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Characterizing a Voltage Controlled Oscillator


Objective:

Students will be introduced to the operation and characteristics of a Voltage Controlled Oscillator (VCO). Component properties that will be examined are the output power and frequency, tuning sensitivity and linearity, harmonics and spurious levels, and frequency pushing. VCO operations will be measured and compared to the device specification sheet provided by the manufacture.


Equipment:

Hewlett Packard IFR A7550 Spectrum Analyzer or Equivalent
Mini Circuits ZOS1025 VCO or Equivalent
VCO Vendor Specifications
Frequency Range: 685MHz - 1025MHz
Power Output Typical (dBm): Main +8, Aux. -13
Tuning Voltage: 1 - 16volts
Pushing (MHz / V): 1.0
Tuning Sensitivity: 30MHz / V
Harmonics (dBc): -25typ, -18max
Power Supply: 12volts, 140ma




Procedure:

1. Connect the circuit as shown in Figure 1. All DC voltages should be carefully measured prior to connecting to the circuit.



2. Vary the Tune Voltage from 0 to 16 volts using the step values in Table 1. At each voltage step using a spectrum analyzer, measure and record in Table 1 the Frequency in MHz, Power Out Main in dBm, Power Out Auxiliary in dBm, and the Second Harmonic in dBc.

3. After the data in Table 1 has been acquired, perform the following:

a) Plot the Frequency Tuning characteristics using the data gather in Table 1

b) Determine the Tuning Sensitivity

c) Determine the and Plot the Tuning Linearity

d) Construct a table and compare the measured values with the vendorís specification sheet values

e) Compare the measured data with the specifications given for the voltage controlled oscillator (VCO) under the Equipment section above

4. Measure the Frequency Pushing

a) Increase the power supply voltage by one volt and perform the tune voltage, frequency measurements. Do not make measurements over the entire range. Pick three points over the frequency range, measure and record the power supply voltage, the tune voltage, and the output frequency.

b) Decrease the power supply voltage by one volt from nominal (11 volts) and perform the tune voltage, frequency measurements as in step 4a above.

c) Plot the values and compare to the VCO vendors specification sheet.


Engineering key words: VCO, oscillator, HP, characterizing, specifications, measurements, harmonics, dB, dBi, dBm, output power, dynamic range, frequency range, tuning sensitivity, spurs, decibels, voltage controlled oscillator, RF, radio frequency, LO, pushing, comparator, spectrum analyzer, network analyzer, tune, minus 3dB point, linearity, computational analysis, out of range, milliamp, DC, noise.


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