MFJ-259C Instruction Manual
HF/VHF SWR Analyzer
7
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-259D, the c
alibration 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-259D 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.
Note that the MFJ-259D also has
Advanced
antenna-measurement modes that are described in Section-5.0.
However,
unless you have a strong working knowledge of RF systems, you may find these added modes of limited value. Most
represent more technical ways of expressing the same data offered by the basic modes.