MFJ-249C User Manual REV1B
Contents
1. C connector All leads should be short 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 50Q low inductance carbon resistor across the ANTENNA connector on the MFJ 249C 11 MFJ 249C Instruction Manual HF VHF SWR Analyzer MF 1 249C S ANTENNA connector All leads should be short Tune the MFJ 249C s frequency until the lowest SWR is reached This is the resonant frequency of the load An external diode detector and volt meter can also be used to measure the resonant frequency of circuits The maximum meter reading occurs at the resonant frequency 50 ohm 1N34 E MF J 249C Pek inate the voltage ANTENNA 10K between these points connector ae with a Hi Z meter All leads should be short Testing RF Chokes Large RF chokes usually have frequencies where the distributed capacitance and inductance form a low impedance series resonance The troublesome series resonance can be detected by slowly sweeping the frequency of the MFJ 249C over the operating range of the choke Peaks in the voltage measured by the RF voltmeter will identify the low impedance series resonant frequencies choke 1N34 gt MF 1 249C oe Measure the voltage ANTENNA 01 between these points connector see with a Hi Z meter All leads should be short Refer to the section on measuring the inductance of RF chokes 7 0 TECHNICAL AS2. allow you to continue testing Caution Measurements made with supply voltages below 11 volts may not be as reliable a Low 9 5V 4 0 MAIN OR OPENING MODE IMPORTANT WARNING Never apply RF or any other external voltages to the Antenna port of this unit This unit uses zero bias detector diodes that are easily damaged by external voltages over a few volts Also confirm the power supply is correct as described in Section 2 0 before operating this unit A basic understanding of antenna theory and transmission line behavior will be helpful for making the best use of the data provided by your MFJ 249C The ARRL Handbook and ARRL Antenna Book provide concise peer reviewed explanations that should suffice for most applications When it comes to the finer points of antenna design there is unfortunately a fair amount of mis information circulating on the web and over the airwaves When it comes to antenna systems there s no black magic Stick with the scientific fundamentals as presented by credible professional sources and everything your analyzer tells you should make sense 4 1___ General Connection Guidelines When conducting SWR and Impedance measurements follow these practical guidelines 1 If connector transitions RF adapters are needed use only high quality parts and check them over for wear oxidation dirt and tight pin contact before proceeding 2 Make all connection electrically secure and keep all leads
3. most amplifiers changes as the drive level is varied Do not attempt to adjust the input network with the tube in an operating condition with the low level of RF from the MFJ 249C 6 6_ Testing RF Transformers RF transformers that are designed with a 50 ohm winding can be easily and accurately tested with the MFJ 249C The 50 ohm winding is connected through a short 50 ohm cable to the ANTENNA connector on the MFJ 249C The other winding s of the transformer is then terminated with a low inductance resistor that is equal to the windings impedance The MFJ 249C can then be swept through the desired transformer frequency range The SWR and bandwidth of the RF transformer can be measured 6 7 Testing Baluns To test balun performance connect the analyzer Antenna jack to the balun s 50 ohm unbalanced input Terminate the balanced side with two equal value load resistors connected in series to make up the required load impedance For example to test a 200 ohm 4 1 secondary use a pair of 100 ohm carbon non inductive resistors in series as shown below in Fig A 50 Ohms Unbal Clip Lead Clip Lead A properly designed current balun works best for maintaining current balance It also has the highest power capability and lowest loss for given materials To evaluate the balun DUT measure SWR while connecting the grounded clip lead to point A B and C When functioning properly a current balun will exhibit low SWR over its entire opera
4. sleep mode The analyzer s current drain is normally around 150 mA which places a moderate demand on the battery pack You can extend the analyzer s running time significantly by using the internal Sleep Mode power saving function In Sleep Mode the analyzer s RF generator shuts down and battery drain drops to under 15 mA Any time Sleep Mode is activated the analyzer operates with a two minute inactivity window During any 2 minute period you must actuate the Mode switch or adjust the frequency by more than 50 kHz at least once for the analyzer to remain awake Any time a two minute inactivity period elapses the power saving circuit automatically switches in When the analyzer goes to sleep a blinking SLP message will appear in the display s lower right corner as shown below 7 1598 MHz 3 7 R 38 X 61 SLP To reawake the unit momentarily press either the Mode or Gate button To Disable Sleep mode 1 Turn the analyzer off 2 Press and hold the Mode button while reapplying power 3 Continue holding the Mode button until the copyright message appears on the screen 4 Release Mode If Sleep Mode was disabled successfully the message shown below will appear on screen The Sleep Mode function becomes re enabled anytime the analyzer is turned Off and On again Power Saving OFF 3 0 _MAIN MENU AND DISPLAY IMPORTANT WARNING Never Apply RF or any other external voltage to the Antenna port of this
