V. G. ELLERBRUCH, F. C. FITCHEN AND R. W. SAWREY 
1113 
from several birds and that the transmission 
distance be one mile. Frequency spaced, con- 
tinuous wave transmitters were used to ac- 
complish the project transmitter requirements. 
Crystal controlled, continuous wave trans- 
mitters were designed to operate at 151.000 
MHz and above. For simultaneous use on several 
subjects, transmitters were frequency spaced 
at 10 kHz increments above 151.000 MHz. 
There are several advantages in adopting such 
a scheme. All the transmitted energy for a con- 
tinuous wave transmitter is contained in a 
single frequency component and not spread over 
a frequency band. Receiver bandwidth can then 
be quite narrow, for noise rejection, but still 
have the capability to receive that energy in 
the single component transmitted by each trans- 
mitter. Conversely, side-bands for a pulsing 
transmitter can consume energy that is never 
received and they are especially objectionable 
when the transmitter is close to the receiving 
antenna because several frequency bands are 
swamped out by side-bands. With birds in the 
wild there isn't any sure control over their 
daily movements and no restriction on roosting 
or nesting areas. They are free to roost or nest 
close to, or far from, the fixed position receiv- 
ing antenna. For a continuous wave system no 
particular problem occurs. It is true that the 
BFO (beat frequency oscillator) signal from 
CW transmission can be disguised by other 
extraneous signals but where there is relatively 
little radio activity in the 151 MHz range no 
difficulty is encountered. 
A sensitive receiving system is obtained by 
employing a high gain antenna preamplifier 
(50 dB) that is coupled to a directional receiv- 
ing antenna. The bandwidth of the receiving 
system is 1 MHz. 
There is not a wide variety of transmitting 
antennas that can be used with pheasants be- 
cause of their rather small size. A whip antenna 
seemed to function the best and was selected. 
The birds are not hindered in their movements 
by carrying a small spring-steel whip and the 
spring-steel flexes freely as the bird moves 
about. The output port of the active circuit of 
Figure 4 is terminated with the whip antenna 
and the design proceeds accordingly. 
A single transistor Hartley oscillator circuit 
1 
Figure 9. — Emitter-biasing for the Hartley- 
oscillator. 
was chosen for the active circuit. The Hartley 
oscillator permitted emitter biasing. This is an 
important feature in the design since the trans- 
mitter is used outside the year around in South 
Dakota where the average temperature is pleas- 
ant, but there can be extremes of — 30°F to 
100°F from winter to summer. The leakage cur- 
rent stability factor for an emitter-biased cir- 
cuit can be, and for this application, is made 
equal to 1. Figure 9 shows the dc circuit. 
Dypre ^ has shown that for a 1-port network 
with Sa > 1 the circuit will oscillate when prop- 
erly terminated. Figure 10 illustrates how two 
networks are coupled together giving a com- 
posite circuit that will oscillate. The gain and 
phase criteria for oscillation are met when the 
active network with reflection coefficient Sa 
is terminated by a passive network that has a 
reflection coefficient, sp, equal to the reciprocal 
of that for the active circuit. It is assumed, and 
1 
1 1 
1 1 
1 Active 
U- 
1 
— j Output j 
1 
[ Termination | 
' Network 
U - 
1 
— 1 (WHIP) 1 
1 
_J 
L .J 
Figure 10. — Combination of one-port networks to make 
an oscillator. 
