MFJ-259C Instruction Manual
HF/VHF SWR Analyzer
7
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-259C. 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 as short as possible. This precaution is especially
important when measuring electrical components that are not part of a 50-ohm coaxial system.
3.) Always use good quality 50-ohm cable and connectors when making SWR measurements. Contaminated,
mismatched, or damaged cable will introduce significant error.
4.) When making Complex Impedance measurements, (R+X) or (Z), remember that any length of transmission
line you install between the load and the analyzer will displace the load from the analyzer's calibration plane.
For simple handheld analyzers like the MFJ-259C, the calibration plane is always located at the analyzer's RF
connector. This is the point where Zo=50 Ohms and Phase shift = 0 degrees. It is the only test point where the
analyzer will be calibrated for complex impedance measurements. Displacing the load away from the analyzer's
calibration plane through random lengths of coax will have little or no impact on SWR readings, but will introduce
enough error through phase shift and transformer action to invalidate virtually any complex impedance
measurement you might make! When measuring Complex Impedance, install the MFJ-259C as close
(electrically) to the DUT as possible!
4.2
Antenna SWR
Use the SO-239 Antenna connector located on top of the MFJ-259B for all RF measurements (except those using
the Frequency Counter mode). Follow the procedure below for measuring SWR:
1.) If your antenna doesn't have a dc-grounded feed system, momentarily short the cable's center conductor to
the shield immediately before connecting it to the analyzer. This simple procedure will discharge any static
buildup on the antenna and prevent damage to the analyzer's sensitive detector diodes.
2.) Connect the antenna lead to the analyzer's SO-239 Antenna connector.
3.) Set the VFO's two Frequency selector band switches to the appropriate range.
4.) Turn on the Power switch while watching the display. Battery voltage should read OK (11-16 volts).
5.) Following the boot screens, the default mode will come up with the working screen for Frequency, SWR,
Resistance (R), and Reactance (X). The SWR and Impedance analog meters will also become active.
6.) Adjust Tune (the VFO capacitor) as needed to find your desired test frequency -- or tune until you obtain a
minimum SWR reading.