Daniels Electronics Ltd. MT-3 Series User manual

Document Number:
Revision:
Revision Date:
Daniels Electronics Ltd.
Victoria, BC
PRINTED IN CANADA
© 1998–2010 Daniels Electronics Ltd. All rights reserved. No part of
this publication may be reproduced, stored in a retrieval system or
transmitted in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise, without the prior written consent
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Canadian and US trademarks of Daniels Electronics Ltd.
The stylized “Daniels Electronics Ltd.” and “DE” logo are trademarks of
Daniels Electronics Ltd.
MT-3 FM TransMiTTer
MainBoard
insTrucTion Manual
Covers Models:
VT-3H035-SXA300
VT-3H045-SXA300
IM20-MT3TXMN
5-0-0
Feb 2010

ii
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
This document has been produced, veried and controlled in
accordance with Daniels Electronics’ Quality Management System
requirements.
Please report any errors or problems to Daniels Electronics’ Customer
Service Department.
The user’s authority to operate this equipment could be revoked through
any changes or modications not expressly approved by Daniels
Electronics Ltd.
The design of this equipment is subject to change due to continuous
development. This equipment may incorporate minor changes in detail
from the information contained in this manual.
DOCUMENT CONTROL
NOTE
Daniels Electronics Ltd. utilizes a three-level revision system. This
system enables Daniels to identify the signicance of a revision.
Each element of the revision number signies the scope of change as
described in the diagram below.
DOCUMENT REVISION
DEFINITION
Major Revisions: The result of a major
change to product function, process or
requirements.
Minor Revisions: The result of a
minor change to product, process or
requirements.
Editorial Revisions: The result of typing
corrections or changes in formatting,
grammar or wording.
1-0-0
Three-level revision numbers start at 1-0-0 for the rst release. The
appropriate element of the revision number is incremented by 1 for each
subsequent revision, causing any digits to the right to be reset to 0.
For example:
If the current revision = 2-1-1 Then the next major revision = 3-0-0
If the current revision = 4-3-1 Then the next minor revision = 4-4-0
If the current revision = 3-2-2 Then the next editorial revision = 3-2-3
The complete revision history is provided at the back of the document.

iii
MT-3 FM Transmitter Mainboard Instruction Manual
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Contents
General Information ...............................................................1
Introduction ................................................................................................1
MT-3 VHF Low Band Performance Specications..................................... 3
Physical Specications ..............................................................................4
Theory of Operation ...............................................................5
MT-3 FM Transmitter Mainboard ...............................................................5
FM Audio Processor................................................................................. 12
Transmitter Alignment .......................................................... 23
Repair Note.............................................................................................. 23
Recommended Test Equipment List ........................................................ 24
General Information ................................................................................. 24
Synthesizer Module Installation and Removal ......................................... 24
Standard Factory Settings and Jumper Congurations ........................... 25
MT-3 FM Transmitter Mainboard Interconnection Pin Denitions ............ 26
FM Audio Processor Alignment................................................................ 27
Troubleshooting ....................................................................................... 31
Temperature Compensation..................................................................... 32
FM Audio Processor Jumper Congurations ........................................... 32
Illustrations and Schematics ................................................ 35
MT-3 FM Transmitter Block Diagram ....................................................... 36
MT-3 FM Transmitter Mainboard Component Layout – Top..................... 37
MT-3 FM Transmitter Mainboard Component Layout – Bottom............... 38
MT-3 FM Transmitter Mainboard Schematic Diagram ............................. 39
Front Panel Board Component Layout Diagram...................................... 40
Front Panel Board Schematic Diagram ................................................... 40
FM Audio Processor Board Component Layout Diagram ........................ 41
FM Audio Processor Board Schematic Diagram ..................................... 42
Parts List .............................................................................. 43
MT-3 FM Transmitter Mainboard.............................................................. 43
Front Panel Board.................................................................................... 47
FM Audio Processor................................................................................. 47
Revision History ................................................................... 51

