MFJ-259B Instruction Manual
HF/VHF SWR Analyzer
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4.) Press the
“GATE”
button again, and the display will indicate distance in feet.
Use the following procedure:
1.) Measure the physical length of the line in feet.
2.) Divide the display reading by the actual feedline length.
Example:
27 feet (physical length) divided by 33.7 feet (measured length) equals .80 . The velocity factor
is .80 or 80%.
7.3
Impedance of Transmission Lines or Beverage antennas
The impedance of transmission lines between a few ohms and 650 ohms can be directly measured with the MFJ-
259B. Lines of higher impedance can be measured if a broadband transformer or resistance is used to extend the
MFJ-259B’s range. Select any measurement mode that indicates resistance (R=) and reactance (X=).
If a
balanced line
is used, operate the MFJ-259B
only
from internal batteries. Keep the MFJ-259B a few feet
away from other conductors or earth, and do not attach any wires (other than the feedline) to the unit. Use the
ANTENNA connector’s shield for one lead and its center pin for the other. Two wire balanced lines
must
be
suspended in a fairly straight line a few feet away from metallic objects or ground.
Coaxial lines
can lay in a pile or coil on the floor. Internal or external power can be used, and the MFJ-259B can
be placed on or near large metallic objects with no ill effects. Coaxial lines connect normally, with the shield
grounded.
Beverage antennas
must be directly connected to the MFJ-259B.
Using fixed resistances:
1.) Terminate the line or antenna in a non-inductive resistance somewhere around the expected value.
2.) Connect the transmission line or antenna directly to the MFJ-259B "ANTENNA" connector. Adjust the
frequency (near the expected operating frequency) until the lowest resistance and lowest reactance is
measured.
3.) Record the impedance value.
4.) Adjust the frequency until the highest resistance and
lowest
reactance is measured.
5.) Multiply the highest resistance by the lowest resistance, and find the square root of the result.
