UM-1097
Revision B
127
Yagi Antennas
Yagi antennas are directional along the central beam of the antenna. The folded element is towards the
back and the antenna should be pointed in the direction of the transmission. Yagis should also be mounted
with at least 1 to 2 wavelengths of clearance from other objects. The polarity of the antenna is the same
as the direction of the orthogonal elements. For example, if the elements are vertical the Yagi transmits
with vertical polarity.
In networks spread over wide areas, it is common for a central unit to have an omni-directional antenna
and the remote units to have Yagi antennas. In this case, as the omni-directional antenna will be mounted
with vertical polarity, then the Yagi’s must also have vertical polarity. Care needs to be taken to ensure
the Yagi is aligned correctly to achieve optimum performance.
Two Yagi’s can be used for a point-to-point link. In this case they can be mounted with the elements
horizontally to give horizontal polarity. There is a large degree of RF isolation between horizontal and
vertical polarity (approx. –30dB) so this installation method is a good idea if there is a large amount of
interference from another system close by transmitting vertical polarity.
An important mounting tip – if a Yagi has drainage holes in the dipole element, do not mount the antenna
with the drainage.
Mounting Near other Antennas
Avoid mounting your network’s antenna near any other antenna even when the other antenna is
transmitting on a different radio band. High RF energy of the transmission from a close antenna can
deafen a receiver. This is a common cause of problems with wireless systems.
Because antennas are designed to transmit parallel to the ground rather than up or down, vertical
separation between antennas is a lot more effective than horizontal separation. If mounting near another
antenna cannot be avoided, mounting it beneath or above the other antenna is better than mounting
beside it. Using different polarity to the other antenna (if possible) will also help to isolate the RF coupling.
Coax Cables
If a coax cable connects to the antenna via connectors, it is very important to weatherproof the connection
using our 1000-2314 or equivalent sealing tape. Moisture ingress into a coax cable connection is the most
common cause of problems with antenna installations. A three-layer sealing process is recommended –
an initial layer of electrical PVC tape, followed by a second layer of self-vulcanizing weatherproofing tape
(1000-2314), with a final layer of electrical PVC tape (see
Section 4.5.2
).
Allowing a drip “U loop” of cable before the connection is also a good idea. The loop allows water to drip
off the bottom of the U instead of into the connection, reduces installation strain and provides spare cable
length in case later the original connectors need to be removed, the cable can be cut back and new
connectors fitted.
Summary of Contents for ViewSmart 1600+
Page 77: ...UM 1097 Revision B 67 4 7 5 4 Programmable Relays Figure 47 Webpage Programmable Relays Menu...
Page 78: ...UM 1097 Revision B 68 4 7 5 5 System Configuration Figure 48 Webpage System Configuration Menu...
Page 134: ...UM 1097 Revision B 124 Appendix 4 Menu Navigation...
Page 141: ...UM 1097 Revision B 131 Wireless Options and Accessories Expansion Options...
