MFJ-249C Instruction Manual
HF/VHF SWR Analyzer
5
The second message shows the software copyright symbol.
The third message provides a power-source check, displaying the internal battery or external power supply voltage
level along with a warning if the source is too low to support reliable operation.
The fourth and final power-up display is the
working screen
for the analyzer’s default operating mode, as described
in Section 3.2 (
SWR, Impedance R&X
).
The MFJ-249C has three (3) Basic Operating Modes that are used for conducting a variety of measurements. If you
tap (momentarily press) the
Mode
button, the analyzer steps to the next
Mode
selection. The three main modes and
their opening screens are described in Section-3.3 below:
3.3
Main MODE descriptions
Press the
Mode
switch to scroll through the analyzer's three operating modes. By "scrolling", we mean that each tap
of the mode switch will step the analyzer ahead to the next menu selection. Each new selection comes up on the
display with an
Identifier Screen
. After 3 seconds, the
Identifier Screen
is replaced by the mode's working screen.
The menu is circular, so after sequencing through all five choices, the sequence starts over. The three basic
operating modes are described in detail below:
1.) SWR Bargraph
: The
SWR Bargraph
mode is the analyzers "default" mode because it is the one most frequently
used for routine antenna adjustments. The MFJ-249C will measure the standing wave ratio (SWR) of any load
referenced to 50 ohms. To measure the SWR of a 50-ohm coaxial line simply connects the line to the
ANTENNA
connector. The display will show the selected frequency and the actual SWR in a numerical and a bar graph format.
The maximum numerical SWR displayed is 25. Any SWR adjustments have to be made at the antenna, since any
adjustments at the transmitter end of the feedline cannot affect the losses, nor the efficiency of the antenna system.
2.) Impedance Magnitude:
This
mode
will provide
magnitude of the impedance
readings for the load connected
to the
ANTENNA
jack. The readings are the combination of the resistive and reactive parts of the load. The
magnitude of the impedance
(
Z
) is the square root of the addition of square of the
resistance
(R) and the
reactance
(X). By considering the definition of
Z
and by adjusting the
TUNE
knob until the lowest SWR
reading is obtained, it is possible to read the antenna’s pure reactance. The point of the lowest SWR is generally
the point of lowest reactance. For the SWR to be 1:1, the load must be an impedance of 50 ohms of pure
resistance (R=50) , with no reactance ( X=0).The top line of the working display shows the
VFO Frequency
in
MHz and the numerical
SWR
reading. The lower line displays the
Resistive
(R)
impedance components for the
attached load. Pressing the
MODE
push button, from the
SWR
mode selection, the Magnitude of the
Impedance (Z) mode is enabled. It will display Z in a range from 0 to 650 ohms. If the impedance is greater
than about 650 ohms the message “(Z>650)” is displayed. The
SWR
value for the connected load will be
displayed in the LCD. The stray output capacitance (around 3pF) will be lower than 650 ohms at frequencies
higher than 60 MHz. This stray capacitance does not affect high frequency measurements considering the
connection of a transmission line.
MFJ-249C
VER 13.40
MFJ-Enterprises
(c)
