1202 
MONITORING 
MULTI-CHANNEL TELEMETRY TRANSMITTER 
EKG ELECTRODES 
PRESSURE SENSORS 
TRANSMITTER 
INDUCTIVE 
PICK-UP COIL 
BATTERY PACK WITH ON-OFF SWITCH 
ACTIVATED REMOTELY BY RF 
ANTENNA 
m 
Figure 4. — Multichannel telemetry transmitter. 
ods or when a highly uncooperative animal is 
being utilized. 
Since the power supply, which is usually a 
battery, must also be implanted, the selection of 
circuits that consume only microwatts of power, 
or at most a few milliwatts, is essential. Each 
experimental design must be evaluated to deter- 
mine the best tradeoff between battery size and 
such factors as telemetry range and operating 
life of the unit. The selection of transducers is 
also a major factor in determining such power 
requirements. Using single channel tempera- 
ture or EKG units as little as 12fiW of power 
are consumed while continuously transmitting 
data for a distance of 3 to 5 feet. A multichan- 
nel system with four pressure transducers con- 
sumes 6mW to transmit 50 feet. A single chan- 
nel electromagnetic flow system consumes 400 
mW to transmit data the same distance. 
An important feature of the designs used in 
the described units were their ability to attain a 
great degree of accuracy utilizing sophisticated 
modulation techniques. The use of subcarrier 
oscillators and automatic calibrations are the 
main factors responsible for these results. The 
methods used for the implanted units are essen- 
tially identical to those used for the larger 
powered telemetry systems developed for space 
research. This allows the accuracy available 
from the selected transducers to be transmitted 
over a radio telemetry link without degrada- 
tion. 
These devices in their present state of devel- 
opment have a variety of potential applications 
distinct from their present use in a laboratory 
environment. Appropriate units could be used 
in animal tracking studies which require phys- 
iologic measurements, as well as information 
