MFJ-1792/1793 Instruction Manual Vertical Antenna
MFJ-1792/1793 Vertical Antenna
Table of Contents:
Introduction ................................................................................................................ 1
Description.................................................................................................................. 1
Bandwidth, SWR, and Power Handling ....................................................................... 2
Choosing a Location for the Antenna........................................................................... 3
Grounding................................................................................................................... 3
Maintenance................................................................................................................ 4
Tools and Time Required for Assembly .......................................................................4
MFJ-1792 Parts List.................................................................................................... 5
Assembly and Installation Procedure............................................................................ 6
Raising the Antenna..................................................................................................... 11
Tuning the Antenna..................................................................................................... 12
Technical Assistance.................................................................................................... 13
MFJ-1792/1793 Instruction Manual Vertical Antenna
MFJ-1792/1793
INSTRUCTION MANUAL
INTRODUCTION
In cases where vertical polarization and low wave angle is desired, at frequencies below 7
MHz, the antenna must a vertical. At these low frequencies, the height of a vertical half
wave dipole antenna is beyond the construction reach. A half wave on 80 meters, for
example, is approximately 133 feet high, which is beyond the doubt very difficult to make.
If the lower end of a vertical antenna is grounded, the antenna height need to be only a
quarter wave length to resonate at the same frequency as the ungrounded half-wave
antenna. The reason for this is that ground having high conductivity acts as an electrical
mirror, and the missing half of te antenna is supplied by the mirror image. The directional
characteristics of a grounded quarter wave antenna is the same as that of a half wave
antenna in free space. Thus, a grounded quarter wave vertical has a circular or omnidirectional pattern in the horizontal plane.
A grounded vertical antenna can be made much shorter than a quarter wavelength and still
be made resonant at the same frequency by loading it with inductance, capacitance, or
both. Loading the antenna can be done several different ways, but not every way yields
the same efficiency. The best efficiency is obtained by top loading the antenna.
The efficiency of a quarter wave or a shorter vertical antenna (shorter than a quarter
wave) can go over 50% if special care is taken in constructing of the ground system and
the loading method. To attain an efficiency comparable with a 1/2 wave antenna in
grounded antennas having heighths of 1/4 wavelength or less, great care must be taken to
reduce ground resistance and the resistance of any required loading inductors. MFJ 1792 /
1793 uses the best technique available to provides maximum efficiency on the 80, 40 and
20 meter bands. On 40 meters the antenna is a 33 foot, full quarter wave, large diameter
antenna. On the 20 meter band, MFJ uses decoupling stub technology for maximum
efficiency, the decoupling stub is a full quarter wave. Top loading technology, the most
efficient form of loading, is used on the 80 meter band.
DESCRIPTION
The MFJ-1792 / 1793 operates as a full quarter wave on 40 and 20 meters, and a top
loaded antenna on 80 meters. Over a good ground system the MFJ-1792 / 1793 has
excellent efficiency on 40 and 20 meters, because no loading coils are used on these bands.
Also, on 80 meters the antenna is a very efficient top loaded antenna. Top loading is the
most efficient loading method known. It is top loaded with a loading coil, wound on
fiberglass with TeflonTM coated wire, and a large diameter capacitor hat (4.5 foot). Toploading is the most efficient loading method known. When loaded on top, the distribution
of current on the antenna element ofa short quarterwave in slmost uniform. Top loading
guaranties the maximum radiation intensity as well as the best efficiency and performance.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
The radiating element on the 80 meter band is 33 feet tall, constructed with large diameter
aluminum tubing. The smallest diameter used is 1 1/8 inches. The antenna has a swivel
base to allow easy mounting and access to the top for tuning the 80 meter band. The
swivel base is constructed with heavy duty thick aluminum, and a large diameter, super
strong, solid fiberglass insulator rod. The antenna can be mounted on a short mast of 2"
maximum diameter. MFJ supplies U-Bolts for use with 1.5" maximum diameter masts,
however you can buy your own 2" diameter U-Bolts and install them in the holes provided
on the base mount. Since the antenna is 35 feet tall it requires guying. Guying anchors
and guy lines are not supplied with the antenna, however you have to se your own guy
wires. For best results, non-conductive marine type nylon cords can be used.
