Chapter 11 Uhf Schematic Diagrams, Overlays, And Parts Lists; Introduction; Notes For All Schematics And Circuit Boards - Motorola EP450 Service Manual

Chapter 11 UHF Schematic Diagrams, Overlays, and
Parts Lists

11.1 Introduction

This section provides schematic diagrams, overlays, and parts lists for the radio circuit boards and
interface connections.

11.1.1 Notes For All Schematics and Circuit Boards

* Component is frequency sensitive. Refer to the Electrical Parts List for value and usage.
1. Unless otherwise stated, resistance values are in ohms (K = 1000), capacitance values are in
picofarads (pF) or microfarads (µF), and inductance values are in nanohenries (nH) or micro-
henries (µH).
2. DC voltages are measured from point indicated to chassis ground using a Motorola DC multi-
meter or equivalent. If the board has been removed from the chassis, the transmitter module
mounting screws may be used for ground connection. (Note: The antenna nut bracket is not
connected to ground.) Operating mode dependent voltages are followed by (RX) for receive
mode, (TX) for transmit mode, (UNSQ) for unsquelched mode, etc.
3. RF voltages on VHF models are measured with a Fluke model 85 RF probe. The indicated
voltages expressed in mV (RF) are DC level readings which correspond approximately 1:1 to
the RF voltage level in mV rms. RF voltages in the Receiver Front End and Receiver Back
End circuits are measured with an on-channel 100 mV (-7 dBm) RF signal applied to the
antenna jack J140.
4. RF voltages on UHF models are measured both with a high-impedance RF voltmeter having
a bandwidth in excess of 500 MHz (levels are expressed in dBm) and with a Fluke model 85
RF probe [levels are expressed in mV (RF)]. These indicated voltages are DC level readings
which correspond approximately 1:1 to the RF voltage level in mV rms, and are only approxi-
mate for UHF frequency measurements. RF voltages in the Receiver Front End and Receiver
Back End circuits are measured with an on-channel 100 mV (-7 dBm) RF signal applied to the
antenna jack J140.
5. Audio voltages are measured with a high-impedance AC rms voltmeter. The indicated volt-
ages are expressed in mV rms. Receive mode voltages are followed by (RX) and are mea-
sured with an on-channel signal with 1 kHz modulation at 60% deviation (3 kHz for 25 kHz
channels, or 1.5 kHz for 12.5 kHz channels). Transmit mode voltages are followed by (TX)
and are measured with a 1 kHz, 10 mV rms signal present at the external microphone input
(accessory connector J471 pin 4 hot and pin 7 ground).
6. Reference Designators are assigned in the following manner:
Ref. No. Series
1-99 RF Front End
100-149 Transmitter RF Stages
150-200 Transmitter Power Control
201-250 Frequency Synthesizer
251-300 VCO
Circuit Block