C. Remember that the value of VCF IN signal is the peak to peak amplitude.
3-7. External Control Of VCF
Within a given range, the FREQ. dial setting normally controls the output
frequency of generator. However, applying voltage at the VCF IN BNC on the front
panel also may control it. There are three basic possible modes of external VCF
control as detailed below,
A. Applying an AC voltage produces FM modulation(previously described in “Use
as FM Signal Generator” paragraph)
B. Applying a specific fixed DC voltage will produce a specific output frequency
described in following “Programmed Frequency Selection”paragraph
C. Applying a ramp voltage(or other type waveform if desired)provides externally
controlled sweep generator operation(described in following “Use as Externally
Controlled Sweep Generator” paragraph)
The following consideration apply to all modes of operation involving external
control of the VCF(voltage controlled frequency)
A. The output frequency of generator is determined by the voltage applied to the
VCF. First of all, this voltage is established by the setting of the FREQ. dial. Any
voltage input drives the VCF TO A HIGHER FREQUENCY. However. The VCF can
never be driven beyond its range limits (the highest and lowest frequencies that can
be attained with the dial on a given range.)
B. With the FREQ. dial set at minimum(0.05) and 0 volts at the VCF in BNC, the
generator output frequency is at the lower limit of the selected range. Increasing the
voltage to + 10 volts drives the generator frequency to the upper limit of the range.
Between 0 and + 10 Volts, the generator output frequency is proportional to the
VCF IN voltage. The VCF IN voltage can be correlated to equivalent dial settings as
given in Table below.
VCF voltage
Equivalent dial Setting
0
0.05
1
.5
2
1.0
3
1.5
4
2.0
5
2.5
6
3.0
7
3.5
8
4.0
9
4.5
10
5.0