BANDWIDTH, SWR, AND POWER HANDLING
- The 40 meter band has a very wide bandwidth (approximately 800 KHz). The entire
band is covered at less than 1.5:1 SWR.
- The 80 meter band is top loaded with a high-Q loading coil. The SWR on this band is
very low (less than 1.4:1.0). The bandwidth is approximately 80 KHz at 2:1 SWR
measurements. The lowest SWR is ensured on this band because the antenna is matched
using a L-network at the feed point on the base of the antenna.
- The 20 meter band tunes very low SWR (less than 1.4:1.0). The bandwidth is
approximately 300 KHz. The 20 meter operating frequency is easily adjusted by
increasing or decreasing the length of the decoupling stub at the bottom of the antenna.
MFJ- 1792/1793 is capable to of handling full legal PEP power as follows:
BAND SSB CW
80 meter 1500 1000
40 meter 1500 1500
20 meter 1500 1000
SAFETY PRECAUTIONS:
1.) THIS ANTENNA IS AN ELECTRICAL CONDUCTOR
2.) ANY CONTACT BETWEEN THE ANTENNA, FEEDLINE OR
SUPPORTING STRUCTURE AND POWER LINES WILL
RESULT IN DEATH OR SERIOUS INJURY.
FOR SAFETY PLEASE:
1.) DO NOT INSTALL THIS ANTENNA WHERE THERE IS ANY
POSSIBILITY OF CONTACT WITH UTILITY LINES.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
2.) DO NOT LOCATE THE ANTENNA SUPPORT WHERE IT CAN
CONTACT POWER LINES IN THE EVENT OF MECHANICAL
FAILURE OR ACCIDENT.
3.) FOLLOW THE GUIDELINES FOR ANTENNA INSTALLATION
AS RECOMMENDED BY THE US CONSUMER PRODUCT
SAFETY COMMISSION.
CHOOSING A LOCATION FOR THE ANTENNA
The ideal antenna mounting location is an open area more than 70 feet away from other
large conducting objects or antennas. If such a location is not available, the least
obstructed location should be selected.
This antenna should be mounted on a rigid support. The mounting U-Bolts are supplied
with this antenna. The antenna accepts masts between one and 1.5 inches outside
diameter. Additional holes in the base mount of this antenna will accept mast clamps up to
2" OD. Soft or thin wall masts should not be used to mount this antenna to any
supporting structure.
The MFJ-1792 / 1793 will perform quite well in ground mounted installations with a good
ground system of either welded mesh chicken wire or 8 or more 33 foot long radials. The
antenna can be mounted a few feet above level with its ground plane hanging down until it
reaches the ground then spreads out. If the antenna is ground mounted, it MUST be
surrounded with a protective non-metallic fencing. This will increase the safety and lessen
the likelihood of damage to the antenna.
GROUNDING
Unlike some other verticals, this antenna requires an RF ground system. However, it is a
good idea to have some sort of earth connection to avoid lightning damage to station
equipment and to improve operator safety. The feedline's shield should be grounded at the
entrance point of the building before it reaches the operating position. Failure to do so
can result in lightning damage to the equipment.
Grounds should consist of a solid copper rod driven into the soil (at least 6 feet deep).
Never use woven flexible braiding for ground connections unless absolutely necessary.
Braiding has a very high resistance to both RF and lightning. Copper flashing, wide
copper foil, or large gauge solid copper wires are the proper materials for use in RF and
lightning grounding applications.
The use of an in-line coaxial lightning arrestor will only offer a minimal improvement in
lightning protection. The best method of protecting the station equipment is to disconnect
the feedline outside the building or, at the minimum, use a switch to disconnect and
ground the feedline.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
MAINTENANCE
Your antenna is constructed of heavy duty non-corrosive materials and should withstand
normal climates for many years. The use of some type of coaxial connector moisture
protection is recommended at the bottom coax connection and also around the matching
network feed point, especially in coastal areas where salty mist is commonplace.
GE makes a pure silicone grease called "SILICONE DIELECTRIC COMPOUND" that
can be applied SPARINGLY to the threaded area of the female connector. This
compound, or even a clear silicone heat sink compound, will prevent moisture from
entering the connector through the threads and protect the connector from corrosion.
THIS IS THE SAME TYPE OF SEALER THAT COMMERCIAL ANTENNA
INSTALLERS AND CATV COMPANIES USE WITH GREAT SUCCESS.
