Kerlink Wirnet iBTS Installation And Maintenance Manual page 168

Distance between antennas to optimize the spacing diversity performance is always a
subject of discussion. There are no miracle formulas helping to determine the distance
because each use case is a particular use case.
However, there are some rules to be followed:
 The minimum distance between antenna must be the half wave length i.e.:
o 18 cm at 868MHz
o 17 cm at 915MHz
 To have uncorrelated antennas it is better to have a minimum distance of 13*λ/8
between antennas i.e.:
o 56 cm at 868MHz
o 53 cm at 915MHz
 The distances can be increased to improve the performance, ideally by steps of a
wavelength. The recommended distances are then:
o 868MHz: 56 cm, 91 cm, 125 cm, 160 cm, etc...
o 915MHz: 53 cm, 86 cm, 119 cm, 151 cm, etc...
Note 1: the distance between the two universal antenna brackets installed on the compact
casing mounting kit is 20cm. This meets the 18cm minimum distance for space diversity
although the performance is not optimum.
Note 2: the universal bracket length is about 20cm. In a 120mm pole mount configuration,
the maximum distance between antennas can be the 20+20+12=52cm which is close to the
optimum distance listed above.
4.5.2.3 Universal antenna bracket
The universal antenna bracket is used with the following antennas:
-
868MHz, 3dBi omnidirectional (see §1.8.1.1).
-
915MHz, 3dBi omnidirectional (see §1.8.1.3).
-
915MHz, 6dBi omnidirectional, except FT-RF antenna (see §1.8.1.4).
The universal antenna bracket is detailed in §1.8.6.2.
The universal antenna bracket has 3 holes dedicated to the LoRa antenna N connector. The
bracket can be then oriented in 3 different positions without compromising the antenna
position.
The universal antenna bracket can be mounted:
-
On a wall: use in this case two M4 screws separated by 19mm.
-
On a pole: use metallic strapping through the two 5mm x 25mm slots.
-
On the compact casing mounting kit, with 2 x M8 bolts and screws as follows.
It is preferred to have the universal antenna bracket installed on the right side of the
compact casing mounting kit (as follow) to have a better isolation between the LoRa
antenna and the GPS/LTE internal antennas.
Classification
Internal Use
Confidential
Strict confidential
4.5.2.2.2 LoRa space diversity
This document is the strict property of Kerlink and shall not be either copied nor sent without express
Kerlink – 1 rue Jacqueline Auriol – 35235 THORIGNÉ-FOUILLARD
Wirnet iBTS
written authorization of Kerlink
Kerlink m2m technologies reserved rights
Document title : Installation and
Maintenance Manual
Version : 2.0
Author : SNI
Date : 04/12/2018
Page 168 / 221