MFJ-269 Instruction Manual HF/VHF/UHF SWR Analyzer
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5.4.1.4 Return Loss and Reflection Coefficient
Return Loss and Reflection Coefficient
mode is the second measurement mode in the
Advanced 1
mode menu.
This mode is reached by pressing and releasing the
MODE
button one time after entering the
Advanced 1
mode
menu. You can also reach it, an all other modes, by stepping through Advanced modes with the
MODE
button
until the display indicates
“Return Loss and Reflection Coeff”
.
The
“Return Loss and Reflection Coeff”
mode measures and displays return loss in dB and voltage reflection
coefficient on the LCD. These terms describe SWR. The meters indicate 50 ohm SWR and the impedance.
To use this mode, connect the load to be measured to the ANTENNA connector, adjust the frequency to the
desired frequency range, and read the results on the MFJ-269 LCD and panel meter displays.
5.4.1.5 Resonance Mode
Resonance mode is reached by pressing the
MODE
button twice while in the opening menus of the
Advanced 1
function. Like all other mode functions, you can step back to this mode as long as you are in the
Advanced 1
menu by stepping through the other modes. When this mode is initialized, the display briefly indicates:
The
Resonance Mode
primarily draws attention to reactance, displaying reactance on the
IMPEDANCE
meter.
In this mode, the MFJ-269 measures frequency, SWR, resistance (Rs= ), and reactance (Xs= ). When reactance
is
zero
in a system that has selectivity, the
system
is said to be
resonant
.
NOTE:
Because of transmission line effects, zero reactance or resonance can occur on frequencies where the
antenna is
not
actually resonant. Conversely, the antenna may appear to contain reactance even at its true
resonant frequency when measured through a feedline.
A less than perfectly matched antenna and feedline, when used with a feedline that is not an exact multiple of 1/4
wavelength (0, 1/4, 1/2, 3/4, etc.), will have reactance added by the feedline. Reactance added by a non-quarter
wave multiple mismatched feedline may coincidentally cancel a non-resonant antenna’s reactance, making the
system resonant.
The SWR of the system, if the feedline is a 50 ohm feedline (or any impedance feedline that matches the
impedance setting of the instrument) with minimal loss and free from common mode currents, will not change as
the feedline length is changed. This is true even if the resonant frequency or reactance changes.