A less desirable but adequate sealer is the automobile seam sealer commonly sold as "coax
seal," a pliable black sealing compound.
When installing any coax sealer, NEVER completely cover the barrel of the coax
connector. The sealer should ONLY be placed near the junction of the threaded part of
the chassis connector and the knurled area of the male connector. This will leave the
bottom of the male connector's outer sleeve open and permit the connector to "breathe" so
it does NOT collect moisture!
WARNING: -Keep this antenna out of reach of adults, children, and
animals.
-Any contact with this antenna while transmitting will cause
severe RF burns and voltages that kill.
-Never place this antenna close to electric power lines or
utility wires.
Tools and Time Required for Assembly
The estimated assembly time for this antenna is two to three hours. An additional one
hour is required to adjust the antenna on all the bands.
The required tools are:
1/4" standard screwdriver
3/8" open end wrench ( if you purchased the 1793 )
5/16" nut driver
7/16" nut driver
7/16" open end wrench
Large wire cutters
#1 or #2 Philips screwdriver
Eye protection
Flat ground or at least 3 saw horses.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
SAFETY PRECAUTIONS!!
1.) THIS ANTENNA IS AN ELECTRICAL CONDUCTOR.
2.) ANY CONTACT BETWEEN THE ANTENNA, FEEDLINE OR
SUPPORTING STRUCTURE AND POWER LINES WILL RESULT
IN DEATH OR SERIOUS INJURY.
FOR SAFETY PLEASE:
1.) DO NOT INSTALL THIS ANTENNA WHERE THERE IS ANY
POSSIBILITY OF CONTACT WITH UTILITY LINES.
2.) DO NOT LOCATE THE ANTENNA SUPPORT WHERE IT CAN
CONTACT POWER LINES IN THE EVENT OF MECHANICAL
FAILURE OR ACCIDENT.
3.) FOLLOW THE GUIDELINES FOR ANTENNA INSTALLATION AS
RECOMMENDED BY THE US CONSUMER PRODUCT SAFETY
COMMISSION.
MFJ-1792 PARTS LIST
- One 1 1/2" x 6' 6061-T6 Aluminum tubing
- One 1 3/8" x 6' 6061-T6 Aluminum tubing
- Two 1 1/4" x 6' 6061-T6 Aluminum tubing
- One 1 1/8" x 6' 6061-T6 Aluminum tubing
- One 1 1/8" x 55" 6061-T6 Aluminum tubing
- Two 1 3/8" x 1' 6061-T6 Aluminum Couplers
- One 1 1/4" x 1' 6061-T6 Aluminum Coupler
- Three 3/8" solid rods (one 55" threaded, and two untreaded 6') for 20 meter element
- One fiberglass 80 meter loading coil assembly with 7 x 27" spokes
- One Angle Bracket to support 20 meter element
- One fiberglass 1 1/4" x 16" solid rod for base mounting
- One Aluminum base mount with matching coil on fiberglass form (attached)
- Two Aluminum guy wire mounts
- Three bags of hardware; including:
HARDWARE BAG #1
[ ] Nine Hose Clamps
[ ] Two Guy Wire Mounts and Clamps
[ ] Three U-Bolt Kit For 1 1/2" Mast
HARDWARE BAG #2
[ ] Eight 1/4-20 x 1 3/4" Bolts
[ ] One 1/4-20 x 2" Bolt
[ ] Seven 6-32 x 1/4" Pointed Screws
[ ] One 10-32 x 1 3/4" Screw
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MFJ-1792/1793 Instruction Manual Vertical Antenna
[ ] One 10-32 Nut
[ ] One 1/4" Id Spacer
[ ] Nine 1/4-20 Nuts
[ ] Nine 1/4" Split Washers
[ ] Two 6-32 Nuts
HARDWARE BAG #3 (20 METER KIT - for 1793 only)
[ ] Two 3/16" Id x 1" Aluminum Couplers
[ ] Three L-Brackets
[ ] Three 4.5" x 3/4" Fiberglass Insulators
[ ] One Triangular Support Bracket
[ ] Nine 6-32 x 1/2" Screws
[ ] Four 6-32 x1/4" Pointed Screws
[ ] Nine 6-32 Nuts
[ ] Two 10-32 Nuts
[ ] Three Hose Clamps
ASSEMBLY AND INSTALLATION PROCEDURE
IF YOU DID NOT PURCHASE OR DO NOT WISH TO INSTALL THE 20 METER
ELEMENT, SKIP SECTIONS 13 THROUGH 16, 22 AND 23.
