Microminiature VHF Subsystems for Small Mammals

Figure 1. CHP Configurations

Introduction

The CHP series of transmitters was developed in the mid 1990s in response to a need by the wildlife field for an ultra small transmitter which could be configured in various ways for small mammals. Most of the technology developed prior to the CHP transmitters was based on miniature circuits from the early 1960s which were made small by simply eliminating components from the circuit itself. These early miniature transmitters were small, but they were very unstable in their performance characteristics. Many of these early designs drifted in frequency and the transmission was cluttered with unwanted spurious signals throughout the frequency spectrum, resulting in a characteristic "chirp" sound. Fortunately, these units were low in radiated power so they often did not interfere with other radio services. However, they wasted power, exhibited very low efficiency, interfered with one another, and often exhibited poor range performance. They also had very unstable pulse rates and pulse widths which made monitoring the units difficult. All these problems were made even worse as the battery voltage changed as the energy capacity of the battery was depleted over the unit's operational life or as temperature conditions changed from one trip a field to the next. For many years there was no alternative to these simple one stage circuits.

CHP technology which appeared in the 1990s, took a different approach to miniaturization as compared to the early technology. The concept was to use virtually the same circuit that was used in larger state-of-the-art wildlife transmitters but in this case, incorporate extremely miniaturized components and highly integrated circuits which retained their satiability but were physically small and could operate at very low voltage required by the small batteries inherent in these subsystems. When first introduced this circuitry was successful but unfortunately, the cost of the systems was higher then the old style units (which sold for around $125 - $150). The performance and reliability however, was very good. In the past few years, the price of the components we use to build these ultra small transmitting units has come down, making these units cost competitive with virtually any technology currently used in manufacturing wildlife transmitters.

Packaging Technology

Any radio transmitter system used in the wildlife field must be as "moisture proof" as possible or it will not achieve its full operational life when deployed. It will leak before it runs out of battery energy and thus fail prematurely. In the case of these very small transmitting units, packaging is still important even though many of the smallest units may only have sufficient battery capacity to operate for a few weeks. In the early days of radio telemetry most companies used epoxies, acrylics, or urethanes. In many case these polymeric materials were virtually painted onto the electronics and battery assembly. Such approaches provided a thin, fragile coating of the polymer moisture barrier. More material could be used to increase the effectiveness of the moisture barrier somewhat; however this was rarely done, as the resulting increase in packaging weight was a major consideration. Unfortunately, this "paint it on" approach often meant that the effectiveness of the water resistant layer was highly variable. It varied with the mix of the polymer selected, the mixing process, and the environmental conditions such as the humidity on the day of assembly, and quite honestly on the level of concentration of the assembler that particular day. The effectiveness of the moisture barrier was variable from a given supplier, and between suppliers. In short, the manufacturing process was difficult to control and not very repeatable.

Fortunately today's polymeric processes are more refined, application techniques are more controlled and the polymers themselves are more suitable to these applications than in the past. The packaging design of Telonics' CHP series transmitters eliminates the variability of previous construction approaches by placing a closely controlled, uniform amount of carefully selected polymer around the electronics and battery - completely eliminating the human variability experienced in previous packaging approaches. In short, the effectiveness of the polymer in its role as a waterproofing agent is better controlled and the reliability of these systems has increased in direct proportion.

The short operational life of many of the very small CHP units means that they must be rebatteried for redeployment. All CHP units are refurbishable to the original condition. (Sensors cannot be added to configurations at refurbishment, they must be specified at when the units are initially procured). The weight of the systems (including the transmitter electronics, battery, antenna, and polymeric package) ranges between 1.2 grams and 13.5 grams. The operational life is directly related to the weight of the subsystem and ranges between three weeks and 25.7 months depending on the pulse rate. The units can be specified to include a temperature sensor. Some models can be equipped with a tip switch for activity sensing capability. The data are transferred to the user by changes in the pulse rate.

Collars for Small Mammals

Figure 2

CHP configurations for small mammals are designed to maximize the operational life of the configuration while providing a reasonable level of protection and durability consistent with maximum operational life. Because these configurations are mounted on very small collars, the antenna is necessarily much shorter then the ideal quarter wavelength monopole "whip" antenna which results in reduced signal radiation. The range of these systems is usually less then a kilometer on the ground. Several collar designs are provided as examples but other collar configurations are possible. Please consult with our staff if the configurations provided do not meet your requirements.
(Tuned loop antennas vs. short whip antennas vs. internal helix antennas)

Key Features

• Small, light weight design suited for small mammals.
• Units can be refurbished. Units can be refurbished to the original configuration and returned to the user with a reinstated warranty.
• Power output is matched to the small battery systems used in these configurations.
• Units are provided with the collar configuration ready for deployment on small mammals.
• Advances in polymeric casting materials and techniques provide excellent resistance and mechanical integrity.

How to use this table: The information contained in the following table is provided in a manner to allow comparison of models. To sort by model attributes i.e. weight, CLICK ON THE COLUMN HEADING. To obtain more specific information for a model, CLICK ON THE MODEL NUMBER.

Notes:
1. Transmitter weight includes a 4" lightweight antenna and Standard Attachment Option.
2. Sizes shown are for the main outline only. Attachment options may increase the overall dimensions.

