Instruction manual

9. BLOCK DIAGRAMS

Block diagrams of the Audio Control System elements are shown in Appendix 4. The following

is a basic description of some of the “blocks” that may or may not be obvious. Please refer to

the ACS Block Diagrams sheets A4-1 and A4-2 when reading the following.

A. Audio Amplifier: This is a Voltage gain of ten amplifier used to amplify the audio level

from the external speaker jack of the receiver/transceiver to a relatively high level for

switching. This amplification also gets the audio to a level that can be detected by the

Activity Monitor (B).

B. Activity Monitor: The Activity Monitor is a voltage doubling rectifier with a transistor LED

driver. The time constant of the rectifier is such that it responds to voice peaks and valleys.

The blinking LED indicates activity on the channel if that channel is not selected. The

Selection Logic (C) forces the LED on continuously if it is selected under some conditions.

C. Selection Logic: The Selection Logic is used to control the analog switch that enables the

receive channel and the state of the LED activity monitor. If the transceiver is selected by

the “TRANSMIT” switch, the receive audio channel is forced on and the LED glows

constant on. If the transceiver channel is not selected for transmit but is selected for

monitoring by pulling out on the volume control knob, the receive channel is also forced on

as long as Push-to-talk (PTT) is not activated. Under this condition, LED activity monitor

glows constant on. During PTT, the receive channel switch is forced off and the LED returns

to normal activity monitoring.

D. Summing Amplifier: The summing amplifier sums all of the selected receive channels (up

to 7). The output of the summing amplifier feeds the “mute” switch and the speaker and

headphone amplifiers as well as the Supervisor Audio output amplifier. Separate amplifiers

are used for these functions because they combine different signals. Following the

summing amplifier, a high pass filter is implemented providing 18+ dBs of attenuation at

100 Hz. This filter reduces the level of output tones from some repeaters that can become

irritating when using a headset.

E. Microphone Amplifiers: Two low noise microphone amplifiers are used to accommodate

two different types of microphones if desired. In the initial configuration these two

amplifiers are identical and designed for use with Heil HC-5 microphone elements. The

amplifier is set to a Voltage gain of 200 with an input impedance of 10K. One is used for

the Boom mic and the other is for the headset mic and selected by a front panel switch. The

output of these amplifiers drives the 6 microphone output amplifiers and the sidetone level

control through the PTT switch. The ICS audio is enabled by the ICS control and not

subject to PTT. This allows more telephone like operation in ICS mode

F. Microphone Level Monitor: The microphone level monitor operates like the receive activity

monitors (B). In this case, however, the circuitry is used to indicate to the operator whether

he or she is speaking too softly or too loud. This monitor is only active in transmit modes

and not in ICS mode.