MFJ-928 Compact IntelliTuner Automatic Antenna Tuner
Instruction Manual
©
2005 MFJ Enterprises, Inc.
11
Miscellaneous
Antenna Memory
The “memory resolution” is the width of frequency spectrum that the tuner recognizes as being the same
as a tuned frequency already in memory. The memory resolution is approximately 0.1 percent of the
lower frequency of each amateur band. For example, the memory resolution on the 40-meter band (7000
to 7300 kHz) is 7 kHz; if the tuner has memorized a setting for 7050 kHz, it will automatically call up this
setting for any frequency from 7047 to 7053 kHz. Memory resolution is smaller at lower frequency to
accommodate the higher antenna Q and larger at higher frequency where the antenna Q is lower. The
memory resolutions for the HF amateur bands 160 through 10 meters are:
Meter
Frequency Range (kHz)
Memory Resolution (kHz)
160
1800 – 2000
2
75/80
3500 – 4000
4
60
5330.5, 5346.5, 5366.5, 5371.5 and 5403.5
5 memory locations
40
7000 – 7300
7
30
10100 – 10150
10
20
14000 – 14350
14
17
18068 – 18168
18
15
21000 – 21450
21
12
24890 – 24990
25
10
28000 – 29700
28
Table 2. Memory Resolution.
The memory resolution for non-amateur frequency bands between 160 and 10 meters is approximately
0.2 percent of the lower frequency of each band. There are over 2500 memory locations for each memory
bank, and each of the two antennas has four memory banks (A-D). Tuner settings are stored in memory
separately for Antenna 1 and Antenna 2 (settings for single-wire antenna are stored as Antenna 1). This
provides memory for up to eight different antennas. See “ANT Button” on page 5. Defaults are memory
banks 1A and 2A ON.
IntelliTune
TM
Algorithm
When
the
tuner cannot find an appropriate setting in its memory, it begins its calculation function. It
measures the complex impedance of the antenna (load) at the transmitting frequency, then it calculates the
LC components needed for a match. Then it fine-tunes the components for minimum SWR. If for any
reason the tuner cannot calculate the load impedance, it proceeds to yet another method of calculation.
LC Limits
The upper limits of inductance (L) and capacitance (C) are factory-limited according to frequency and
maximum power rating; i.e., higher frequencies need less inductance and less capacitance when the L-
network is properly tuned. These limits are built into the MFJ-928 to prevent matching of extreme load
impedance outside the tuner’s specification, which may result in excess voltage and/or current across the
tuner’s components.
Summary of Contents for Compact IntelliTuner MFJ-928
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