MFJ-993BRT 300 Watt IntelliTuner
TM
Automatic Remote Antenna Tuner Instruction Manual
© 2011 MFJ Enterprises, Inc
MFJ-993BRT Version 1A
6
Tuning Resolution
Meter Frequency Range (MHz) Memory Resolution
160 1.800-2.000 2
75/80 3.500-4.000 4
60 5.3305, 5.3465, 5.3665, 5.3715, and 5.4035 5 memory locations
40 7.000-7.300 7
30 10.100-10.150 10
20 14.000-14.350 14
17 18.068-18.168 18
15 21.000-21.450 21
12 24.890-24.990 25
10 28.000-29.700 28
Figure 8 Tuning Window Resolution Chart
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.
Tuner settings are stored in memory. Refer to Figures 15 and 16 for the on-screen Memory indicator.
Defaults are memory banks 1A ON. To clear the antenna memory bank, turn off the power to the tuner,
then press and hold both [TUNE] and [C-UP] buttons while turning on the power. A DELETE BANK
message will appear. “Total Reset” erases both antenna memories and returns all tuner settings to their
factory default states. To achieve this, turn power off, press and hold [TUNE], [C-UP] and [L-UP] buttons
while turning on the power. A TOTAL RESET message will appear.
Transceiver Foldback Circuit
Any in-line amplifier must ALWAYS be bypassed prior to tuning. Modern transceivers with solid-state
finals usually have a foldback circuit to protect the final transistors from high SWR, which can damage or
destroy them. A foldback circuit detects the SWR during transmit and reduces the output power as the
SWR rises above a preset threshold, usually 2:1. The higher the SWR the lower the power is set to
prevent damage. If your transceiver has a foldback circuit, you can simply key down and tune at any
power level from 5 to 100 watts. If your transceiver does not have a foldback circuit, you must manually
set the power level to 20 watts or less for tuning. At higher power levels, the reflected power occurred
during tuning can damage your transceiver and causes component arcing which can damage the relays
in the tuner. Check your transceiver owner's manual to see if yours has a foldback circuit. The use of the
AM mode normally will drop the radio to around 20 to 40 watts or so. This is a convenient way of reducing
power and supplying a continuous carrier for tuneup.
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