5. unit The MF J 249C uses zero bias detector diodes that may be damaged by external voltages Read Section 2 0 before applying power Incorrect supply voltages will also damage this unit 3 1 General Connection Guidelines 1 Antenna Jack When making RF measurements connect your Device Under Test DUT to the SO 239 connector located on the top of the case You ll use this port for SWR and all other RF measurements excluding the Frequency Counter function 2 Power connector 2 1 mm type is described in Section 2 0 Be sure to read Section 2 0 before operating your unit Using an incorrect power sources can permanently damage the analyzer 3 Frequency Counter Input BNC connector used for frequency counter functions only 3 2 Power up Display After turning on the Power switch or after applying external power with the switch on a sequence of three message screens appear on the display The first screen presents the analyzer s software version VER MFJ 249C Instruction Manual HF VHF SWR Analyzer MFJ 249C VER 13 40 The second message shows the software copyright symbol MFJ Enterprises c The third message provides a power source check displaying the internal battery or external power supply voltage level along with a warning if the source is too low to support reliable operation Voltage Low 9 54 Voltage OK 14 7V TT LL The fourth and final power up display is the working s
6. Connect the MFJ 249C ANTENNA connector to the tuner s 50 ohm input and the desired antenna to the normal tuner output This connection can be made with a manual RF switch to facilitate rapid changeover WARNING Always connect the common rotary contact of the switch to the tuner The switch must connect either the MFJ 249C or the station equipment to the tuner The Station Equipment Must Never Be Connected To The MF J 249C 1 Connect the MFJ 249C to the tuner input 2 Turn on the MFJ 249C and adjust it to the desired frequency 3 Adjust the tuner until the SWR becomes unity 1 1 4 Turn off the MFJ 249C and re connect the transmitter 6 5 Adjusting Amplifier Matching Networks The MFJ 249C can be used to test and adjust RF amplifiers or other matching networks without applying operating voltages The tubes and other components should be left in position and connected so that stray capacitance is unchanged A non inductive resistor that equals the approximate driving impedance of the tube is installed between the cathode of the tube and the chassis or a resistor should be connected between the anode and the chassis that equals the calculated plate impedance of the tube The appropriate network can now be adjusted The antenna relay if internal can be engaged with a small power supply so that the coax input and output connectors are tied to the networks MFJ 249C Instruction Manual HF VHF SWR Analyzer CAUTION The driving impedance of
7. MFJ HE VHF SWR Analyzer Model MFJ 249C INSTRUCTION MANUAL CAUTION Read All Instructions Before Operating Equipment MFJ ENTERPRISES INC 300 Industrial Park Road Starkville MS 39759 USA Tel 662 323 5869 Fax 662 323 6551 VERSION 1A COPYRIGHT 2014 MFJ ENTERPRISES INC MFJ 249C Instruction Manual HF VHF SWR Analyzer TABLE OF CONTENTS LEO INTRODUCTION iaa 1 1 1 A Quick Word about ACCULaCy eccccccscssscesscesscesscseeeeeeeeececssecsaecssecaeceseceseceeeseeeseseceseeeseeeseeesaeeaeens 1 1 2 A AS 2 1 3 EUA RO e oia 2 2 0 POWER SOURCES ui Aia eaae tasa Ec 2 2 1 External Power SUPplV ito Dias ira 2 22 Using Internal Batteries iria At Att 3 2 3 Using Rechargeable AA Type Batteries ccccccccccssecsseceseceneceseceecseeceseceseecseeesaecsaecaecnsecnaeenseenes 3 2 4 Using Conventional AA Drycell Batteries ccccccsesseceseceseceeceseceeecseecseeeeeneesaecaecstecnseenseenaeenes 3 2 5 Power Saving Mode sleep mode ccccccccessesseeseesecsecesecesecesecesecseeseeeseeeceseeeseessecsaecnseeneeeaeeags 4 3 0 MAIN MENU AND DISPLAY A A 4 3 1 General Connection Guidelines ccececcseccesesseeescesecseeecesecaeeeseeseceaeeaeeseceaecaeeeeeeeeeaecaeeeeeeaeenaeeaeenees 4 3 2 Power up Display a da Ii aiii 4 3 3 Main MODE descriptions s cssccansads tw sedsvacd nae a na iA PARE ao Ah E iS Aa 5 3 4 Blinking VOLTAGE LOW display warning cccccccsccsseceseceseceeeceeeceseecsee
