Figure 3-13. Synthesizer Block Diagram (Vhf) - Motorola APX 1000 Detailed Service Manual

3-16
3.1.4 Frequency Generation Unit (FGU)
The frequency-generation function is performed by several ICs; multiple voltage-controlled
oscillators (VCOs); and associated circuitry. The reference oscillator provides a frequency standard
to the Trident IC, which controls the VCOs via the port expander. There are also buffers that amplify
the VCO signal to the correct level for the next stage.
Figure 3-16 below shows a block diagram of the FGU Section.
VHF: Two VCOs are employed: one to generate the first RX LO and the other to generate the
transmit injection signals.
UHF1/UHF2: Two VCOs are employed: one to generate the first RX LO and the other to generate
the transmit injection signals.
700/800 MHz: Three VCOs are used to cover the entire 700/800 MHz band.
• VCO1 covers the RX 800 MHz band and the TX 700 MHz (764–776 MHz) band
• VCO2 covers the TX 700/800 MHz (794–824 MHz) band
• VCO3 covers the TX 800 MHz (851–870 MHz) band and the RX 700 MHz band
900 MHz: Two VCOs are employed: one to generate the first RX LO and the other to generate the
transmit injection signals.
NOTE: Refer to
listing of FGU-related schematics that will aid in the following discussion.
16.8MHz
BUFFER
16.8MHz
Table 8-1, "List of Transceiver Schematics and Board Overlays," on page 8-1
16.8 MHz REFERENCE CLOCK (To Controller and Abacus IC)
LOOP
FILTER
TRIDENT IC
PRESCALAR

Figure 3-13. Synthesizer Block Diagram (VHF)

Figure
TX VCO
PRE
BUFFER
RX VCO
BUFFER
Theory of Operation: Main Board
3-13, Figure 3-14, Figure 3-15
TX
BUFFER
VHF TX
VHF RX
and
for a
TX LO
RX LO