Continuous Transmitters

Continuous transmitters are useful for experiments where the scientist needs to track individual animals from a boat using VEMCO's tracking receivers (VR100 and VR28). Continuous transmitters ping continuously from the first ping until power is lost unless deactivated by the user. These transmitters are identified by the operating frequency, and the period if they do not transmit data. Continuous transmitters come in a variety of sizes, and power outputs and several frequencies.

The frequencies available for continuous pingers are restricted so as to not interfere with longer term studies based on coded transmitters at 69 kHz. Continuous pingers are normally used with high repetition rates and short life spans. Additional frequencies can be made available for closed systems. For more information contact our VEMCO sales department. The table below shows comparisons of the various options available for continuous pingers.

Data from continuous ultrasonic transmitters is encoded in the time interval between successive pulses. The rate at which pulses may be transmitted is limited by the reverberation time (ie. time required for echoes to decay). For animal tracking transmitters, the interval between pulses varies between 300 milliseconds and 1200 milliseconds. For high power and long range data telemetry, the time between pulses varies between 800 milliseconds and 2 seconds.

Single Channel Continuous Transmitters
Single channel telemetry transmitters provide a simple linear relationship between the period and the data transmitted. The method referred to as Linear Interval Code (or INTERVAL) is illustrated in Figure 10. The calibration of these transmitters is represented by two numbers, the slope and the intercept of the line shown. Single channel is defined here as the transmission of one data type for each transmission.

Multiple Channel Continuous Transmitters
When more than one sensor must be accommodated on a single transmission frequency, the data is encoded by a series of pulses. To identify which interval represents a particular parameter, a synchronization interval is added. The synchronization pulse is added to "inform" the receiver that two data types will be transmitted next. The following diagram (Figure 11) shows a comparison between single and dual channel (temperature and depth) transmissions. The data in dual channel transmitters is encoded in the same way as a single channel. For example, a dual channel transmitter transmits two data types (eg. temperature and depth).

¹ Battery life will be lengthened or shortened depending on various options chosen.