8. SISTANCE If you have any problem with your MFJ 249C first check the appropriate section of this manual If the manual does not reference your problem and the problem isn t solved by reading the manual you may call MFJ Technical Service at 662 323 0549 or the MFJ Factory at 622 323 5869 We can serve you best if you have your unit manual and all pertinent information about your difficulty handy so you can answer questions the technicians may ask You can also send questions by mail to MFJ Enterprises Inc 300 Industrial Park Road Starkville MS 39759 by FAX to 662 323 6551 or by e mail to techinfo mfjenterprises com Send a complete description of your problem an explanation of exactly how you are using your unit and a complete description of your station 12 FULL 12 MONTH WARRANTY MFJ Enterprises Inc warrants to the original owner of this product if manufactured by MFJ Enterprises Inc and purchased from an authorized dealer or directly from MFJ Enterprises Inc to be free from defects in material and workmanship for a period of 12 months from date of purchase provided the following terms of this warranty are satisfied 1 The purchaser must retain the dated proof of purchase bill of sale canceled check credit card or money order receipt etc describing the product to establish the validity of the warranty claim and submit the original or machine reproduction of such proof of purchase to MFJ Enterprises Inc at the
9. as short as possible This precaution is especially important when measuring electrical components that are not part of a 50 ohm coaxial system MFJ 249C Instruction Manual HF VHF SWR Analyzer 3 Always use good quality 50 ohm cable and connectors when making SWR measurements Contaminated mismatched or damaged cable will introduce significant error 5 0 ADJUSTING SIMPLE ANTENNAS Most antennas are tuned for operating frequency by varying the element length and most homemade verticals and dipoles are very simple to adjust 5 1 Dipoles Because the dipole is a balanced antenna it s always a good idea and good engineering practice to install a balun at the feed point A balun could be as simple as several turns of coax wrapped several inches in diameter or it could be a complicated affair with many windings on a ferromagnetic core A 1 1 Guanella current balun wound on a toroid core made from material with the appropriate permeability is usually the most effective choice The height of a dipole above ground as well as any surrounding objects will influence the feed point impedance and SWR Typical residential heights usually result in minimum SWR readings below 1 5 1 when using 50 ohm coaxial cable In general the only adjustment available for tuning a simple wire dipole is its length If too long it resonates too low in the band If too short it resonates high You may be able to improve the match SWR by raising or lowering the el
10. creen for the analyzer s default operating mode as described in Section 3 2 SWR Impedance R amp X The MFJ 249C has three 3 Basic Operating Modes that are used for conducting a variety of measurements If you tap momentarily press the Mode button the analyzer steps to the next Mode selection The three main modes and their opening screens are described in Section 3 3 below 3 3 Main MODE descriptions Press the Mode switch to scroll through the analyzer s three operating modes By scrolling we mean that each tap of the mode switch will step the analyzer ahead to the next menu selection Each new selection comes up on the display with an Identifier Screen After 3 seconds the Identifier Screen is replaced by the mode s working screen The menu is circular so after sequencing through all five choices the sequence starts over The three basic operating modes are described in detail below 1 SWR Bargraph The SWR Bargraph mode is the analyzers default mode because it is the one most frequently used for routine antenna adjustments The MFJ 249C will measure the standing wave ratio SWR of any load referenced to 50 ohms To measure the SWR of a 50 ohm coaxial line simply connects the line to the ANTENNA connector The display will show the selected frequency and the actual SWR in a numerical and a bar graph format The maximum numerical SWR displayed is 25 Any SWR adjustments have to be made at the antenna since any adjustments at the
11. cseecsaeeaecnaecnseenaeenaeenes 6 40 MAIN OR OPENING MODE dada 6 4 1 General Connection Guidelines ccecesceecceesseeescesecseeenesecaceeseeseceaesaeseeceaecaeeeeeeeceaecaeeneeaeenaeeaeenees 6 50 ADJUSTING SIMPLE A NTENNAS ini o ein 7 5 1 A NN 7 5 2 MC a o A ee a as 7 5 3 Tuning a Simple antennas A A as 7 6 0 TESTING AND TUNING STUBS AND TRANSMISSION LINES 1 000 ceccceecsesecseeeeseeseeecceeecaeeeeaeeaeeeeeaeeeeens 8 6 1 TESIS UDS AA AA cups de shes sheet Cade AA tati 8 6 2 Velocity Factor of Transmission Lines cccccccsccesseesseeseceseceseceseceseceaeeeseeeseecseeesaecsaecsaecnseseaeenaeeaes 8 6 3 Impedance of Transmission Lines or Beverage antennas oooococococonoconononononnnon nono nconnnon nooo no corona nncnnanass 9 6 4 ACGJUSTIMG B ta TE E wand dads suedsdee vale deadeatndoaucvon E 9 6 5 Adjusting Amplifier Matching Networks cccccccccssesecseseeesceeseecsceesaecsaeenaecseceeeseneeeseeeseeeeecaeesaees 9 6 6 Testing RF Transformers 0 ccceccccssecssessseesceesceeeecaecesecesecesecseeseeseeeseeeeeaeeeseecseecsaecssecaeceseeseenaeeaas 10 6 7 Testing Balsa dt ia ii les 10 6 8 Measuring Inductance and Capacitance ccccceccsecsseesseesseceeceseceseceseceeeseeeseneseeecaaecsaecsaeceseenseenseeeas 10 Measure Capacitance ii ti a dd tido 11 Measure inductance a a a a ae aa a a 11 6 9 Resonant Frequency of Tuned Circuits cccccccssccsssceseceseceseceeeceeceeneeeeaeeeseeeseecseeesaeesaecnaecnseesseena