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 especially careful while moving or installing this antenna. This antenna is bulky
enough to cause a loss of balance if handled by an inexperienced person, or if a
capacitance spoke accidentally becomes snagged on a gutter, a tree limb, or any
other object.
2. Mount the antenna in a location completely out of reach, or protect it with a non-
cunductive fence. The ends of the capacitance spokes and other parts of the antenna
can cause eye injury, serious RF burns, or both.
3. Be sure the mast is sturdy enough to support more than 20 pounds of weight and a
wind load of approximately 3 square feet.
NOTE: WEAR SAFETY GLASSES WHENEVER
WORKING ON OR NEAR THIS ANTENNA.
During assembly please refer to the figures listed in the
following steps as well as the figures on the inside front cover.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
NOTE: This antenna can be mounted on ground or roof
level mounts only!
1- Prepare a ground-level mounting mast that will permit
easy initial testing and adjustment. Set up stable supports
(table, saw horses etc.). Also a flat ground can be used.
2- Sort out parts you have unpacked into groups of similar
parts. Be sure all parts are available.
3- After examining the antenna parts, gather the tools
needed for basic assembly. At the minimum these consist
of:
- #1 Philips screwdriver for capacitance spokes screws.
- #2 Philips screwdriver for other 6-32 and 10-32 screws.
- 1/4" standard screwdriver or 5/16" nut driver for hose clamps.
- 3/8" wrench for the stub nuts.
- Two 7/16" open end wrenches or wrench and one nut
driver for U-bolts and coupling bolts.
- Large wire cutter for trimming capacitance spokes.
- Safety glasses.
FIGURE 1
4- Insert End B of Tube 2 into End B of Tube 1. Line up the holes. Bolt tubes together
with a 1/4 - 20 x 1 3/4" bolt, 1/4 - 20 nut and split washer. Place and secure a hose clamp
over the slit. See Figure 1.
5- Insert End B of Tube 3 into End A of
Tube 2. Line up holes. Bolt tubes
together with a 1/4 - 20 x 1 3/4" bolt, 1/4
- 20 nut and split washer. Place and
secure a hose clamp over the slit. See
Figure 1.
6- Slide a guy wire clamp and guy wire
mount over the end of Tube 3, and set
them on End B of Tube 3.
7- Slip End B of Coupler 2 over End A
of Tube 3. Line up holes. Bolt tube
andcoupler together with a 1/4 - 20 x 1
3/4" bolt, 1/4 - 20 nut and split washer.
Place and secure a hose clamp over the
FIGURE 2
slit. See Figure 2.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
8- Insert End B of Tube 4 into End A of Coupler 2. Line up holes.
Bolt tube and coupler together with a 1/4 - 20 x 1 3/4" bolt, 1/4 - 20
nut and split washer. Place and secure a hose clamp over the slit. See
Figure 2.
9- Insert End B of Tube 5 into End A of Tube 4. Line up holes. Bolt
tubes together with a 1/4 - 20 x 1 3/4" bolt, 1/4 - 20 nut and split
washer.
10- Slide a guy wire clamp and guy wire mount over Tube 5 and place
them above the 1/4 - 20 x 1 3/4" bolt at end B of Tube 5. Place and
secure a hose clamp over the slit. Refer to Figure 1.
11- Slip End B of Coupler 3 over End A of Tube 5. Line up holes.
Bolt tubes together with a 1/4 - 20 x 1 3/4" bolt, 1/4 - 20 nut and split
washer. Place and secure a hose clamp over the slit. See Figure 2.
12- Insert End B of Tube 6 into End A of Coupler 3. Line up holes.
Bolt tube and coupler together with a 1/4 - 20 x 1 3/4" bolt, 1/4 - 20
nut and split washer. Slide and secure a hose clamp over the slit. See
Figure 2.
NOTE: Steps 13 - 16, 22 and 23 are for 1793 assembly only !!
13- Assemble insulators to L brackets using 6-32 x 1/2" screws and
5/16" hex nuts. See Figure 4.
