MFJ-1798 Vertical Antenna Instructions
22
2.) If you suspect the resonant frequency is lower than your
equipment can detect
, for example below 3.5 MHz, take one 80
meter spoke entirely off the antenna. Make another attempt to
measure the resonant frequency. If you still can not find the
resonant frequency, check another band. If none of these tests
produce a good SWR on any frequency, substitute a 50 ohm load for
the antenna to test the feedline. If the SWR checks good, you
will have to double check the antenna assembly for shorts or
opens at the feedpoint.
3.) If the antenna operates normally higher in the band after
one spoke is removed,
install all the spokes and trim one spoke
in one inch steps until you find the resonant frequency is within
the range of your equipment.
4.) Once you find the resonant frequency,
the correct length of
spoke length change to operate on the desired frequency change
can be determined. Use the chart on the following page. When
adjusting 80, 40, and 30 meters, adjust the antenna in order from
the lowest band to the highest band.
CAUTION: Never trim the outer (rounded) end of the spokes. The
sharp end that remains can be a safety hazard and the
power handling of the antenna will be greatly reduced on
some bands.
5.) The entire antenna must be accessible during initial tuning
and testing.
Any repair or adjustment of the antenna after it is
installed on a tall support will be both difficult and time
consuming.
PLEASE READ THE FOLLOWING CAREFULLY BEFORE
TUNING THE ANTENNA!
It is best to install the antenna on a short temporary mast or
pipe located in a reasonably clear location for tuning. The
simplest way to adjust the antenna is by mounting the antenna on
a pipe that can be tilted over. This can be accomplished by
mounting the antenna on a separate pipe from the temporary mast
and using rope or long bolts to secure them.
The 20, 30, 40, and 80 meter adjustments generally do NOT affect
the higher bands, so the 17 meter and higher frequency
adjustments can be made with the loading coil and 20 meter
adjustments removed. The loading adjustments at the bottom can be
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