User Manual
Table Of Contents
- 1GENERAL
- 1.1Introduction
- 1.2Manual Organization
- 1.3VT-4B 136 - 174 MHz Transmitter Family Models
- 1.4Performance Specifications
- 1.4.1General
- 1.4.2Audio Specifications
- 1.4.3Physical Specifications
- 2THEORY OF OPERATION
- 2.1Transmitter Operation
- 2.2Transmitter Programming
- 2.2.1Transmitter Wide Options
- 2.2.1.1Disable Front Panel Led
- 2.2.1.2Secure Hardware Equipped
- 2.2.1.3Allow Emergency Transmissions
- 2.2.1.4Allow Radio Inhibit
- 2.2.1.5Allow Radio Check
- 2.2.1.6Enable Status
- 2.2.1.7Frequency Band
- 2.2.2Channel Wide Settings
- 2.2.2.1Frequency
- 2.2.2.2Voice/Signal Type
- 2.2.2.3Squelch Type
- 2.2.2.4CTCSS Tone
- 2.2.2.5Enable Reverse Burst
- 2.2.2.6DCS Code
- 2.2.2.7DCS Invert
- 2.2.2.8Enable Turn Off Code
- 2.2.2.9Transmitter Power
- 2.2.2.10Channel Bandwidth
- 2.2.2.11Deviation
- 2.2.2.12Time Out Timer
- 2.2.2.13Channel Status
- 2.2.2.14Transmitter Pre-emphasis
- 2.2.2.15NAC Transmitter Code
- 2.2.2.16NAC Transmitter
- 2.3Transmitter Programming using Motorola Radio Service Software
- 2.4Secure Communications
- 2.5Transmitter Assembly and Adjustment
- 2.5.1Controller Board Alignment
- 2.5.1.1Reference Oscillator Adjustment
- 2.5.1.2Transmitter Deviation Balance Adjustment
- 2.5.1.3Transmitter Deviation Limit Adjustment
- 2.5.2Amplifier Alignment
- 2.5.3Frequency Change
- 2.6Recommended Test Equipment List
- 2.7Repair Note
- 2.8Printed Circuitboard Numbering Convention
- 3ILLUSTRATIONS
- 3.1MT-4 Base Transmitter Front Panel
- 3.2MT-4 Transmitter Case - Exploded View
- 3.3Digital Base Transmitter Block Diagram
- 3.4Digital Base Transmitter Schematic Diagram
- 3.5Digital Base Transmitter Main Board Component Layout (Bottom)
- 3.6Digital Base Transmitter Main Board Component Layout (Top)
- 4PARTS LIST
- 4.1P25 Base Transmitter Main Board Parts List
- 4.1.1P25 Base Transmitter Main Board Electrical Parts List
- 4.1.2P25 Base Transmitter Mechanical Parts List
- 5REVISION HISTORY
DE
DANIELS
ELECTRONICS
2-8 VT-4B150 VHF Project 25
Digital
Base
Transmitter
Instruction
Manual
2.5.2
Amplifier Alignment
The RF power output of the amplifier is set to its rated value of 2.0 Watts or 8.0 Watts at the
factory. This should not require adjustment under normal circumstances. However, should it be
necessary to correct the output power, follow the procedure in the Amplifier Manual. Adjustment
may also be required when the transmitter's operating frequency is changed. When a large
frequency change has been programmed into the transmitter, the amplifier should be aligned at the
new frequency according to the Amplifier Manual.
2.5.3
Frequency Change
The transmitter is initially aligned at the factory for the frequency stamped on the 'Factory Set
Operating Frequency' label (see section 3.1). This label should list the frequency at which the last
complete transmitter alignment was performed. For a small frequency change, a simple channel
change (see section 2.2) may be all that is required. A larger frequency change may involve the
realignment of other modules. The frequency change in question is the
accumulated frequency
change
in relation to the frequency stamped on the label. For example, if the frequency were
changed by 0.5 MHz from that stamped on the label, then a second frequency change of 1 MHz in
the same direction would result in a total change of 1.5 MHz. The action taken would be on the
basis of the 1.5 MHz value. Failure to perform a realignment after a large frequency change could
result in unreliable transmitter operation or transmitter operation that does not conform to the
published specifications. The allowable frequency change is summarized below.
Note:
It is advisable to confirm these frequency ranges with the Amplifier, as they are subject to
change with updated versions. The values in the module manuals take precedent over
those tabulated (following page).
Size of Frequency Change
Modules to be Aligned
less than ± 1 MHz
no alignment required, check output power
greater than ± 1 MHz
Transmitter Power Amplifier
2.6 Recommended Test Equipment List
Alignment of the transmitter requires the following test equipment or its equivalent.
Dual
Power Supply:
Regulated
+9.5
Vdc at 2 A.
Regulated
+13.8
Vdc at 2 A - Topward TPS-4000
Oscilloscope
/
Multimeter:
Fluke 97
Scopemeter
Current
Meter:
Fluke 75
multimeter
Radio
communications
test set :
Marconi
Instruments 2955R (analog only)
Motorola
R2670 with Project 25 option
Alignment
Tool:
Johanson 4192
It is recommended that the radio communications test set be frequency locked to an external
reference (WWVH, GPS, Loran C) so that the high stability oscillator may be accurately set to
within its ±1 ppm frequency tolerance.