TRANSMITTERS AND BATTERIES

What are transmitters?
How big are they?
What about antennas?
What do they do?

Temperature Monitors

Activity Monitors

Position Monitors

Mortality Monitors

Hibernation Monitors

Sleeper Cycling Transmitters

Trap Function Monitors

How long will they last?

Transmitters

Radio transmitters are small electronic devices that emit a pulsed radio frequency (rf) signal. Rf signal can be received and demodulated into audible sound and into visual analog signal strength presentation by the use of an rf receiving system consisting of a receiver and a receiving antenna. All of AVM’s transmitters are two-staged, containing both an oscillator and an amplifier. Transmitters can be made to emit signals of varying signal strengths and characteristics. AVM's most frequently produced transmitters, as well as the power sources appropriate to power them, are described on this page.

All transmitter collars and non-collared modules manufactured by AVM are custom-designed for each individual project. Many applications, however, have become standards in certain areas of research because of their overwhelming success on particular projects. But the needs of one researcher may not be the needs of another researcher, in spite of the fact that they may be studying the same species. Therefore, AVM's website gives detailed weights, measurements, and electronic specifications of sub-system components so that researchers can "design on paper" the layout and the specifications of a transmitting system that fits the needs of their studies. These layouts can either spec the final package or it can be used as a starting point for consultation with AVM's staff on the design of the most appropriate instrumentation package for his study. Or you can let AVM do everything for you.

Although the primary function of most radiotelemetry transmitters is direction finding, many transmitters can perform special functions at the same time, as you will see below in the section on special function additions.

The G3-1V

Table 1

The G3:

The MP2:

Table 2A

Table 2B

Transmitter Dimensions and Weights:

Transmitters	Dimensions	Unencapsulated Weight
G3-1V	13 x 8 x 5 mm	0.90 grams
G3	17 x 10 x 5 mm	1.25 grams
MP2	17 x 10 x 8 mm	1.43 grams

About Transmitting Antennas

The ideal antenna is 1/4 wavelength, which is usually 45-50 cm. Since this is not always practical, we find that the most commonly used antenna length is 30 cm. Try to pick an antenna that is the greatest length that you think your study species can comfortably tolerate. Remember, the longer the antenna, the stronger the signal. But sometimes exiting whip antennas aren't practical at all. AVM also designs collars with capacitively tuned loop antennas for animals like mustelids (see Collars for details). AVM also designs non-collared modules with perimeter loop antennas for animals like turtles (see Perimeter Loop Modules for details).

SPECIAL FUNCTION ADDITIONS TO TRANSMITTERS

AVM's Special Function Additions allow other parameters to be monitored in addition to location.

TEMPERATURE SENSORS
Each of AVM's transmitters can be made to function as temperature monitors by the addition of either Temperature Option A or Temperature Option B. Temperature monitors can be used as direction locators at the same time temperature data are being transmitted. However, if temperature transmitters are required for use in laboratory or controlled-environment studies only, their longevities can be greatly extended, by lowering their current drain and power output.

Note that the determination of the longevity of a temperature transmitter is a bit more complicated than a standard battery/transmitter combination because as the temperature of the transmitter increases, so does its current drain. This means that as the temperature increases, the theoretical longevity of the transmitter/battery combination decreases. An approximation of longevity can be obtained by understanding that the current drain of the transmitter goes up 0.10 mA for each 10° C the temperature increases. Thus, if a transmitter is drawing 0.030 mA at 22° C, it will draw 0.130 mA at 32° C.

Temperature readings are determined by analysis of the change in the pulse rate of the transmitter's signal. The user establishes a correlation curve, plotting temperature against either pulse rate or pulse interval, for each individual transmitter.

Temperature transmitter pulse rates may be counted using a stopwatch or AVM's Pulse Interval Timer (PIT) may be used to determine temperatures. See Receiver Accessories for information about the PIT.

Temperature Option A is primarily used to monitor body core temperature in mammals. It covers a range of approximately 8 Celsius degrees, with resolution to an accuracy of 0.1. This does not mean that the unit cannot monitor temperatures outside the range of the 8 Celsius degrees selected by the researcher. It means that the Temperature A unit will be accurate to 0.1 within the 8 degrees, then its level of accuracy will decrease as temperatures outside the selected range are detected.

Temperature Option B relays temperature readings from 0 to 40 degrees Celsius, with resolution to 0.5 degrees. It is most commonly used to monitor herps and ambient temperatures. It can be built into implant modules designed to monitor body core temperature of herps and hibernating mammals. Temperature B transmitters can be used as habitat identifiers by designing the package such that the thermistor is placed as far away from the body of the animal wearing the transmitter as possible, for instance, on the exterior surface of the collar. Thus, the researcher can determine, by monitoring the temperature of the collar, when the animal moves from the warmth of a nest to the ambient cold of the winter night.

Randall Reiserer, of the University of California at Berkeley's Museum of Vertebrate Zoology, doctoral candidate of Harry Greene, has generously allowed AVM to use one if his great temperature calibration curves. See Goliath the Mojave Rattler's transmitter calibration curve by clicking on the snake!

TWO TYPES OF ACTIVITY MONITORING DEVICES
The activity of radio-tagged animals can be monitored by the same transmitter used to determine location, by the addition of one of two styles of activity monitor to a transmitter package.

Active/Inactive Activity gives a "yes/no" indication of activity. Active/Inactive transmitters contain a microprocessor, actually a microcontroller device that is programmed to switch pulse modes when activity is sensed. The sensor used is a tiny mercury switch that opens and closes the input to the microcontroller circuit when it senses motion.

