Grounding Considerations; Maintenance - MFJ -1775 Instruction Manual

MFJ-1775 Rotatable Mini-Dipole
TYPICAL FINAL SPOKE LENGTHS FOR HF CW BAND OPERATION
•
40 Meters: 31-1/4" (full length) for two spokes on one loading coil only. 24-1/2" length for the
remaining six 40 meter spokes.
•
20 Meters: 12-1/4" length for all eight spokes.
•
15 meters: 12-1/4" length for all eight spokes.
• 10 meters: 10.5" length for all eight spokes.
TYPICAL 6- AND 2-METER STUB LENGTHS
•
50.150 MHz: 54 inches (flat side of aluminum mounting bracket to end of stub)
o Note: A fixed non-tunable resonance will also be seen at approximately 43 MHz, and a
tunable higher frequency resonance will be seen at approximately 52 MHz.
•
147 MHz: 13.5 inches (flat side of aluminum mounting bracket to end of stub)
o Note: A fixed non-tunable resonance may also be seen at approximately 144 MHz.

GROUNDING CONSIDERATIONS

Although this antenna is designed to operate efficiently without the requirement of an earth ground, safety
grounding must still be provided to protect equipment, property and persons from the hazards of lighting
strikes and other weather related electrical discharges. In addition, the coaxial cable feeding the antenna
should have the shield grounded to eliminate the risk of any indoor equipment failure allowing hazardous
voltages that could create a shock hazard.
Adequate protection can be accomplished by grounding the shield of the coax to a good earth ground
where it enters the building, or directly burying the cable in the earth for several feet before it enters the
building. For maximum lightning protection, the coaxial cable should be totally disconnected from the
station during threatening weather conditions.
A less effective method of protecting station equipment is to install an in-line coaxial lightning arrestor
with a heavy duty ground wire to a suitable earth ground, or a safety switching system as part of the basic
ham station equipment.

MAINTENANCE

Your antenna is constructed of heavy-duty non-corrosive materials and should withstand normal climates
for many years. The use of some type of coaxial connector moisture protection is recommended at the
balun coax connection, and also around the center-feed connections, especially in coastal areas where
salty mist is commonplace.
GE makes a pure, silicone grease called "SILICONE DIALECTRIC COMPOUND" that can be applied
SPARINGLY to the threaded area of the female connector. This compound, or even a clear silicone
heatsink compound, will prevent moisture from entering the connector through the threads and protect the
connectors from corrosion. This is the same type of sealer that commercial antenna installers and CATV
companies use with great success.
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Instruction Manual