14- Assemble Aluminum couplers using 6-32 x 1/4" screws. See
Figure 4.
15- Next Assemble the 20 meter element parallel to the main antenna as
follows:
Couple the two 6' rods together using one of the Aluminum couplers.
Slide one insulator assembly over the top section and 2 others over
the bottom one. Couple the bottom section (the one with two insulators)
to the 55" threaded rod. See Figure 3.
FIGURE 3
FIGURE 4
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MFJ-1792/1793 Instruction Manual Vertical Antenna
16- Screw a #10 nut over the threaded rod.
Slide the threaded end of the 55" rod
through the triangular support bracket with
the angle pointing down. Thread another
#10 nut over the rod to sandwich the bracket
between the two nuts. Refer to Figures 4
and 5. (NOTE: Do not attach angle bracket
to Tube 1 yet, it will be installed later.)
17- Mount the matching network to the base
mount by inserting the 6-32 x 2 1/4" screws
into the provided holes then threading a 6-32 nut
over both of them. See Figure 6.
18- Line up End A of the fiberglass rod with the 1/4"
holes in the U-channel of the Aluminum base mount. Bolt
End A of the fiberglass rod to the U-Channel with a 1/4 20 x 1 3/4" bolt, 1/4 - 20 nut, 1/4" spacer, and a split
washer.
NOTE: Use the 1/4" spacer between the fiberglass rod
and mount wall as shown in Figure 7.
FIGURE 5
19- Insert 2 U-bolts in the base mount designated holes.
Thread 1/4 - 20 nuts and split washers over them. See
figure iside front cover.
20- Insert End B of Coupler 1 into End A of Tube 1.
Insert the solid fiberglass rod into Coupler 1. Line up
holes. Bolt tube, coupler, and rod together with a 1/4 20 x 2" bolt, 1/4 - 20 nut and split washer (Refere to
Figure 1 for an example of tube insertion).
Do not secure this bolt yet if you are planning to install
the 20 meter element !
21- Place a hose clamp over end A of Coupler
1. Do not attach the solder lug of the
feedline, as shown in Figure 6, at this time!
22- With the help of another person, lay the 20
meter element parallel to the antenna. Insert the
1/4 - 20 x 1 3/4" bolt through the 1/4" hole in
the triangular support bracket of the 20 meter
element and secure bolt. See Figure 5.
FIGURE 6
FIGURE 7
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MFJ-1792/1793 Instruction Manual Vertical Antenna
23- Attach the 20 meter element to the
antenna using hose clamps over the Lbrackets. Secure hose clamps. See
figure inside front cover and figure 3.
24- Place guy wires on guy wire
mounts. Make sure the guys are nonconductive and long enough to reach
their attaching ground position when
antenna is up. Use the formula:
C = SQRT (A2+B2) to estimate the
length of the wire. Add a few extra feet
to your calculation to be on the safe
side. See Figure 8.
FIGURE 8
NOTE: It is possible to use a single set of guy lines to secure this antenna. This set
of guy lines can be placed on top of either the hose clamp or the 1/4 - 20 x 1 3/4" bolt
of Tube 4 end B.
25- Thread six 6-32 x 1/4" screws in the capacitor hat ring on the loading coil assembly.
Do not tighten them yet. See Figure 9.
IMPORTANT: Do not use a high torque electric screwdriver to mount the
capacitance spokes. The screw heads will be shredded off if too
much torque is applied.
FIGURE 9
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MFJ-1792/1793 Instruction Manual Vertical Antenna
26- Assemble the Loading coil assembly by placing six of the 27" long spokes into the ring
assembly. Tighten the 6-32 x 1/4" screws until the spokes are snug. See Figure 9.
27- With the help of another person, move the antenna to the location of the ground pole.
Place the swivel base mount over the ground pole, while the antenna is still laying on the
ground, and tighten the U-bolts.
WARNING: Do not allow the ground pole to pass beyond the edge of the base
mount.
RAISING THE ANTENNA
WARNING: Be especially careful when moving or mounting this antenna. The
weight and length of this antenna can cause a loss of balance if
handled by an inexperienced person, or if a capacitance spoke
accidentally becomes snagged on a gutter, a tree limb,
or any other object.
28- Attach two of the guy wire sets to their ground position. Use the third set as a pulling
wire to help raise the antenna into position.
