MFJ 1779B Manual de usuario

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1

MFJ-1779B 80-40 Meter Dipole Antenna

INTRODUCTION

The MFJ-1779B one-half wavelength, single-band, dipole is a center-fed

antenna that can be tuned for operation on any frequency between 80 meters and

40 meters. (3.5-7.3 MHz) The antenna will handle full legal limit power. The

dipole is made using #14 copper wire, a durable center insulator enclosing an

SO-239 connector, and terminated with ceramic insulators. The ends of the

dipole are adjustable and should be cut to the desired length of operation. A

suitable length of wire comes with each antenna to achieve resonance at the low

end of each band.

WARNING: Never place the antenna in a location where contact

with power lines is possible. Death, serious injury, and

damage can occur.

CHOOSING A LOCATION

Choose a location clear from obstructions such as other antennas, buildings, and

power lines. Never place the antenna near power lines. Try to keep the

antenna away from metal buildings and other such structures, which will affect

the performance of the antenna. The optimum height of the antenna is 1/2

wavelength of the operating frequency above ground. This can be calculated by

dividing 468/ (frequency in MHz). Optimum antenna height will vary due to

different ground conditions and nearby objects.

The MFJ-1779B can be suspended from many different supports. The most

common being two trees. The antenna should be suspended using a weather

resistant, non-metallic, nylon rope. Always leave a few extra inches in the

support rope to allow for wind movement of the antenna. This is especially

important when trees are used for supports. If the rope is to tight the antenna

could be damaged.

The antenna can be installed in three different ways:

HORIZONTAL ANTENNA

This installation requires two supports with a minimum distance of the overall

length of the antenna. It is a good idea to also provide a support for the center

insulator of the antenna, which will relieve the stress on the center insulator.

MFJ-1779B ½ Wavelength Dipole Antenna Instruction Manual

2

INVERTED ANTENNA

This installation only requires one tall and two short supports. The center

insulator of the antenna should be the highest point of the antenna.

SLOPED ANTENNA

This installation requires one tall and one short support.

TOOLS AND ACCESSORIES NEEDED FOR ASSEMBLY

• SWR Analyzer (MFJ-259) OR SWR Meter And HF Radio

• Weather Resistant Non-Metallic Nylon Rope

• Wire Cutters (large enough to cut #14 wire)

• Coax

FREQUENCY ADJUSTMENT

The MFJ-1779B dipole antenna can be tuned for use on any amateur band from

3.5 to 7.3 MHz. Refer to the tuning chart below for approximate lengths.

ALWAYS HANG THE ANTENNA IN THE DESIRED OPERATING

LOCATION FOR TUNING. CHECK THE RESONANCE POINT OF THE

ANTENNA BEFORE ANY WIRE IS REMOVED.

1. Remove the antenna and parts from the packaging.

2. Decide on the center frequency of operation. The table below has

approximate lengths for each band. Column A gives the approximate lengths

of the entire antenna. Column B gives the length of each side of the dipole.

The lengths can also be determined by using the following formula. This

formula will give the length of the ½ wavelength dipole. This must be

divided by two in order to get the length of each side of the dipole.

468/frequency (MHz)=1/2 wavelength

3. Attach a coax to the antenna and place it in the desired location. Be sure to

leave enough rope so the antenna can be lowered for adjustment. Raise the

antenna into is normal operating position using a strong nylon rope. Check

Band A B

80 134 ft 67 ft

40 67 ft 34 ft

30 47 ft 24 ft

MFJ-1779B ½ Wavelength Dipole Antenna Instruction Manual

3

the resonance point. If the resonance point is below the desired frequency the

antenna will need to be shortened.

4. Adjust the antenna according to your calculations or the chart above. Equal

lengths should be removed from each side of the antenna.

5. Install the insulators on each end of the antenna temporarily by placing the

wire through one end hole of the insulator and winding it back around the

dipole wire. Extra wire can be wrapped back around the dipole temporarily

while testing. Always check the resonance point each time wire is removed.

6. When the desired frequency is reached make 5-7 wraps of the wire on the

ends of the dipole for permanent installation. Then raise the antenna until the

desired height is reached and secure it in place by connecting the nylon rope

to a stable support.

TECHNICAL ASSISTANCE

If you have any problem with this unit first check the appropriate section of this

manual. If the manual does not reference your problem or your problem is not

solved by reading the manual you may call MFJ Technical Service at 662-323-

0549 or the MFJ Factory at 662-323-5869. You will be best helped if you have

your unit, manual and all information on your station handy so you can answer

any questions the technicians may ask.

You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial

Park Road, Starkville, MS 39759; by Facsimile to 662-323-6551; or by email to

techinfo@mfjenterprises.com. Send a complete description of your problem, an

explanation of exactly how you are using your unit, and a complete description

of your station.