Antenna Diversity; Example; Line-Of-Sight Installations - Weidmuller WI-MOD-E-G User Manual

Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-E-G/A User Manual
Note: When only one antenna is used, it must be connected to the TX/RX connector.

Antenna Diversity

There are two main reasons for using Antenna diversity; the first is to improve the reliability of a radio link that may be
affected by multipath signals. Often if radio signals are transmitted in built-up area the signal can get reflected off different
surfaces and when these signals are received they can cancel each other out due to slightly different time delays. Using
more than one antenna the radio is able to choose the best signal thus providing a more robust radio link.
The second reason to use antennas diversity is to increase the received radio signal into the receiver. All countries have
radio licensing regulations that can often limit on the amount of transmitted power and radiated power from the antenna.
In the US this is 400 millwatts transmit power and 4 watts EIRP (Effective Isotropic Radiated Power) from the antenna. If a
high gain antenna is used to try and improve the receive signal it will also increase the transmit level and push it over the
EIRP regulation limit.
Using Antenna diversity allows two antennas to be used, one for receive and the other for transmit/receive. The TX/RX
antenna has the normal restriction on gain to keep it below the regulation limit, however the receive antenna has no
regulatory limits as it does not radiate power so any higher gain antenna can be used to receive weaker signals.
See Section 3.10 - "Advanced Radio Configuration" for details on configuring Antenna Diversity
In North America the maximum allowable radiated power (EIRP) for a WI-MOD-E-G is 4 Watts, which is 10dB higher that
the modules transmit power of 400mW. Therefore we can increase the antenna gain as long as overall system gain
(antenna Gain – coax loss) does not go above 10dB.

Example


If using 10m (33ft) of Cellfoil coax cable (approximately 6dB of loss) and an 8 dBi gain antenna this would equate
to approximately 2dB of gain, which is well below our 10dB limit.

If using 20m (66ft) of Cellfoil coax cable (approximately 12dB of loss) and an 18 dBi Antenna this would equate to
approximately 6dB of gain, which is also below our 10dB limit.

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 maximum net gain of the antenna/cable configuration connected to the TX/RX connector is 0dB in Europe (100mW
ERP). In USA, Canada and Australia (4W ERP), the maximum gain is 10dB for the WI-MOD-E-400 or 16dB for the WI-
MOD-E-100.
There is no gain restriction for antennas connected to the RX connector.
(*) 20dB attenuator must be fitted if radio distance is less than 33ft (10m).
Antenna
Dipole
Collinear
Directional
Cable Loss
RG58 Cellfoil
RG213
LDF4-50
Rev. 2.16
WI-MOD-E-G Gain (dBi)
2 dBi
5 or 10 dBi
18 dBi
dB per 30 m / 100 ft
-17 dB
-16.2 dB
-3.6 dB
www.weidmuller.com
WI-MOD-E-A Gain (dBi)
6 dBi
10 dBi
10 – 20 dBi
dB per 30 m / 100 ft
-24.5 dB
-28.6 dB
-5.5 dB
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