MFJ-269 Instruction Manual HF/VHF/UHF SWR Analyzer
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This mode tells you length of a line in electrical degrees if you know the physical length and velocity factor. You
can also directly measure the electrical length using the distance to fault mode (sec 5.5). This mode is useful for
calculating the length in degrees of matching sections and phasing lines.
If this mode is entered after using distance to fault (sec 5.5), VF and length will be programmed automatically
using distance to fault data. The physical or electrical length of the line can also be programmed manually. If a
length is not programmed, a default length of 100 feet is selected automatically.
When changing UHF frequency with a 100 foot line, the display rotates through 360 degrees rapidly. This
demonstrates how highly frequency sensitive a long (in terms of wavelength) transmission line is. With lines that
are very long in terms of wavelength, cutting the line to an exact electrical degree is almost impossible. This is
true over extremely narrow frequency ranges.
1.) Simultaneously press and hold
GATE
and
MODE
buttons until Advanced 2 appears. The display will show
the velocity factor (factory default to 0.66):
2.) Set VF to the desired value.
GATE
increases VF,
MODE
decreases VF. When the desired VF is reached
simultaneously press and hold the
GATE
and
MODE
buttons until “Distance to Fault” appears.
VELOCITY FACTOR?
VF= 0.70
Note: If you know the true electrical length in feet, set VF to VF=1.0 and enter the electrical length in
feet.
3.) Press the
MODE
button. A display showing length in feet and length in degrees will appear.
1 4 .3 1 5 M H z
L= 1 0 0 .0 ft= 7 3
o
4.) The display will now show the electrical degrees for the line length entered (default is 100 feet) at the
velocity factor you entered in step 1. By adjusting the frequency controls, the analyzer will recalculate the results
for any frequency desired.
5.) Pressing
MODE
takes the display to section 5.5.3.2. Pressing
GATE
takes the display to a line length
adjustment function.