Vectronics SWR-584C - Manual (Page 17)

SWR-584C Instruction Manual HF/VHF/220MHz SWR Analyzer
17
5.7 Match Efficiency: Also called Percentage of Transmitted Power, this measurement is
directly related to Percentage of Reflected Power. By definition, the Percentage of Transmitted
Power
plus the Percentage of Reflected Power equals = 100% (see the SWR equivalency
chart at 5.1). If the Percentage of Reflected Power measures 25%, then the Percentage of
Transmitted Power
will equal 75% (100% - 25% = 75%).
Important Accuracy Note:
Note that this measurement is very easy to misinterpret because it
contains the word "Transmitted Power"
(implying "radiated power"). The Percentage of
Transmitted Power simply represents the percentage of forward vs. reflected power present in
the feedline at any given moment, and not the percentage of the transmitter's output power
that ultimately performs work. Reflections occur at both ends of the transmission line, so the
"real" power ultimately absorbed by the load after multiple bounces could be significantly more
or less than the Match Efficiency value suggests!
To enter Match Efficiency:
[ ] Connect the DUT to the Antenna jack
[ ] Enter Advanced Mode
[ ] Press Mode four times to access Match Efficiency and wait for the working screen:
Note that if SWR exceeds the analyzer's 25:1 measurement limit, this message appears:
Percentage of Reflected Power: To calculate Percentage of Reflected Power from Match
Efficiency
, simply subtract the Match Efficiency from 100%: Using the example above, %
Reflected Power = (100% - 94%) = 4%.
6.0 Adjusting Simple Antennas
6.1 General: This chapter focuses on practical tips to help you get the most from your back-
yard antennas using the SWR-584C. To begin, here are some pointers to keep in mind when
working with amateur radio antenna system:
1. Impedance and Calibration Plane: When measuring impedance and reactance, we've
emphasized how important it is to "position" the analyzer's Calibration Plane close to the
element feedpoint (or DUT). Alternatively, you may physically separate the calibration plane
from the load by installing a precisely cut electrical half-wave of cable in between. Doing so
rotates phase a full 360 degrees so there appears to be no phase shift ( = 0°) or impedance
transformation (Z) error. This strategy works well, but is a "single frequency" solution. Even a
small excursion (more than ± 2° of phase shift) from the cable's "cut" frequency will skew
impedance readings as the cable becomes non-resonant and begins to reintroduce its own
Match
Efficiency 14.150 MHz 1.4
Match = 94% SWR
29.538 >25
Power< 15% SWR