MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
12
1.
Connect the 50-ohm cable, attenuator, transmission line type balun, or transformer under test to the
Antenna
connector. Confirm the distant end of the DUT isn't terminated by a resistance.
2.
Turn the analyzer
On
and toggle the
Mode
switch once to the
Coax Loss
screen.
3.
Tune the analyzer's
VFO
(Tune)
to the frequency where you wish to measure loss. The loss in dB will
be displayed for any specific frequency you select between 0.53 and 230 MHz.
4.4
Capacitance (Function-3)
Access the capacitance
mode by stepping to the
Capacitance
screen using the
Mode
switch. The top line
of the working display shows the
Frequency
in MHz and the Capacitive Reactance
(Xc)
of the DUT at
that specific frequency. The lower line displays the computed
Capacitance
in
pF
. Normally, the
measurement range is from a few pF to a few thousand pF.
Important Note:
Capacitance measurements tend to become inaccurate below 7 ohms and above 650
ohms. If reactance falls into the inaccuracy range,
C(X<7)
,
C(X=0)
, or
C(Z>650)
will be displayed on
the screen as error messages. The MFJ-269D will not display "data" when the measurement accuracy is
questionable (see examples below):
Reactance Sign:
The MFJ-269D measures the DUT's reactance
(X)
and mathematically converts it to a
capacitance value (
Xc
). However, the analyzer's processor can't determine if the reactance it measures is
actually capacitive or inductive. You can usually confirm the sign by simply adjusting the VFO. If tuning
down
in frequency causes reactance to
increase
, the load is likely capacitive (-jX) because the reactance
of a capacitor normally increases with a decrease in frequency.
To measure a capacitor:
1.
Turn on the analyzer and toggle the
Mode
switch twice to bring up the
Capacitance
identification
screen.
2.
Connect the capacitor across the
Antenna
connector with the shortest leads possible, or include the
lead length normally used in the actual circuit to include stray lead inductance in your measurement.
3.
Adjust the
VFO
(
Tune
) to your frequency of interest. If a range warning comes up, find the closest
frequency where no warning appears. Warnings are
C(Z>650)
,
C(X<7)
, and
C(X=0)
-- and the
C(X=0)
warning indicates the capacitor appears as a near-perfect short.
When measuring a capacitor, it's displayed value in pF will typically change with the test frequency. This
change occurs because stray inductance inside the capacitor and in the wires leading to the analyzer