V. G. ELLERBRUCH, F. C. FITCHEN AND R. W. SAWREY 
1107 
dc 
Supplies 
Signal 
Source 
_iZol_ 
Bias 
Tee 
Directional 
CouDler 
Adjustable 
Line 
Test 
Jig 
Vector 
Voltmeter 
Directional 
Coupler 
Bias 
Tee 
Figure 3. — Block diagram of measurement system. 
urements of V2+, V2~ and Vi~ will specify S12 
and S22- These six voltages completely specify 
the set of s-parameters for a given 2-port net- 
work. A more complete block diagram of the 
measurement system is shown in Figure 3. 
DESIGN CONCEPTS 
A simple biotelemetry transmitter can be 
visualized as consisting of 3 main parts; (1) 
active network, (2) input termination and (3) 
output termination. Figure 4 illustrates, in 
Active 
Circuit 
Output 
TerminatitMi 
Input 
Termination 
Figure 4. — Transmitter block diagram Biotelemetry 
transmitter design methods. 
block diagram form, such a transmitter. The 
active network might consist of only one tran- 
sistor plus biasing circuitry or it might consist 
of a complete subsystem such as a transistor 
combined with a filter network. 
If more complex circuits are required, then 
the active network might be a complex inte- 
grated circuit (IC). The reason more ICs are 
not presently being used in the biotelemetry 
business is because they are expensive unless 
mass produced, and their power drain is often 
excessive. The power drain of an ordinary IC 
is usually prohibitive for applications requiring 
wireless implantable transmitters or for lon- 
gevity transmitters such as those used on wild- 
life subjects that are allowed complete freedom 
of movement in their habitat. 
The time should come when standard, low 
energy circuits will be readily available for 
biotelemetry systems. Then ICs will be economi- 
cal from both energy and cost standpoints. 
