NX-700/700H

NX-700/700HCIRCUIT DESCRIPTION3-3. IF circuitThe first IF signal is passed through a four-pole monolithiccrystal filter (XF202) to reject adjacent channel signal.The filtered first IF signal is amplified by the first IF amplifier(Q204, Q205) and then applied to the lF system IC (IC202).The IF system IC provides a second mixer, AGC amplifier,and RSSI (Received Signal Strength Indicator).The second mixer mixes the first IF signal with the57.6MHz of second local oscillator output and produces thesecond IF signal of 450kHz.The second IF signal is passed through the ceramic filter(CF201, CF202) to reject the adjacent channel signal. Thefiltered second IF signal is amplified by AGC amplifier.The signal from AGC amplifier is input to AD converter(IC510) through ceramic filter (CF203) and operational amplifier(IC201 and IC704).ANTRF Circuit (Front end)IC202MIX. AGCCF203BPFIC2012nd OSCX1VCTCXO19.2MHzQ203x3BPFCF201CF202IC704IC510IC701IC707SWIC711(2/2)IC712VOLQ710MUTESWIC715AF AMPINT. SPDSPAMTINAMTSWEXT. SPIC502Q709Fig. 33-4. Audio amplifier circuitAudio processing (high-pass filter, low-pass filter, deemphasizedand so on) at FM mode and decoding at NXDNmode are processed by DSP. Audio signal from IC510,IC502 goes through the amplifier (IC701). The signal thengoes through mute switch (IC707), amplifier (IC711), andelectronic volume control (IC712).While busy, INAMT becomes High, turn switch (Q709)on and Mute switch (Q710) off, and signal is fed to AF PowerAmp (IC715). While Non-busy, INAMT is become Low,turn switch (Q709) off and Mute switch (Q710) on, thenthere is not AF output.3-5. Squelch CircuitIt amplifies the demodulated noise signal from IC510after filtering through BPF circuit. Then, the amplified signalis converted to DC signal by the detection circuit. The convertedsignal is fed back to IC510.IC202IC705 (2/2)FMDETBPFQ702AMPD703RECTIC705 (1/2)ASQDETAMPIC510IC203 (1/2)VAGCAMPIC203 (2/2)RSSIAMPFig. 418