MFJ 986 Version 6C
User Manual: MFJ-986
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MFJ-986 Instruction Manual MFJ-986 Differential-T Tuner Introduction The MFJ-986 roller inductor tuner is a 3000 watt PEP input, 1500 watt PEP output antenna tuner. These power ratings are for load impedances of 35-500 ohms. The MFJ-986 is designed to match 50 ohm output amplifiers, transmitters or transceivers to virtually any antenna. Peak and average forward power, reflected power, and SWR are displayed on the MFJ-986's illuminated cross-needle meter. The MFJ-986 Differential-T 3kW Tuner uses a differential capacitor to make tuning easy. It continuously tunes all frequencies from 1.8 through 30 MHz, including MARS and all the WARC bands. It will match dipoles, inverted-vee's, verticals, mobile whips, beams, random wires, and many other antennas. The roller inductor lets you tune down your SWR to the absolute minimum. The MFJ986 also features a peak reading cross-needle, SWR/Wattmeter, and a new current balun that will work with balanced open wire, twinlead, or twin-axial feedlines. An internal six position antenna-selector switch selects two coaxial line outputs, a single wire linebalanced line output, or an external dummy load connection. The coaxial line outputs can be selected in tuned (with tuner's matching network in line) or direct (no matching circuit) configurations. Understanding Power Ratings There are no standardized power rating systems for tuners. The names used (i.e. 3 kW Tuner) carry over from the time when amplifiers were rated by peak power input, and not the true RF power output. For example, the one thousand watt Johnson Matchbox was rated to handle a 1000 watt plate modulated AM transmitter (four kilowatts PEP 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 1200 watts PEP SSB. The FCC has changed the power rating system of amplifiers, and tuners no longer follow amplifier power ratings. Most typical 1500 watt tuners remain able to safely handle 400-600 watts CW, and 600900 watts PEP SSB. Load conditions and control settings also greatly affect the power handling capability of the tuner. Tnetworks typically handle more power on higher frequency bands into higher load impedances. The worst operating condition for T-network tuners are low impedance capacitive reactance loads. Tnetwork tuners always handle the least power when operated on 160 meters into low impedance capacitive reactive loads. Follow the guidelines in this manual to avoid exceeding the ratings of this tuner. Peak Reading SWR/Wattmeter The cross-needle meter measures the peak or average FORWARD power, REFLECTED power, and SWR. The illuminated cross-needle meter operates with the antenna tuning circuit in or out of line. The wattmeter can be used without the tuning network by setting the ANTENNA SELECTOR to either of the two COAX DIRECT positions of the antenna selector. The wattmeter is active in all positions of the ANTENNA SELECTOR. 1 MFJ-986 Instruction Manual The meter's full scale forward and reflected power range is controlled by the left POWER switch that selects 2000W (HI) or 200W (LO). If your transmitter runs more than 200 watts of output power, set this switch to the 2000W HI (in) position. If your transmitter has less than 200 watts of output, set this switch to the 200W LO switch position (out). Peak envelope power (PEP) is measured when the PEAK or AVG POWER push button (right-hand side) in placed in the PEAK (in) position. Peak power and average power values are equal with steady unmodulated carriers, FSK, or FM. The meter reading on these modes will be the same whether the PEAK / AVG button is pressed or released. On SSB, the PEP meter reading should be twice the average power with two tone test modulation. On SSB, the ratio of PEP to average power varies with different voice characteristics. With most voices, the PEP reading is three to five times higher than the average voice power reading. The most accurate peak envelope power readings are obtained only with sustained carrier, voice or two tone test modulation. During normal voice modulation the wattmeter will typically indicate only 70% of the true peak envelope power. Forward power is displayed on the left-hand FORWARD meter scale. This scale is calibrated from 0 to 200 watts and is read directly in the 200 watt position. Each picket (scale mark) represents 5 watts below 40 watts and 10 watts between 40 and 200 watts. In the 2000W (HI) position the forward power scale must be multiplied by 10. Each picket represents 50 watts below 400 watts and 100 watts from 400 to 2000 watts. The reflected power is read on the right-hand REFLECTED meter scale. This scale indicates 50 watts full scale when the 200W power sensitivity is selected, and 500 watts full scale when the 2000W power scale is selected. This scale has a picket every watt below 20 watts and every 5 watts above 20 watts. This scale is also multiplied by 10 when using the 2000W power position. The most accurate power readings occur in the upper half of the meter scales. When trying to measure power with a less than perfect match, the reflected power should be subtracted from the forward power reading. The SWR is read directly from eleven red SWR curves that range