MFJ-259C Instruction Manual
HF/VHF SWR Analyzer
13
5.4
Return Loss and Reflection Coefficient mode
From Advance Mode, open the Return Loss and Reflection Coefficient display by tapping Mode one time. The
identification screen is shown below:
On the working screen, the VFO frequency and SWR are displayed on the top line, while the bottom line presents
the equivalent Return Loss (in dB) and the Voltage Reflection Coefficient (
ρ
). The analog meters display SWR and
impedance.
5.5
Distance to Fault mode
From Advance Mode, enter Distance to Fault by tapping Mode twice. The identification screen is shown below:
This mode is useful for finding the physical or electrical length of a random piece of cable, or for finding the
distance to a transmission line fault. Unbalanced lines need not be isolated during testing and may be coiled on the
floor. For balanced lines (ladder line, open-wire feeders, etc), run the MFJ-259C on internal batteries and keep it
at least a few feet away from earth and other conductors. Attach only the DUT (no other wires) -- one lead to the
center pin of the Antenna connector and the other to the case via the grounding stud. Suspend two-wire balanced
feeder in a straight line so it remains clear of metallic objects and ground by at least a few feet.
The Distance to Fault test measures the electrical distance to the transmission line's abnormality. To obtain the
physical distance, multiply electrical distance times the feed line’s specified Velocity Factor (Vf). For example, if
the analyzer display reads DTF = 75 feet and the transmission line is typical RG-8 with a specified velocity factor
of 0.66, the physical distance to the fault will be: 75 x .66 = 49.5 feet.
An open or a short-circuit at the fault yields best accuracy -- some resistive and reactive loads or L/C terminations
may skew the results or simply not work. To conduct the test, follow the specific sequence of steps outlined below.
To measure fault distance:
1.) Connect the DUT to the analyzer's Antenna connector. From Advanced mode, tap the Mode switch twice to
bring up the Distance to Fault ID screen. The top line of the working screen will display the VFO frequency in
MHz followed by 1st blinking at a rapid rate. The 1st indicates the analyzer is waiting for entry of the first
X=0 frequency. The lower line displays DTF (no data showing) and X with the Reactance reading in ohms.
2.) Begin by searching for the lowest VFO frequency where the Impedance meter shows a sharp null and where the
reactance value on the screen approaches zero (X=0). If possible, find an exact frequency where X=0:
3.) When you've found the first X=0 null, tap the Gate button once to enter it. The blinking 1st will change to a
blinking 2nd. Now, tune to the next higher X=0 null. A minimum reading of a few ohms is acceptable if the X
display won't zero.
42.648 MHz 2nd
DTF X=1
21.324 MHz 1st
DTF X=0