Maxon Telecom SP210 - Manual (Page 36)

Maxon SP200/210 Radio SP200/210
DETAILED FUNCTIONAL DESCRIPTION Issue 1.0
Page 5-8 03/01
5.7 Receiver
The receiver comprises:
Rx
VCO
~
Local
Oscillator
~
Audio
Filter
FM Limiter-
Discriminator
Audio
Amplifier
Squelch
Circuit
Figure 5-4 - Receiver Block Diagram
Antenna Switch
In receive, the diodes D5 and D6 are reverse biased. L13 is now in circuit, passing the signal from the
antenna to the front end without signal loss.
Front End
The receive signal is routed to the RF Front End module, pin 1. It passes through a matching circuit
consisting of C601 to C603 / L601 & L602.
Diode D601 serves as protection from RF overload from nearby transmitters.
The input signal is coupled to the base of Q601 which serves as an RF amplifier. The output of Q601
is then coupled to a bandpass filter consisting of C604 to C620 / L603 to L607.
The output of the front end module, pin 6, is then coupled to the double-balanced mixer D9.
The receiver front end module is factory pre-tuned and requires no adjustment. Repair is effected by
replacement of the entire module.
The modules are:
VHF 146 MHz to 174 MHz
UHF 440 MHz to 470 MHz.