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When the radial field is set up for the four vertical antennas, copper strap or heavy solid buss wire
should be used to provide cross bonding of the radials that meet each other. See
Figure 6
.
Figure 6
Tuning the Vertical Antennas for the Four Square Array
Impedance measurements are to be taken with only the one antenna installed, using an analyzer
which displays complex impedance.
Tune the first antenna to resonance targeting 30-40Ω R+/- j0. This is the impedance you would
expect to find at the feedpoint of a ground-mounted quarter-wave vertical with a very good radial
system, as described in this manual.
Set the resonance to the low edge of your desired operating range. This is because array
performance peaks approximately four percent higher in frequency than the low resonant point of
each individual element.
Example:
To obtain minimum dump power for 3.650 MHz, each vertical
is tuned for resonance at 3.51 MHz.
Measure the physical dimensions of this antenna. Physically build each of the three remaining
vertical antennas to the same resonant frequency at the same target impedance using the physical
dimensions of the first antenna.
Erect all four vertical antennas in preparation for connection to the system phasing unit.
Measurements of the impedances at the feedpoints of the antennas after they have been erected will
not yield useful information.
If you measure antenna SWR through a transmission line more than a few inches long, measure it
through exactly 1/2 electrical wavelength of low-loss cable. This could be two of the 1/4 electrical
wavelength 75Ω feedlines connected in series, or a single 50Ω cable that is exactly 1/2 electrical
wavelength long. SWR readings are is not a reliable method for adjusting a ground-mounted
vertical to resonance. The use of an analyzer is highly recommended.
Note:
Very thin elements
, such as wire vertical elements, may have to be set slightly lower in
frequency than thicker elements. The maximum required deviation is only 1 to 2 percent.