12. e detectors Unlike costly lab grade analyzers using frequency selective receivers broadband detectors admit out of band signals Unfortunately the offending interference can t be filtered out using common low pass or band pass circuitry because the L C elements would act like lengths of transmission line and transform the impedance readings as a function of frequency Increasing generator power output can in some instances overpower interfering signals but the current needed to deliver the additional RF power greatly reduces battery life In fact over 70 of the analyzer s 150 mA current drain is already allocated to the VFO and its amplifier stages for generating a low harmonic level amplitude test signal Most RF interference problems occur at lower frequencies and are caused by high power AM broadcast stations These signals couple efficiently into large antenna arrays and are especially problematic for 160 meter verticals In the event you encounter intense local interference we recommend using the MFJ 731 Tunable Analyzer Filter It is designed to attenuate off frequency signals between 1 8 and 30 MHz without introducing significant errors 2 Component Limitations At very low voltage levels diode detectors become nonlinear a condition that reduces accuracy The MFJ 249C minimizes this problem by using special microwave zero bias Schottky detectors with linearity enhanced by compensating diodes Using this technique each analyzer is individ
13. eenes 11 Testing RE CHOKES a ceeds couticasuvencensea e a A E wees aetiact eda cession R EAE TE SNEER 12 70 TECHNICAL ASSISTANCE sia E E O AS 12 ii MFJ 249C Instruction Manual HF VHF SWR Analyzer 1 0 INTRODUCTION Attention Read Section 2 0 before attempting to use your analyzer Incorrect power supply voltages or excessive external voltage applied to the Antenna connector will damage it Description The MFJ 249C is a compact battery powered RF impedance analyzer that combines four basic circuits a 50 ohm bridge eight bit micro controller frequency counter and a 0 53 230 MHz variable frequency oscillator with switched coverage of nine overlapping bands These four sub elements are integrated to provide a wide variety of useful antenna and impedance measurements including coaxial cable loss and distance to an open or short Although designed primarily for analyzing 50 ohm antennas and transmission line systems the MFJ 249C also measures RF impedance from a few ohms to several hundred ohms In addition it functions as a discrete signal source RF Signal Generator and independent frequency counter 1 1 A Quick Word about Accuracy Inexpensive impedance meters have limitations The main causes of measurement error are 1 Signal ingress from external RF sources 2 Component limitations 3 Stray reactance from connectors pc traces and wires 1 Signal Ingress Virtually all low cost handhelds use simple broadband diod
14. ement in relationship to ground However doing so may impact other parameters such as the best take off angle for distant or local contacts TOA Anytime the antenna impedance and feedline impedance do not precisely match each other as is usually the case the feedline will act like a transformer and modify the Impedance of the load placed at the opposite end However if you use good quality 50 ohm cable the SWR should remain constant except for a small reduction caused by resistive loss as the line is made longer If changing the coax length by a relatively small amount changes SWR at your test frequency the feedline either has common mode current flowing on the outer surface of the shield that is detuning the antenna or the feedline itself is not really 50 ohm cable Common mode current caused by conduction typically occurs when no balun has been installed at the feed point to choke it off Common mode induction currents may also result from other installation errors such as running the feedline parallel rather than perpendicular to the radiating element Repositioning the feedline may reduce unwanted inductive coupling 5 2 Verticals Verticals in the monopole class require a ground plane To simplify installation and cut costs manufacturers sometimes incorrectly downplay the importance of an effective radial system When installed over a good ground the impedance of a quarter wave radiator may be quite low with SWR running nearly 2 1 Iro
15. n when the analyzer is turned off Again the MFJ 1312D supply fulfills all power supply and charging requirements for the MFJ 249C and is recommended When using rechargeable batteries the internal black plastic jumper must be set to the proper position If it is not set properly the batteries will not charge As described above the jumper is located inside the analyzer near the external power jack on the back side of the circuit board For rechargeable batteries set the jumper as shown below CHARGER odo lt Charger enabled ON OFF 2 4 Using Conventional AA Drycell Batteries Whenever possible install a fresh matched set of high quality alkaline batteries Conventional zinc cells will work but alkaline batteries offer a lower risk of damage caused by leakage Alkaline cells also provide longer running time and superior shelf life When using any non rechargeable dry cell battery always remove them immediately when they become weak to avoid damage from leakage Also never store your analyzer for extended periods longer than a month with non rechargeable batteries installed MFJ 249C Instruction Manual HF VHF SWR Analyzer IMPORTANT WARNING When Using Non Rechargeable Batteries The Analyzer s Internal Charging System Must Be Defeated To Defeat The Charger Set The Internal Jumper To The Charger Off Position As Shown Below CHARGER lt Charger disabled ON OFF 2 5 Power Saving Mode
