Iridium IMF 1000- Calls being dropped in specific areas or on specific headings
Summary:

This artical describes the problem when calls drop out when specific areas or on specific headings using a Iridium IMF 1000
Article:

Symptoms Too many dropped calls in specific areas or on specific headings Causes · Interference from other Radio Frequency (RF) Sources on the ship (especially Inmarsat B). Troubleshooting and Resolution · Relocate Iridium antenna out of the path of directional Inmarsat antennas (e.g., Inmarsat B) · Install an Iridium-approved RF filter between the ECI phone and antenna