Global Specialties 4005 - Manual User Manual

Page 19

HIGHEST FREQ.

FREQ. DEVIATION FOR EACH

RANGE

OBTAINABLE(Hz)

0.1 VOLT VCF IN CHANGE(Hz)

0.05

0.5

500

50K

500

500K

50K

Frequency Deviation vs VCF IN Voltage.

B. For an example, it is assumed that we wish to generate a 455 KHz signal with FM deviation of ±15

KHz (30 KHz swing). The 500k range will be used to obtain the 455 KHz carrier with the FREQ. dial

set to 4.55. The highest frequency obtainable in this range is 500kHz. One percent of 500kHz is 5

KHz. Our requirement of 30 KHz deviation is 6 times greater than 5 KHz deviation produced by a

0.1 volt VCF IN swing, thus we will use 6 times as much peak-to-peak voltage swing, or 0.6 V.

For Instance:

desired deviation 30 KHz
1% deviation 5KHz

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 a 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 the

“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 the

“Use as Externally Controlled Sweep Generator”

paragraph)

The following considerations apply to all modes of operation involving external control of the VCF
(voltage controlled frequency)

A. The output frequency of the generator is determined by the voltage applied to the VCF.

X 0.1 V = required VCF IN

signal

x 0.1 = 6 x 0.1V = 0.6V