MFJ-266 HF/VHF/UHF Antenna Analyzer
Instruction Manual
©
2011 MFJ Enterprises, Inc.
10
frequency.
The technical definition for
resonance
is t
he frequency where inductive and
capacitive reactance cancels, leaving a purely resistive load (
±
j = 0)
. The minimum SWR and
resonant frequencies may be close, but they rarely coincide.
13.9
14.0
14.1
14.2
14.3
14.4
1.5
2.0
1.0
Min. SWR Freq.
Bandwidth
Lower 2:1 Freq.
Upper 2:1 Freq.
Min. SWR
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.
6.6 Antenna matching
If your antenna doesn’t exhibit 1:1 SWR at the minimum SWR frequency, then some mismatch
is present relative to 50-Ohms. For simple dipoles and ground-independent verticals, mounting
height above ground may be the primary cause. Generally, it’s best to ignore SWR readings
under 2:1 and mount these antennas as high as possible where they’ll perform best. For antennas
that feature adjustable matching networks (Yagis etc), SWR can usually be improved by
following the manufacturer’s antenna setup instructions. Note that matching and tuning settings
may interact, so readjustment of both the antenna’s element length and matching network may be
needed to obtain best results.
6.7 Matching Antennas Through A Tuner (ATU)
