Determining Resonant Frequency; Determining Characteristic Impedance; Testing Baluns - AEA CIA-HF Operating Manual

DETERMINING RESONANT FREQUENCY

Example: Using the 50-ohm accessory connector constructed for the above example to
determine the resonant frequency of an LC-tuned circuit.
Process:
1. Use the test leads of the 50-ohm accessory connector to connect the inductor and capacitor
in series.
2. Turn the Analyzer on. Maintain the default S screen.
3. Find the resonance point of the circuit by locating the lowest SWR point.
4. Use the FREQ keys to center the lowest SWR point.
5. Access the Data screen to read the 2:1 SWR bandwidth and the Q factor directly.

DETERMINING CHARACTERISTIC IMPEDANCE

For this type of measurement, you will need to assemble another accessory connector using a
500-ohm potentiometer (Figure 4).
FIGURE 4. 500 OHM POTENTIOMETER CONNECTOR
Example: Determining the characteristic Impedance of an unknown coax cable.
Process:
1. Attach the unknown cable to the Analyzer's antenna connector. Attach the potentiometer
accessory connector to the unterminated end of the cable using a PL-258 barrel connector.
2. Use the F5 softkey to scroll to the R screen. Press 2 5 0 0 0 ENTER to select a new center
frequency value of 25 MHz, and press the WIDTHp key until the width is set to 1 MHz. Use
the F4 softkey to set the vertical scale to 100 ohms full scale.
3. Depending on the length of the cable (hopefully at least 25 feet), two or more sine waves will
appear on the display.
4. Use the potentiometer to adjust the plot for minimum amplitude variance on the sine waves.
5. Now, disconnect the potentiometer from the cable. Use a volt-ohmmeter to determine the
Resistance of the potentiometer. Usually a 50-ohm cable will read between 49 and 52 ohms
of Resistance. It is also possible to read the Resistance value of the potentiometer by
disconnecting it from the cable and plugging it directly into the Analyzer. Use the F5 softkey
to scroll to the Data screen; once there, identify the Resistance (R:) value.

TESTING BALUNS

Example: Using the 500-ohm potentiometer accessory connector constructed for the above
example to determine the output (or input) Impedance of an unknown balun.
Process:
1. Insert the 50-ohm port of the balun into the Analyzer, and the potentiometer connector into
the balun's vacant port.
2. Turn the Analyzer on. Maintain the default S screen.
3. Adjust the potentiometer for minimum SWR. (The balun may not flat line over a wide range of
frequencies.)
4. To identify the balun's useful range, experiment with different center frequency and width
values. You may see larger SWR values at the extreme lower and upper frequencies.
5. To determine the balun's Resistance, disconnect the potentiometer from the balun and plug it
directly into the Analyzer. Then, access the Data screen (F5 softkey) to identify the
Resistance (R:) reading.
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