MFJ-1798 B Grade
80-2m ground independent vertical antenna
SAVE MONEY WITH THIS B GRADE MODEL, FULL AS NEW WARRANTY
The MFJ-1798 is an 80-2m ground independent vertical antenna.
This antenna has
several unique features including an inverted radiating element, a fully elevated counterpoise,
lumped constant end loading, and linear stub decoupling. These unique features eliminate the
traditional problems encountered in ground independent multi-band vertical designs.
Established antenna theory dictates that maximum radiation occurs in the high current portion of
the antenna. While conventional antennas generally place the highest current at the bottom or
center of the radiating element, the MFJ-1798's unique design places the highest current and the
maximum radiation point at the very top of the radiating element. This feature produces the
lowest wave angle possible for a given antenna height, and elevates the radiating section away
from the lossy earth.
It is a well-documented fact that bending or folding a radiating element at a high current point
reduces antenna system efficiency. The MFJ-1798 eliminates all bending or folding of the
important high current areas by using linear decoupling stubs on frequencies above 14 MHz.
These linear decoupling stubs provide low loss operation without compromising bandwidth.
Efficient lumped constant end loading produces the highest efficiency possible on frequencies
below 14 MHz.
Counterpoises must be an appreciable fraction of a wavelength above ground if losses are to be
minimized. The MFJ-1798 design places the counterpoise at the top of the radiating element.
This provides maximum separation between the counterpoise and the lossy earth. For example, a
ground mounted MFJ-1798 has a counterpoise elevation of one half wavelength on 10 meters.
The MFJ-1798 is a multi-band vertical that operates on every amateur band between 80 and two
meters. The inverted radiating element is constructed from heavy duty 6061-T6 aluminum
tubing. This antenna performs as a full size inverted ground plane on all bands above 14 MHz,
and as an efficient end loaded vertical on 30, 40, and 80 meters.
The 12 feet diameter counterpoise is constructed by mounting four six feet long tubes on a
fiberglass insulated plate at the top of the antenna. The tubing has a wire that circles the
perimeter of the counterpoise to stabilize the support and increase the capacitance of the hat.
A 1/4 wave two meter vertical is mounted above the counterpoise.
Four linear decoupling stubs are tuned for 10, 12, 15, and 17 meters. These stubs are constructed
from 3/16" solid aluminum rod and supported by fiberglass insulators.
small adjustable "T" section near the bottom allows adjustment of the resonant frequency of
the full size radiating element on 20 meters.
A three section loading coil with capacitance hats for 30, 40, and 80 meters is mounted next to
the 20 meter "T" adjustment near the lower end of the antenna.
The base section contains the air core high power choke balun. This balun uses Teflon insulated
coaxial cable. The base section normally mounts on masts below 1-1/2" diameter, but additional
holes are provided to accept masts up to 2" diameter with user supplied clamps.
10 1500 2500 1250 2.0MHz
6 300 750 300 2.4MHz
2 200 200 200 7MHz
CHOOSING A LOCATION FOR THE ANTENNA
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.
For the best performance on receiving and transmitting, mount this antenna in a clear location at
least a few feet above or 70 feet away from buildings, towers, feedlines, utility wires, and other
antennas. While your own ingenuity and particular circumstances will determine the final
mounting method, we will pass along few rules that can not be neglected.
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.
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 component heating.
The following chart lists the power rating and the 2:1 VSWR bandwidth of this antenna:
Band Power Bandwidth
- CW SSB RTTY
- 80 1000 1500 750 35KHz
- 40 1250 1500 1000 25KHz
- 30 1500 1500 1500 370KHz
- 20 1500 2500 1500 700KHz
- 17 1500 2500 1500 680KHz
- 15 1500 2500 1500 800KHz
- 12 1500 2500 1250