9
For access to the jumpers in the active matching units, remove cover. The circuit board and jumper
headers will be visible, as shown in
Figure 3
. By default, there are no jumpers across any pins.
Place a jumper across
L1MF
. Do not jumper any other positions.
See the Active Antenna User
Manual for more information about additional peak response jumper settings.
Station Feedline, Active Antenna Feedline and Delay Lines
The weakest link in an antenna system, such as the
DXE-RFS-SYS-2P
, is often the coax cable
connections. All connections must be high quality and weather tight to prevent contamination and
corrosion, which can cause the feedline impedance to change. This can affect the signal-to-noise
ratio and the directivity of the array. In addition, the
DXE-RFS-3
uses the shield as a ground return
path for the active element power.
Note: The total loop resistance of the ground path must be under 30 Ω for reliable operation.
If the resistance of the shield increases due to contamination, the elements may not function
properly. Any splices in the feedline should be high quality and entirely weather tight. The
DXE-
RFS-3P
system has been designed to use only 75 Ω coax.
High quality, flooded 75 Ω CATV F6 type coax is recommended.
DXE-F6-1000
Flooded cables
automatically seal small accidental cuts or lacerations in the jacket. Flooded cable also prevents
shield contamination and can be direct-buried.
DX Engineering offers an inexpensive preparation tool, part number
DXE-CPT-659,
that readies
the coax for connectors in one operation and comes with an extra cutting cartridge. To ensure
weather tight connections, use
DXE-SNS6-25
Snap-N-Seal compression style connectors.
DXE-
SNS6-25
contains 25 Snap-N-Seal connectors, enough for the entire array plus some spares. The
Snap-N-Seal connectors cannot be installed with normal crimping tools or pliers, so you must use
an installation tool like the
DXE-SNS-CT1
, available from DX Engineering, for proper connector
installation.
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 ARAV active 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 coax acting as a jumper
between the two connectors. Jumper electrical length is critical. Careful measurements and the use
of 75 Ω coax with a known Velocity Factor (VF) is very important.
Solid Teflon® or polyethylene dielectric coax cable has a VF of approximately 0.66. Foamed coax
cables typically range anywhere between 0.75 and 0.90 VF, depending on the ratio of air-to-
dielectric material in the cable core.
