The mentioned answer can be obtained if the value of frequencies is substituted in the gain magnitude equation
5. Determine the gain of the first order low pass filter if the phase angle is 59.77o and the passband gain is 7.
Given the phase angle
=> f/fH=- φtan(φ)
=> f/fH= -1.716.
Substituting the above value in gain of the filter
= AF/√ (1+(f/fH)2)
6. In a low pass Butterworth filter, the condition at which f=fH is called
A. Cut-off frequency
B. Break frequency
C. Corner frequency
D. All of the mentioned
The frequency, f=fH is called cut-off frequency, because the gain of the filter at this frequency is down by 3dB from 0Hz. The cut-off frequency is also called break frequency, corner frequency, or 3dB frequency.
7. Find the High cut-off frequency if the passband gain of a filter is 10.
High cut-off frequency of a filter
fH = 0.707×AF
8. To change the high cutoff frequency of a filter. It is multiplied by R or C by a ratio of the original cut-off frequency known as
A. Gain scaling
B. Frequency scaling
C. Magnitude scaling
D. Phase scaling
Once a filter is designed, it may sometimes be a need to change its cut-off frequency. The procedure used to convert an original cut-off frequency fH to a new cut-off frequency is called frequency scaling.
9. Using the frequency scaling technique, convert the 10kHz cut-off frequency of the low pass filter to a cutoff frequency of 16kHz.(Take C=0.01µF and R=15.9kΩ)
To change a cut-off frequency from 10kHz to 16kHz, multiply the 15.9kΩ resistor.