MFJ-259C Instruction Manual HF/VHF SWR Analyzer
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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.
6.2 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. Ironically, 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.
6.3 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.
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.
6.) First, determine if the antenna needs to be shorter (higher in frequency) or longer (lower in frequency).
7.) To make it shorter ( higher), divide the present frequency by the desired frequency (scaling factor <1).
8.) To make it longer (lower), divide the desired frequency by the present frequency (scaling factor >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 = 0.96. Next calculate the new
length: 132 feet x .96 = 126.7 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.
7.0 TESTING AND TUNING STUBS AND TRANSMISSION LINES
7.1 Testing Stubs
To measure Resonant Frequency for a matching stub or transmission line, select the SWR/Impedance mode in the
Basic Menu (opening mode). Note that DUTs measuring 1/4λ and odd multiples (1/4λ, 3/4λ, 5/4λ, etc) are
terminated with an open circuit at the far end. DUTs measuring 1/2λ and even multiples (1λ, 1-1/2λ, 2λ) are
terminated with a short circuit.
Coaxial lines may be piled or coiled on the floor and the analyzer operated on external power. Coax lines are
connected to the analyzer's SO-239 connector with the shield grounded. For balanced line, run the analyzer on its
internal batteries, keep it a few feet away from other conductors and earth, and do not attach any stray wires (other
than the feedline itself). Connect the DUT with one lead to the analyzer's ground stud and the other lead to the
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