The maximum recommended signal drop from the satellite antenna to the Iridium transceiver (either in the 9505A phone, 9505A LBT, or a Beam product) is 3dB. 
Cable: For optimal performance, we recommend using the shortest length of cable and the fewest number of connectors possible.  You must ensure that the cable used conforms to this.  An example of attenuation for RG213 cable is 0.33dB per metre @ 1.6Ghz, therefore the maximum cable length is 8m (allowing up to 0.5dB for cable interconnections).  LMR400 cable in comparison has a better attenuation figure of 0.18dB per metre.Satellite Line Of Sight: For best performance, the user’s antenna must be able to “see” the entire sky from approximately 8 degrees above the horizon. Nearby tall buildings or similar structures, heavily leafed trees, mountains, etc. can degrade performance as they block the signal between the equipment’s antenna and the satellites. Having a completely open view of the sky plays a very important role in maximizing performance, as the Iridium satellites cross the sky from horizon to horizon during a call connection.A good rule of thumb is that all surrounding obstructions should be lower than the top of a fist, which is extended at arms length, and the bottom of the fist placed on the horizon. Note that Iridium performance is immune from natural environments such as clouds, fog, rain, snow, wind and smoke.

Refer also to “Assuring Quality of Iridium Service” in the Antenna Installation Guide

All wireless devices, including satellite telephones, are susceptible to RF (Radio Frequency) interference from other electronic devices. This problem is especially evident when numerous antennas and broadcasting devices are located within close proximity to each other.

A good example would be onboard a ship. It is important that certain considerations be taken into account for best performance when an Iridium system is installed.

Causes of RF Interference:
Some subscribers have contacted Iridium regarding the loss of signal quality when they operate their equipment near active INMARSAT terminals. The power with which INMARSAT units transmit can overpower the Iridium unit’s ability to properly maintain a quality connection with the Iridium satellite constellation. INMARSAT terminals are often found in the same locations as Iridium subscribers, such as harbors, airports and especially onboard ships.

The location of the INMARSAT unit’s antenna in relation to the Iridium unit’s antenna plays a significant role in determining the degree of signal degradation that an Iridium subscriber can expect to experience. All Iridium units are susceptible to this interference, regardless of the type of antenna being used.

Generally speaking, an Iridium unit, be it a handset using its integral antenna or a fixed terminal when attached to an externally mounted antenna and located within 15 and 45 meters (50 to 150 feet, respectively) of an operating INMARSAT mini-M or Standard-C terminal, will likely experience degraded performance.

Other sources of RF interference such as Globalstar units, radar devices and broadcast stations can provide interference for Iridium units, but usually are not encountered as frequently as INMARSAT terminals.

Refer also to “Assuring Quality of Iridium Service” in the Antenna Installation Guide