MFJ-266 HF/VHF/UHF Antenna Analyzer
Instruction Manual
©
2011 MFJ Enterprises, Inc.
13
7.4 Measuring Unknown Capacitance
To measure capacitance, connect the unknown component to the
Antenna
connector (usable
range is from approximately 15 pF to 1200 pF). To enter the
Capacitance
mode, begin with the
analyzer turned off, then
press and hold
the
Up
button while pressing the
PWR
switch (see
Section 3.6). The screen will display the approximate value of the unknown capacitor in pF
along with the stimulus frequency where the measurement is being made. Note that you will not
have full control over stimulus-frequency
Band
selection in this mode. Of the bands offered, the
best accuracy is typically obtained on
Band C
,
w
hich may be selected using the
Up/Down
switches. Note that any capacitor and lead combination that approaches self-resonance at the
stimulus frequency will trigger the C
= Xc >1.5K
Ω
message and will be un-measurable. Attempt
to re-measure at a lower frequency.
7.5 Measuring Unknown Inductance
To measure inductance, connect the unknown component to the
Antenna
connector. To enter the
Inductance
mode, begin with the analyzer turned off, then
press and hold
the
Down
button
while pressing the
PWR
switch on (see Section 3.6). The screen will display the approximate
value of the unknown inductor in uH along with the stimulus frequency where the measurement
is being made. You will not have full control over the stimulus-frequency
Band
selection and the
best accuracy is usually obtained on
Band B or C
(selected using the
Up/Down
switches). Note
that any inductor approaching self-resonance at the stimulus frequency will trigger the
L = X
L
>1.5K
Ω
message and will be un-measurable. Try to re-measure at a lower frequency.
7.6 Tuning a ¼-Wave or ½-Wave Coaxial Stub
To accurately tune a coaxial stub, begin by calculating the
free-space length at the stub's
intended operating frequency:
For
1/4-
λ
in inches =
2951
÷
MHz
For 1/4-
λ
in feet =
246
÷
MHz
For 1/2-
λ
in inches =
5902
÷
MHz
For 1/2-
λ
In feet =
492
÷
MHz
Next
,
multiply the
free-space length
times your cable's
velocity factor.
Finally, add at least 10%
to this length for a margin of error (better too long than too short). Cut the cable to this initial
length. Connect one end of the cable to the analyzer's
Antenna
connector. For a 1/4-
λ
stub, leave
the far end open. For a 1/2-
λ
stub, short the far end. Next:
(1.)
Set the MFJ-266 to
Analyzer
mode (Section-3)
(2.)
Initially, set the
Range
,
Band
, and
Tune
for the
desired stub frequency
(Section-4)
(3.)
*Tune
down in frequency to find lowest
impedance-magnitude
reading (the load is a
short).
(4.) Write your
measured frequency
down.
(5.) Divide the measured
frequency
by the
desired stub frequency
to obtain a correction
factor
(6.) Multiply the
present stub length
by the
correction factor
to get the
desired stub
length
.
