MFJ MFJ-249 - Page 6

MFJ-249 SWR Analyzer Instruction Manual
OPERATION OF THE MFJ-249
After the MFJ-249 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.
Upon initial power up with no load connected, the frequency counter should display some
digits, the red LED in the upper right hand corner of the unit. should blink very fast, and the
meter should read near full scale.
MFJ HF/VHE SWR ANALYZER ,
1.8-17
MODEL MFJ-249
FREQUENCY
eis etle Dai fete Det thes
f 0.01 O17 1.0 10 LOW BATT
26.2. 2.5 10-28. 2
62.5-1 13 410
TUNE FREQUENCY
MHz
SWR and the MFJ-249
Some understanding of transmission line and antenna behavior is necessary in order to use the
MFJ-249 properly. For a thorough explanation the ARRL Handbooks or other detailed
textbooks can be used for reference.
SWR is the ratio of a load impedance to source impedance. Since nearly all feedlines and radio
equipment used in amateur service are 50 ohms, this instrument 1s designed to measure the
system SWR normalized to 50 ohms. For example a 150 ohm load placed across the
"ANTENNA" connector will give an SWR reading of 3:1 .
The MFJ-249 measures the actual SWR. The load must be 50 ohms of pure resistance for a
-meter reading of 1:1 . The common misconception that 25 ohms of reactance and 25 ohms of