Global Specialties 4005 - Manual - Manual (Page 20)

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B. This voltage is first 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 its minimum ( 0.05) and 0 volts at the VCF in BNC, the generator
’s
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 the table below.
VCF voltage Equivalent dial Setting
0 0.05
1 0.5
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
Correlation Between the VCF IN Voltage and the Equivalent Frequency Dial Setting
(dial set to 0.05)
C. The FREQ dial is usually set to 0.05 when using external VCF control. This reduces the dialed
VCF voltage to zero and allows the external VCF voltage to exercise complete control. It also
reduces the effects of dial setting inaccuracy.
D. If the summed dial setting and VCF IN voltage exceeds +10 volts, oscillation ceases and no
output is produced. If the swing of the VCF IN signal is too great, oscillation will cease each time
the instantaneous voltage reaches the limit.
3-8. Programmed Frequency Selection
A specific output frequency can be selected each time a specific VCF input voltage is applied
(assuming a common dial setting). Such operation may be advantageous where there is a
requirement to return to a specific frequency periodically. Eliminating the need for frequency
measurement reduces set-up time and precision tuning each time frequency is needed. Just set the
dial against its lower stop and turn on the external VCF voltage. Using multiple DC voltage values,
which may be selected by a switch or electronic switching circuits, may be valuable in programming
a set of two or more specific frequencies. This type of operation would be desirable in production
testing where signals at several specific frequencies are required for various tests. FSK (frequency
shift keying) signals also may be generated in this manner. To maintain the original accuracy each
time the operation is repeated, the FREQ dial must be accurately set to the same position. Probably
the easiest way to assure this common dial setting is to set it against its lower stop (0.05).