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MFJ-220B
User Manual
14 pgs68.79 Kb0

MFJ MFJ-220A, MFJ-220B, MFJ-220C, MFJ-220D, MFJ-220E User Manual

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MFJ-220 SWR Analyzer
Table of Contents
Introduction ..............................................................................................................................1
Powering The MFJ-220............................................................................................................2
Battery Installation ...................................................................................................................2
Operation Of The MFJ-220......................................................................................................3
SWR and the MFJ-220.................................................................................................3
Measuring SWR ...........................................................................................................4
Customizing the Frequency Range...............................................................................4
Adjusting Simple Antennas......................................................................................................6
Quad Elements..............................................................................................................6
Tuning an Antenna.......................................................................................................7
Measuring the Feedpoint Resistance of Antennas .......................................................7
Testing and Tuning Stubs and Transmission Lines..................................................................8
Velocity Factor of Transmission Lines ........................................................................8
Impedance of Transmission Lines................................................................................9
Estimating Transmission Line Loss .............................................................................10
Adjusting Matching Networks .................................................................................................10
Adjusting Amplifier Networks.....................................................................................10
Using the MFJ-220 as a Signal Source ....................................................................................11
Technical Assistance................................................................................................................11
Notes.........................................................................................................................................12
MFJ-220 Instruction Manual Customized SWR Analyzer
INTRODUCTION
The MFJ-220 SWR Analyzer is an easy to operate, versatile test instrument for analyzing nearly any 50Ω RF system using customized frequency ranges. You must select an operating range for the MFJ-220 between the minimum and maximum frequencies listed in the following chart.
Minimum Maximum
23.3 MHz 49.5 MHz
44.4 MHz 91.7 MHz
66.6 MHz 134.9 MHz
136.0 MHz 259.3 MHz
184.88 MHz 351.32 MHz
The chosen frequency range can be modified (within the selected band) by adjusting the internal control resistors. In addition the MFJ-220 can be used as a signal source.
M FJ-2 20
Rev . 1.00
M FJ-Enterprise s
(c) 2000
The MFJ-220 combines three basic circuits; a voltage controlled oscillator, a 50Ω RF bridge, and a calibrated bridge unbalance indicator. This combination of circuits allows measurement of the SWR (referenced to 50Ω) of any load connected to the ANTENNA connector.
The MFJ-220 displays the actual frequency on the LCD.
The MFJ-220 has a N-type connector for the antenna.
The MFJ-220 can be used to adjust or measure the following:
• Antennas: SWR, resonant frequency, bandwidth
• Amplifiers: Input and output networks
• Coaxial transmission lines:SWR, velocity factor, losses, resonance
• Networks: SWR, resonant frequency, bandwidth
• Stubs: Resonant frequency
WARNING: Please read this manual thoroughly before using this instrument. Failure
to follow the operating instructions may cause false readings or cause damage to this unit.
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MFJ-220 Instruction Manual Customized SWR Analyzer
POWERING THE MFJ-220
The MFJ-220 requires between 13.7 and 18 volts for proper operation. Any power supply used with the MFJ-220 must be capable of supplying 34 mA of current. An optional power supply, the MFJ-1315 B (supplying 15 volts for loads driving such a current), is available from MFJ Enterprises, Inc. or authorized MFJ dealers.
The battery level will be indicated by the display in in the power up.
The MFJ-220 has a standard 2.1 mm DC coaxial jack at the bottom of the case. This jack is labeled 15VDC and has the word POWER near it. A pictorial polarity marking appears on the case near the power jack. The outside conductor of the plug must connect to the negative supply voltage and the center conductor of the plug must connect to the positive voltage. If ten AA 1.5 volt batteries are connected, the batteries will be automatically disconnected when an external power plug is inserted in this jack.
SWR measurement will be inaccurate when the supply voltage falls below 13.7 volts. To avoid false readings maintain fresh batteries and always use the correct power supply. If the power supply falls below the minmimum required level it will be indicated on the display.
WARNING: Never apply AC, unfiltered or incorrectly polarized DC to this jack. Peak
voltage must never exceed 18 volts.
Power saving
The unit will fall in a power saving mode seven minutes after the power is turned ON. It will be indicated with a blinking SLP sign.
223.10 M Hz > 5
The power should be turned back ON again to reinitialize operations.
BATTERY INSTALLATION
To install a batteries, first turn the unit OFF. Remove the six phillips head screws of the case. Insert the batteries securely into the battery holder.
Carefully check to ensure any wires are not pinched between the cover and the chassis.
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MFJ-220 Instruction Manual Customized SWR Analyzer
After the batteris are installed, reinstall the six cover screws.
MFJ recommends the use of ten 1.5V ALKALINE batteries to reduce the risk of equipment damage from battery leakage. Avoid leaving any batteries in this unit during periods of extended storage. Remove weak batteries immediately!
When using a battery with this unit, quickly make a measurement and turn the unit off. If the unit is left on for long periods of time, battery life may be short.
OPERATION OF THE MFJ-220
After the MFJ-220 is connected to a proper power source the red ON/OFF button can be depressed to apply power. When pressed, the red button should lock into position.
The ANTENNA connector (N-type) on the top of the MFJ-220 provides the SWR bridge output connection. To measure SWR, this connector must be connected to the load or device under test.
WARNING: Never apply power to the "ANTENNA" connector.
SWR and the MFJ-220
Some understanding of transmission lines and antenna behavior is necessary to use the MFJ­220 properly. For a thorough explanation the ARRL Handbooks or other detailed textbooks can be used for reference.
Since nearly all feedlines and radio equipment used in amateur service are 50Ω, this instrument is designed to measure the system SWR normalized to 50Ω. The SWR will vary with the ratio of source to load impedance. For example a 150Ω resistive load placed across the ANTENNA connector will give an SWR reading of 3:1.
The MFJ-220 measures the actual SWR. The load must be 50Ω of pure resistance for a meter reading of 1:1 . The common misconception that 25Ω of reactance and 25Ω of resistance in a load will give a 1:1 SWR is absolutely not true. The actual SWR in this condition will be measured as 2.6:1 . The MFJ-220 is not "fooled" by mixtures of reactive and resistive loads.
Another common misconception is that changing a feedline's length will change the SWR. A feedline impedance of 50Ω and a load impedance of 25Ω produces an SWR of 2:1. The SWR will remain 2:1 even if the feedline length is changed. If line loss is low it is perfectly acceptable to make SWR measurements at the transmitter end of the feedline. The feedline does not have to be any particular length. As line loss increases, and as SWR increases, error is introduced into the SWR reading. The error causes the measured SWR reading to appear better than the actual SWR at the antenna. Refer to the section on Estimating Transmission Line Loss.
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