MFJ-989D VersaTuner V Instruction Manual
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even half-wave length of line, the load will be repeated at the far end. Either condition can turn a
perfectly good radiator into something difficult or impossible to tune. Extreme High-Z loads are "the
enemy" because they produce RF-potentials topping several thousand volts to invite insulation
breakdown, arcing, and RF heating.
3.) Correcting Problems: The following strategies will help you to prevent most matching problems:
[ ] Never center feed a doublet style multi-band antenna with high-impedance feedline measuring near
an odd-multiple of a quarter wave.
[ ] Never center feed a full-wave antenna with any feedline measuring near an even multiple of a half-
wave.
[ ] If the tuner doesn't match one particular band on your multi-band array, try adding or subtracting
1/8-wave of feedline (as measured on the dysfunctional band).
[ ] Never try to load a G5RV or a center-fed dipole on any band below its half-wave design frequency.
[ ] To operate a 80 meter dipole on 160 meters, it's best to short the feed conductors at the tuner and
load it as a long-wire or "T" against the station ground. When fed conventionally, this antenna will be
extremely reactive with only a few ohms of feed-point resistance. In other words, it will be nearly
impossible to match.
[ ] When feeding any dipole with high-impedance line, use the approximate lengths shown in the table
below. Note that the worst possible lengths are also shown:
160-meter dipole: 35-60, 170-195, 210-235 feet [Avoid 130, 260 ft]
80-meter dipole: 34-40, 90-102, 160-172 feet [Avoid 66, 135, 190 ft]
40-meter dipole: 42-52, 73-83, 112-123, 145-155 feet [Avoid 32, 64, 96, 128 ft]
*Some slight trimming or adding of length may be necessary to accommodate the higher bands.
Factory Technical Assistance
If you have any problem with your MFJ-989D, first check the appropriate section of this manual. If the
manual does not reference the problem or succeed in solving it, call (a.) MFJ Technical Service at 662-
323-0549 or (b.) the MFJ Factory at 662-323-5869. For best service, have the unit, its manual, and a
full description of your station setup handy so you can answer any questions the technician may ask.
You may also send questions by mail to MFJ Enterprises, INC., 300 Industrial Park Road, Starkville,
MS 39759; by Facsimile (FAX) to 662-323-6551; or by email to techinfo@mfjenterprises.com. Send a
complete description of your problem, an explanation of exactly how you are using your tuner, and a
complete description of your station.
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