16. nector with a 50 Q 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 1 C pF PE 09003048 2L F MHz L sl 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 Q 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 1 Lie H 9003948 F2C F MHz C pF 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 MF 249C S 50 ohms ANTENNA Hi
17. nically over a poor ground minimum SWR for the same antenna could improve to 1 1 However if the ground system is poor antenna performance will be compromised despite favorable SWR readings Far better to install the best ground system possible and configure a matching network at the base of the vertical element to match into a 50 ohm feed system Verticals tune the same as dipoles add length to lower the operating frequency and shorten to raise it Another class of verticals are considered ground independent because they come with a counterpoise or rigid radial system built into the design These antennas are usually configured as multiband OCFDs off center fed dipoles with the longer leg being the dominant vertical radiator Ground independent verticals tend to work more efficiently when elevated well above ground rather than when installed in close proximity to it because of reduced ground losses Many use multiple resonators or traps and have a matching network at the feed point Most ground independent vertical elements are asymmetrical and require a highly effective baluns to prevent the feedline from becoming part of the antenna system 5 3 Tuning a simple antenna To tune a basic dipole fed with 50 ohm coax follow the steps outlined below 1 Momentarily short the center conductor and shield to bleed off static then connect to the Antenna jack 2 Set the analyzer s band switches and VFO tuning for the desired band MFJ 249C In
18. oducts 8 Out of Warranty Service MFJ Enterprises Inc will repair any out of warranty product provided the unit is shipped prepaid All repaired units will be shipped COD to the owner Repair charges will be added to the COD fee unless other arrangements are made 9 This warranty is given in lieu of any other warranty expressed or implied 10 MFJ Enterprises Inc reserves the right to make changes or improvements in design or manufacture without incurring any obligation to install such changes upon any of the products previously manufactured 11 All MFJ products to be serviced in warranty or out of warranty should be addressed to MFJ Enterprises Inc 300 Industrial Park Rd Starkville Mississippi 39759 USA and must be accompanied by a letter describing the problem in detail along with a copy of your dated proof of purchase and a telephone number 12 This warranty gives you specific rights and you may also have other rights which vary from state to state Rev 04 08 2011 MFJ ENTERPRISES INC MFJ 249C Manual 300 Industrial Park Road Version 1A Starkville MS 39759 Printed In U S A
19. quency display 2 0 POWER SOURCES 2 1 External Power Supply MFJ offers an optional power supply the MF J 1312D that satisfies all external supply requirements We strongly recommend using this supply If you use a different power source note that the voltage output must be greater than 11 volts and less than 16 volts when the analyzer is powered on and running loaded power source The maximum voltage in Sleep Mode unloaded power source should never exceed 18 volts AC adapters must be well filtered and the plug must have a grounded sleeve and positive center lead The ideal voltage source specification is 13 8 VDC at 150 mA Confirm your supply can deliver this output level safely without overheating or introducing excessive AC ripple MFJ 249C Instruction Manual HF VHF SWR Analyzer Please read the battery installation instructions Section 2 3 if you plan to install batteries Never connect external DC power if non rechargeable batteries are installed and the battery charger is enabled Permanent damage could result o gt 2 1 mm The MFJ 249C has a recessed 2 7 mm power jack located on the top right hand side of the unit It is labeled Power 13 8 VDC The jack s outside barrel contact is negative and the center pin is positive Inserting a power plug into the power jack automatically disables the internal batteries as a power source However the batteries will be trickle charged if the charger circuit is enabled 2 2 Using In
