MFJ MFJ-269D - Page 26

MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
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1. Calculate length in feet of a transmission line or conductor for the number of electrical degrees (up to
359 degrees) of a transmission line or conductor for the velocity factor and length entered and the
frequency selected (see section 5.5.2.1).
2. Calculate electrical degrees (up to 359 degrees, at which point it repeats again at zero) for the velocity
factor entered, the electrical length programmed, and the frequency selected (see section 5.5.2.2).
5.5.2.1 Line Length in Degrees
This mode tells you length of a line in electrical degrees when you know (a.) the physical length and (b.)
the velocity factor. You can also measure the electrical length directly using the Distance to Fault mode
(sec 5.5). This mode is useful for calculating the Length in Degrees for matching sections and phasing
lines.
If you enter this mode after using Distance to Fault (sec 5.5), the Vf and Length will be programmed
automatically using your Distance to Fault data. The physical or electrical length of the line may also be
programmed in manually. If a length is not programmed in, a default length of 100 feet will be 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 wavelengths) transmission line is.
With lines that are very long (in wavelengths), 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 until Advanced-2 appears. The display shows the
default Vf (0.66):
2. Set Vf for the desired value (press Gate to increase and Mode to decrease). To lock you value, press
and hold Gate and Mode 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 Mode, and a display showing Length in Feet and Length in Degrees will appear.
14.315 MHz
L=100.0 ft= 73
o
4. The display now shows the Electrical Degrees for the entered line length (default is 100 feet) at the Vf
you entered in step 1. By adjusting the Frequency and Tune controls, the analyzer will recalculate the
results for any frequency you wish (see sample screens below):