MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
24
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):