Figure 2 -15 Discriminator Circuit Waveforms.

TM 11-5820-509-35

consists of the circuits associated with transistors Q8,

essentially drift-free output frequency at Q22 This output

Q9, and Q10, while channel B consists of the circuits

is routed through the bandpass filter consisting of

associated with transistors Q11, Q12, and Q13.

capacitors C105 through C109 and inductors L24

Selection of these transistors into matched pairs and the

through L26 to remove any spurious frequencies that

careful adjustment of bias and coupling components in

may have been in-troduced in the desired signal due to

these two channels assures nearly identical stage gains

mixing. The 700- to 601-kHz signal is clipped by limiter

in each of the two signal paths. Capicitor C21 and

CR7-CR8 to form a squarewave that is coupled to the

resistor R34 form a phase-shift network in the reference

discriminator circuit.

signal path from follower Q23 to the input of Q11. The

d. The O.9- to 1.8-MHz signal from limiter Q19 is

reference signals are summed with the unshifted output

routed through follower Q24 before being heterodyned

of clipper CR9-CR15 in both channels and the resulting

in diode quad mixer CR10 with the 5-to 14-MHz signal

signal at the output of Q8 and Q11 is similar to the

from Q18 in signal data translator A3. Since each of

waveform shown at the top of figure 2-15.

The

these input signals is variable (depending on the setting

repetition rate of these two envelopes is

of the KILOCYCLES indicator on the front panel of the

receiver-transmitter), the output of mixer Q10 is also

variable and may be any 100-kHz channel between 3.2-

and 13.1-MHz. This output frequency is routed through

follower Q25 and further mixed in diode quade CR11

with the hf oscillator signal from Q5 of signal data

translator A3. The difference-frequency at the output of

mixer CR11 is also variable and may be any 1-kHz

channel between 601- and 700-kHz.

This signal

contains an increment of hf oscillator error frequency.

The mixer output is amplified by Q26, filtered by the

circuit consisting of capacitors C169 through C177 in

association with inductors L29 through L32. Further

amplification is obtained by Q27 before routing the

signal to forward-limiting clipper CR9-CR15.

The

squarewave output of this clipper is applied to both

channels of the discriminator circuit.

e. The discriminator circuit has two modes of

operation: the frequency control mode, and the phase

control mode. When the hf oscillator output frequency

is within 50 kHz of the reference standard the

discriminator is said to be in the frequency control mode

and it compares the 601-to 700-kHz reference signal

from follower Q23 with the 601- to 700-kHz(plus hf

oscillator error) signal from clipper CR9-CR15. The

Figure 2 -15 Discriminator Circuit Waveforms.

resulting dc output is applied to the varicap control

circuit of signal data translator A3 to reduce the hf

equal to the difference between the two input

oscillator error toward zero.

When the difference

frequencies and represents the frequency error

between the hf oscillator output frequency and the

associated with the hf oscillator. Either envelope may

reference signal is less than approximately 5 kHz, the

lead the other along the time base, depending upon

discriminator assumes the phase control mode. In this

whether the hf oscillator frequency is higher or lower

mode, the circuit monitors the changing phase-

than the reference frequency. The outputs of amplifiers

difference between the two input signals and corrects

Q8 and Q 11 are further amplified by Q9 and Q12

the error voltages until this phase-difference approaches

respectively and the individual signals are then detected

zero. When the phase error is zero, the hf oscillator

by diodes CR3 and CR4. In the frequency control

output frequency is identical with the reference oscillator

mode, the leading edge of the envelope in each channel

output frequency. Discriminator channel A

is used to trigger transistor-pair Q10-Q13 so that they

alternately conduct. These transistors operate as a

bistable multivibrator with a switching rate equal to the

repetition rate of the envelope in each channel. The

resulting clipped

2-30