Figure 5-6(2). Pin connections of integrated circuits (part 2 of 2).

TM 11-6625-922-15

Transistors Q4 and Q7 together give a voltage gain of

follower Q17. The vfo signal and the modulated 2-MHZ

signal are mixed in stage Q13, 14; the output is sent to

slightly less than unity, with feedback from the emitter to

the base of Q4. Four active filter sections in cascade

compound emitter-follower Q15, Q16, and then to a low-

provide the desired frequency response; near unity gain

pass inductance-capacitance (lc) network to select only

from dc to near 25Hz, then rapid attenuation of higher

the difference frequency, 0- to 600-kHz modulated sine

frequency components. An external variable resistor

wave.

(front panel DELAY ZERO ADJ control) is used across

e. 200-kHz Modulator Mixer. A15 (fig. 9-11). The

R16 in the fourth stage to give a variable phase shift for

operation of this circuit is similar to that of the 2-MHz

setting initial conditions. The input at pin V is a signal

modulator mixer. The inputs are a 200 kHz square

with 25 Hz modulation; the output at pin Y is the 25-Hz

wave, a sine-wave modulating signal at pin A, and a vfo

sine wave. The operation of the 83-1/3-Hz and 250-Hz

200- to 260-khz square wave.

The output is a

active filters are similar. Resistors R61, R63, and R65

modulated sine wave, between 0 and 60 khz.

are selected values used only on A13 to give a fixed

f. Low-Pass Active Filters 1A7 and A13 (fig. 9-

phase shift in the filters. On A7, the phase shift is

13). Transistors Q4 and Q7 represent a single active

adjustable by the DELAY ZERO ADJ front panel control.

filter section. The products of R13 and C4, and R16 and

C7 determine the cutoff frequency of the low-pass filter.

Figure 5-6(2). Pin connections of integrated circuits (part 2 of 2).

5-11