20. r end of the transmission line with a non inductive 250 ohm potentiometer 3 Connect the transmission line to the MFJ 249C ANTENNA connector and set the analyzer to the 1 4 wave frequency 4 Observe the SWR as you vary the TUNE from end to end of the FREQUENCY range selected 5 Adjust the potentiometer until the SWR reading varies as little as possible over the TUNE range Note that the value of the SWR is not important Only the change in SWR as the frequency is varied is important 6 The value of the potentiometer will correspond closely to the line impedance Line Impedance Using a Potentiometer or Resistor Decade Box Limit these measurements to the HF region because stray reactance from a potentiometer or decade box could become a significant source of error at VHF frequencies Also use only non inductive resistances no wire wound resistors If needed you may install a broadband transformer of know performance accuracy to extend the measurement range 1 Connect the DUT to the Antenna connector 2 Terminate the far end with a potentiometer or resistance decade box 3 Adjust the analyzer s VFO frequency and note only the SWR change SWR need not be low 4 Adjust termination resistance until SWR remains constant over the widest possible range 5 The resistance of the termination resistor is the line impedance or surge impedance of the system 6 4 _ Adjusting Tuners The MFJ 249C can be used to adjust tuners
21. re line The line does not have to be 50 ohms The stub to be tested should be attached with a 50Q noninductive resistor in series to the center conductor of the ANTENNA connector with a coaxial line The shield should be grounded to the connector shell For two wire lines the 50Q resistor connects in series between the ground shell of the PL 259 and one conductor The other conductor of the balanced line connects directly to the center pin of the connector Coaxial lines can lay in a pile or coil on the floor two wire lines must be suspended in a straight line a few feet away from metallic objects or ground The lines must be open circuited at the far end for odd multiples of 1 4 wave stubs i e 1 4 3 4 1 1 4 etc and short circuited for half wave stub multiples like 1 1 1 2 etc Connect the PL 259 to the ANTENNA connector of the MFJ 249C and adjust the line or stub by the following method For critical stubs you may want to gradually trim the stub to frequency 1 Determine the desired frequency and theoretical length of the line or stub 2 Cut the stub slightly longer than necessary 3 Measure the frequency of the lowest SWR It should be just below the desired frequency 4 Divide the measured frequency by the desired frequency 5 Multiply the result by the length of the stub This is the necessary stub length 6 Cut the stub to the calculated length and confirm that it has the lowest SWR near the desired frequency 6 2 Velocit
22. struction Manual HF VHF SWR Analyzer 3 Select any analyzer operating mode that will display SWR 4 Read the SWR and adjust the VFO tuning for minimum SWR Write down the frequency 5 To re tune your antenna accurately without a lot of cut and try calculate a Scaling Factor 5 First determine if the antenna needs to be shorter higher in frequency or longer lower in frequency 6 To make it shorter higher divide the present frequency by the desired frequency scaling factor lt 1 8 To make it longer lower divide the desired frequency by the present frequency scaling factor gt 1 9 Multiply the scaling factor by the present length to calculate the new length For example suppose your 132 foot dipole has low SWR on 3 750 MHz and you want to move it to 3 900 MHz It needs to be shorter to tune higher so you calculate the scaling factor 3 750 3 900 0 95 Next calculate the new length 132 feet x 96 125 7 feet Note that scaling only applies to full size verticals and dipoles that don t use loading coils traps stubs resistors capacitors or capacitance hats Antennas with these features should be adjusted according to the manufacturer s instructions 6 0 TESTING AND TUNING STUBS AND TRANSMISSION LINES 6 1 Testing Stubs The proper length of quarter and half wave stubs or transmission lines can be found with this unit and a 50Q carbon resistor Accurate measurements can be made with any type of coaxial or two wi
23. ternal Batteries Before installing batteries for the first time check the position of the Charger Jumper To gain access remove the eight screws securing the analyzer s back cover and separate it from the unit Look for a 3 pin header with a small black plastic shorting plug that fits over two of its pins It is located at the top of the main pc board near the OFF ON switch and power connector The shorting plug must be properly positioned for the type of battery you intend to use either rechargeable or non rechargeable While you have the analyzer s case removed you may install batteries into their tray or install them later by removing the battery tray door that is attached to the rear of the case with two screws 2 3 Using Rechargeable AA Type Batteries IMPORTANT WARNING Do not use an external power sources that deliver less than 13 8 volts with rechargeable batteries installed If the external supply voltage is too low the charger will not work properly and batteries will eventually discharge We recommend charging batteries with the MF J 249C power switch off and allowing enough charging time to establish full battery charge A minimum of ten hours is recommended When using rechargeable batteries your power source must deliver a minimum of 13 8 volts to meet the minimum charge voltage threshold Typical charging current is 10 20 mA trickle charge rate The charger circuit functions any time external power is connected eve
