MFJ-269 Instruction Manual HF/VHF/UHF SWR Analyzer
16
Note:
The MFJ-269 measures reactance, and converts reactance to inductance. The MFJ-269 can not determine
if the reactance is actually inductive or capacitive. You can usually determine the type of reactance by
adjusting frequency. If frequency is increased and reactance (“X” on the display or impedance on the
IMPEDANCE meter) decreases, the load is capacitive at the measurement frequency. If frequency is
reduced and reactance decreases, the load is inductive at the measurement frequency. This does not apply
to antennas or to loads measured through a transmission line longer than a fraction of a wavelength long.
“Inductance in
µ
H
”
, the third mode, measures inductor values in microhenries (
µ
H) at an adjustable frequency.
Normal measurement range is from less than .1
µ
H to a maximum of about 120
µ
H. The front panel
IMPEDANCE
meter indicates reactance (X in ohms) of the inductor. Inductance is calculated using measured
reactance (X) and operating frequency, and displayed on the LCD.
The MFJ-269 becomes inaccurate measuring reactance below 7 ohms or above 1500 ohms. If component
reactance is in the inaccurate range,
“L(X<7) [X]”
or
“L(Z>1500)”
will be displayed. An inductance value will
not be displayed if measurement range is questionable.
To measure inductance:
a.) Turn the MFJ-269 on and step the mode switch through until the
“Inductance in
µ
H
”
display appears.
b.) Connect the inductor across
ANTENNA
connector with the shortest leads possible, or with the lead length
normally used in the working circuit.
c.) Adjust to a frequency to the working frequency, or a frequency as close to the working frequency as possible
that does not produce a range warning. “
L(Z>1500)”
is one warning, and “
L(X<7)”
is another. “
L(X=0)”
indicates the inductor appears as a near perfect short to the MFJ-269, and probably indicates frequency is too low
or inductance is too small to measure.
Note:
Lead length and placement, as well as inductor design, will affect inductance readings and in-circuit
performance. With increasing frequency, measured inductance usually increases because of stray
capacitance. At some frequency an inductor often becomes an “open” circuit, with infinite reactance. At
others it becomes a short.
4.2.5 Frequency Counter
The
Frequency Counter
mode is the final
MAIN
mode. It is reached by pressing the MODE button four times
from the opening menu, or by stepping through the
MAIN
modes until the
“Freq. Counter”
message appears.