Cooper Bussmann BU-945U-E 802.11 DSSS user manual Bench test and Demo System Setup, Antennas

Cooper Bussmann Wireless Ethernet & Device Server BU-945U-E 802.11 DSSS User Manual

Bench test and Demo System Setup

Care must be taken with placement of antenna in relation to the radios and the other antennas. Strong radio signals can saturate the receiver, hindering the overall radio communications.

When setting up a Bench test/Demo or a short range system the following considerations should be taken into account for optimum radio performance and reduced signal saturation.

•If using Demo Omni antennas (BU-DG-900-1 and BU-WH-900) it is recommended that only the Access Point be fitted with an antenna.

•If using Demo Omni antennas on each end, 20dB coax attenuator must be connected in-line with the coax cable.

•If using Demo Omni antennas, modules and antennas must be kept a suitable distance from each other. Check the receive signal strength on the “Connectivity page” of the module and ensure the level is not greater than -45dB

Demo Whip antennas should not be used in the final installation as the maximum performance of the modem cannot be guaranteed.

If using a BU-DG-900-1 antenna, it is better to keep the antennas at least 3ft (1m) away from the module so as to limit RF saturation.

Plant and Factory Installations

Most installations in industrial plants and factories use single omni-directional antennas. Installations can suffer from “multi-path fading” effects where multiple reflected radio signals adversely affect the signal strength. This can be checked by moving the antenna a short distance (10cm or 4 inches) - if the signal increases significantly then there are multi-path effects.

In a “static” installation, where the radio path is not changing, moving an antenna to the position of maximum signal solves this problem. However where the radio path changes because the BU-945U-E is mounted on moving equipment, or if there is moving equipment in the area, then the solution is to use two antennas. Because the two connectors are separated, the RF signal at each connector will be different in the presence of multi-path fading. The BU-945U-E unit will automatically select the higher RF signal.

Generally directional antennas are not normally used in plant and factory installations unless required for increased signal level.

Line-of-sight installations

In longer line-of-sight installations, the range may be increased by using a high gain antenna on the TX/RX connector. However, the gain should not cause the effective radiated power (ERP) to exceed the permitted value. A second higher gain antenna can be connected to the RX connector without affecting ERP - this will increase the operating range provided any interference in the direction of the link is low.

Antennas

Antennas can be either connected directly to the module connectors or connected via 50 ohm coaxial cable (e.g., RG58 Cellfoil or RG213) terminated with a male SMA coaxial connector. The higher the antenna is mounted, the greater the transmission range will be, however as the length of coaxial cable increases so do cable losses.

The net gain of an antenna/cable configuration is the gain of the antenna (in dBi) less the loss in the coaxial cable (in dB). The BU-945U-E maximum net gain for US and Canada is 10dB (4W ERP) and 0dB for Australia and NZ (1 W ERP). There is no gain restriction for antennas connected to the RX connector unless “TX Diversity” is enabled on the Radio page.

The gains and losses of typical antennas are

Antenna	BU-945U-E Gain (dBi)
Omni Dipole	0 dB
Omni Collinear	5 or 8 dBi
Yagi Directional	10 – 15 dBi
Cable Loss	dB per 30 m / 100 ft
RG58 Cellfoil	-9 dB
RG213	-7.4 dB
LDF4-50	-2 dB

10 www.cooperbussmann.com/BussmannWirelessResources 3A1582Rev1.6