MFJ MFJ-1048 User Manual
MFJ-1048 Instruction Manual Passive Preselector
MFJ-1048 PASSIVE PRESELECTOR
Introduction
The MFJ-1048 Passive Preselector is designed to reduce receive overload from
strong out o f band signals. It contains selective circuits that cover 1.6 to 33
MHz in six steps, providing the greatest selectivity on the lowest frequencies
where overload is most common.
The MFJ-1048 also features internal transmit-receive switching with adjustable
time delay. A rear panel jack is available for an external control that will switch
the MFJ-1048 into a bypass mode (we strongly recommend using the external
control line for switching to avoid pull in timing errors).
The MFJ-1048 has two rear panel SO-239 connectors for RF connections and a
standard 2.1mm power receptacle for 10 to 16 volt DC voltage. If DC voltage is
not applied, the MFJ-1048 will remain in a bypass mode.
Installation
Connect the MFJ-1048 Passive Preselector between your antenna and receiver or
transceiver antenna connector as shown in Figure 1. The Radio connector goes
directly to the transceiver or receiver with a short well shielded lead; the
Antenna co nnector go es to the antenna through any amplifier, TVI filter, or any
other station equipment.
Figure 1
WARNING: NEVER connect an amplifier or radio with more than 200 watts
output to the MFJ-1048 Passive Preselector. NEVER use an
internal antenna tuner to correct for high SWR if the tuner is in
the radio or on the radio side of the MFJ-1048 Passive
Preselector. Failure to follow this warning may allow your MFJ1048 Passive Preselector or other equipment to be damaged.
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MFJ-1048 Instruction Manual Passive Preselector
The Control line connects to the transceiver's normally open S/R (T/R) relay
contact, and bypasses the passive preselector when transmitting (See Figure 2).
Figure 2
: We highly recommend you use the transceiver's T/R connection instead of
Note
the internal RF switching circuit. This will normally prevent or reduce the
chance of "hot-switching" the MFJ-1048 Passive Preselector's relay.
Operation
With the MFJ-1048 Passive Preselector properly connected, simply turn the
Band switch to the desired band and adjust the Tune control for maximum
signal level. With the Power switch depressed and power applied, the MFJ1048 Passive Preselector becomes active.
Adjust t he Tune cont rol fo r maximum s ignal l evel. The max imum loss on the
desired amateur band is less than 5dB if the correct frequency range is selected.
Note
: Always use the highest fr eque ncy band range that co ver s the de sire d ba nd
for minimum loss.
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