MFJ-974_Manual操作说明书手册

MFJ Balanced Line TunerIntroductionSpecial Note:This manual applies in allrespects to both the MFJ-974H and MFJ-974,except that in the case of the MFJ-974 allreferences to 160 Meters should be ignored.The MFJ-974H balanced line antenna tuner is a fully balanced true balanced line antenna tuner,providing superbcurrent balance throughout a very wide matching range -12 to 2000 ohms-and frequency range-1.8 through54 MHz (3.5 through 54 MHz for the MFJ-974),continuous.It is rated at 300 watts SSB PEP transmitter outputand 150 watts CW transmitter output.The MFJ-974H is designed to match 50 ohm output transmitters or transceivers to virtually any antenna.Peakand average forward power,reflected power,and SWR are displayed on the MFJ-974H's illuminated cross-needlemeter.The MFJ-974H is a fully balanced wide range T-Network using four gear driven 1000 volt air variable capacitorsand a high-Q air wound tapped inductor for 80 through10 Meters.Separate inductors are used for 6 and 160Meters.The tuning components are mounted symmetrically to ensure electrical balance and are centrally locatedin the cabinet for better isolation.A 1:1 current balun is placed on the low impedance 50 ohm input(transmitter)side to convert the balanced T-Network to unbalanced operation.The balun is made of 50 ferrite beads on RG-303 TeflonTM coax to giveexceptional and efficient isolation.It stays cool even at the tuner's maximum rated power.The MFJ-974H will match virtually any balanced-line-fed antenna:dipoles,inverted-vees,verticals,mobilewhips,yagi beams,quad loops,horizontal loops,sterba curtain arrays,random wires,and many other antennas.The MFJ-974H has rear panel connectors for coaxial and single or two wire feedlines.The built-in balun workswith balanced open wire,twinlead,or twin-axial feedlines.Understanding Power RatingsThere are no standardized power rating systems for tuners.The names used(i.e.3 kW Tuner)carry over from thetime when amplifiers were rated by peak power input,and not the true RF power output.For example,the onethousand watt Johnson Matchbox was rated to handle a 1000 watt plate modulated AM transmitter (four kilowattsPEP transmitter input and 3000 watts PEP RF output).The Heathkit SB-220 was called a two kilowatt amplifier,and the rated CW output was approximately 600 watts.Matching tuners were called 2 kilowatt tuners,and these tuners safely handled 600 watts of CW power and 1200watts PEP SSB.The FCC has changed the power rating system of amplifiers,and tuners no longer follow amplifier power ratingsMost typical 1500 watt tuners remain able to safely handle 400 to 600 watts CW,and 600 to 900 watts PEP SSB.Load conditions and control settings also greatly affect the power handling capability of tuners.T-networkstypically handle more power on higher frequency bands into higher load impedances.The worst operatingcondition for T-network tuners are low-impedance capacitive reactance loads.T-network tuners always handlethe least power when operated on 160 me