from 1:1 to infinity. SWR is measured by observing the point where the forward and reflected power needles cross. The SWR is indicated by the red curve closest to the needle crossing point. No cumbersome or time consuming SWR sensitivity adjustments are required with this meter. The wattmeter has an internal lamp that backlights the meter scale. The lamp circuit requires power from an external 12 Vdc source, such as the optional MFJ-1312B power supply. The rear panel jack accepts a 2.1 mm coaxial plug with the center conductor positive (+) and the sleeve negative (-). The negative lead is grounded inside the tuner. The METER LAMP ON / OFF switch turns the meter lamp off and on. Antenna Selector The ANTENNA SELECTOR allows you to select 2 rear panel SO-239 coaxial connectors, either direct or through the tuner, an external dummy load connection, or a balanced feedline. The External Dummy Load position lets you connect a dummy load, like the MFJ-250 Oil-filled VERSALOAD or the MFJ264 DRY LOAD for tuning. 2 MFJ-986 Instruction Manual Current Balun The MFJ-986 uses a CURRENT balun to force equal currents into the two antenna halves so you get minimum balanced currents. Minimum unbalanced current reduces field pattern distortion which concentrates your power for a stronger signal. Installation CAUTION: Locate the tuner so the rear is not accessible during operation. 1. Locate the tuner in a convenient location at the operating position. If random wire or balanced line operation is used, the ceramic feed through insulators may have high RF voltages. These voltages can cause serious RF burns if the terminals are touched when transmitting. Be sure to locate the tuner so these terminals can not be accidentally contacted during operation. 2. Install the tuner between the transmitter and the antenna. Use a coaxial cable (such as RG-8/U) to connect the transmitter (or amplifier) to the connector marked TRANSMITTER on the rear of the tuner. If you are using a linear amplifier, then connect the output of the transceiver to the input of the amplifier and the output of the amplifier to the MFJ-986. 3. Connect the antenna(s) to the tuner as follows: A. Coaxial feedlines from your antenna(s) connect to the coax connectors COAX 1 and/or COAX 2. Coax lines may be fed direct or through the tuner as selected by the ANTENNA SELECTOR switch. B. Any antenna fed with a single wire should be connnected to the center hole of COAX 1 or COAX 2. C. Any balanced feedline (open wire, twinlead, or twin-axial lines) is connected to the ceramic BALANCED LINE terminals on the back of the unit. D. Use the GROUND post to ground the tuner to the transceiver, amplifier, and earth ground. E. A dummy load could be connected to the EXTERNAL DUMMY LOAD connector. This will give you the convenience of not having to connect or disconnect your dummy load from the MFJ-986 every time you tune your radio. Use coax cable such as RG-8/U. Operation The roller inductor has a minimum inductance when the knob is rotated fully clockwise. When rotated fully counter-clockwise, it has maximum inductance. Note: The MFJ Air Core™ Roller Inductor is designed with an exclusive Self-Resonance Killer™ that keeps potentially damaging self-resonances away from your operating frequency. This feature is switched in and out of the circuit with a built-in switch in the roller. Therefore, as you turn the roller up and down, you may feel a bump. This is normal and you should not be alarmed. 1. 3 First, rotate the knob fully counter clockwise. Then, use a small screwdriver or a pencil and push the reset lever through the hole beside the counter. The counter should reset to "000"; this is the maximum inductance. Turning the knob clockwise will now increase the numbers and decrease the inductance of the MFJ-986. MFJ-986 Instruction Manual 2. Tune the exciter into a dummy load (most solid state transmitters are "pre-tuned" to 50 ohms and do not require loading with the dummy load). 3. Select the desired antenna with the ANTENNA SELECTOR. 4. Position the capacitor control at the following settings: 160 M: 80 M: 75 M: 40 M: 30 M: 20 M: 17 M: 15 M: 12 M: 10 M: Then place the POWER switch in the LO and AVG meter positions. 5. Starting from the minimum INDUCTOR position (highest number), turn the INDUCTOR control to add more inductance while applying a slight amount of power (less than 25 watts). Tune for the lowest reflected power and maximum forward power (lowest SWR). The lowest reading should occur somewhere above the following recommended inductor positions. Tuning Chart Frequency (MHz) 1.8 1.8 2.0 2.0 3.5 3.5 3.75 3.75 4.0 4.0 7.15 7.15 10.1 10.1 14.2 14.2 18.1 18.1 21.2 21.2 24.9 24.9 28.5 28.5 Capacitor Value Inductor (counter indicator) Load (ohms) 50 600 50 600 50 600 50 600 50 600 50 600 50 600 50 600 50 600 50 600 50 600 50 600 4 MFJ-986 Instruction Manual 6. Adjust the CAPACITOR control for lowest reflected power (and SWR). 7. If the SWR did not reach 1:1 in step 5, turn the INDUCTOR control clockwise (to a higher number) again and repeat Step 5. For maximum power handling and efficiency, always adjust the capacitor to the lowest front panel number that allows proper antenna matching. This insures maximum power handling and lowest power loss in the tuner. 