Adjusting Antenna Tuners; Measuring Cable Length/Distance To Fault - AEA CIA-HF Operating Manual

ADJUSTING ANTENNA TUNERS

Example: Adjusting an antenna tuner without transmitting a signal on the air.
Process:
1. Connect a cable from the input of your antenna tuner to the center connector of a two-
position coax switch (be sure to use a switch that shorts the unused portion).
2. Connect the open position of the switch to the output of your transceiver.
3. Connect a cable from the closed position of the switch to the antenna connector on the
Analyzer.
4. Turn the Analyzer on. Set the center frequency and width values of your choice. Use the F5
softkey to scroll to the Z screen.
5. Adjust the tuning on the antenna tuner (with the proper antenna connected to the antenna
tuner output) until the center frequency displays an Impedance value of 50 ohms.
6. Use the F5 softkey to scroll to the X screen to make sure Reactance is zero.
7. Use F5 to scroll to the S screen. Note the low SWR value at the center frequency. Flip the
coax switch to the transceiver. The low SWR presented to the Analyzer will now be presented
to the transceiver.

MEASURING CABLE LENGTH/DISTANCE TO FAULT

NOTE: The following data block will be referenced in this addendum:
"Fc:xxx VF:xxx FT:xxx (x)"
The Analyzer measures the physical length of a coax cable, or the distance to the first short or
open present on a coax cable, by determining the frequency at which cable impedance goes to
zero. This frequency is inversely proportional to the length of the cable, and is used, along with
the user-programmable velocity factor, to compute the distance to the end of the cable.
Generally, an open cable will exhibit a nearly zero impedance at the ¼ wavelength frequency.
Example: Determining cable length/the distance to an open or short present on a coax cable.
Process:
1. Attach the coax cable under test to the antenna connector. Turn the Analyzer on.
2. Press F1 to access the user Menu screen. Use the WIDTHq key to scroll down to the "VF:50
(open)" (velocity factor) selection
3. Use the FREQp and FREQq keys to change the velocity factor to a value between 0.50 and
0.99. (The velocity factor for your cable is listed in the Radio Amateur's Handbook or in the
ARRL Antenna Handbook, or is available directly from the manufacturer.) If you toggle past
0.99, the velocity factor value will revert to 0.50, and the fault type indicated in parentheses
will change from OPEN to SHORT and vice versa. NOTE: A correct velocity factor is critical
in obtaining accurate distance measurements.
4. Press F1 to return to the real time graphing screen. Use F3 to scroll to the "W:xxx Fc:xxx"
data block. Input 5 0 0 0 ENTER to set the center frequency to 5.000 MHz. Use the WIDTHp
key to set the width to 1 MHz.
5. Use F5 to scroll to the Z (impedance) screen.
6. Depending on the length of the cable, you should observe one or several dips in the
impedance curve. Select the LOWEST center frequency value (above zero) that displays a
full dip. Experiment with the center frequency value until it is as close to the center of the dip
as possible. As a general rule, enter lower center frequencies for longer cables and higher
center frequencies for shorter cables. For example, enter a center frequency of 5.000 MHz to
display the dip of a 32-foot long cable possessing a velocity factor of 0.66.
7. Press ENTER to reverse data block scrolling. Press F3 once to display the "Fc:xxx VF:xxx
FT:xxx (x)" data block. Consult the "FT:" reading to determine the length of the cable. If the
footage reading is shorter than expected, an open or short may be present on the cable at
the distance indicated.
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Center Frequency, Velocity Factor, Feet, (O) Open or (S) Short