MFJ-962E Instruction Manual
9
ground is not available, RF will usually find it's way back into the power line (RFI), transmitter
audio circuits (RF feedback), or the operator (RF burns).
Water pipes and ground rods provide good dc and ac safety grounds, but they are often
inadequate for RF grounding because they are single conductors. Ground rods by themselves are
almost useless for dependable RF grounding.
RF grounds work much better when "spread out" over a large area, especially when they employ
multiple connections directly to the equipment ground point. Water pipes, heating ducts, and
fences may work (especially if they are connected together with multiple wires), but the best RF
grounds are radial systems or multi-wire counterpoises. Radials and counterpoises provide large,
low resistance surfaces for RF energy.
RF and lightning travels on the surface of conductors. Braided or woven conductors have high
surface resistance to lightning and RF. Ground leads for RF and lightning should have wide
smooth surfaces. Avoid the use of woven or braided conductors in RF and lightning grounds
unless the lead needs to be flexible.
CAUTION: For operator safety, a good outside earth ground or water pipe ground
should always be installed and connected to the case of the MFJ-
962E. Make certain the safety ground also connects to the transmitter
and other station accessories. A wing nut post marked GROUND is
provided for ground connection(s).
Antenna System Hints
For operator safety, a good outside earth ground or water pipe ground should always be installed
and connected to the case of the MFJ-962E. Make certain the safety ground also connects to the
transmitter and other station accessories. A wing nut post marked GROUND is provided for
ground connection(s).
Location
For the best performance, an end-fed longwire wire antenna should be at least one quarter-
wavelength long at the operating frequency. Horizontal dipole antennas should be at least a half-
wavelength long and located as high and clear as possible. While good RF grounds help the
signal in almost any transmitting installation, it is extremely important to have good RF grounds
with long wire or other Marconi style antennas.
Matching Problems
Most matching problems occur when the antenna system presents an extremely high impedance
to the tuner. When the antenna impedance is much lower than the feedline impedance, an odd
quarter-wavelength feedline converts the low antenna impedance to a very high impedance at the
tuner. A similar problem occurs if the antenna has an extremely high impedance and the
transmission line is a multiple of a half-wavelength. The half-wavelength line repeats the very
high antenna impedance at the tuner. Incorrect feedline and antenna lengths can make an
otherwise perfect antenna system very difficult or impossible to tune.
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