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2) Considerations
A. The approximate frequency deviation for a given VCF IN signal can be
determined as follows, The 0.1 V change at the VCF IN BNC produces a
frequency change of 1% of the highest frequency obtainable on a given
range. For example(FG-7002C), the highest frequency obtainable on the 100
K range is 200 KHz. One percent of 200 KHz equals 2 KHz. Therefore, 0.1 V
change at the VCF IN BNC will deviate the output frequency 2 KHz on the
100K range. Following table summarizes the frequency deviation versus
VCF IN voltage for all ranges.
HIGHEST FREQ.
OBTAINABLE(Hz)
FREQ. DEVIATION FOR EACH
0.1 VOLT VCF IN CHANGE(Hz)
RANGE
FG-7002C
FG-7005C
FG-7002C
FG-7005C
1
10
100
1K
10K
100K
1M
2
20
200
2k
20k
200k
2M
5
50
500
5k
50k
300k
5M
0.02
0.2
2
20
200
2K
20K
0.05
0.5
5
50
500
5k
50k
Frequency deviation versus VCF IN voltage for each model.
B. For an example(FG-7002C), it is assumed that we wish to generate a 455
KHz signal with FM deviation of
±
15 KHz (30 KHz swing). 1M range will be
used to obtain the 455 KHz carrier with the FREQ. dial set to 0.455. The
highest frequency obtainable on the 1M range is 2 MHz. One percent of 2
MHz is 20 KHz. Our requirement of 30 KHz deviation is 1.5 times greater
than 20 KHz deviation produced by a 0.1 volt VCF IN swing, thus we will use
1.5 times as much peak-to-peak voltage swing or 0.15 V.
STATED ANOTHER WAY: SUBSTITUTING THIS EXAMPLE:
desired deviation
30 KHz
1% deviation 20 KHz
x0.1 V = required VCF IN signal
x 0.1 = 1.5 x 0.1V = 0.15V
C. Remember that the value of VCF IN signal is the peak to peak amplitude.
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