- 11 -
Station Feedline, Active Antenna Feedline and Delay Line
The weakest link in an antenna system is often the coaxial 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. If the coaxial cable is compromised the shield will then pick up unwanted signals. This is
why the shield connections are most critical. In addition, the
DXE-RCA8B
uses the shield as a
ground return path for the active element power.
All feedlines must be 75Ω and can be any length as long as they are all equal and they should come
from the same roll of cable so they have the same velocity factor (VF).
If the resistance of the shield increases due to contamination, the active elements may not function
properly. Any splices in the feedline should be high quality and entirely weather tight. Do not use
splices in the delay line cable. The
DXE-RCA8B
system has been designed to use only 75Ω coax.
High quality, flooded 75Ω CATV F6 type coax is recommended. The
DXE-F6-1000
flooded cable
automatically seals small accidental cuts or lacerations in the jacket. Flooded cable also prevents
shield contamination and can be direct-buried.
Feedline connections must have good integrity and be weather resistant. Highly recommended for
any DX Engineering array, and specifically designed for the
DXE-F6-1000
flooded cable is the
Snap-N-Seal® F connectors, model
DXE-SNS6-25
which contains 25 connectors; enough for the
entire array plus spares. Snap-N-Seal® connectors cannot be installed with normal crimping tools or
pliers. The
DXE-SNS-CT1
Compression Tool for Snap-N-Seal® 75Ω Coax Connectors is an
essential tool for proper connector installation.
Lightly coat threads of F connectors with
pure clear non-hardening silicon dielectric compound
,
such as
DXE-22058
Permatex Dielectric Grease, to improve reliability of electrical connectors.
This will lubricate threads, seal connector threads from water ingress, and reduce chances of
unwanted bonding or welding of connector threads.
If dielectric grease is not used, the potential for
damage to the various connectors may result and is not covered under warranty.
Note:
DO NOT
use pliers or other tools to excessively tighten the type F connectors; they
do not require high torque to make a good connection.
F connectors are very
reliable strong connectors for their size, but carelessness can damage them.
Excessive tightening torque can loosen the chassis mounting-nut, allowing the
connector body to rotate and fracture the mounting tabs on either installation or
removal of the connector. F-connectors require modest torque, typically 6-12 inch-
pounds. 20-30 inch-pounds are FAR too high. That value, although commonly used,
is just wrong.
Damage to the various connectors may result and is not covered
under warranty.
Use a tool such as the
DXE-CIT-1
F Connector Tightening Tool.
Additional weatherproofing protection can be provided when using the
DXE-22058
Permatex Dielectric Grease on all coaxial connections. Dielectric grease is ideal for
keeping moisture from entering your coaxial connectors. It also acts as a lubricant
allowing easy connector removal by stopping corrosion of electrical connectors.
