Introduction
Iridium telephones were originally designed to operate with a passive antenna,
either an element attached directly to the handset, or a remote aerial
connected with a short length of coaxial cable. Unfortunately, a signal loss of
more than 3dB in a remote antenna’s connecting cable degrades
performance due to attenuation of both the received and transmitted signals.
A 3dB loss corresponds to approximately 10m of RG213U or 3m of RG58U
coaxial cable, lengths that clearly restrict the mounting options for the antenna
using standard down-leads.
AD511 active Iridium antenna (figure 1 & figure 2) is designed for use with up to
160 meters of coaxial cable terminated with type ‘N’ connectors, and with
coax lengths starting from 27meters – subject to AST advice.
Designed for harsh environments, the AD511 consists of two RHCP dipole
antenna housed within a 4mm thick GRP radome mounted on a common
base. One antenna is for signal transmission and one for reception.
AD511 has a linear power amplifier within the base and connected to the
transmitting antenna compensates for signal loss incurred mainly by the
connecting cable. Similarly, a low noise amplifier is attached to the receiving
antenna via a low loss ceramic filter to boost the signal sent to the telephone.
The ceramic filter has a bandwidth of 25 MHz centred on the Iridium band
designed to attenuate any out of band interference that may arise, for
example from nearby Inmarsat uplinks.
Using manufacturing techniques proven for a range of extremely rugged
GPS/DGP active antenna, the base is milled from aluminium and hard
anodised, giving an attractive finish, which is mechanically resilient and
resistant to corrosion. The antenna’s mass is 0.8kg.
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General