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TEL 444
Wireless Systems
Fall 2007
WESTERN CAROLINA UNIVERSITY
DEPARTMENT OF ENGINEERINIG AND TECHNOLOGY
TEL 444 WIRELESS SYSTEMS
LAB #4 – Pierce Crystal Oscillator
Performed on Monday, Oct. 8, 2007
Report Due Friday, Nov. 2, 2007
Equipment list:
One 10 k variable resistor
One 10 M resistor
A collection of various resistors
One 1 nF capacitor
One 2N5485 Field Effect Transistor
(FET)
Breadboard
Small printed circuit board
8.00 MHz crystal
Radio frequency choke
Soldering iron and solder
8-pin wire wrap socket
Wire wrap tools
Wire cutters
Long nose pliers
Oscilloscope
Spectrum analyzer
DC power supply
Connecting leads
BMC and N-type cables
Parts for the DC regulator circuit (Optional):
TPS7230 Three Volt regulator
One 250 k resistor
One 0.1 F capacitor
9 volt battery
Battery clip and holder
Procedure:
1) Connect a Pierce crystal oscillator circuit on a breadboard using an 8 MHz crystal. Cut the
leads short to reduce noise sensitivity.
2) Provide a 3 volt DC power supply to the crystal oscillator circuit.
3) Monitor the output sine wave on the oscilloscope. Verify that the frequency of the generated
sine wave is 8 MHz and the output voltage is at least 1 volt peak-to-peak.
4) Disconnect the output sine wave from the oscilloscope. Monitor the output sine wave on the
spectrum analyzer. The spectrum analyzer has a 50  input impedance, which will excessively
load the output signal. So monitor the output signal with the spectrum analyzer ground
unconnected.
TEL 444
Wireless Systems
Fall 2007
5) Set the center frequency to 50 MHz and the frequency span to 100 MHz. Insert a 10 k
variable resistor between the crystal and the capacitor. Adjust the variable resistor so that the
harmonics are at least 10 dB below the fundamental. Be sure to take your hand away fronm
the PC board and the variable resistor, before taking measurements on the spectrum analyzer.
A screen shot of the frequency spectrum of a 11 MHz Pierce oscillator circuit is shown in
Figure 1. Notice that the power of the 2nd harmonic (22 MHz) is about 14 dB below the power
of the fundamental frequency (11 MHz), and the power of the 3rd harmonic (33 MHz) is about
24 dB below the fundamental frequency. The more you can reduce the harmonics while
keeping the power of the fundamental frequency unchanged, the less distorted the generated
sine wave will be.
Figure 1. Frequency Spectrum of a 11 MHz Pierce Oscillator.
6) When you have a desirable frequency spectrum, pull out the variable resistor and measure its
resistance.
Measured resistance = ___________
7) Find a fixed resistor or several resistors in series that closely match the measured resistance.
Place the fixed resistor(s) in the circuit, and observe the frequency spectrum on the spectrum
analyzer. If you do not have a desirable frequency spectrum, try different values of fixed
resistance.
TEL 444
Wireless Systems
Fall 2007
8) When you have a spectrum that exceeds the 10 dB specification described in part 5, disconnect
the spectrum analyzer and connect the oscilloscope to the generated sine wave. Verify that the
frequency is 8 MHz and the output voltage is at least 1 volt peak –to-peak. If these
requirements are met, continue to step 9. If the frequency is 8 MHz, but the output voltage is
less than 1 volt peak –to-peak, then change resistors to get at least 1 volt peak-to-peak and then
go back to step 7.
9) Layout the circuit on a printed circuit board. Start with the wire wrap socket and solder it is
place. Use the socket for the FET.
10) Next layout the capacitor, your chosen resistor(s), and the crystal all in series on the board.
One good way to lay them out is place them all in a parallel pattern, but solder them all in
series on the reverse side. Solder one end to the FET gate and the other end to the FET drain.
Solder connecting wires as necessary to do this.
11) Decide on a place to put DC power (3 volts) and ground. You may want to soledr a wire wrap
pin for the + terminal and another wire wrap pin for the – terminal (ground).
12) Layout the 10 M resistor on the board so that one end will be near the FET gate and the othe
end near ground. Solder this end to the FET gate and one end to ground. Solder connecting
wires as necessary to do this.
13) Layout the coil on the board so that one end is near the FET drain and the other end near the +
DC power terminal. Solder one end to the FET drain the other end to the + DC power
terminal.
14) Solder the FET source to ground. Solder connecting wires as necessary to do this.
15) Solder a output test wire to the drain.
16) Connect the oscilloscope to monitor the output sine wave.
17) Connect 3 volts DC power to the circuit.
18) Monitor the generated sine wave using the oscilloscope.
19) Monitor the frequency spectrum of the generated sine wave using the spectrum analyzer.
20) If the circuit generates a sine wave, but does not meet the design specifications, try adding
extra capacitance a various points in the circuit.
21) When the circuit is working to specification, save a screen shot of the frequency spectrum of
the generated sine wave on the spectrum analyzer. Make sure the screen shot shows that all
harmonic are at least 10 dB below the power of the fundamental frequency. Have the instructor
inspect this step.
Instructor Initials________
22) When the circuit is working to specification, save a screen shot of the generated sine wave on
the oscilloscope. Make sure the screen shot shows at least a 1 vol peak-to-peak sine wave.
Have the instructor inspect this step.
Instructor Initials________
TEL 444
Wireless Systems
Fall 2007
Optional regulated power supply (if time permits or do outside of lab time)
As an optional endeavor for extra credit, solder the 3 volt regulated power supply shown in Figure
2 onto your printed circuit board. Solder a 9 volt battery clip to the input of the regulator (pins 4
and 5). The 3 volts output is at pins 3 and 7. Solder this 3 volt output to your pierce oscillator
circuit. Verify correct operation, and have the instructor inspect.
Figure 2 – TPS7230 3 volt regulated power supply
Lab Report
In the theory section, discuss how crystals work and how crystal circuits work.
In the results/analysis section, discuss the circuit implementation (how you designed, tested and built
it), and present and discuss the results. In this section, include figures of:
 an oscilloscope screen shot of the generated sine wave
 an spectrum analyzer screen shot of the generated sine wave
 a scanner image or a photograph of the final circuit board
 a schematic diagram of the final design