14
Included with the
DXE-RFS-SYS-4S
package is the coaxial cable preparation tool, part number
DXE-CPT-659,
that readies the coaxial cable for connectors in one operation and comes with an
extra cutting cartridge. To ensure weather tight connections, use
DXE-EX6XL-25
compression
style F connectors are also included.
DXE- EX6XL-25
contains 25 compression F connectors,
enough for the entire array plus some spares. The compression F connectors cannot be installed
with normal crimping tools or pliers, so you also receive the installation tool
DXE-SN
S
-CT1
, from
DX Engineering with the
DXE-RFS-SYS-4S
package for proper connector installation.
Active Antenna Feedlines
Use 75 Ω coaxial cable from each antenna element to the
DXE-RFS-3
. The four feedlines from the
DXE-RFS-3
phasing unit to the active elements can be any length needed to accommodate the size
of the array, but must all be the same length, velocity factor and type. Note the orientation and
numbering of the elements by using
Figure 2
.
Be sure the appropriate antenna element is connected
to the proper ANT connector on the phasing unit. The default (zero control voltage) forward
direction is towards Element 1. Element 3 is the rear or null direction.
Delay Lines
The
DXE-RFS-3
uses a time delay system, not a traditional phasing system. Delay line lengths are
dictated by array dimensions rather than operating frequency. This results in phase being correct for
a rearward null at any frequency. This system is especially effective when used with DX
Engineering
ARAV4
active vertical elements. User-supplied passive elements can also provide
exceptional performance for single or dual band operation where high dynamic range is required.
The
DXE-RFS-3
phasing unit has three sets of delay line connections marked DLY1, DLY2 and
DLY3. Each of these connection pairs will have a specific length of coaxial cable acting as a jumper
between the two connectors. Jumper electrical length is critical. Careful measurements and the use
of 75 Ω coaxial cable (included in this package system) with a known Velocity Factor (VF) is very
important.
If you are not using the included
DXE-RG6UFQ-1000
quad shield coaxial cable, keep in mind that
solid Teflon
®
or polyethylene dielectric coaxial cable has a VF of approximately 0.66. Foamed
coaxial cable cables typically range anywhere between 0.75 and 0.90 VF, depending on the ratio of
air-to-dielectric material in the cable core. If you do not know the VF of the coaxial cable you are
using, you must directly measure the electrical length of the coaxial cable you have or obtain cable
with a known VF. The included DX Engineering
DXE-RG6UFQ-1000
75 Ω quad shield coaxial
cable has a nominal VF of 0.82. For best performance, the coaxial cable for the delay lines should
be from the same batch or spool.
The first step is to determine the required
electrical
length of DLY3. This is based on the corner-
to-corner or diagonal distance between two diagonal corner elements of the square forming the
array. You can directly measure this distance, or it can be calculated by multiplying the side length
of the array by 1.4142. The
electrical
length of delay line DLY3 should be slightly shorter than the
actual physical distance between the two diagonal corners of the array. An electrical length 95% of
the physical distance works well (diagonal distance times 0.95).
Table 3
shows these calculations
for three common side lengths.