29- Insert the 10-32 x 1 3/4" screw into the hole provided on end A of Tube 6. Thread a
10-32 nut over the screw and tighten. This will help to secure the loading coil.
30- Slide a hose clamp over the top of the antenna. Insert the base of the 80 meter
loading coil into end A of Tube 6 (1 1/8" tube). Place the solder lug under the hose clamp
and secure it well. Make sure that the Loading Coil is secured in place!
WARNING: DO NOT TRY TO LIFT THE ANTENNA BY YOURSELF !!
GET HELP FROM AT LEAST ONE OTHER PERSON. SERIOUS
INJURIES ORDEATH CAN RESULT IF THIS ANTENNA FALLS
ON YOU !!
31- With the help of at least one other person. Start walking the antenna in a straight
line toward the base, while the other person pulls in the same direction with the third guy
wire set. When the antenna is completely up, the two sets of guy wires will be almost
snug. Hold the antenna base while the other person fastens the third guy wire in place.
NOTE: DO NOT SECURE GUY LINES
COMPLETELY AT THIS TIME !!
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MFJ-1792/1793 Instruction Manual Vertical Antenna
32- Secure Antenna to the base mount, by placing a U-bolt Saddle Clamp between the
fiberglass solid rod and the Aluminum wall. (see inside front cover) Line up the Saddle
Clamp with the 1/4" holes. Insert the U-Bolt through. Thread two 1/4" - 20 nuts and split
washers onto the U-bolt. Secure the U-bolt and the bottom 1/4"- 20 bolt.
33- Straighten up the antenna, and secure guy wires (not permanently). Make the
grounding connection necessary.
34- Place the solder lug of the feedline under the Coupler 1 hose clamp at the base of the
antenna and tighten the hose clamp. See Figure 6.
35- Antenna assembly is completed now, it can be tested using a transceiver on low power
or with an analyzer such as the MFJ-249, or the MFJ-259, then fine tuned before
mounting it permanently.
TUNING THE ANTENNA
Measure and record the frequency on which the lowest SWR occurs for the 80, 40 and 20
meter bands. The MFJ-1792 is tuned for lowest SWR either at the lower frequency of
each band or slightly below.
NOTE: Make sure to disconnect the connection to the matching network before lowering
the antenna to tune the 80 or 40 meter bands. Failure to do so will damage the
matching network feed wire !!!
40 Meter Band:
The MFJ-1792 generally does not require tuning on the 40 meter band. It covers
the entire 40 meter band with very low SWR. However, the location and the ground
system may cause the antenna to slightly detune. Retuning the antenna can be
accomplished by sliding Tube 5 into Tube 4 to decrease or increase the length of the
radiator, which in turn increases and decreases the frequency respectively. Use the
information below for your adjustment.
40 m: 1' of length equals approximatly 200 KHz
80 Meter Band:
80 meter bands has narrower bandwidths. It should be tuned to the most desired section
of the band by shortening one or more spokes in the capacitance hat, from the inner side
according to the information given below.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
80 m: 1" trimmed off a spoke equals approximately 10 KHz
WARNING: Shortening the spokes from the looped end will affect the
performance of the antenna and degrade its power handling capabilities.
If the resonant frequency on 80 meter is lower than your equipment can detect, take
one spoke off the capacitance hat to raise the resonant frequency. Measure the
resonant frequency again. Estimate the approximate resonant frequency as if the
spoke was in place using the information above.
Example: The antenna measured 3.47 MHz, the desired frequency is 3.95 MHz (less .05
MHz) for a difference of .43 MHz or 430 KHz. This would require the trimming of 43"
from one spoke. Instead, cut 4.3 inches from all six spokes and measure the new
resonant frequency. Assume the new resonant frequency is 3.82 MHz. A single spoke
can now be trimmed 8" to adjust the antenna to resonance.
20 Meter Band
The 20 meter band is tuned by lengthening or shortening the threaded portion of the stubs.
This adjustment is very coarse. If frequency is too low with the stub element extension at
minimum, the unthreaded end of the stub can be trimmed.
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 601-323-0549 or the MFJ Factory at
601-323-5869. 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 (FAX) to 601-323-6551; 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.
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MFJ-1792/1793 Instruction Manual Vertical Antenna
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