MFJ MFJ-862 User Manual
MFJ-862 SWR/Wattmeter
MFJ-862 VHF/UHF 144/220/440 SWR/Wattmeter
General Information:
The
MFJ-862
and reflected power and indicates SW R for the
bands. The MFJ-862 has 2 power scales for each band selected with the
front panel rotary switch. The low power scale reads from
forward
forward
and
and
VHF/UHF 144/220/440 SWR/Wattmeter measures forward
0-6 watts reflected
0-60 watts reflected
144, 220
. The high power reads from
. SWR is indicated from
, and
1:1
440 MHz
to
0-300 watts
ham
0-30 watts
.
5:1
MFJ-862 Theory of Operation:
The MFJ-862 senses RF energy traveling along a 50 ohm stripline. A
forward and reflected stripline couple to the 50 ohm stripline to make a
directional coupler. A voltage is produced in the forward and reflected
striplines that is proportional to the current and voltage traveling along the 50
ohm stripline. This signal is rectified by a diode and smoothed by a capacitor.
Because the directional coupler's sensitivity increases with frequency,
trimpots are used to adjust for dif f er ent f requenc y and power settings (high or
low power).
Connections:
Connect your transmitter to the connector labeled
antenna to the connector labeled
good quality coax and connectors that are designed for VHF/UHF.
ANTENNA
TRANSMITTER
. It is important that you use
and your
If you want to measure the power c apability of a transm itter/am plifier or to recalibrate the MFJ-862 you should connect a quality dummy load (50 ohm s)
that is designed for VHF/UHF to the antenna jack.
1
MFJ-862 SWR/Wattmeter
F
I
F
I
The MFJ-862 has a lighted m eter. To pr ovide power for the meter light, a 12
Vdc supply such as the MFJ-1312B should be used. Use a standar d 2.1 mm
coaxial plug with the center conductor positive and the sleeve ground.
Using the MFJ-862:
To measure forward and reflected power turn the selector switch to the
correct frequency and power setting. Transm it and read the power from the
meter. Each unmar ked hatch on the scale is an even division between the
two marked num bers. SW R is read directly from the sc ale where the meter
needles cross.
If a more exact reading for SW R is needed you may use the equation for
SWR. Measur e the forward and reflected power and put the values into the
following equation:
SWR = 1 +
Pr = Reflected Power
Calibration:
Note that the readings for forward and reflected power (and thus SW R) are
less accurate if the power levels you are reading are not near the calibration
power level or within the correc t power range. For an acc urate reading of 10
watts forward use the low power scale. If your transmitter only transmits 10
watts, re-calibrate the low power scale at 10 watts for maximum accuracy.
The MFJ-862 has been calibrated at the factory for 10 and 100 watts. If recalibration is necess ary you will need a 50 ohm dum my load, good quality 50
ohm coax, and a transm itter of known power or another accurate wattmeter
to use as a standard.
Connect the transmitter to the
of coax between the
a known power level and adjus t the f o rward or r ef lec ted sens itivity pot, for the
power scale and frequenc y you are using, until the correct reading is shown
on the meter.
G
H
Pf = Forward Power
TRANSMITTER
ANTENNA
Pr
J
Pf
K
connector and a good length
connector and the dumm y load. Transmit at
1-
G
H
Pr
Pf
J
K
2
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