8. Advance the power (do not exceed 100 watts) and, if necessary, touch up the CAPACITOR and INDUCTOR controls for minimum reflected power and maximum forward power (lowest SWR). Remove the power. 9. After adjusting the tuner for minimum SWR, the amplifier may be turned on. The METER switch should be placed in the HI position, and the amplifier tuned according to the manufacturer's instruction. 10. For quick retuning of the tuner, record the INDUCTOR and CAPACITOR settings for each band. Note: Maximum power handling occurs when both the CAPACITOR AND INDUCTOR are set at the lowest front panel numbers for capacitance and highest inductance that permit matching the antenna. Following this guideline will insure maximum power handling capability and efficiency, and the least critical tuning adjustments. Operating Notes 1. While this tuner is designed to have as large a tuning range as possible, there are limits to the tuning range of the capacitor. Some antennas may require more or less capacitance than the controls have. In these cases, the SWR may not be reduced to 1:1. If the SWR is higher than the limits on your rig, try changing the length of the antenna or feedline to bring the impedance within the tuning range of the tuner. 2. When adjusting the tuner, use the lowest amount of CAPACITANCE and INDUCTANCE that produces a good SWR. This will reduce tuner losses and increase the power rating of the tuner. 3. If the INDUCTOR counter slips out of calibration, turn the INDUCTOR fully counter clockwise. Then, with a small screw driver or pencil, push the reset button through the hole to the right of the counter. This resets the counter to "000". 4. The following table can be used as a guide to tune your MFJ-986 to a specific operating band. When the MFJ-986 is properly tuned, the counter reading should approximately match the number on the table. If the counter is too far from the number on the table, then the tuner is not properly tuned. If this is the case, repeat the tuning process. BAND 160 M 80 M 40 M 20 M 15 M 10 M INDUCTOR INITIAL TUNE-UP INDUCTOR SETTINGS 5 MFJ-986 Instruction Manual WARNING: 1. Never operate the tuner with the top removed. Contact with the components inside the tuner while transmitting will result in painful RF burns. 2. Never rotate the ANTENNA SELECTOR switch while transmitting. Doing so may permanently damage the switch. 3. Locate the tuner so that the rear terminals ARE NOT accessible during operation. The single wire and balanced line connections may have high voltage while being used. 4. Disconnect all antennas from the tuner during lightning storms. 5. Always tune with low power (i.e. less than 100 watts). Apply maximum power only after tuning up. 6. Be sure to adjust the SWR before transmitting at high power (above 100 watts). Do Not transmit with a high SWR for extended periods of time. In Case Of Difficulty If the tuner fails to tune, please double check all connections and follow the tuning procedures again. Be sure you are using enough inductance and have the capacitors open far enough. If the tuner arcs, please double check all connections and follow the tuning procedures again. The power rating of this tuner is 1500 watts PEP RF power. If this tuner arcs at these power levels, make sure you are using the least amount of inductance and the greatest capacitance possible that still allows matching the load on the operating frequency. If you are still unsuccessful, but the tuner does adjust and operate when switched to a dummy load or another antenna, please read the ANTENNA HINTS section. Grounding Hints To minimize RFI, single wire feedlines (such as used with Windom or longwire antennas) should be kept away from other wiring. Radiation will be minimized if the single wire feeder runs parallel and reasonably close to the wire that connects the tuner to the outdoor ground. The antenna feed wire should be adequately insulated to prevent arcing or accidental contact. For safety, please use good dc and RF grounds. It is particularly important to have a good RF ground while using a single wire feeder. When using a single wire feeder, the tuner needs something to "push" against in order to force current into the single wire feedline. If a good RF ground is not available, RF will usually find it's way back into the power line (RFI), transmitter audio circuits (RF feedback), or the operator (RF burns). Water pipes and ground rods provide good dc and ac safety grounds, but they are often inadequate for RF grounding because they are single conductors. Ground rods by themselves are almost useless for dependable RF grounding. 