Circuit Description

TM 11-5895-1097-40

oscillator Q6 is a crystal controlled oscillator running at the

by the ceramic filter FL2, to the if. amplifier Q7, Q8, and Q9

fundamental frequency of the crystal Y1, which is 17.645 MHz.

which provides overall gain. The amplified if. signal is then

The crystal Y1 operates as a series collector base feedback

dectected and compared against a set value, determining the

path. C40 and C41 provide phase shift to ensure oscillation.

operability of the RCVR XTAL MODULE under test. If the rcvr

The oscillator signal at the base of Q7 is coupled by C39 to the

xtal under test is good, the rcvr comparator portion of U6 will

second mixer input. (Q5)

drive the rcvr logic NOR gates of U7. This output will drive the

(4) Second Mixer.

The second mixer, Q5,

GO lamp driver QI I and light the GO lamp. If the rcvr xtal

receives the 18.1 MHz if. signals from FL1 and the 17.645

under test is no good, the output of the logic gates will be

MHz local oscillator signals from Q6. Q5 heterodynes the two

inverted. This output will drive the NO GO lamp driver QIO,

signals ? and produces an output at the second if. of 455 KHz.

and light the NO GO lamp.

(5) Ceramic filter. The second if. signal from the

b. Xmit Xtal Circuit. The XMIT XTAL MODULE under

second mixer stage is coupled through FL2, the 455 KHz filter,

test forms the crystal portion of a local oscillator QI and Q2.

and applied to the input of the if. amplifier.

This signal is then amplified by Q3 and Q4. The amplified

(6) If. amplifier. The if. amplifier chain, Q7, Q8,

signal is then detected and compared against a set value,

and Q9 provide approximately 40 dB gain for the 455 KHz

determing the operability of the XMIT XTAL MODULE under

signal.

test. If the xmit xtal under test is good, the xmit comparator

(7) First detector. The amplified if. signal is

portion of U6 will drive the xmit logic NOR gates of U7. This

detected by a detector circuit using components CR8, CR9,

output will drive the GO lamp driver Q 11, and light the GO

and C48. The output level of the detector is compared by the

lamp. If the xmit xtal under test is no good, the output of the

comparator circuit U6A.

logic gates will be inverted. This output will drive the NO GO

(8) Rcvr circuit amplifier. Q12 and Q13 are

lamp Q10, and light the NO GO lamp.

general purpose high frequency amplifiers. They amplify the

c. Counter Buffer Amplifier Circuit. The input to the

signal from the local oscillator of the RCVR XTAL MODULE

counter circuit is the xtal overtone frequency before detection

under test. This amplified signal, sampled through the

of either the rcvr or xmit circuits, whichever is being used. This

secondary of transformer T3, is fed to the overtone buffer

signal is amplified, buffered, filtered and fed to a BNC

amplifier where is is again amplified by Q 14 and detected by

connector (COUNTER OUTPUT) on the front panel.

the second detector CR5, CR6, and C31.

d. Power Supply Circuit. The power supply circuit

(9) Comparator. U6 is a quad single supply

consists of a transformer mounted on the front panel, full wave

comparator, used for level detection. The signal levels

rectifiers CRI and CR2, a 12 Vdc regulator, and a 6.2 Vdc

detected from the if. amplifier and the overtone buffer amplifier

regulator on the main circuit card A1.

are compared against set voltage levels. The outputs of both

2-3. Circuit Description (fig. FO-2, FO-3)

comparators U6A and U6C are fed to the logic NOR gates

a. Rcvr Xtal Circuit. The rcvr xtal circuit consists of a first

U7C.

mixer, crystal filter, second mixer, second local oscillator,

(10) Rcvr logic U7C and U7B. Both of the

ceramic filter, if. amplifier, overtone amplifier, two detectors,

comparator outputs are input to U7 which verifies the presence

two comparators and two logic gates.

of the correct signals and performs inversions where they are

(1) First mixer. Components U4, T1, T2, C21

required. If both signals are correct, NOR gate U7C would bias

through C26, R22, R23 and L5 comprise the first mixer. The

the GO driver Q1 1 to light the GO lamp. If either one or both

first mixer is of a balanced design to minimize signals in the

of the signals is correct, U7B, by inversion of U7C output,

output. Its purpose is to combine the incoming RF and LO

would bias the NO GO driver to light the NO GO lamp.

signals, from the rcvr xtal module, into a single if. of 18.1 MHz.

b. Xmit Xtal Circuit. The xmit xtal circuit consists of an

The first mixer converts the RF and first local oscillator energy

oscillator buffer amplifier, detector, comparator and two logic

to the 18.1 MHz if. by vector addition of the two signals. This

gates.

difference frequency is picked off by the selectivity of TI

(1) Oscillator. The oscillator, a modified Butler

resonating with C22 and C25.

circuit, is made up of Q1, Q2 and the XMIT XTAL MODULE

(2) Crystal filter. The 18.1 signal from the first

under test. The output of Q2 is the second harmonic of the

mixer stage is coupled through FLI, the 18.1 MHz crystal filter,

crystal inserted into the test socket.

and applied to the input of the second mixer. C32, C43, C35,

(2) Buffer amplifier. Q3 and Q4 amplify the

R27 and L9 form a network to match the crystal filter

oscillator signal to a detectable level.

impedance to the second mixer input.

(3) Detector. The amplified signal is detected by a detector

(3) Second local oscillator. The second local

circuit using components CR3, CR4, and C17. The output

level of the detector is compared by the comparator U6B.

2-2