Glenayre Document Number: 9110.00148
RL-903 Receiver
Issue 1, Rev. C: 12/10/96
THEORY OF OPERATION
The dual-conversion, synthesized, narrowband FM receiver covers 922 to 960 MHz. The
optional tone board provides tone decoding and keying logic. The optional line driver
circuit supplies receiver audio to telephone lines.
Table 4-3, Internal Connections among Assemblies, shows the interconnections among
assemblies.
6.1
PS/A Board
Figure 7-6, PS/A Board Controls and Indicators, shows a view of the pc board.
6.1.1
Power Supply
Table 2-1, Specifications, lists the electrical requirement for input power. Refer to
Figure 10-5, PS/A Board Schematic. Unregulated power entering from TB1-2 is fused by
pc-board-mounted F1 and is controlled by front-panel-mounted SW1. Switch converter U1
and associated components provided filtered, regulated power (approximately 15.1 Vdc) to
the input of linear voltage regulator U2, which supplies twelve volts to the rest of the unit.
6.1.2
Audio Amplifier
Op-amps in U4 amplify and deemphasize the audio supplied to speaker driver U3. Front-
panel VOLUME control R27 controls the speaker level.
6.2
RF Amplifier/First Mixer
Figure 7-4, RF Assembly - Adjustments, shows a view of the assembly. Refer to Figure 10-
3,
Front End Schematic. The RF input is at rear-mounted BNC connector J1 on the left of
the back of the chassis, as viewed from the rear. The desired signal is passed by helical
filters L2, L3, L4, L7, L8, and L9 and is amplified by Q1 while undesired signals are atten-
uated. The RF output is matched by L10 to one input of mixer U1. The l.o. signal from the
synthesizer arrives at SMB receptacle J3 and is passed to the second input of mixer U1. The
output of mixer U1 is a 45-MHz IF signal which exits the RF board at J2. Receptacle J4 is
used with a network analyzer in the factory for tuning the front end.
6.3
Synthesizer and VCO Block-Diagram Description
Figure 7-1, Synthesizer Controls and Indicators, shows a view of the pc board. The synthe-
sizer tunes in 6.25-kHz steps to accommodate the channel spacing of 12.5 or 25 kHz. Refer
to Figure 6-1, Synthesizer Functional Diagram and Figure 10-4, VCO Board Schematic.
Print Date: 12/05/96
Copyright
©
1996 Glenayre
Page: 6-1