MFJ 1798 - Page 27

MFJ-1798 Vertical Antenna Instructions
26
TUNING 17 THROUGH 2 METERS
Frequency adjustments on 17 through 2 meters are accomplished by shortening or lengthening
the various stub elements. Since the counterpoise is electrically large on these bands, and the
elements are full size, the bandwidths are fairly broad. This makes tuning fairly non-critical.
There is also very little interaction between adjacent bands or with the lower bands.
There are two methods of tuning the stubs on these bands. One method involves loosening the
nuts at the threaded end of the stub and moving the stub up or down in the counterpoise support
plate, the other would involve cutting the ends of the rods with a large wire or small bolt cutter.
While cutting the stub is more convenient, care must be exercised to avoid removing too much
material. For this reason, we suggest removing only enough material to move the antenna slightly
on the low side of the desired resonant frequency.
TUNING 2 METERS.
2 meters can be adjusted with the antenna in nearly any position, including lying down. The only
restriction is that the 2 meter element must be at least 3 feet above the ground and away from
other objects.
TUNING 6 METERS
Six meters shares a common stub with 17 meters. There is no separate six meter adjustment. If
you would like to optimize six meters for the best low angle performance, one of the four stubs
can be cut to approximately five feet in length and then trimmed for lowest SWR at the operating
frequency.
TUNING 10 THROUGH 17 METERS
All these bands are tuned by lengthening or shortening the threaded portion of the stubs, or by
trimming the stubs at the bottom. The adjustments are very coarse. If frequency is still too low
with the stub extension at minimum, the unthreaded ends of the stubs can be trimmed.
Shortening the stubs length raises the operating frequency, while extending the stub length
lowers the operating frequency.
Note: Tuning the 17 meter stub affects the 6 meter band.
Once the antenna tuning is completed and double checked, the antenna can be moved to a
permanent location. Although performance will be better if the antenna is elevated, the
performance will probably still be acceptable with heights as low as six feet 6'.
The special TOP FEEDING TECHNOLOGY (TFT) allows the major radiating portion of
the antenna to be at least 16' above ground level, even with the base at ground level.