International Dredging Review

International Dredging Review

Ohmex has released the ‘LR’ modem a new long range digital radio telemetry modem to complement its tide gauge and weather station products. Housed in a robust IP68 aluminum case the modem is suitable for use in license-free marine applications throughout the world.

Applications include standard radio telemetry for data RTK differential corrections from base station to rover and new uses such as the rebroadcast of Virtual Reference Station data to multiple site based rovers.

Associated British Ports agreed to field test the unit by transmitting data from an existing tide gauge mounted in the Southampton container dock to the receiver at the VTS control center some six kilometers away. The site was chosen for the test as it was known to be noisy with existing radio equipment because there is no direct line of sight between stations a large number of container ship movements in the area and many other working radio systems.

Commenting on the two-month test the ABP Hydrographic Surveyor William Heaps said “The spread spectrum radios are working flawlessly the receiver is up high but the transmitter is still not in a good position yet no problems so far!”

The radios use a spread spectrum technology to avoid interference and provide clear data communications between modems at baud rates up to 115.2 Kbps. The radio system is within the ISM frequencies (2.4-2.483 GHz) and makes use of a proprietary channel hopping technique to use up to eight channels within a 105 channel band. The technique was developed for military applications and is inherently immune from interference and jamming at ranges of up to 20Km. The radios can be set up in secure master slave or repeater modes providing point to point and point to multipoint network combinations.