Rx Audio Circuit - Motorola P100 Serie Servicehandbuch

Handfunkgeräte

Vorschau ausblenden Andere Handbücher für P100 Serie:

Inhaltsverzeichnis

Verfügbare Sprachen

RX Audio Circuit

The RX audio circuit consists of Audio Processor IC, Audio amp, speakers & Sub-tone system.

(from IF IC)

The RX Audio from U201 is channeled to Audio processor IC. VR3 controls the received

demodulated signal level from -4.0 dB to +3.5 dB in 0.5 dB steps. RX LPF eliminates high-frequency

audio components > 3 kHz. TX/RX HPF eliminates low-frequency audio components lower < 250Hz.

Descrambler (if ON) inverts the spectrum distribution of audio signals with respect to scrambling

frequency. De-emphasis (if ON) restores high-frequency component of audio signal which has been

emphasized by the pre-emphasis circuit in transmitting radio. Expander (if ON) expands audio signal

by 0.5 dB to restore the original signal compressed by transmitting radio. VR4 amplifies RX audio

level by -18.0 dB, with -4.5 dB to +4.5 dB in 0.25 dB steps adjustment range. Smoothing filter (SMF)

eliminates high-frequency and clock components, generated by ASIC.

Sub-audio Programmable LPF totally eliminates voice audio from Audio signal to extract sub-audio

tone. VR5 regulates the output level of extracted sub-audio tone and sends it to a high pass filter

(U105-A,B) with 4 selectable cut-off frequencies and finally passes through a comparator (U105-C),

to square the signal and sends it to the MCU.

The output audio signal of Audio Processor IC is directed to volume control switch (SW/VOL1) which

is controlled by user and is finally amplified by U601BTL Audio Amplifier to a sufficient level to drive

either the external or internal speaker.

-4 to +3.5dB /

Programmable

-6 to +6dB /

(tone detect)

Figure 2-4. RX Audio Block Diagram

Audio Processor IC (AK2347)

Theory Of Operation: Major Assemblies

-18, -4.5 to + 4.5dB /

Inhaltsverzeichnis