VHF1 (136
‐
174 MHz)
Circuit Description
25
5.3.2
Receiver Circuit
The receiver utilizes double conversion superheterodyne technique. The first IF is 44.85 MHz and the
second IF is 2.25 MHz. The first local oscillator signal is provided by the PLL circuit U8001, and the
second local oscillator signal (47.1 MHz) is provided by the PLL circuit U6001. The major units are BPF
and LNA, Mixer, IF filter, IF amplifier and IF processor.
8
MHz
AD9864
Band-pass Filter1
LNA
Band-pass Filter2
Mixer
IF Filter
IF Processor
IF Amp
LPF
OSC level:>
17dBm
TV
1
2
Attenuator Control
10dBm
Attenuator
5VA&3V3D&3V3A
3V3A
V
A
V
A
OMAP
LO
ANT
Receiver Front-end
RF signals are sent to the low-pass filter to remove out-of-band signals, and are applied to the two-stage
electrically tunable band-pass filter to acquire useful signals. After passing through the RF band-pass
filter and LNA (Q6102), the RF signals together with the first LO signal are sent to the mixer for the first
frequency conversion, to generate the first IF signal of 44.85 MHz. The mixer that employs the passive
diode can ensure good dynamic range and port isolation. The LO signal (3 – 5 dBm) from the VCO is
sent to Q6103 to acquire a gain of 17 dB. The first LO signal (44.85 MHz) passes through the crystal
filter (Z6100) to filter the out-of-band spurious signals, and then is sent to the two-stage IF amplifier
circuit (composed of Q6006 and Q6007) for amplification. Finally the amplified signals go to the IF IC for
digital processing.
Summary of Contents for MD652
Page 1: ...DIGITAL MOBILE RADIO...
Page 5: ...UHF1 400 470 MHz...
Page 15: ...Exploded View and Packaging Guide UHF1 400 470 MHz 8 3 2 Packaging Guide...
Page 53: ...43 9 PCB View Front Panel PCB View Top Layer X...
Page 54: ...44 Front Panel PCB View Bottom Layer...
Page 55: ...45 Main Board PCB View Top Layer...
Page 56: ...46 Main Board PCB View Bottom Layer...
Page 106: ...VHF1 136 174 MHz...
Page 116: ...Exploded View and Packaging Guide VHF1 136 174 MHz 8 3 2 Packaging Guide...
Page 154: ...43 9 PCB View Front Panel PCB View Top Layer...
Page 155: ...44 Front Panel PCB View Bottom Layer...
Page 156: ...45 Main Board PCB View Top Layer...