Revised 14 June 2003
E-4
Antenna Settings for 2D-40A Mounted at 70 feet
(one half wavelength)
Frequency
(MHz)
Delta
(inches)
Tip Length
(inches)
6.962
0
50.5
7.030
-5
45.5
7.099
-10
40.5
7.170
-15
35.5
7.241
-20
30.5
7.313
-25
25.5
Figure 2-E
Tip Lengths vs Frequency (70 feet)
If the antenna is to be installed at this recommended minimum height of approximately
1/2 wavelength, the sliding shorts used to adjust tuning and matching for the array should
be preset as follows:
The
tuning
(rear) shorting bar should be set to a distance of 22 inches back from the
element end of the parallel line on which the shorting bar slides. Note that this distance
is to the center of the shorting bar and does not include the length of the straps that
connect the parallel tuning line to the element.
The
matching
(front) shorting bar should be set to a distance of 41.5 inches back from
the element end of the parallel line on which the shorting bar slides. Note that this
distance is to the center of the shorting bar and does not include the length of the straps
that connect the parallel tuning line to the element.
All of the above settings apply only to an antenna which has fixed element half-lengths
(center of boom to end of element
without
the tip section installed
) of 358.5 inches for
the front element and 386 inches for the rear element. Some prototype and early
production antennas were produced with element dimensions that differ from those
shown above. If your antenna's element half-lengths
not including the adjustable tip
section
differ from these values, please consult the factory.
We recommend that you use the element tip length settings shown in figure 2-E and the
hairpin settings shown above as a starting point. Once the antenna is installed, you
should find that when set to the factory recommended settings the array SWR
approaches 1 to 1 at some frequency very near the one for which you set the element
length. Since the performance of the array doesn't change significantly over the entire
2:1 SWR range (and somewhat beyond 2:1 on the high frequency side), the exact
location of the minimum point may not cause you to wish to take the effort move it.
