User Guide

PAMS
System Module DB6
NHB–3
Technical Documentation
Original 26/97
Page 4–43
First Mixer
The first mixer is a single balanced passive diode mixer. The local signal is bal-
anced by a printed circuit transformer. The mixer down converts the received
RF signal to IF signal.
First IF Amplifier
The first IF amplifier is a bipolar transistor amplifier.
First IF Filter
The first IF filter is a microstripline filter. The IF filter rejects some spurious and
blocking signal coming from the front end of the receiver.
2nd Mixer
The 2nd mixer is a single balanced passive diode mixer. The local signal is bal-
anced by a printed circuit transformer. The mixer down converts the 1st IF sig-
nal 313 MHz to 2nd IF signal 87 MHz.
2nd IF Amplifier
The 2nd IF amplifier consists of two bipolar transistors. The bias current is ON
only during the reception.
2nd IF Filter
The second IF filter (SAW) makes the part of the channel selectivity of the re-
ceiver. It rejects adjacent channel signals (except the 2nd adjacent). It also
rejects blocking signals and the 3rd image frequency.
Receiver IF circuit, RX part of CRFRT
The receiver part of CRFRT consists of an AGC amplifier of 57 dB gain, a mixer
and a buffer amplifier for the last IF. The mixer of the circuit down converts the
received signal to the last IF frequency. After external filtering the signal is am-
plified and fed to baseband circuitry. The supply current can be switched OFF
by an internal switch, when the RX is OFF.
Last IF Filter
The last IF is a ceramic filter, which makes the part of the channel selectivity of
the receiver.