MFJ-269C Instruction Manual LF/HF/VHF/UHF SWR Analyzer
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If balanced line is used, operate the MFJ-269C only from internal batteries and keep it a few feet away
from other conductors or earth. Do not attach any wires (other than the stub) to the unit. Use the Antenna
port shield for one lead and the center pin for the other. Two-wire balanced lines must be suspended in a
straight line a few feet away from metallic objects and ground.
Coaxial lines can lay on the floor and external power used (isolation net required). Coax is connect
normally, with the shield grounded.
The Distance to Fault mode measures the Electrical Length of a transmission line when a Vf of 1 is
entered. To obtain Vf factor for an unknown cable, you must know both the Electrical and Physical length
of the line. If the Length in Feet displayed (with a Vf entry of 1.0) is 75 feet, and the transmission line
actually measures 49.5 feet long, the velocity factor will be 49.5 divided by 75, for a result of 0.66 Vf.
Note
: The far end of the line may be either open or shorted, but the line can not be terminated in any
impedance other than an open or short.
To confirm reliability, make two or more groups of measurements on different starting frequencies at
least one octave apart. If measured distances agree, they are almost certainly very reliable.
Use the following method:
1. Using procedures in 5.5 Advanced-2, measure distance to fault with Vf set at 1.00.
2. Measure the Physical Length of the line in feet.
3. Divide the measured Physical Length by the display reading.
Example: 27 feet (actual physical length) divided by 33.7 feet (measured electrical length) equals .80.
The velocity factor is .80 or 80%.
4. If the analyzer is now set to Vf= .80 and the line measured, the result should be the correct physical
length.
7.3 Impedance of Transmission Lines or Beverage antennas
The impedance of transmission lines between a few ohms and 1500 ohms can be directly measured with
the MFJ-269C. Lines of higher impedance can be measured if a broadband transformer or resistance is
used to extend the MFJ-269C’s range. Select any measurement mode that indicates resistance (R=) and
reactance (X=).
If a balanced line is used, operate the MFJ-269C only from internal batteries and keep it a few feet away
from other conductors or earth. Do not attach any wires (other than the feedline) to the unit. Use the
Antenna connector’s shield for one lead and the 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.
Setup for coaxial line need not be isolated, and Beverage antennas may be directly connected to the MFJ-
269C.
Using fixed resistances:
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