Receiver Front-End; Figure 8-2 Diagram Of Receiver Circuit - Hytera MD78X Service Manual

UHF1 (400-470MHz 25W) Information Service Manual

Figure 8-2 Diagram of Receiver Circuit

8.2.1

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 (73.35MHz). 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 (73.35MHz) 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.
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