To Next Page

To Previous Page

VHF Theory of Operation: Receiver (for all models except those with PCB 8486473Z04) 6-3

6.2 Receiver (for all models except those with PCB 8486473Z04)

Figure 6-2. VHF Receiver Block Diagram

6.2.1 Receiver Front-End

(Refer to VHF Receiver Front End Schematic Diagram on page 9-326, VHF Receiver Back End

Schematic Diagram on page 9-327, and VHF Transmitter Schematic Diagram on page 9-330).

The RF signal is received by the antenna and applied to a low-pass filter. For VHF, the filter consists

of L3531, L3532, C3532 to C3563. The filtered RF signal is passed through the antenna switch. The

antenna switch circuit consists of two PIN diodes(D3521 and D3551) and a pi network (C3531,

L3551 and C3550).The signal is then applied to a varactor tuned bandpass filter. The VHF bandpass

filter comprises of L3301, L3303, C3301 to C3304 and D3301. The bandpass filter is tuned by

applying a control voltage to the varactor diode (D3301) in the filter.

The bandpass filter is electronically tuned by the DACRx from IC404 which is controlled by the

microprocessor. Depending on the carrier frequency, the DACRx will supply the tuned voltage to the

varactor diodes in the filter. Wideband operation of the filter is achieved by shifting the bandpass filter

across the band.

The output of the bandpass filter is coupled to the RF amplifier transistor Q3302 via C3306. After

being amplified by the RF amplifier, the RF signal is further filtered by a second varactor tuned

bandpass filter, consisting of L3305, L3306, C3311 to C3314 and D3302.

Both the pre and post-RF amplifier varactor tuned filters have similar responses. The 3 dB bandwidth

of the filter is about 12 MHz. This enables the filters to be electronically controlled by using a single

control voltage which is DACRx.

Crystal

Filter

Mixer

Varactor

Tuned Filter

RF Amp

Varactor

Tuned Filter

Pin Diode

Antenna

Switch

RF Jack

Antenna

Control Voltage

from ASFIC

First LO

from FGU

Second

IF Amp

Demodulator

RSSI

Recovered Audio

U3220

16.8 MHz

Reference Clock

SPI Bus

Squelch

Synthesizer

LO VCO

AGC

Brand	Motorola
Model	HT Series
Category	Two-Way Radio
Language	English

Motorola HT Series User Manual

Table of Contents

Other manuals for Motorola HT Series

Questions and Answers:

Motorola HT Series Specifications

Related product manuals