The AD511 Active Iridium antenna is designed for use with 40m (131 feet) of RG213U coaxial cable terminated with type ‘N’ connectors.
Iridium telephones were originally designed to operate with passive antennae: either an element attached directly to the handset, or a remote aerial connected with a short length of low-loss 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 which restrict the mounting options for the antenna with standard cabling.
Designed for harsh environments, the AD511 consists of two RHCP dipole antennae housed within a 4mm thick GRP radome, figure 1. One antenna is for signal transmission and one for reception. 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 interdigital filter to boost the signal sent to the telephone. The interdigital filter has a bandwidth of 25 MHz centred on the Iridium band and is designed to attenuate any out of band interference that may arise for example from nearby Inmarsat uplinks or mobile phone masts.
The AD511 should be mounted to give an unobstructed view of the sky from horizon to horizon. The bracket provided with each antenna can be attached to a mast or spar up to 60mm in diameter using the V-bolts provided.
Using manufacturing techniques proven for a range of extremely rugged GPS/DGP active antennae, the antenna base is milled from aluminium and hard anodised and sealed, giving a matt medium grey finish, which is mechanically resilient and resistant to corrosion. The antenna’s mass is 2.6kg.