MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
21
5.5
Advanced- 2 Modes
This mode measures physical or electrical
Distance To A Fault
(such as a short, open, or large impedance
bump in a line). It also measures
Electrical Length
in degrees and calculates
Wavelength
in feet or
meters. To access
Advanced-2
, hold the
Mode
and
Gate
buttons until it appears on the display. You can
also reach it by stepping through the
Advanced
modes (hold
Mode
and
Gate
simultaneously until
Advanced-2
appears on the screen:
Advanced 2
The opening measurement function in
Advanced-2
is:
This prompt asks the operator to enter the
factory-specified velocity factor
for a cable being tested
(DUT). To increase velocity factor above the default of 0.66, press
Gate.
To decrease it, press
Mode
.
When the
Vf
value is correct,
press both buttons simultaneously
to lock the value in. The
Vf
entry is
necessary for determining the
Physical Length
of a line in feet. To obtain
Electrical Length
in feet, set
Vf
for unity (1.00).
Note:
Incorrect
Vf
settings do not cause errors in electrical measurements such as
Length in Degrees,
but
do cause errors in physical length calculations such as
Dist. to Fault
displayed in feet. Note that
"distance" calculations aren't available at UHF frequencies because the internal capacitance of the diodes
and lead lengths through the connector and connections create errors in other measurements. Only SWR
and SWR related functions are displayed for the UHF band.
5.5.1
Distance to Fault (DTF) (for HF/VHF only)
With
Vf
entered in the previous function, the next function in the display menu is:
Distance to Fault in Feet
measures any line type (or impedance), including the length of a Beverage or
other antenna (any terminations must be removed). Section 5.5.1.4 outlines the measurement procedures,
or "how" to measure something. Sections 5.5.1.1 through 5.5.1.3 describe a few practical things that can
be measured.
5.5.1.1
DTF Balanced Lines
Line placement is critical when measuring balanced line and the MFJ-269D
must run on internal
batteries
to maintain isolation. Also, you must keep the case a few feet away from other conductors and
earth. No wires (other than the balanced line) can be attached. 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 reasonably
straight line and held at least a few feet away from other objects using good insulators. Avoid laying the
line against anything -- including non-conductors -- for any distance, and keep it several conductor
spacings away from other conductive surfaces (even poor conductors like earth or concrete).
5.5.1.2
DTF Coaxial lines
Coaxial line placement is not critical -- you may lay in a pile or coil it on the floor. Use internal batteries
or external power to run the analyzer, and place it on any convenient surface (conductive or not).
Connect coaxial lines normally, with the shield grounded to the outside of the connector.