Section II. DETAILED FUNCTIONAL OPERATION
summing function of the received 26.3 kHz signal. This
6-3. Detailed Functional Analysis (fig. FO-2,
output drives a 26.3 kHz tuned amplifier (Q7) which is
located at rear of manual).
fixed tuned with a bandwidth of approximately 6 kHz.
The output of the 26.3 kHz tuned amplifier passes
Detailed block diagram of the intrusion detection system
signals between 23.3 and 29.3 kHz for driving two R-C
(fig. FO-2) highlights the functions within the processor
phase shift networks (45 degree lead, C16 and R22 for
and the transceiver as well as signal flow paths between
the digital channel, and a 45 degree lag, C 18 and R21
functions. Blocks are identified with their function and
for the analog channel). Each phase shifted signal is
the main components comprising the function.
mixed by its respective mixer (Q9 and Q8) with the 26.3
a. Transmit function. In the processor, oscillator
kHz oscillator signal by way of oscillator shaper Q5.
Q1 generates a 26.3 kHz signal which drives buffer
The difference output from each mixer is the Doppler
amplifier Q2. The output of the buffer amplifier drives
signal resulting from a moving object in the surveyed
power amplifier Q3 and Q4 and oscillator shaper Q5.
area. Mixer outputs each pass through a Doppler
bandpass filter which has a 3 dB cut-off frequency set at
isolation between the power amplifier and the transmit in
12 Hz (corresponding to 0.25 feet per second) and 800
the transceiver. The output of the power amplifier feeds
Hz (corresponding to 16.7 feet per second).
the transmitting transducers (one through twenty
transceivers connected in parallel). The transformer
also prevents unbalanced 26.3 kHz currents from
forming on the ground shield of the signal lead from the
Any unbalanced currents
Higher speed movements are detected
present would cause an increase in the level of 26.3 kHz
on the slopes of the 800 Hz cut-off filter.
carrier fed back into the receiving circuits which could,
in turn, bring the receiver circuits closer to saturation
and cut down on its dynamic range. The equipment
must be capable of handling a wide amplitude range of
(2 f/c)v = 48.97 v
26.3 kHz signals in order to be able to accommodate the
wide range of normal room backscatter from the sum of
Doppler frequency in Hz
up to twenty transceivers. The transmit transducer
operating frequency = 26,300 Hz
emits an ultrasonic signal of 26.3 kHz which is above
velocity of sound (sea level at 20° )
the human hearing range.
target radial velocity in ft./sec3
The signal developed by the lead phase shift
Subharmonics mechanically generated
network is the digital channel and the signal developed
by the lag phase shift network is the analog channel.
The digital channel signal passing through the bandpass
are within the human hearing range
filter is amplified and peak limited by Z1 and amplified
and hard limited by Z2. When the noise output of
b. Receive Function. The receive function is
amplifier and peak limiter Z1 is of a high density
more complex than the transmit function and operates
(jamming condition) the bipolar detector Q18 and Q19
operates to actuate the alarm circuit. The output of
The output of each
amplifier and hard limiter Z2 is a limited square wave of
receiver transducer is amplified and isolated from the
50 percent duty cycle with a period directly proportional
interconnections by a preamplifier. The preamplifier has
to the detected velocity of the moving target.
a manual RANGE control for setting the sensitivity
(range) for each individual transceiver in relation to the
This square wave is applied through a
area being surveyed. A single preamplifier is configured
differentiator (C30, R43, and R.44) to the base of Q14,
to have a very high output impedance compared to the
and also applied through an integrator (R42 and C31)
input impedance of the line terminating summing
and a divider (R34 and R77) to the base of Q13.
amplifier Q6 in the processor.
preamplifiers connected in parallel the combined
Q14 (normally off) is turned on by the positive
impedance of the worst condition (twenty) will not
going transition of the square wave, and is held on for
swamp the input to the summing amplifier.
110 microseconds due to the differentiator time
The line terminating
As a result, a negative-going 110
summing amplifier Q6 offers a compatible impedance
microsecond pulse appears at the Q14 collector, and is
match for the interconnecting cables and multiple
then inverted to positive polarity by Q15.
number of receiving preamplifiers and also performs a