MFJ MFJ-1796 User Manual

MFJ-1796 Vertical Antenna Instructions

MFJ-1796 Vertical Antenna

INTRODUCTION

The basic 40 meter quarter wave vertical antenna is 33' tall and requires a reasonably good ground or counterpoise system to function properly. The usual way to eliminate the requirement for a complicated and space consuming ground system is to center feed a 1/2 wave (in this example a 66' tall) antenna.

MFJ solved these problems by combining efficient end loading with a balanced center feedpoint design. The result is a physically small vertical antenna that gives good performance and does not require any type of RF ground system.

The reduction in size is accomplished by adding separate loading coils and capacitance hats at each end of the antenna for the HF bands. The efficient end loading coils are wound on fiberglass forms. The high quality materials and construction of the HF loading system allows a maximum power rating of 1500 watts on 40, 20, 15 and 10 meters. The continuous CW power ratings are 500 watts on 40 meters, 750 watts on 20 or 10 meters and 1000 watts on 15 meters.

The six and two meter amateur bands are covered with the addition of four quarter wave decoupling stubs. The power rating of the antenna is 750 watts on six meters and 300 watts on two meters.

WARNING: Improper installation and assembly can be hazardous! Read these instructions thoroughly before attempting to assemble, install or operate this product! High power transmitting devices produce voltages that can cause severe burns or other injuries.

CHOOSING A LOCATION FOR THE ANTENNA

The best performance on receiving and transmitting will be obtained by mounting the antenna in a clear location above or away from buildings, towers, feedlines, utility wires, and other antennas. While your own ingenuity and particular circumstances will determine the final mounting method, we'll pass along a few ideas for both permanent installation and portable operation.

Never mount this antenna in a location that will permit unsuspecting people to come in contact with the loading spokes or any other part of the antenna. Never mount this antenna where a mechanical failure might allow the antenna to contact power lines or other utility wires. Always ground the feedline at the point where it enters a building to a good earth ground for lightning protection.

WARNING Always mount this antenna so that it is out of the reach of adults as well as children. The capacitance elements can cause injury and or severe RF burns.

MFJ-1796 Vertical Antenna Instructions

Permanent Installation

The ideal installation is a rigid pole or roof mount that puts the antenna completely in the clear. If the ideal installation is not possible, choose the best compromise. TV mast, heavy-duty rigid electrical conduit, or steel water pipe are suitable mast materials. This antenna will mount on masts between 1 and 1-1/2" OD. The use of soft or thin wall masts is not recommended

The MFJ-1796 will perform quite well even at ground level, which means the lower capacitance hat should be at least 5 ft above ground level on a short rigid mast. However, the antenna installation MUST be protected (with non-metallic fencing) to provide personal safety and to prevent damage to the antenna itself.

Portable Operation

This antenna may be disassembled to the extent necessary for transporting to a temporary location. If possible, only remove the two HF loading coil assemblies. Leave the two main elements with the 2 and 6 meter stub assemblies intact. Some retuning may be required after moving the antenna.

Even for temporary or portable operation, do not be casual about selecting a suitable mast. If the antenna falls it will be damaged and may cause serious injury. Whatever type of installation you choose, remember that the antenna should be installed where it can never be contacted by people or animals.

TOOLS AND TIME REQUIRED FOR ASSEMBLY

The estimated assembly time for this antenna is two hours. Antenna assembly requires the following hand tools:

1/4" nut driver 3/8" open end wrench 5/16" nut driver (or 1/4" blade standard screwdriver) 7/16" nut driver 7/16" open end wrench Large wire cutters #1 phillips screwdriver at least 6" long or longer #2 phillips screwdriver suitable eye protection

In addition, you will need two stable supports at least 30" tall (such as saw horses or trash cans) and a short (6-8') temporary mast (1 to 1-1/2" OD) for temporary mounting during tuning.

MFJ-1796 PARTS LIST

MFJ-1796 Vertical Antenna Instructions

As you unpack your antenna you should find the parts in the following list.

[ ] 2 Fiberglass Coil Assemblies [ ] two bundles of wire capacitance spokes 28 short, 12 medium, (and 4 spare long spokes) [ ] one bag of clamps 10 hose clamps and 2 saddle bolts [ ] 5' upper radiator, 6061-T6 AL tubing, 1 1/8" OD with the 6 and 2 meter stubs inside [ ] 5' lower radiator, 6061-T6 AL tubing, 1 1/8" OD (this tube has two holes through it) [ ] one bag of short 6-32 stainless screws (you will only use 40, the rest are extra) [ ] 4 small "L" brackets with holes one end [ ] 4 long "U" channel "L" brackets [ ] 4 flat fiberglass insulators [ ] 2 hollow white nylon insulators [ ] 1 solid rod fiberglass center insulator [ ] 5 split ring 1/4" washers [ ] 5 1/4" dia. 7/16" head bolts [ ] 5 1/4-20 x 7/16" nuts [ ] 20 6-32 x 1/2" stainless screws [ ] 20 6-32 x 1/4" nuts [ ] 8 10-32 x 3/8 nuts

For installation you will need some items not supplied with the antenna installation kit.

