Don Honorio Ventura Technological State University
College of Engineering and Architecture
Department of Electronics Engineering
Bacolor, Pampanga
INDIVIDUAL REPORT
Course Code:
COMMS 1 (LAB)
Course Title:
COMMUNICATIONS THEORY 1 (LABORATORY)
Year and Section:
BS ECE- 2B
Room/Time/Date:
ECE LABORATORY / 07:30-10:30 a.m. / JAN. 07, 2020
Experiment No.:
EXPERIMENT 1
Experiment Title:
FILTERS
Date Experiment Performed: JANUARY 07, 2020
Date Experiment Final Due: JANUARY 07, 2020
Group Number: 4
Experiment Leader:
GONZALES, DANE MACKLYN Y.
Experiment Members:
MERCADO, KIMBERLY JOY Y.
SIYTOO, JAILAH JOY V.
Instructor: Engr. Enmar T. Tuazon
Date Final Received:
Day Late:
VILLEGAS, CHESKA MAE B.
INTRODUCTION:
In electronic circuits systems, it is often helpful to separate a specific range of
frequencies from the total spectrum. It is a type of circuit that passes a specific range of
frequencies while rejecting other frequencies. A passive filter consists of passive circuit
elements such as capacitors, inductors and resistors. Further, it is a device that changes
the amplitude of an AC voltage as the frequency of the input voltage changes. Filters
have two terminals, the input terminals take in the input voltage, which passes through
the filter and onto the output terminals, where the resulting output waveform can be
observed.
Typically in electronic systems such as filters and communication channels, cutoff
frequency applies to an edge in a lowpass, highpass, bandpass, or band-stop
characteristic , a frequency characterizing a boundary between a passband and a
stopband. From a graph, it can be find the by finding the frequency where the magnitude
of the output voltage is 70.7% off from the maximum value. In another way, the frequency
when the signal magnitude is Vpp/sqrt(2). It can also be calculated from the R and C
values as:
𝑓𝑐𝑜 =
1
2𝜋𝑅𝐶
There are several types of filters, but in the experiment, we will be looking at three
types.

A low-pass filter is a filter that allows a signal of a low frequency (i.e. a low
amount of oscillations per second) to pass through it. Consequently, it
attenuates (reduces) the amplitude of an input signal whose frequency is
higher than the cutoff frequency.
R = 10kW
Vin

C = 47nF
Vout
A high-pass filter is a filter that passes high frequencies well, but attenuates
(or reduces) frequencies lower than the cutoff frequency.
C = 47nF
Vin
R = 10kW
Vout

A band-pass filter is a device that passes frequencies within a certain range
and rejects (attenuates) frequencies outside that range.
L = 10mH
C = 47nF
Vin
R = 1kW
Vout
DISCUSSION:
We started the experiment by constructing the given low-pass filter in the
simulation software Multisim, consisting of a resistor and a capacitor. The input is
connected in series with the resistor, and the output is the voltage across the capacitor.
The input and output have one common terminal, which is the low (ground, or reference)
side of each. We then set up the function generator so that it produces a sinusoidal
waveform, with a peak to peak voltage of 10V and put the oscilloscope to verify this and
a multimeter to measure the voltages. Next, we use Channel 1 of the scope to display
Vin, and Channel 2 to display Vout. Starting at 50Hz, we vary the frequency of the input
signal up to 2500Hz (2.5kHz) in a sufficient number of intervals and record the peak to
peak voltage of the output for each frequency, and tabulate the data obtained. Lastly, we
plot a graph of the amplitude of Vout against the frequency and calculated for the cut-off
frequency.

Low-Pass Graph
Moreover, we constructed an RC network that behaves as a high-pass filter on the
Multisim, and the high-pass filter is the same as the low-pass filter, but with the positions
of the resistor and capacitor interchanged. Here the input is in series with the capacitor
and the output voltage is taken across the resistor. We just repeated the steps we did on
the low-pass filter, but, this time we started our frequency readings at 100Hz and work
our way up to 10kHz, and recorded the data obtained.

High-Pass Graph
Lastly, we constructed the circuit for band-pass filter on the simulation software,
the output voltage is taken across the resistor and the input is in series with the inductor
and the capacitor. We then also repeat the same procedures we did on the previous filters
but started frequencies from 2kHz up to 30kHz and recorded the data obtained and
plotted them on a graph.

Band-Pass Graph
CONCLUSION:
The discrepancies between the theoretical and measured value are relatively
small. The cut cut-off frequency can be changed by adjusting the value of either the
resistor or the capacitor as can be noticed from the formula. Meanwhile, a potentiometer
is an alternative way to be utilized for varying, adjusting, or tuning circuits.
Low-pass filter allows the frequencies below the cut-off frequency to pass and
attenuates those above its cut-off frequency. Conversely, high-pass filter allows the
frequencies above the cut-off frequency to pass and attenuated those below it. On the
other hand, a band-pass filter allows certain range of frequencies around the center
frequency to pass and rejects those above and below the center frequency. Applications
of low-pass and high-pass are audio amplifiers and speaker systems. Band-pass filters
are used for wireless transmitters.
Additionally, low pass filter inhibits that when a greater frequency is set up, the
lower the voltage, high-pass filter shows that a greater frequency, the greater voltage
obtained. Meanwhile, band-pass filter demonstrates that as the frequency increases, the
voltage approaches the amplitude but as it reach closer to the amplitude, it decreases.
Reference: Experiment Manual