24. time of warranty service MFJ Enterprises Inc shall have the discretion to deny warranty without dated proof of purchase Any evidence of alteration erasure of forgery shall be cause to void any and all warranty terms immediately 2 MFJ Enterprises Inc agrees to repair or replace at MFJ s option without charge to the original owner any defective product provided the product is returned postage prepaid to MFJ Enterprises Inc with a personal check cashiers check or money order for 12 00 covering postage and handling 3 MFJ Enterprises Inc will supply replacement parts free of charge for any MFJ product under warranty upon request A dated proof of purchase and a 8 00 personal check cashiers check or money order must be provided to cover postage and handling 4 This warranty is NOT void for owners who attempt to repair defective units Technical consultation is available by calling 662 323 5869 5 This warranty does not apply to kits sold by or manufactured by MFJ Enterprises Inc 5 Wired and tested PC board products are covered by this warranty provided only the wired and tested PC board product is returned Wired and tested PC boards installed in the owner s cabinet or connected to switches jacks or cables etc sent to MFJ Enterprises Inc will be returned at the owner s expense un repaired 6 Under no circumstances is MFJ Enterprises Inc liable for consequential damages to person or property by the use of any MFJ pr
25. ting range with the clip lead installed at any of those three positions A well designed voltage balun should show low SWR over its operating range with the clip lead installed at position B but show poor SWR with the clip lead is installed at A or C note however that the SWR readings should measure about the same whether connected to A or C A voltage balun should also be tested using the configuration shown in Fig B with the resistors in parallel If it is operating properly SWR will be remain low with the resistors connected from either output terminal to ground 6 8 _ Measuring Inductance and Capacitance F To measure capacitance or inductance you will need some standard value capacitors and inductors These should be collected and tested for accuracy MFJ suggests the following sets of values Inductors 3304H 56 WH 5 6 uH 47 uH Capacitors 10 pF 150 pF 1000 pF 3300 pF Readings will be the most accurate if the standard test values used are between 0 5 uH to 500 uH to measure capacitance or 10 pF and 5000 pF to measure inductance Take a component of unknown value and connect it in series with a standard component to make a series LC circuit Attach the series LC circuit to the ANTENNA connector in series with a 50 Q resistor 10 MFJ 249C Instruction Manual HF VHF SWR Analyzer Measure Capacitance 1 Connect an unknown capacitor in series with the highest value standard inductor 2 Connect the LC circuit to ANTENNA con
26. tion of a transmission line A PRAISE MFJ 249C Instruction Manual HF VHF SWR Analyzer 3 Frequency Counter The third mode converts the analyzer into a discrete frequency counter Connect the RF source DUT to the BNC connector labeled Frequency Counter Input As with many counters the sensitivity threshold for a locked in reading gradually decreases with increasing frequency The measurement threshold at 0 53 MHz is around 10 millivolts and this level gradually increases to around 200 millivolts at 230 MHz The never exceed limit for safe testing is 2 volts peak to peak The counter s default gate time is 0 1 second but you may reset it to either 01 second very fast or 1 0 second very slow by tapping the Gate button A 1 0 second gate times provide increased frequency resolution more digits to the right of the decimal point and the 01 gate provides very fast response with less resolution see sample screens below Freq Counter 14 15 MHz 0 01s 21 324MHz 0 1s 144 2389MHz 1s Freq Counter Freq Counter Freq Counter IMPORTANT WARNING Never apply more than two volts of peak voltage or any dc voltage to the Frequency Counter BNC port 3 4 Blinking VOLTAGE LOW display warning If the external de source or battery voltage drops below 11 volts a blinking Voltage Low warning will come up on the display Pressing Mode during a low voltage warning will disable it and
