MFJ MFJ-213 - SWR, Bandwidth, and Resonanci; Antenna Tuning

MFJ-213 HF/VHF/UHF Antenna Analyzer Instruction Manual
6.4 SWR, Bandwidth, and Resonance
The amateur-radio industry's standard for maximum SWR is 2:1. Most
modern transceivers operate safely and deliver full power within this
mismatch range. The antenna bandwidth is the frequency interval between
its two 2:1 SWR points. This specification, along with minimum SWR and
minimum SWR frequency, is often included on antenna specification sheets.
Note that minimum SWR is sometimes wrongly confused with resonant
Srequency. The technical definition for resonance is the frequency where
inductive and capacitive reactance cancels, leaving a purely resistive load
(4 = 0). The minimum SWR and resonant frequencies may be close, but
they rarely coincide.
6.5 Antenna Tuning
Where possible, make adjustments to your antenna that will yield SWR
readings under 2:1 over the frequency range where you normally operate. If
the minimum-SWR frequency measures low in the band (or below the band
edge), your antenna is probably too long and will need to be shortened. If the
Minimum SWR frequency is too high, it should be lengthened. To calculate
the required change in length:
(1.) Write down the desired minimum SWR frequency (ex: 14.200 MHz)
(2.) Use the analyzer to measure the present minimum SWR frequency (ex:
14.050 MHz)
(3.) Divide the present frequency by the desired frequency (ex 14.050 +
14.200 = .989)
(4.) Multiply the present length by the result (33.3 feet x .989 = 32.94 feet)
Note that this formula applies to full-sized antennas, but not to elements
shortened by coils, traps, or capacitive hats.
Version | 9 © 2012 MFI Enterprises, Ine