceed as follows to use the frequency generator as a frequency-modulated signal generator:
• Make the basic settings for the function generator as described in chapter 8.1. Set the carrier frequency with the
adjustment button "FREQUENCY" and the amplitude with the adjustment button "AMPL".
• Apply a pure alternating voltage signal (modulation voltage without direct voltage share) to the VCF-input (5) via a
BNC measuring line (HF-cable).
• Change the applied modulation voltage (max. 10 Vpp), until the desired frequency deviation is reached.
An approximate illustration of the interrelation between frequency modulation and the alternating voltage applied to
the VCF input (modulation voltage) is described as follows:
A change to the alternating voltage at the VCF-input (VCF IN) by 0.1 V leads to a frequency change of 1 % of
the maximum frequency setting possible (MAX-area of the adjustment button "FREQUENCY") of the respective
frequency range set.
If, e.g., the switch "100k" is pushed in the filed "FREQUENCY RANGE (Hz)", the maximum frequency that can be
achieved in this area is approx. 1 MHz. A change by 0.1 V corresponds to a frequency change by 10 kHz. In the
following table, the interrelation between the set area or the max. frequency achieved and the frequency change per
0.1 V voltage change at the VCF-input is illustrated.
Example:
If a 455 kHz-signal is to be generated with a lift of +/-15 kHz (= 30 kHz-vibration), the switch "100k" in the field
"FREQUENCY RANGE (Hz)" must be pushed at the frequency generator.
The adjustment button "FREQUENCY" sets the 455 kHz-carrier frequency. The maximum frequency that can be set
in this frequency area is approx. 1 MHz.
1% of 1 MHz correspond to 10 kHz (= 0.1 V).
30 kHz is 3 times 10 kHz.
3 times 0.1 V therefore is 0.3 V.
Frequency range in [Hz]
1
10
100
1 k
10 k
100 k
1 M
Maximum poss. frequency in [Hz] Frequency lift in [Hz] per 0.1V
10
100
1 k
10 k
100 k
1 M
10 M
voltage change at VCF IN
0,1
1
10
100
1 k
10 k
100 k
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