Unlike the older style pulse-rate based activity and mortality monitors, the pulse rate of the output signal does not change. The pulse mode changes from a single to a dual pulse burst mode, indicating activity or absence of activity. Change in pulse burst mode means a change from the traditional beep beep beep signal to a double pulse burst mode: bibeep bibeep bibeep. The active or inactive mode can be programmed to be indicated by either the single or double pulse burst mode. The choice of the indicator pulse should be determined by the state in which the study animal exists the most frequently. For instance, if the animal is quiescent most of the time, the single pulse burst should be chosen to indicate this, as it draws less current than the double pulse burst mode.

Position-based Activity: Where an instant transmission of the orientation of a given body part of a study animal is desired, the addition of a position-based activity monitor to transmitter/ battery combination is useful. The position-based activity indicator switches between two predetermined pulse rates based on the body position of an animal. An example of the use of this method is its use to sense whether a bird is flying or perched. Another example is the use of a position indicator to monitor egg-laying in chelonians.

Position-based Activity can be incorporated into either the G3-1V or the G3 transmitter.

MORTALITY SENSING DEVICES
Mortality Sensor-equipped MP2 Transmitters depend on the absence of motion of the tagged animal. Mortality signal is presented in the same way as Active/Inactive Option presents its signal, by single or dual pulse bursts. elapsed time between absence of motion and mortality circuit triggering can be selected by the end user; the most common requests we receive are two, four and eight hours.

END OF HIBERNATION INDICATOR
Hibernating animals can be monitored by a very slow pulse, to conserve battery life because location of the animal is known. Power is conserved by using a transmitter similar to a mortality monitor but pulsing at a resting transmission single pulse burst. Transmitters can be programmed to indicate the movement of the study animal, at the end of a non-active period, by switching to a double pulse burst mode.

MULTIPLE OPTIONS
A combination of Mortality and Active/Inactive indicators can be programmed into our MP2 transmitter. In this configuration, the pulse modes changes between single pulses (beep beep beep), to double pulse bursts (bibeep bibeep bibeep), and to triple pulse bursts (bibibeep bibibeep bibibeep). The function indicated by each pulse burst mode can be requested by the user.

SLEEPER MODE
Transmitters built including the Sleeper options can be programmed to turn themselves on and off at intervals of your choosing. Non-running transmitters can even be placed on animals and be programmed to turn themselves on at a predetermined date.

AVM can program Sleepers to your specifications, to perform in several modes, separately or in combination. Here are some of the advantages that this new transmitter can give you in the field.

TRAP SPRINGING MONITORS
Remote monitoring of trapsites is possible using transmitters pulsed by one of two options. Spring-type traps can be outfitted with a transmitter module containing a logic circuit which broadcasts a slow pulse rate before the trap is sprung and a faster pulse rate when the trap is sprung. The module itself is attached to a fixed element of the trap or to a nearby stake or tree, while a cord attached to the magnet which controls the mode-switch of module is attached to the trap's spring mechanism. When the trap is triggered, the magnet is pulled off the module, changing the transmitter's pulse mode from slow to fast.

A trap monitor dependent on transmitter position, is also available. Units containing this type of indicator are valuable for use on sapling-incorporated snare traps. Position indicators can be built into any transmitter and battery combination.

The advantage of the logic circuit trap springing monitor is that it can be placed high in a tree for long range signal transmission.

TRANSMITTER BATTERIES

Match the voltage required by the transmitter you have selected with the voltage of the cells in one of the three tables below. Divide the battery's capacity by the current drain of the transmitters to determine days of transmitting life. Note that the longevities in the right hand columns are just sample calculations, and that other longevities can be achieved by using current drains other than those listed.

NOTE: In AVM's battery tables, we list two longevity columns for each typical transmitter current drain, one for the theoretical life and one for the warrantied life of each application using each given battery. Battery manufacturers specify battery capacity for each cell; these capacities are determined under ideal conditions and can be affected by many ambient factors. Therefore, they do not always accurately predict the longevity of a given transmitter/battery combination, under all field conditions.

Table 1. Batteries used to power G3-1V Transmitters. All batteries in Table 1 produce 1.5 volts.

Battery	Weight in grams	Capacity in mAd	Diameter in mm	Height in mm	Longevities of G3-1V's at highest and lowest current drains
					0.02 mA		0.03 mA
					Theoretical life	Warrantied life	Theoretical life	Warrantied life
Ag335* Ag317 Ag364 Ag397 Ag392 Ag393 Ag389 Ag386 Ag357	0.14 0.19 0.31 0.51 0.57 1.13 1.36 1.7 2.27	0.21 0.48 0.79 1.54 1.79 2.9 3.54 5.0 7.3	5.8 5.8 6.8 7.9 7.9 7.9 11.6 11.6 11.6	1.25 1.65 2.2 2.7 3.6 5.35 3.0 4.3 5.35	10.5days 24days 39days 77days 89days 4.6mo. 5.7mo. 8.0mo. 11.7mo.	X 12days 19days 38days 44days 2.3mo. 2.8mo. 4mo. 5.8mo.	7days 16days 26days 51days 59days 3.1mo. 3.8mo. 5.3mo. 7.8mo.	X 8days 13days 25days 29days 1.5mo. 1.9mo. 2.6mo. 3.9mo.
*This battery is available by special request only. If a collar or module contains a transmitter that requires power from a 3-volt or higher battery and if the package size or shape must be smaller than would be possible if a single Table 2 battery were used for power, two small Table 1 batteries may be used in series. If this is done, the battery voltage doubles while the capacity of only one cell is used. It is usually preferable to use one table 2 battery, if possible.