30 MHz Switch

TM 11-6625-467-34

of diode CR2 reverse bias the diodes and thereby

frequencies of the discriminator).

keep them nonconducting with no grounds applied

d. As the frequency of the incoming signal swings

to the gate inputs. Capacitor C14 couples the 30

below 500-kHz and approaches the resonant fre-

megahertz signal to one side of the diode switch

quency of inductor L1 and capacitor C4 and C7, the

c o m b i n e d impedance decreases. T h i s decrease

With neither gate input grounded, both diodes are

reverse biased and block the 30 megahertz signal

r e s u l t s in an increase in the voltage developed

f r o m the output. With the positive gate input

across capacitor C7. During one half cycle, diode

grounded, diode CR3 conducts on the negative half

C R 3 conducts and bypasses the current around

cycles of the 100-HZ square wave The conduction

c a p a c i t o r C7 during the next half cycle, and

path is from the square wave Input terminal through

capacitor C7 charges and then discharges through

R24, L2, CR3, and 1,3 to ground. During the conduc

one-half of inductor L1, dropping resistor R32, and

tion period, diode CR3 acts as a short circuit and the

load resistor R34. The current flow through resistor

30-megahertz signal passes through diode CR3 and

R34 produces a negative discriminator output. As

capacitor L13 to the output. The positive half cycle

the frequency continues to decrease below 500-kHz,

of the 100-HZ square wave reverse hisses diode CR3

the voltage developed across capacitor C7 increases,

and blocks the 30-megahertz signal from the output

and subsequently the discriminator output becomes

With the negative gate grounded, the opposite ac-

more negative.

tion occurs. Diode CR2 is forward biased on the

e. When an excursion of the incoming signal is

positive half cycles and allows the 30-megahertz

above the center frequency, an opposite site of con-

signal to pass through CR2 to the output. With both

ditions exists. The impedance of the series lc circuit,

the negative and positive gates grounded, a con-

consisting of capacitors C5, C6, C9 and C10 and in-

stant amplitude, 30-megahertz signal appears at the

ductor L1, decreases and current flow through this

output. The output waveforms for each gate condi-

circuit increases. The rectifying action of diode CR2

tion are shown in B, figure 2-29.

causes current to flow through one-half of inductor

b. Inductors L.1 through L5 have a high imped

L1, dropping resistor R32 and the load resistor R33.

ante at 30-megahertz and a low impedance at 100

In this case, the current flow through the load re-

Hz. Inductors L1 and L3 block the 30-megahertz

sistor is opposite in direction to the current flow

signal from the power supply and gate circuits. In

when the signal swings below the center frequency;

ductor L2 passes the 100-Hz square wave hut pre

therefore, the discriminator output signal depends

vents the 30-megahertz signal from entering the

on how greatly the signal deviates from the center

external circuit. Inductor Lt5 prevent the 100-Hz

frequency, 500-kHz. A deviation toward a higher

square wave from feeding back to the 30-megahertz

frequency produces a negative voltage output. The

oscillator circuit. Inductor 1.4 provides a high ac

frequency versus output voltage curve of the dis-

impedance ground return for the 30 megahertz out

criminator is shown in B, figure 2-28.

put signal.

f. Resistor R40 is adjustable and sets the output

amplitude of the discriminator. Inductor L2 and ca-

2-35. Frequency Selection Circuit

pacitor C11 are resonant at 500-kHz. The tuned cir-

(fig. 2-30 thru 2-32)

cuit is in series with the signal path and forms a

a. General. F r e q u e n c y s e l e c t i o n f o r t h e '

band elimination filter for 500-kHz frequencies that

AN/ARC-54 RF subchassis is performed by FRE-

might be present at the output of the discriminator.

QUENCY SELECTOR-MC switches S7, S8 and S9.

Transistor Q6 amplifies the audio output of the dis-

The frequency selection is accomplished by three

criminator, and the circuit output is taken at the col-

five-wire reentrant, open seeking switching cir

lector of Q6.

cuits. Figure 2-30 is a schematic diagram of simple

open-seeking reentrant system. With the, switches

2-34. 30 MHz Switch

in the positions shown,switch S1. applied ground to

(fig. 2-29)

terminal 1 of S2. Ground from terminaL C of S2, to

motor B1 causes the motor to operate, aind S2 is

The 30-megahertz switch receives two signal in-

turned in a clockwise direction. When the open seg-

puts: a 30-megahertz sine wave from the 30-mega-

ment of S2 reaches terminal 2, the circuit o p e n s a n d

hertz oscillator and a 100-HZ square wave from the

the motor stops. The action is the same for any posi-

AN/ARC-54 homer module.

tion set by S1. Note that switches S1 and S2 are

a. By connecting grounds to the gate inputs, the

physically complementary. All reentrant systems

switch circuit produces signals that check the diode

have this characteristic. Figure 2-31 is a schematic

switch circuit in the AN/ARC-54 homer module.

diagram of the test set FREQUENCY SELECTOR-

The 27.5 volts dc connected to the anode of diode

MC switches. Although the switching arrangement

CR3 and the 27.5 volts dc connected to the cathode

2-71