Preparing an Air Test

An air test is a good way to make sure the whole system is running and functional before introducing the complexities of the ocean. Once reliable communication is achieved, you can test sending commands such as range.

Although the PMM4511 modem is designed to operate acoustically in an ocean environment, it can also communicate in air (although somewhat less reliably). Acoustic energy transmitted from Modem 1 can propagate through the air for short distances and be received by Modem 2. Assuming multipath energy from sound reflections off the walls is not too damaging, this signal can be detected and demodulated.

Air test setup.

Guidelines

• Separate the two modems by a couple of meters
• Make sure acoustic reflections are minimized with sound-absorbing materials such as foam or cloth
• Make sure there are no acoustic interferers in the room
• Use a lower transmit-power setting in software when practical. Settings below ping 10 are generally preferred for air tests because they reduce excess acoustic energy and help limit multipath effects. Settings above ping 10 should be treated as high power for air testing.
• If room multipath prevents detection, repositioning either the transmitter or receiver transducer can usually make reliable communication possible.