Receiver Front-End; Receiver Back-End; Figure 15-3 Diagram Of If Processor - Hytera MD78X Service Manual

Service Manual VHF (136-174MHz 50W) Information
15.2.1

Receiver Front-end

RF signals feed to the low-pass filter to remove out-of-band signals, and are applied to the two-stage
electrically tunable band-pass filter to get useful signals. After passing through the RF band-pass filter
and LNA (Q6102), the RF signals together with the first LO signal feed to the mixer for the first
frequency conversion, to generate the first IF signal (44.85MHz). The mixer that employs the passive
diode can ensure good dynamic range and port isolation. The LO signal (3-5dBm) from the VCO feeds
to Q6103 to get a gain (17dB). The first LO signals (44.85MHz) pass through the crystal filter (Z6100)
to remove out-of-band spurious signals, and then feed to the two-stage IF amplifier circuit (composed
of Q6133 and Q6134) for amplification. Finally the amplified signals go to the IF IC for processing.
15.2.2

Receiver Back-end

Figure 15-3 Diagram of IF Processor

The first IF signal (44.85MHz) output by the IF amplifier goes into IF IC via Pin 47, where the signal is
converted to the second IF signal (2.25MHz). Then the un-demodulated digital I/Q signal output from
the SSI interface is sent to U302 for demodulation. IF IC employs a reference frequency of 19.2MHz
and shares the crystal with U302. The second LO VCO consists of the external transistor, varactor and
some other components, to provide the second LO signal. The 18MHz clock frequency is generated by
541