Lab Report 3
Analog Communication System
Submitted by:
Name Abdul Mobeen
Reg no Fa19-bee-028
Submitted to:
Sir Fahad Sharief
Lab#3 Voltage Control Oscillator on LabVolt: VCO-LO
and VCO-HI
Objectives
At the completion of this exercise, you will be able to
Generate the low and high frequency signals using VCO-LO and VCO-HI modules of the
LabVolt
Use an oscilloscope to make signal measurements.
Pre Lab
The two voltage-controlled oscillators (VCOs) on the circuit board are the VCO-LO circuit block
(452 kHz or 1000 kHz) and the VCO-HI circuit block (1455 kHz). These oscillators provide the
high frequencies that are necessary for transmitting and receiving the low-frequency message
signal.
PROCEDURE A -OSCILLATOR CIRCUIT BLOCKS
In this PROCEDURE section, you will examine and use the VCO-LO and VCO-HI circuit
blocks. The VCO-LO circuit block is an oscillator circuit that performs three functions: it can
output a 1000 kHz signal, a 452 kHz signal, or an FM signal. The VCO-HI circuit block outputs
a signal in the 1455 kHz range.
5. Locate the VCO-LO circuit block on the ANALOG COMMUNI- CATIONS circuit board.
Insert a two post connector in the 1000 kHz terminals.
6. On the VCO-LO circuit block1 set the potentiometer knob completely counter clockwise
(CCW). Does this pot adjust the VCO- LO frequency or the VCO-LO amplitude?
ANSWER:
Yes amplitude changes, pot adjusts the VCO-LO amplitude.
7. Set the NEGATIVE SUPPLY knob on the left side of the base unit completely CCW. Does
the NEGATIVE SUPPLY knob adjust the VCO-LO frequency or the VCO-LO phase?
Answer:
NEGATIVE SUPPLY knob adjust the VCO-LO frequency.
8. Set the oscilloscope channel 1 to 100 mV/DlV and set the sweep to 0.5 µs/DIV. Connect the
channel 1 probe to OUT on the VCO-LO circuit block, and connect the probe ground clip to a
ground terminal on the circuit board.
• With channel 1 set to 100 mV/DIV, how many vertical oscilloscope gratitude divisions will
equal a 300 mVpk-pk signal?
Answer:
4-Blocks.
• Slowly turn the VCO-LO potentiometer knob clockwise (CW) until the output signal on
channel is 300 mVpk-pk·
3. While observing the signal on channel 1, slowly turn the NEGATIVE SUPPLY knob about a
quarter turn CW. Use the top portion of the NEGATIVE SUPPLY knob for fine adjustments, and
use the bottom
portion for coarse adjustments. Did the VCO-LO frequency increase or decrease?
Answer:
VCO-LO frequency increase.
4. With a sweep setting of 0.5 µs/DIVI how many horizontal oscilloscope graticule divisions equal
one cycle of a 1000 kHz signal?
Answer:
There are 2 division horizontal on oscilloscope we’ve observed.
5. Adjust the NEGATIVE SUPPLY knob so that the VCO-LO output frequency is 1000 kHz
Answer:
We adjust the NEGATIVE SUPPLY knob so that the VCO-LO output frequency is
1000 kHz on oscilloscope.
10. Remove the two-post connector from the 1000 kHz terminals and insert it in the 452 kHz
terminals. Adjust VCO-LO potentiometer knob to set the output signal on channel 1 to 200 mVpkpk
11. With a sweep setting of 0.5 µs/DIV, how many horizontal oscilloscope graticule divisions equal
1 cycle of a 452 kHz signal?
Divisions = 1/frequency/sweep setting
Answer:
Four graticule divisions
12. Adjust the NEGATIVE SUPPLY knob so that 1 cycle of the channel 1 signal equals 4.425
divisions, which sets the VCO-LO frequency at 452 kHz.
13. Locate the VCO-HI circuit block on the ANALOG COMMUNI- CATIONS circuit board, and
set the potentiometer knob, which adjusts the amplitude completely CCW
14. Set oscilloscope channel 1 to 100 mV/DIV and set the sweep to 0.5 µs/DIV. Connect the
channel 1 probe to OUT on the VCO-HI circuit block, and connect the probe ground dip to a ground
terminal on the circuit board.
15. Slowly turn the VCO-HI potentiometer knob CW until the output signal on channel 1 is
300 mVpkpk·
16. While observing the signal on channel 1, slowly turn the POSITIVE SUPPLY knob about a
quarter turn CW. Use the top portion of the NEGATIVE SUPPLY knob for fine adjustments and the
bottom portion for coarse adjustments. Did the VCO-HI frequency increase or decrease?
Answer:
The VCO-HI frequency decrease.
17. Set the oscilloscope sweep to 0.2 µs/DIV. How many horizontal oscilloscope graticule
divisions equal one cycle of a 1455 kHz signal?
Divisions = 1/1,455,000/(0. 2 x 10-6).
Answer:
Observe the graticule divisions are 3.45 blocks.
Calculate graticule divisions are 3.43 blocks.
18. Adjust the POSITIVE SUPPLY knob so that one cycle of the channel 1 signal covers
3.436 divisions. This adjustment set the VCO-HI frequency at 1455 kHz.
Critical Analysis:
In this lab, we have learned to control frequency by VCO low and VCO high and note the changes
on the implemented signal. By doing this lab we are able to describe phase-locked loop operation
by using the VCO-LO and PHASE-LOCKED LOOP circuit blocks on the ANALOG
COMMUNICATIONS circuit board. We learned about angle modulation and demodulation by
using the VCO-LO, PHASE MODULATOR, and QUADRATURE DETECTOR circuit blocks
on the ANALOG COMMUNICATIONS circuit board.
