MFJ-948 Versa Tuner II
7
Grounding Hints
To minimize RFI, single wire feedlines (such as used with Windom or longwire antennas)
should be kept away from other wiring. Radiation will be minimized if the single wire
feeder runs parallel and reasonably close to the wire that connects the tuner to the outdoor
ground. The antenna feed wire should be adequately insulated to prevent arcing or
accidental contact.
For safety, please use both dc and RF grounds. It is particularly important to have a good
RF ground while using a single wire feeder. When using a single wire feeder, the tuner
needs something to "push" against in order to force current into a single wire feedline. If a
good RF 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. RF grounds work much
better when "spread out" over a large area with multiple connections directly to the
equipment ground point. Water pipes, heating ducts, and fences may work (especially if
they are all connected together with jumper wires), but the best RF grounds are radial
systems or multi-wire counterpoises that provide large low resistance surfaces for RF
energy. Ground rods by themselves are almost useless for dependable RF grounding.
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.
Antenna Hints
WARNING: For operator safety a good outside earth ground or water pipe ground
should ALWAYS be installed and connected to the case of the MFJ-948.
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 antennas should be at least a half
wave long and high and clear of surrounding objects. 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 antennas.
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