MFJ-249C Instruction Manual
HF/VHF SWR Analyzer
11
Measure Capacitance
1.
Connect an unknown capacitor in series with the highest value standard inductor.
2.
Connect the LC circuit to ANTENNA connector with a 50
Ω
resistor in series.
3.
Adjust the tune knob through the bands until you get the lowest SWR. If you do not get a low SWR,
change to the next inductor with a lower value and try again. Continue the process until you obtain
low SWR.
4.
Solve this equation using F as the resonant frequency and L as the inductance of the standard
inductor,
C(pF) =
1
00003948F L
F = MHz L = H
2
.
μ
Measure Inductance
1.
Connect an unknown inductor with the highest value standard capacitor in series.
2.
Connect the series LC circuit to "ANTENNA" connector with a 50
Ω
resistor in series.
3.
Adjust the tune knob through the bands until you get the lowest SWR. If you do not get a low SWR,
change to the next smaller value standard capacitor and try again. Repeat the process until you get
low SWR.
4.
Solve this equation using F as the resonant frequency and C as the capacitance of the standard
capacitor.
L( H) =
1
00003948F C
F = MHz C = pF
2
μ
.
6.9
Resonant Frequency of Tuned Circuits
The MFJ-249C can be used to measure the resonant frequency of tuned circuits by two methods. The
first method involves placing a 50 ohm resistor in series with the MFJ-249C "ANTENNA" connector.
The MFJ-249C connects through the resistor to the parallel tuned circuit. This circuit is for high
capacitance values.
Tune the MFJ-249C's frequency until the highest SWR is reached. This is the resonant frequency of the
load.
"ANTENNA"
To the MFJ-249B's
connector
All leads should be short
50 ohms
Hi - "C"
For high inductance values a series LC circuit should be used to measure resonant frequency. The
inductor and capacitor should be connected in series through a 50
Ω
low inductance carbon resistor across
the "ANTENNA" connector on the MFJ-249C.
MFJ-249C
