Section II. DETAILED FUNCTIONAL OPERATION

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

Transformer T1 provides impedance matching and dc

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

NOTE

also prevents unbalanced 26.3 kHz currents from

forming on the ground shield of the signal lead from the

receiving preamplifier.

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

NOTE

and cut down on its dynamic range. The equipment

must be capable of handling a wide amplitude range of

FD =

(2 f/c)v = 48.97 v

26.3 kHz signals in order to be able to accommodate the

where

wide range of normal room backscatter from the sum of

FD =

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.

1074.15 ft/sec.

target radial velocity in ft./sec3

NOTE

The signal developed by the lead phase shift

Subharmonics mechanically generated

network is the digital channel and the signal developed

at , 1/3, etc. of the oscillator frequency

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

as follows:

operates to actuate the alarm circuit. The output of

(1)

Transceiver.

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.

With multiple

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

(2)

Processor.

The line terminating

constant.

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

6-2