27. transmitter end of the feedline cannot affect the losses nor the efficiency of the antenna system 2 Impedance Magnitude This mode will provide magnitude of the impedance readings for the load connected to the ANTENNA jack The readings are the combination of the resistive and reactive parts of the load The magnitude of the impedance Z is the square root of the addition of square of the resistance R and the reactance X By considering the definition of Z and by adjusting the TUNE knob until the lowest SWR reading is obtained it is possible to read the antenna s pure reactance The point of the lowest SWR is generally the point of lowest reactance For the SWR to be 1 1 the load must be an impedance of 50 ohms of pure resistance R 50 with no reactance X 0 The top line of the working display shows the VFO Frequency in MHz and the numerical SWR reading The lower line displays the Resistive R impedance components for the attached load Pressing the MODE push button from the SWR mode selection the Magnitude of the Impedance Z mode is enabled It will display Z in a range from 0 to 650 ohms If the impedance is greater than about 650 ohms the message Z gt 650 is displayed The SWR value for the connected load will be displayed in the LCD The stray output capacitance around 3pF will be lower than 650 ohms at frequencies higher than 60 MHz This stray capacitance does not affect high frequency measurements considering the connec
28. tubs SWR resonant frequency bandwidth MAPS ci at aches Resonant frequency and approximate Q Tuned Circuits Resonant frequency Small capacitors Value RF chokes and inductors Self resonant frequency series resonance and value Transmitters and oscillators Frequency The MFJ 249C as a non precision signal source VFO output is leveled at approximately 3 Vpp or around 20 milliwatts into a 50 ohm load This signal is relatively pure with harmonics better than 25 dBc dB below the fundamental frequency carrier The internal source impedance Zo is 50 ohms A more complete description of the MFJ 249C s features along with proper measurement methods can be found by reading sections covering the particular measurement you wish to make Consult the table of contents for various applications 13 Frequency Range The MFJ 249C covers 0 53 to 230 MHz without frequency gaps using a precision reduction drive VFO tuning capacitor and two band switches Bands of coverage are Main Switch 155 230 MHz 113 155 MHz 67 113 MHz 28 67 MHz 11 28 MHz Lower Range Lower Range Switch 4 7 11 MHz 2 1 4 7 MHz 1 0 2 1 MHz 0 53 1 0 MHz Note that LF coverage may be shifted from 0 53 1 0 MHz down to 0 47 0 94 MHz for 600 Meter and maritime frequency coverage To retune remove the cabinet and use a small hex wand 2 mm to adjust inductor L12 while watching the LCD fre
29. ually optimized to provide the highest accuracy possible with both high and low impedance loads making the A D converter s 8 bit resolution the analyzer s primary accuracy limitation 3 Stray Reactance The length of electrical connections between components within the bridge circuit and the line between the bridge and antenna connector may introduce inaccuracy at higher frequencies and when the load impedance is very high or very low However the MFJ 249C minimizes this problem with careful pc layout and by using low capacitance microwave grade surface mount components with virtually no lead length While some analyzers may display misleading exact readings falling outside the reliable measurable range the MFJ 249C does not Instead it is programmed to generate a display warning for out of range results For example if Z gt 650 appears on your display it means the impedance being measured is greater than 650 ohms and outside the reliable measurement range MFJ 249C Instruction Manual HF VHF SWR Analyzer 1 2 Typical Uses The MFJ 249C may be used to adjust test or measure the following Antennas 0cccc cece SWR impedance resistance resonant frequency and bandwidth Antenna tuners SWR bandwidth frequency Amplifiers o oo co Input and output matching networks Coaxial transmission lines SWR velocity factor loss resonant frequency Matching or tuning s
30. y Factor of Transmission Lines Velocity Factor of Transmission Lines The MFJ 249C can accurately determine the velocity factor of any impedance transmission line Measure the velocity factor with the following procedure 1 Disconnect both ends of the transmission line and measure the physical length of the line in feet 2 Set up the line to measure 1 4 stubs as in the section on Testing and Tuning Stubs 3 Find the lowest frequency across all the bands at which the lowest SWR occurs The dip should occur slightly below the 1 4 wavelength frequency 4 Read the frequency from the frequency counter display This is the 1 4 resonant wavelength frequency of your transmission line Note that you will get low SWR reading at all odd multiples of 1 4 wavelength 5 Divide 246 by the measured frequency This gives you the free space 1 4 wavelength in feet MFJ 249C Instruction Manual HF VHF SWR Analyzer 6 3 Impedance of Transmission Lines or Beverage antennas The impedance of transmission lines between 15 and 150 ohms can be measured with the MFJ 249C a 250 ohm potentiometer and an ohm meter Lines of higher impedance can be measured with a higher resistance potentiometer if a broad band transformer is used see the section on testing transformers to transform the line impedance to approximately 50 ohms 1 Measure the 1 4 wavelength frequency of the transmission line to be tested as in Testing and Tuning Stubs section 2 Terminate the fa
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