Maxon SP-1102, Руководство по обслуживанию, Страница: 23 / 35

Service Manual SP - 1402
Page 23 of 35
UHF Receive
The receiver is comprised of:
Front End Filter / RF amplifier
First mixer and first IF amplifier
Second mixer, second IF amplifier and FM detector (AN29160AA)
Mute (Squelch) circuit (AN29160AA)
Speaker audio amplifier (AN29160AA)
Front End Filter / RF amplifier
The receive signal by the antenna is routed through the low pass filter, then onward to the
antenna switching circuit consists of L5,D5 The front RF amplifier transistor Q15 consists of the
band pass filter C180,C601-610 and L601-603 amplified by Q15 and output to second band pass
filter consists of C211,C613-624and L14,605-607 These are frequency range 440.025 to
469.975 MHz.
First mixer and first IF amplifier
This stage is mixed signals , the signal from front-end RF amplified through band pass filter fed
to the gate 1 of the first mixer Q23 .And the first local oscillator signal from the VCO that fed to
the gate2 of Q23 .So these the mixer output at drain of Q23 is 45.1MHz and then fed through
the XF1-2 these are 45.1 MHz IF crystal filter The crystal filter provides a bandwidth of +/-7.2
KHz from the operating frequency providing a high degree of spurious and intermediation
protection. Additionally, a 90 MHz trap (XF1) is also placed at the filter output to provide
additional attenuation of the second order IMD. The output of the filter is impedance matched by
C137 and R5 to the base of the first of filter IF amplifier Q34