Hi Tony,

I'm 99% sure the antenna is passive, not active. Check the solder
joints where the four helical wire antennae join onto the board at the
bottom. I've had one experience with faulty connections (came loose
due to excessive vibration) here.

If a visual inspection of the antenna otherwise looks OK, check the
coaxial cable, in particular the connector at the antenna end. Has
any water got in here?

Iridium antennas don't have much gain, and any additional losses in
the coax cable and connectors really reduce the receive signal.

Regards
Vaughan Henderson