Coded Transmitters

VEMCO coded tags come in a variety of sizes, power outputs, battery life and sensor options. The following table provides a quick comparison of what's available to help you choose the most appropriate tags for your study. For more details on options available, click on the links in the table below to see the individual datasheets for each tag family.

Coded tags emit a series of pings called a pulse train which contains ID and error checking information. This allows the user to individually track multiple fish. VEMCO provides various tag coding techniques that provide millions of unique pinger IDs and tens of thousands of unique sensor tag IDs. The time between pulse trains is varied randomly about a nominal point and can be 10s of seconds to multiple minutes long. The off time, or Delay as it is called, is required to ensure that other transmitters have a chance to be detected by the receivers. After the Delay is completed, the cycle repeats. An example is shown below.

Collisions and Selecting the Delay
"Collisions" happen when two or more tags transmit all or part of their pulse train at the same time. When this happens, the pings overlap and neither transmission can be detected by the receiver. Although collisions are inevitable, tag Delay is randomized to eliminate the possibility of any two tags continuously colliding with each other. Assuming the Delays are set long enough and the fish stay in range for a long enough period of time, randomization of Delay ensures that the receiver will eventually detect all the tags. Therefore the Delay choice is critical to the success of a study and should be chosen to optimize performance based on the maximum number of fish expected to be resident around the receiver at one time. We encourage users to choose the longest Delay time acceptable to their study as a longer Delay period will result in fewer collisions. As well, a longer Delay will provide substantially longer battery life for the tag allowing for longer study periods. In some cases, multiple years is possible. The table below shows expected time to detect multiple tags for varying numbers of tags present within the detection range of the receiver and selected Delay times.

Optional Dormancy Periods
VEMCO coded tags can be programmed with preset dormancy periods. During dormancy, the transmitter goes to sleep to conserve power and is scheduled to turn back on at a later date. This feature has enabled scientists to study the behaviour of young fish in rivers and estuaries and then continue to study the same fish several years later when they returned to the river to spawn. The tags are capable of being programmed with multiple on/off phases.

Options like dormancy periods are possible due to advanced processing capabilities existing in VEMCO coded tags. Other custom variations can be considered as well. Please contact the VEMCO sales team to discuss your specific needs.

Sensor Tags
VEMCO coded tags are also available with sensor options. Our standard products are available with temperature and/or pressure sensors for most sized tags. VEMCO is also continually working with researchers to uncover other useful sensor technologies and integrating them into our transmitters.