MFJ MFJ-1795 User Manual

MFJ-1795 Vertical Antenna Instructions

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MFJ-1795 Vertical Antenna

INTRODUCTION

The MFJ-1795 HF antenna was designed to provide portable or permanent operation from
restricted locations. When combined with the MFJ Ground-Coupled™ Portable Antenna Base or
other suitable grounding system, such as radial system, the result is a small vertical antenna
under 10 feet in height.

The reduction in size is accomplished by adding separate loading coils and capacitance hats for
each band at the top of the antenna. 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 SSB PEP on 40, 20, 15 and 10 meters.

The power rating of this antenna varies from band to band. The PEP ratings are primarily
determined by the voltage breakdown of the components, while the CW ratings are generally
determined by the components heating.

The following chart lists the power rating and the 2:1 VSWR bandwidth of this antenna:

Band Power Bandwidth

CW SSB RTTY

40m 700 1500 500 100KHz
20m 1250 1500 750 400KHz
15m 1250 1500 1000 1800KHz
10m 1250 1500 750 1200KHz

The weight and wind load of this antenna are 10 pounds and approximately two square feet
respectively.

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, feed-lines, utility wires, and other
antennas. While your own ingenuity and particular circumstances will determine the final
mounting method, we will pass along a few ideas for both permanent and portable installation.

MFJ-1795 Vertical Antenna Instructions

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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.

•

Never place this antenna in a location that will permit people to encounter the loading

spokes or any other part of the antenna.

•

Never place this antenna where a mechanical failure might allow the antenna to contact

power lines or other utility wires.

•

Always ground the feed-line at the point where it enters a building to a good earth ground

for lightning protection.

•

Follow the guidelines for antenna installations as recommended by the US consumer

product safety commission.

ANTENNA HEIGHT

The height of the radiating element is adjustable from 5 to 8 feet. Maximum radiation will be
obtained by setting the height of the radiating element at 8 feet. Some installations may require
the antenna height to be reduced. An example may be the installation of the antenna inside a
backyard fence for concealment. Height adjustment will be discussed in the assembly section of
this manual.

INSTALLATION

The MFJ-1795 was designed as a low profile, portable antenna. When combined with the MFJ
Ground-Coupled™ Portable Antenna Base the antenna will provide permanent or portable
communications. This is an ideal antenna for restricted locations. However, the antenna
installation MUST be protected with non-metallic fencing to provide personal safety and to
prevent antenna damage. The antenna can be installed using the supplied mounting bracket and
a suitable ground radial system.

IMPORTANT: A suitable ground plane must be installed with this antenna.

PORTABLE SETUP

The antenna may be disassembled to the extent necessary for transporting to a temporary
location. Before the antenna is disassembled, some type of marks should be placed on the mast
of the antenna to ensure it will be the same height as before. Some retuning may be required

after moving the antenna.

MFJ-1795 Vertical Antenna Instructions

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WARNING: 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 1 hour. Antenna assembly requires the following
hand tools:

[ ] soldering iron and solder
[ ] 5/16" nut driver (or 1/4" flathead screwdriver)
[ ] 7/16" open end wrench
[ ] large wire cutters
[ ] small pliers
[ ] #1 phillips screwdriver
[ ] #2 phillips screwdriver
[ ] suitable eye protection

In addition, you will need two stable supports at least 30" tall (i.e. saw horses or trash cans) and a
short (6 to 8 feet) temporary mast (1 to 1-1/2 inches outside diameter) for temporary mounting
during tuning.

MFJ-1795 PARTS LIST

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

[ ] 3 bundles of wire capacitance spokes 12 short, 4 medium, (and 4 spare long spokes)
[ ] 5' radiator 1 1/8"
[ ] 30”x 1” radiator
[ ] 9”x 1 1/8” radiator
[ ] loading coil assembly
[ ] base mounting bracket
[ ] hollow fiberglass rod insulator
[ ] One Hardware Bag containing

[ ] 4 1.5” hose clamps
[ ] bag of short 6-32 stainless screws
[ ] 4 U-bolts with hardware
[ ] two plastic tie wraps
[ ] 2 solder lugs

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

MFJ-1795 Vertical Antenna Instructions

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[ ] Quality low-loss 50-Ohm coax with a PL-259 to go from the antenna to the transmitter.
[ ] Either a SWR meter or Analyzer (MFJ-259, 269)

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 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 become entangled in obstructions.

2. Mount the antenna in a way 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 a mast, if used, is sturdy enough to support the weight and the wind load.

ASSEMBLY AND INSTALLATION PROCEDURE

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

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

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 on the lug.

STEP-BY-STEP PROCEDURE

[ ] 1. Prepare a temporary work surface, such as a table, two saw horses, or trash cans, to be

used while installing the parts onto the antenna.

[ ] 2. 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
[ ] 1/4" flathead screwdriver or a 5/16" nut driver for hose clamps.

MFJ-1795 Vertical Antenna Instructions

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[ ] Two 7/16" open end wrenches or one wrench and one nut driver for the U-bolts.
[ ] Heavy Wire cutters for trimming capacitance spokes.
[ ] Safety glasses.

[ ] 4. Decide on the approximate height of the antenna. Maximum height will be just under 10

feet while minimum will be 6 1/2 feet.

[ ] 5. The 6 1/2 foot level can be reached by using the 5’ radiator. If this is the desired height

steps 6-8 may be skipped. Heights above this level will be reached using the additional
pieces of tubing.

[ ] 6. Now take the 1.0” x 30” piece of aluminum and place at a minimum 2 inches into the

long aluminum element (5’ x 1 1/8”). The end of the long (5’) piece used should be the
one without the hole drilled in it. See Figure 1.

[ ] 7. A hose clamp should be placed around the 1 1/8” pipe to secure it in place. Tighten it with

the 5/16” nut driver.

[ ] 8. A minimum of 2 inches of the 9” x 1 1/8” pipe should be placed onto the 1.0” x 30” piece

of aluminum and secured with a hose clamp.

Figure 1

NOTE: The length of tubing placed inside 1 1/8” tubing will determine the overall height of

the antenna.

[ ] 9. Now the hollow fiberglass insulator should be placed approximately 3 1/2” into the 60” x

1 1/8” aluminum tubing. See Figure 2.

Fiberglass Insulator

Solder Lug

60 x 1 1/8 Mast Pipe

Antenna Feed Point

Hose Clamp

Figure 2