[ ] A 6'-8' rigid mast or other mounting pipe between 1" and 1.5" outside diameter. (suitable

materials include TV mast sections, galvanized iron pipe, or heavy duty rigid conduit.) [ ] Quality low-loss 50-Ohm coax with a PL-259 from antenna to transmitter. [ ] Either a SWR meter or Analyzer (MFJ-207 or MFJ-249)

SAFETY PRECAUTIONS:

WARNING! You can be killed if the antenna, feedline, or the equipment used to install the

antenna accidentally contacts any utility lines. Never install an antenna near power lines!

1. Be careful while climbing and carrying the antenna. It is heavy enough to cause you to lose your

balance if it is handled too casually or if the capacitance spokes are snagged on a gutter, ladder,

tree limbs and so forth.

2. Mount the antenna high enough so that it is out of reach. The ends of the capacitance spokes can

cause eye injury, serious RF burns or both.

3. Make sure that the mast is sturdy enough to support the 15 pounds weight and the wind load of

approximately 2 square feet.

ASSEMBLY and INSTALLATION PROCEDURE

MFJ-1796 Vertical Antenna Instructions

During assembly of this antenna refer to the figures in this manual and the picture on Page 1.

The assembly instructions tell you how to first install the balun and then connect the upper and

lower elements. Then the 2 and 6 meter stub elements are installed. Last the loading coil

assemblies are assembled and installed on the upper and lower elements.

If you do not wish to install the 6 and 2 meter stubs operation on the other bands will not be

affected. Skip steps 4, do not install the hose clamps in step 10 and skip steps 13-18.

After the antenna is assembled it is checked and adjusted for resonant frequency and SWR. It

can then be mounted on a tower or rooftop and given final adjustments.

NOTE: Wear safety glasses whenever working near or on this antenna.

Warning: Do not tighten the screws that connect the loading coil terminal lugs to the

capacitance hats or you will BREAK the fiberglass form. If the terminal lugs loosen tighten the NUT down on the lug.

Step-By-Step Procedure

[ ] 1. Prepare a temporary ground-level mounting mast that will permit easy initial testing and

adjustment. Set up saw horses or any other stable support (plastic trash cans or folding tables, etc.) near the mast.

[ ] 2a. Sort out the parts you have unpacked into groups of similar parts. Be sure all the parts are

available.

[ ] 3. After examining the antenna parts, gather the tools needed for basic assembly. At the

minimum these consist of:

[ ] #1 Long Phillips screwdriver for capacitance spoke screws [ ] #2 Phillips screwdriver for other 6-32 screws [ ] 1/4" standard screwdriver or a 5/16" nut driver for hose clamps. [ ] 3/8" wrench for 6 and 2 meter stub nuts [ ] Two 7/16" open end wrenches or one wrench and one nut driver for "U" BOLTS and

center insulator bolts.

[ ] Wire cutters for trimming capacitance spokes. [ ] Safety glasses.

IMPORTANT: Do not use a high torque electric screwdriver to mount the capacitance

spokes. The screw heads will be sheared off if too much torque is applied.

MFJ-1796 Vertical Antenna Instructions

[ ] 4. Assemble the four small "L" brackets to the 4 long fiberglass insulators with the 6-32 x

1/2" screws and the 6-32 x 5/16" nuts as shown in Figure 1.

[ ] 5. Bolt the top balun hole loosely to the top hole in the base mounting assembly with a 1/4-

20 x 7/16" nut and the 1/4" x 7/16" head bolts. Use the hollow white nylon spacers to separate the balun from the mounting bracket. Finger tighten only. See Figure 2.

[ ] 6. Bolt the bottom balun hole to the bottom hole in the base mounting assembly as in Step 5.

[ ] 7. Tighten the balun bolts with a 7/16" wrench.

[ ] 8. Bolt the coax connector assembly to the base mounting assembly with four 6-32 x 5/8"

screws and 6-32 nuts. See Figure 2.

[ ] 9. Slide the bottom radiator (the one with two sets of holes) over the fiberglass rod with the

holes that are 2" from the end toward the base mounting bracket. Slide a hose clamp to the bottom of the element. The radiator should butt against the insulating plastic of the base mounting bracket. Install a 1/4 x 7/16" bolt through the element and fiberglass rod and tighten with a lock washer and 1/4 x 7/16" nut.

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