Wildlife Transmitters and Tracking Systems Animal tracking radio transmitters
In this discussion, there is a simplified explanation of radio tracking of wildlife. Very simplified in fact, there are many variables to consider.
There are also a variety of transmitter types, programming options, so one simple explanation does not expect to cover all requirements.
From this basic understanding, you would have an idea of what needs to be considered when putting together a study using radio transmitters. This will help you discuss your requirements with your ATS consultant.
Radio Tracking - There are basically two main components when radio tracking;
1. Transmitter – this sends the radio signal
2. Receiver/antenna – this hears the signal
The transmitter is an electronic device that emits a “beep” at an interval determined by the transmitter’s circuitry and/or processor program. In its simplest form it emits a pulse at a regular interval; this is called the Pulse Rate, and is usually expressed as PPM, or Pulses per Minute.
Wildlife VHF transmitters are radio frequency (RF) devices that operate in the VHF band, and most commonly in the range of 140 MHz to 174 MHz. Other frequencies may be available. Not all frequencies available on some models of ATS transmitters.
The transmitter comes in various configurations, and its simplest form is comprised of four main components; transmitter, antenna, battery and attachment method.
When deciding which ATS transmitter to use, a number of factors need to be considered. Each individual factor will also affect another factor, so some compromises usually have to be made.
1. The animal that the study will involve will determine the type of ATS transmitter to be used, but in practice, more than one configuration can be considered.
a. An important specification of a transmitter is the weight of the transmitter, and this includes its attachment method. There maximum transmitter weight that
is determined for that animal, and this is generally determined as a percentage of the animal’s body weight. A rough guide would be 3-5% for airborne,
and 5-10% for terrestrial. This is but an indication, and you will determine what weight that might be when you put your study
together with input from your colleagues, supervisors, Ethics Committee, etc. This consideration for weight, in conjunction with other factors,
is generally for the benefit of the animal’s well-being, its health, and to ensure that it can still perform its normal behaviours.
b. The transmitter will need to be attached to the animal somehow. The size and shape of the animal are usually the biggest contributors to how the transmitter is to be attached. The attachment method used for a particular animal will also be limited by the weight allowed. Any weight added to the basic transmitter package obviously adds to the transmitter weight.
2. The study will determine what outcomes are required, or desired.
a. The length of deployment of the transmitter is a significant specification.
How long do you wish to have the transmitter operate on the animal?
The length of time that the transmitter will operate for is called the Battery Life.
The transmitter uses energy to run itself, transmit its Pulses, and perform other “tasks”, determined by its circuitry, and in some transmitter types, programming.
Simply put, and if the transmitter circuit is the same, a transmitter with a greater battery life will need to have a larger battery fitted.
A larger Battery will have a larger weight, and therefore has to be considered in the overall specification.
b. Range is an important factor. Range is how far one would expect to "hear" the transmitter with a receiver. Many factors affect the range of a transmitter, they are primarily; transmitter design, receiver/antenna design, and environmental factors.
The Receiver and Antenna
A tracking receiver designed for radio telemetry should be used to pick up the transmitter’s signal. An antenna is cabled to the receiver.
The frequency range of the receiver must match up with the frequencies the transmitters are using.
Advanced receivers utilize digital signal processing techniques, or DSP. Special filters are used to digitally sample the input audio signal and digitize it, using algorithms to process the data. This helps filter out spurious signals in very noisy environments, such as in urban areas.
For larger projects, receiver-data-loggers are used. This allows you to easily save tracking data while in the field, or leave the receiver in unattended operation.
In a simple homing system, a single antenna is used. Multiple antennas may be used in more complex operations. The antenna is connected to the receiver using coaxial cable, usually type RG-58. To maximize antenna gain and minimize signal loss, the shortest possible length of cable should be used.
Carry spare antenna cables while in the field. The weakest point in the system is the cable and its connectors; they receive continual stress tracking in heavy brush.