CHP Conventional Control Options

OPT. S2 Temperature Sensor. Sensor provides pulse rate which varies according to temperature within the transmitting subsystem. User specifies desired pulse rate at anticipated median temperature and approximate range of temperatures to be monitored. Pulse rate increases at higher temperatures and decreases at lower temperatures.

Frequently Asked Questions

How much range can be achieved from these small transmitters under field conditions?
The range of any transmitting system is a function of all the components of the system including the sensitivity, bandwidth, and noise figure of the receiver, the loss in the coaxial cable that connects the receiver to the antenna, the gain, impedance match and tuning of the antenna, the antenna on the transmitter on the animal, the ability of the battery to supply the necessary current to the transmitter so it can be converted to a radio signal, the ability to remain in line of sight, the density and composition of the vegetation, and the efficiency and RF output power level of the transmitting device. Because of all the variables that collectively determine range performance, manufacturers of radio telemetry cannot honestly guarantee a certain range performance from a telemetry system. It is commonly assumed by end users that if the range of a system is not what was expected, the most likely explanation is that the transmitter's output is the most likely problem. Often that is not the case. In fact, with state-of-the-art transmitters, the actual power level is well controlled over the battery life and specified operational temperature range of the battery. If a yard stick is required to plan a program the following rule of thumb helps. Most very small transmitting units must operate using very small power/battery systems which are restricted to temperatures above zero degrees centigrade. The battery voltage and current delivery capability generally determine how much transmitted power we can expect to deliver to the antenna. If we assume that the rest of the system is state-of-the-art, then small transmitters using the CHP technology can deliver range performance of 0.5-2 km on the ground to a handheld antenna and 5 km or more to an aircraft circling above with a properly mounted aircraft antenna system.

Will I get more range if I use bigger antennas at the receiving site?
The answer to this question must also be qualified... but in general the answer is yes. The rated gain of an antenna is directly related to range performance. For every 6db of gain added to the antenna the line-of-site range doubles. BUT... to achieve the rated gain of the antenna the user must mount the antenna in a manner which does not detune the antenna or disrupt the pattern of the antenna. This is not always a very easy assignment. The larger the antenna the more difficult it is to use in the field. In general, larger antennas really means more antenna elements which means that the entire antenna must be properly mounted further off the ground and away from conductive surfaces. If one does not accomplish proper mounting of the antenna there is no increase in range performance and all you end up with is more metal in the air to attract lighting strikes.

How long does it take between time of order and receiving CHP equipment?
The typical delivery schedule is about 8 weeks when the frequency determining crystals must be ordered specifically for your study. Premium delivery of crystal is sometimes possible but can add 20-40 dollars to the cost of the unit. We do carry crystals in stock for many commonly used frequency bands. If crystals are in stock the lead time is typically 4 weeks.

Can units be rebatteried?
Yes. This process is called refurbishment. The process actually involves much more than simply putting on a new battery. It really involves recovering the electronics, retesting the electronics and rebuilding the configuration to its original configuration. When the unit is returned to you from our factory it is like new and has a like new warranty. The cost to refurbish a unit is about two thirds the current cost of the configuration.

Can the user replace the batteries to save money?
The transmitter does belong to you or your agency. You can do as you will with the unit. Because of the complexity involved, if you decide to replace the batteries we can't offer any support for that system in the future. Unfortunately, various groups and individuals have different skill levels and access to support services. Some individuals may be capable of accomplishing the tedious work without doing damage to the unit, others cannot. Since there is no way for Telonics to oversee the refurbishment we can not support or warranty the results.

Can the configuration be changed for use with another species?
Yes in the case of the larger two of the three models, the CHP-5P and CHP-6P (i.e., a 6P can be converted to a 5P and the converse). The CHP-8P, the smallest configuration in the CHP series, utilizes unique techniques of miniaturization which do not interchange with the larger models and therefore cannot be modified to other configurations. The CHP-5P and CHP-6P units can be retrofitted to another configuration using the same pulse rates, pulse widths, and sensors. They can even be changed from a unit that mounts on a bird to a unit with a collar for a small mammal. However, the process can, in some cases cost more then a refurbishment. Thus in some cases a new unit is a better option.

Can the user get a custom configuration if the existing configuration does not meet the study requirements exactly?
Yes. Specific CHP configurations have been developed for various groups of animals and some of the options are listed below. As with all systems the least expensive approach is to use an existing configuration. In many cases there is a certain history associated with a configuration and often the field testing has already been completed and the design is refined. However, Telonics often does custom configurations for specific applications. Those custom applications necessarily cost more to cover the consulting, engineering, procurement of special materials, custom building, and documentation of the application. Please also recognize that any new design involves additional risk for the user because there is no history of use in the field. So if cost is the main driver in your choice of a telemetry transmitting subsystem try to select from existing configurations. Remember however, that for each of the many configurations listed, some researcher tried it for the first time. Our engineers and biologists have the experience to provide the advice for special applications which will significantly increase your probability of success.

For more information on CHP Microminiaturized Subsystems, please contact info@telonics.com.

932 E. Impala Ave., Mesa, AZ, 85204-6699 U.S.A.
Tel: 480-892-4444 FAX: 480-892-9139
Email - info@telonics.com