MFJ MFJ-713, MFJ-714 User Manual
MFJ-713/714 Instruction Manual
MFJ-713/714 2-Meter FM Intermod Filter
General Information:
The MFJ-713 HT Filter and the MFJ-714 Mobile Filter are especially designed to
eliminate squeaks, squawks, bleeps, and other strange noises caused by intermodulation
distortion. These "
signals and out-of-band traffic from pagers, public-service repeaters, aircraft, and other
powerful sources. Intermod signal are not only annoying, in many congested areas they
can render your sensitive wide-band radio useless!
The only cure for intermod is to get rid of the out-of-band signals that cause it. Your
MFJ Intermod Fighter
sections to form a razor-sharp network. This knock-out combination passes signals
falling within the two meter band, while attenuating out-of-band interference.
Attenuation of unwanted commercial FM signals approaches -50 dB in most cases, and
that's the difference between extremely strong and completely gone! When the filter is
engaged, intermod vanishes. During transmit, RF sensing automatically switches the
filter off-line.
The MFJ-713 HT version comes with BNC connectors and is self-powered from a
internal 9-volt battery. The MFJ-714 Mobile version uses standard SO-239 connectors
and runs on external 12-VDC. Both models uses state-of-the-art surface-mount
construction and special high-Q porcelain chip capacitors to ensure top performance.
Both are housed in a RF-tight case with an On/Off switch and power LED. The mobile
version uses a standard 2.1mm x 5.5 mm DC plug.
MFJ-713 Installation:
Before attempting to use the MFJ-713 on your HT, you must install a 9-volt battery. To
do this, remove the two case screws, slip the battery into its spring holder, and install the
snap-clip lead connector. Use a premium-quality Alkaline-type battery for best results.
You may then plug the MFJ-713 directly into your HT's BNC antenna connector.
Important Note: The filter's by-pass switching circuit draws power whenever the MFJ713's power switch is turned on. For longest battery life, be sure to turn the unit off when
not in use--and whenever intermod conditions do not require using the filter to copy
stations. If your 9-volt battery should run down while the unit is turned on, the MFJ-713
will automatically default to its "pass-through" mode, and no damage will result.
Important Note: A 50-mW or greater transmit signal is needed to activate the unit's
automatic by-pass switching. Do not exceed a transmitter RF output power of 50 Watts,
or damage may result. If using an external HT amplifier, install the MFJ-713
HT and amplifier.
phantom signals"
uses three high-Q bandpass sections plus two low-pass L-
are caused by unwanted mixing between ham-band
between
the
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MFJ-713/714 Instruction Manual
MFJ-714 Installation:
The MFJ-714 may be powered directly from your automotive or 13.5-VDC AC station
power source. Install a standard 2.1 mm x 5.5 mm coaxial-type DC power plug on the
supply line with (+) connected to the center and (-) connected to the barrel. A plug is
supplied with the unit, and extras may be obtained from Radio Shack or other electronic
supply houses. Use standard PL-258 coaxial connectors on the radio and antenna side of
the filter.
Important Note: Be sure to observe the
Radio
and
Antenna
markings when installing the
filter. If you reverse these connections, the filter's RF-sensing circuit will not work
properly and damage to filter components may result! Also, do not use with transceivers
where RF output power rating exceed 50-60 Watts.
The MFJ-714 will draw a small amount of power to operate the by-pass switching and RF
sensing circuits whenever the unit is switched on. Be sure to switch the unit off when not
in use. Also, the insertion attenuation of the filter is approximately 6-8 dB, and in-band
signals will be attenuated by this amount whenever it is turned on. While this will not
affect reception in most signal areas, i t may degrade reception of very weak signals
good rule-of-thumb when operating mobile is to leave the MFJ-714 off
it
.
unless you need
.
A
If power is accidentally removed from you unit while in operation, there is no danger to
your transmitter or to the filter--the MFJ-714 will default to the "pass-through" mode on
both transmit and receive.
In Case of Trouble:
Your MFJ
Intermod Fighter
Matter What
filter is protected by MFJ's one-year unconditional
guarantee. If anything goes wrong during the first year, we'll replace or
No
repair your unit at no charge. However, before contacting the factory, please check for
the symptoms listed below. These are simple difficulties you can fix yourself.
Filter fails to turn on: Check the power source. For MFJ-713, check battery
condition. For MFJ-714, check condition of power plug and power source.
Filter fails to disengage during transmit: For MFJ-713, is HT power setting on ultralow power? For MFJ-714, are
Radio
and
Antenna
connectors reversed?
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