MFJ -998 Manuel d'instructions télécharger pdf (Page 8)

MFJ-1625 Instruction Manual Window/Balcony Mount Antenna

Grounding Hints

To minimize RFI, antennas should be kept away from other wiring as much as possible. Also,

the antenna should be adequately insulated to prevent arcing or accidental contact if placed near

other objects.

For safety, it is always best to use both dc and RF grounds. A DC ground may not be practical in

some portable locations, however.

It is always important to have a good RF ground, provided by the counterpoise, when using any

whip or long-wire antenna. This is because the MFJ-1625 tuner needs something to "push"

against in order to force current into the antenna. If a good RF ground is not available, RF will

usually find its way back into the power line (RFI), transmitter audio circuits (RF feedback), or

the operator (RF burns).

Water pipes provide good dc and ac safety grounds, but they are often inadequate for RF

grounding because they are long single conductors. RF grounds require large "spread out"

surfaces with direct multiple connections to the equipment ground point. Water pipes, heating

ducts, or multiple ground rods may work (especially if they are all connected together with

jumper wires), but the best RF grounds are radial systems or multi-wire counterpoises.

Antenna Hints

WARNING:

For operator safety, a good earth ground should be installed and connected

to the case of the MFJ-1625. Make certain the safety ground connects to

the same terminal that connects to the transmitter and other station

accessories. A binding post labeled "COUNTERPOISE" is provided for

counterpoise or other RF ground connection(s). This post will not provide a

safety ground.

Matching Problems

Most matching problems occur when the antenna system presents extremely high impedance to

the tuner. This occurs when the antenna is approximately a half-wavelength long at the

frequency at which you are trying to tune.

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MFJ -998 Manuel d'instructions Page 8