Section IV. CIRCUIT FUNCTIONING

TM 11-5820-554-12

Section IV. CIRCUIT FUNCTIONING

injection signal within the mixer and translates the

3-14. Block Diagram (fig. FO-1)

bandpass IF signal to the desired operating band.

c. RF and ALC Circuits. The output of transmit

The Collins KWM-2/2A is an ssb or a cw transceiver

mixer V6 is applied to receive/transmit amplifier V7.

operating in the range between 4.0 to 30 MHz. It

The amplified output of V7 is applied to driver V8 to

consists of a double-conversion receiver and a double-

drive power amplifier V9 and V10. The output of the

conversion exciter-transmitter. The transmitter and

power amplifier is fed to the antenna through contacts of

receiver circuits use common oscillators, a common

transmit-receive relay K3. Negative feedback from the

mechanical filter, and a common RF amplifier. The

pa plate circuit to driver V8 reduces distortion in the

transmitter low-frequency IF and the receiver low-

output signal. Both the driver and pa stages are

frequency IF is 455 kHz. The high-frequency IF for both

neutralized to insure stability. When the RF driving

is 2.955 to 3.155 MHz. This a bandpass IF which

voltage to the pa becomes great enough that positive

accommodates the full 20-kHz bandwidth.

peaks drive the pa grid positive, the grids begin to draw

3-15. Transmitter Circuits

current and the signal is detected. This produces an

a. A,f Circuits. Microphone or phone patch is

audio envelope. The audio is rectified by ALC rectifier

connected to first transmit audio amplifier VIA,

V17A, which is connected to produce a negative d.c.

amplified and connected to second transmit audio

voltage. This voltage is filtered and is used to control

amplifier V11B. The output of V11B is coupled to third

the gain of transmit IF amplifier V4A and

transmit audio amplifier V3A, amplified and coupled to

receiver/transmit RF amplifier V7. This system allows a

balanced modulator CR1 through CR4. In the TUNE,

high average level of modulation without overdriving

LOCK, and CW positions of the EMISSION switch, the

power amplifier V9 and V10 which would result in

output of tone oscillator V2B is applied to second

increased distortion.

transmit audio amplifier V11B. The amplified tone

3-16. Receiver Circuits

oscillator signal at the output of V11B is applied to vox

a. RF Circuits. The signal input from the antenna is

amplifier V14B to activate the vox circuits in cw

applied through relay contacts to receive/transmit

operation. This signal is also applied to first receiver at

amplifier V7. The output of V7 is fed to first receive

amplifier V16A for cw monitoring.

mixer V13B.

b. Balanced Modulator and Low-Frequency IF

b. Receiver Mixers. The high-frequency injection

Circuits. Audio output from third transmit audio

signal is fed to V13B. The difference product of the first

amplifier V3A and beat-frequency oscillator (bfo) V11A

mixer is applied to variable IF tuning T2. The output of

voltage are applied to the balanced modulator (CRT,

T2 in the range of 2.995 to 3.155 MHz is applied to

CR2, CR3, and CR4). Both upper and lower sideband

second receive mixer V17B. The vfo injection signal is

outputs from the balanced modulator are applied to

applied to V17B. The 455-kHz difference product is

transmit IF amplifier V4A. The output from the IF

applied to mechanical filter FL1.

amplifier is applied to mechanical filter FL1. The

c. IF Circuits. The output from FL1 is applied to

passband of FL1 is centered at 455 kHz. This passes

first receive IF amplifier V1B. The output of V1B is

either the upper or lower sideband depending upon the

applied to second receive IF amplifier V3B and to the

sideband selected when the EMISSION switch connects

age detector. The output of V3B is fed to product

the bfo upper or lower sideband crystal. The single-

detector V15B. The beat-frequency oscillator signal is

sideband output of FL1 is applied to first transmit mixer

applied to the product detector, and the product of the

V5. The mixer cancels the vfo signal energy and

mixing is the detected audio signal. The output of the

translates the 455-kHz single-sideband signal from the

age rectifier circuit is applied to the two receive IF

balanced modulator to a 2.955- to 3.155 MHz single-

amplifiers and to receive/transmit RF amplifier V7. This

sideband signal. The output of the first transmit mixer

avc voltage controls the gain of the receiver and

is applied through variable IF tuning T2 to second

prevents overloading.

transmit mixer V6. The high-frequency injection energy

d. If Circuits. The output from the product detector is

from crystal oscillator V13 A is also applied to mixer

applied to first audio amplifier V16A. The amplified

V6. This arrangement cancels the high-frequency

audio output of V16A is applied to second

3-15