Galaxy DX 44V Manuel du propriétaire - Page 4

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IGNITION NOISE INTERFERENCE

Use of a mobile receiver at low signal levels is normally limited by the

presence of electrical noise. The primary source of noise in automobile installations

is from the generator and ignition system in the vehicle. Under most operating

conditions, when signal level is adequate, the background noise does not present a

serious problem. Also, when extremely low level signals are being received, the

transceiver may be operated with vehicle engine turned off. The unit requires very

little current and therefore will not significantly discharge the vehicle battery.

Even though the transceiver has ANL and NB controls, in same installations

ignition interference may be high enough to make good communications

impossible. The electrical noise may come from several sources. Many possibilities

exist and variations between vehicles require different solutions to reduce the noise.

ANTENNA

A vertically polarized, quarter-wavelength whip antenna provides the most

reliable operation and greatest range. Shorter, loaded-type whip antennas are more

attractive, compact and adequate for applications where the maximum possible

distance is not required. Also, the loaded whips do not present the problems of

height imposed by a full quarter-wavelength whip.

Mobile whip antennas utilize the metal body of the vehicle as a ground plane.

When mounted at a corner of the vehicle they are slightly directional, in the

direction of the body of the vehicle. For all practical purpose, however, the

radiation pattern is nondirectional. The slight directional characteristic will be

observed only at extreme distance. A standard antenna connector (type SO239) is

provided on the transceiver for easy connection to a standard PL 259 cable

termination.

If the transceiver is not mounted on a metal surface, it is necessary to run a

separate ground wire from the unit to a good metal electrical ground in the vehicle.

When installed in a boat, the transceiver will not operate at maximum efficiency

without a ground plate, unless the vessel has a steel hull.

Before installing the transceiver in a boat, consult your dealer for information

regarding an adequate grounding system and prevention of electrolysis between

fittings in the hull and water.

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TUNNING THE ANTENNA FOR OPTIMUM SWR

Since there is such a wide variety of base and mobile antennas, this

section will strictly concern itself to the various types of mobile adjustable

antennas. Because the antenna length is directly related to the channel frequency, it

must be tuned to resonate optimally all 40 channels of the transceiver. Channel 1

requires a longer antenna than Channel 40 because it is lower in frequency. Due to

the various methods of adjusting antennas for proper SWR we have chosen what

we think is the optimum method:

A. Antennas with adjustment screws (set screws)

1. Start with the antenna extended and tightens the set screw lightly enough so

that the antenna can be lightly tapped with your finger for easy adjustment.

2. Set your transceiver to Channel 21. @ Low band D or Hi band A. Press the

PTT (push-to-talk) switch, and tap the antenna (making it shorter). The SWR

meter will show a lower reading each time the antenna is tapped. By

continuing to shorten the antenna you will notice the SWR reading will reach a

low print and then start riding again. This means that you have passed the

optimum point for Channel 21. Extend the antenna a short distance and again

follow the procedure above.

When the lowest point has been reached, switch to Channel 1 @ Low band A

or Hi band E and then to Channel 40 @ Low band D or Hi band H and

compare SWR readings. They should be almost equal.

B. Antennas which must be cut to proper length.

1. Follow the same procedure as above, but adjust the length by cutting in 1/8"

increments until a good match is obtained.

2. Be very careful not to cut too much at one time, as one it is cut, it can no

longer be lengthed.

3. The whip is easily cut by filing a notch all the way around and breaking the

piece off with pliers.

THE PROPER SETTING IS ACHIEVED WHEN THE SWR IS

1.5 OR BELOW, AND WHEN IT HAS THE SAME READING

FOR CHANNELS LOW BAND A1 AND HI BAND D40.

If you are having difficulties in adjusting your antenna, check the following:

A. All doors must be closed when adjusting the antenna.

B. Make sure the antenna base is grounded.

C. Check your coaxial cable routing (it may be pinched when routed into the

car).

NOTE

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