Ericsson NPC-50 Uživatelský manuál stáhnout pdf (Strana 4)

Figure 1 - Radio Block Diagram

RECEIVER

The receiver converts the received RF signal to an audio sig-

nal. The receiver contains the following:

• Antenna switch

• First RF amplifier

• First IF mixer

• First IF pre-amplifier

• IF IC

• De-emphasis

• Highpass filter

• Audio muting

• Volume controller

• Audio power amplifier

• Squelch control

The receiver is a double-conversion type with intermediate

frequencies of 59.85 MHz and 455 kHz. The receiver frequency

range is from 146 to 174 MHz and the bandwidth, without

alignment, is 28 MHz (VHF) or 438 to 470 MHz and the band-

width, without alignment, is 32 MHz (UHF). The filters in the

receive section perform the receiver characteristics such as se-

lectivity, image and spurious rejection and reduction of other

undesirable frequencies.

Antenna Switch (FT401)

The antenna switch in the receive mode permits RF signal to

pass to the receiver. In the transmit mode the circuit switches off

the receiver and allows the RF signal from the transmitter to

feed the antenna through the transmit harmonic filter.

First RF Amplifier (Q101)

The antenna switch sends the received signal to Q101

through the bandpass filter. The received signal is filtered to re-

duce undesired frequencies outside the frequency band.

Q101 amplifies the filtered signal to recover the losses of

the antenna switch and the filters and to increase sensitivity.

Then this amplified signal is sent to the receive mixer through a

bandpass filter.

First MIxer (D101)

The received channel frequency is mixed with the first local

oscillator frequency to produce the first IF frequency (59.85

MHz). The first IF signal is sent through the 59.85 MHz crystal

bandpass filters (FT1 and FT2) to reduce adjacent channel un-

desired frequencies.

AE/LZB 119 1658 R1A

1 2 3 4 5 6 7 8 9 ... 53 54

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