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Keeping Track with Digital Encoding

Lotek has introduced a "field-proven" Digitally Encoded Radio Telemetry System that dramatically improves your ability to keep track of all tagged animals. The system is designed to transmit and record a data burst containing a unique identity code for each member of a large group of individuals on a single frequency.


Most fisheries and wildlife tracking is still performed by a trained operator listening for the familiar beep-beep-beep. Conventional telemetry systems provide identification of individuals through use of frequency separation combined with a variety of pulse rates. These methods require a large amount of frequency bandwidth which in turn imposes a significant scan-time overhead with a corresponding increase in the probability of missing an animal. These methods are not particularly well suited to automatic monitoring, especially in noisy environments and/or where the number of available frequencies is limited.

Lotek's Digitally Encoded System provides unique numerical identification, e.g., "4897", which is consistent, exact and distinct for every animal on the system, whether it be in manual or automatic tracking applications. Code sets permit large numbers of animals per frequency, i.e., over 500 per frequency, and are highly distinguishable even in noisy environments. The system optimizes use of limited frequency space and minimizes sampling time required to obtain data on all target animals.

The System

The system is designed for extended duration studies where large numbers of individuals are being monitored. All components of the system are compact, portable and rugged to facilitate use in the field. Removal of the system from the field is not necessary for data retrieval. Data may be stored as required for particular applications and later transferred via RS-232 communication port to a laptop or remote computer (via phone, cellular or satellite link) .

There are a number of significant benefits to Lotek's coding system when compared with other currently available systems. Some of these are:

  • Qualification of codes by pulse width is no longer necessary, thus enhancing the ability to accurately identify each individual;
  • Probability of code collision has been minimized, again maximizing ability to identify specific animals;
  • Power savings inherent in the design can now be used for: higher peak outputs thereby increasing range; smaller package sizes; longer operational life; and
  • Ability to pick exact codes out of ambient noise has been improved dramatically over conventional systems and, overall, provides a robustness not previously available.


The system consists of:

  • One or more transmitters
  • An SRX_400 datalogger/receiver with encoding firmware
  • Antennas appropriate to the experiment
  • File management and communication support software

System options include:

  • Remote two way communication
  • Simultaneous monitoring of multiple frequencies
  • Automatic antenna switching
  • Encoded sensor outputs

Transmitters: Digital encoding can be incorporated into virtually all transmitters currently available from Lotek. Contact us for specification detail pertinent to a particular species or project.

Receiver: The SRX_400 compact, field portable datalogger/receiver provides real time processing and storage of transmitted data. Algorithms in the receiver's firmware ensure fast (8 ms) decoding thereby enabling the receiver to provide reliable and accurate identification. In addition, the firmware is designed to support operations with a number of peripheral devices including a multiple antenna switcher, remote two-way communication and a multi-channel monitor. The latter provides the ability to monitor multiple frequencies simultaneously, as opposed to sequential scanning of frequencies, thereby further reducing delays in sampling due to scan dwell time. Multiple antenna switching, when combined with signal strength, provides position relative to the antenna. Some receiver/datalogger configurations will accept and store GPS locations obtained during mobile tracking operations.

Lotek's Digitally Encoded System has numerous advantages over current technology. Some of its features are:

Data Compression and Customized Reporting
Continuous Record or Group functions enable the user to reduce data accumulation and/or compress data by specifying the timeframe or number of valid signal pulses before recording into memory. Hex dump routines are provided to significantly decrease data downloading time.

Enhanced Noise Immunity
Automatic monitoring programs utilize a user-configurable noise blanking algorithm which discriminates valid signal pulses from ignition, power lines and other impulsive noise sources. Noise or interference not removed by the noise blanker is suppressed by a two-tier gain reduction strategy which acts to optimize receiver sensitivity for specific environments. In addition, the code generation algorithms improve code collision discrimination to further enhance system performance in noisy environments.

Increased Energy Efficiency
Small burst intervals provide a power saving not encountered in other coding systems.

Enhanced Auditory Recognition of Signal
Digital codes provide better audible detectability of signal from noise in mobile applications. This has particular advantage where operator fatigue is possible, e.g., extended telemetry flights over large expanses.

Peripherals Support
The coding system supports the use of a number of peripherals which provide antenna switching, simultaneous monitoring of a large number of frequencies and remote two-way communications.

Potential Applications
Manual/mobile tracking is typically undertaken to search for, locate and possibly follow specific individuals over a broad geographic area. Telemetry flights are frequently associated with this mode of tracking. Examples include tracking waterfowl dispersing from wintering areas to breeding areas, mortality studies of migratory ungulates, or monitoring movements of wide ranging species/individuals such as wolves or male ursids.

Increased operator fatigue associated with flights of longer duration can result in a corresponding increase in the probability of missing a signal, particularly when combined with background noise. Coding enhances audible detection of signal from noise in these situations. In addition, the ability to place many animals on one frequency decreases scan time through the frequency table thereby decreasing the probability of missing an animal, even at higher flight speeds.

Since all studies have their own objectives, each one must be considered on its own merits when determining the specific equipment required. However, the principle of how the system works is common to all applications. The receiver, the SRX 400, listens for all frequencies at each antenna and records into memory the antenna number, time, date, channel number, i.e., frequency, signal strength and animal identification number. The following describes two "typical" or "generic" system installations.

In the first situation, the objective is to listen, at a fixed site, to each of eight high-gain directional antennas to determine if a particular animal is in the area, for what duration and in what direction relative to the receiving site. This is especially applicable in avian, marine and terrestrial applications where:

  • Large numbers of individuals move relatively swiftly through a large area, e.g., migrating waterfowl through a staging or refuge area; or
  • Individuals are in view for a relatively short duration, e.g., surfacing seals, or sea turtles near an oil rig.

Where multiple receiving sites can be appropriately deployed, location of the subject may be ascertained through automatic triangulation.

In the second situation the objective is to determine the movement of animals as they move through a site containing a number of structures of interest. This is done by subdividing the area into a number of smaller areas. This is especially applicable to situations where:

  • Large numbers of individuals have the potential to rapidly pass a structure, e.g., migrating or escaping fish passing through a high flow situation such as a turbine or spillway versus a fish ladder or other mitigation device.