6 MFJ-986 Instruction Manual RF grounds work much better when "spread out" over a large area, especially when they employ multiple connections directly to the equipment ground point. Water pipes, heating ducts, and fences may work (especially if they are connected together with multiple wires), but the best RF grounds are radial systems or multi-wire counterpoises. Radials and counterpoises provide large, low resistance surfaces for RF energy. RF and lightning travels on the surface of conductors. Braided or woven conductors have high surface resistance to lightning and RF. Ground leads for RF and lightning should have wide smooth surfaces. Avoid the use of woven or braided conductors in RF and lightning grounds unless the lead needs to be flexible. CAUTION: For operator safety, a good outside earth ground or water pipe ground should always be installed and connected to the case of the MFJ-986. Make certain the safety ground also connects to the transmitter and other station accessories. A wing nut post marked GROUND is provided for ground connection(s). Antenna System Hints For the best performance, an end-fed longwire wire antenna should be at least one quarter-wavelength long at the operating frequency. Horizontal dipole antennas should be at least a half-wavelength long and located as high and clear as possible. While good RF grounds help the signal in almost any transmitting installation, it is extremely important to have good RF grounds with long wire or other Marconi style antennas. Matching Problems Most matching problems occur when the antenna system presents an extremely high impedance to the tuner. When the antenna impedance is much lower than the feedline impedance, an odd quarterwavelength feedline converts the low antenna impedance to a very high impedance at the tuner. A similar problem occurs if the antenna has an extremely high impedance and the transmission line is a multiple of a half-wavelength. The half-wavelength line repeats the very high antenna impedance at the tuner. Incorrect feedline and antenna lengths can make an otherwise perfect antenna system very difficult or impossible to tune. One example where this problem occurs is on 80 meters when an odd quarter-wave (60 to 70 foot) open wire line is used to feed a half-wave (100 to 140 foot) dipole. The odd quarter-wave line transforms the dipole's low impedance to over three thousand ohms at the tuner. This is because the mismatched feedline is an odd multiple of 1/4 wavelength long. The line inverts (or teeter-totters) the antenna impedance. A problem also occurs on 40 meters with this same antenna example. The feedline is now a multiple of a half-wave (60 to 70 foot) and connects to a full-wave high impedance antenna (100 to 140 foot). The half-wave line repeats the high antenna impedance at the tuner. The antenna system looks like several thousand ohms at the tuner on 40 meters. This places enormous strain on the balun and the insulation in the tuner, since voltages can reach several thousand volts. This can cause component arcing and heating. 7 MFJ-986 Instruction Manual The following suggestions will reduce the difficulty in matching an antenna with a tuner: 1. Never center feed a half-wave multi-band antenna with a high impedance feedline that is close to an odd multiple of a quarter-wave long. 2. Never center feed a full-wave antenna with any feedline close to a multiple of a half-wave long. 3. If this tuner will not "tune" a multi-band antenna, add or subtract 1/8 wave of feedline (for the band that won't tune) and try again. 4 Never try to load a G5RV or center fed dipole on a band below the half-wave design frequency. If you want to operate an 80 meter antenna on 160 meters, feed either or both conductors as a longwire against the station ground. To avoid problems matching or feeding any dipole antenna with high impedance open wire lines, keep the lines around these lengths. The worst possible line lengths are shown in parenthesis: Dipole: 160 meters; 80 meters; 40 meters; Recommended: 35-60, 170-195 or 210-235 ft. 34-40, 90-102 or 160-172 ft. 42-52, 73-83, 112-123 or 145-155 ft. Avoid: (130, 260 ft) (66, 135, 190 ft) (32, 64, 96, 128 ft) Some slight trimming or adding of feedline may be necessary to accommodate the higher bands. WARNING: To avoid problems, a dipole antenna should be a full half-wave on the lowest band. On 160 meters, an 80 or 40 meter antenna fed the normal way will be extremely reactive with only a few ohms of feedpoint resistance. Trying to load an 80 meter halfwave dipole (or shorter) antenna on 160 meters can be a disaster for both your signal and the tuner. The best way to operate 160 meters with an 80 or 40 meter antenna is to load either or both feedline wires (in parallel) as a longwire. The antenna will act like a "T" antenna worked against the station ground. Technical Assistance: If you have any problem with this unit first check the appropriate section of this manual. If the manual does not reference your problem or your problem is not solved by reading the manual, you may call MFJ Technical Service at 601-323-0549 or the MFJ Factory at 601-323-5869. You will be best helped if you have your unit, manual and all information on your station handy so you can answer any 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 601-323-6551; through Compuserve at 76206,1763; or by email to 76206.1763@Compuserve.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. 8 MFJ-986 Schematic 9 Instruction Manual MFJ-986 Instruction Manual Tuning Chart Use the chart below to log values for your station. You may want to copy this chart and post it by your tuner. Frequency (MHz) 1.8 1.8 2.0 2.0 3.5 3.5 3.5 3.75 3.75 3.75 4.0 4.0 4.0 7.15 7.15 10.1 10.1 14.2 18.1 18.1 21.2 21.2 24.9 28.5 Capacitor Inductor (counter indicator) 10
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