MFJ MFJ-269C, Instruction Manual, Page: 20 / 40

MFJ-269C Instruction Manual LF/HF/VHF/UHF SWR Analyzer
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5.4.1.1 Magnitude and Phase of Load Impedance
Magnitude and Phase of Impedance is the first selection in the
Advanced-1
menu, and it comes up
automatically upon entering
Advanced-1
Mode. If already using one of the Advanced-1 functions, you
may "step" or "scroll" to the Magnitude and Phase of Impedance mode by holding down Mode and Gate
switches. The opening display first indicates:
and then flashes to:
In this mode, the LCD displays
Frequency
, Impedance Magnitude (
Z)
(in ohms), and Phase Angle of the
Impedance (
θ
). The meters indicate 50-ohm normalized
SWR
and the load Impedance (
Z
). The maximum
impedance limit is set at 1500 ohms. Exceeding this limit results in an impedance display of
(Z>1500)
.
Note:
Stray connector capacitance will be lower than 1500 ohms at frequencies higher than 30 MHz, and
lower as adapters and leads are added to the
Antenna
port. This small stray capacitance will not affect
high frequency measurements, and produces only minor errors in measurement of impedances under a
few hundred ohms at VHF.
Phase angle of Impedance
is another way of expressing R and X. Instead of providing R and X as
separate numerical quantities, it presents a vector-type description of measured impedance. Impedance
(Z) is still described as the length (magnitude) of a line representing the complex impedance (this is the
same Z as given in other functions). Besides
Z , an angle between zero and 90 degrees is shown. This
angle represents the phase difference between current and voltage at the terminals of the analyzer.
When a reactance is present, voltage and current are no longer in phase (or exactly out-of-phase) and so
the phase angle increases from 0 degrees to a maximum angle of 90 degrees. The angle becomes 90
degrees when the load is a pure reactance, and zero degrees when the load is a pure resistance.
This analyzer will determine the angle in degrees, but it will
not describe the load reactance specifically
as either capacitive or inductive. It is a simple matter to determine the direction by adding a small amount
of reactance in series with the load and watching the angle change. If the angle decreases, the load
reactance is opposite to the sign or type of test reactance. If the angle increases, the load reactance is the
same sign as the added reactance.
5.4.1.2 Series Equivalent Impedance
The
Advanced-1
display sub-mode is reached by pressing the
Gate
button once while in the
Magnitude
and Phase of Load Impedance
mode. This mode displays the series-equivalent impedance of the load.
It is the most common form used to describe antenna system impedance. In this mode, the load impedance
is described as a
resistance in series with a reactance . In order to cancel the reactance without changing