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1
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
GENERAL
INFORMATION
INTRODUCTION
The MT-3 FM Transmitter Mainboard integrates
the MT-3 Front Panel Board, MT-3 FM Audio
Processor, Synthesizer module and Amplier
module together to comprise a MT-3 series
transmitter.
The front panel board and the audio processor
are soldered directly to the transmitter
mainboard while the amplier and the
synthesizer modules are frequency band
sensitive, plug-in modules.
Circuitry and jumpers on the transmitter
mainboard control the operation of the modules
as well as the overall operation of the MT-3 FM
transmitter. Power and signal connections are
made through the 48-pin Type F connector on
the rear of the transmitter mainboard where they
are then routed to the other MT-3 modules.
The transmitter enclosure is formed by the front
panel face plate and aluminum shell attached
to the transmitter mainboard and the rear panel
plate attached to the aluminum shell.

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General Information 3
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
MT-3 VHF LOW BAND PERFORMANCE SPECIFICATIONS
Parameter Specication
Frequency Range: 29 to 38 MHz (VT-3H035-SWA300)
38 to 50 MHz (VT-3H045-SWA300)
Carrier Frequency Stability: ± 5.0 ppm (-30°C to +60°C, Optional -40°C to +60°C)
Channel Spacing: 20 kHz
Channel Selection: 5.0 or 6.25 kHz increments
Number of Channels: 16
Compatibility: MT-3 Series Radio Systems
RF Output Power: 0.5 to 3.0 W
Emission Designator: 16K0F3E
Impedance (Input): 50 Ω; Type-N connector
Duty Cycle: 100 % (-40°C to +60°C)
Undesired Emissions (Conducted Harmonics):
Undesired Emissions (Conducted Spurious):
<= -90 dBc
<= -80 dBc
VSWR Protection: < 20:1 VSWR at all phase angles
Operating Temperature Range: -30°C to +60°C
Operating Humidity: 95% RH (non-condensing) at +25°C
Operating Voltage: +13.8 VDC nominal input (range +10 to +17 VDC)
+9.5 VDC regulated
Transmit Current: <1.2 A for 3.0 W output
Stand By Current: 15 mA (Mode 1)
160 mA (Mode 2)
185 mA (Mode 4)
PTT Time-Out-Timer: Nominal – 5 minutes
Range – 1 sec to 8 hours, disable
Audio Input: 600 Ω balanced or unbalanced input (5 K Ohm)
-25 dBm to 0 dBm
Audio Frequency Response: Pre-emphasis: complies with TIA-603C
Flat: +1 dB/-3 dB 100 Hz to 3 kHz
Audio Deviation Limiting: ± 5.0 kHz
Audio Distortion: <2.0% @ +23°C
<2.5% -40°C to +60°C
FM Hum and Noise Ratio: <= -55 dB (0.3 to 3.4 kHz, de-emphasis off)
IC Certication No.: 142A-VT3X0X5S (RSS-119)
FCC ID: H4JVT-3H040-S (FCC Parts 22, 90)

General Information
4
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
PHYSICAL SPECIFICATIONS
Physical Dimensions: Width: 7.1 cm (2.8 in) Height: 12.8 cm (5.05 in) Depth: 19 cm (7.5 in)
Module Weight: 1.4 kg (3.0 lbs)
Corrosion Prevention: Anodized aluminum construction•
Stainless steel hardware•
Gold-plated module connectors•
Module Design: Compact Eurostandard modular design•
Plug-in modules mate with the Daniels standard MT-3 Repeater Subrack•
Subracks / modules comply with IEEE 1101, DIN 41494 and IEC 297-3•
(mechanical size / modular arrangement)
External Connections: RF Connection – Type-N connector located on the module front panel.
Motherboard connections (Audio, Power, and Control) are made through a
48-pin, gold-plated, Type-F connector on the rear of the module.
User connection is made through mated motherboard assembly of the
radio subrack. Type-F connector complies with DIN 41612 Level 2 (200
mating cycles, 4-day 10 ppm SO2 gas test with no functional impairment
and no change in contact resistance).
Handle Text Colour: Orange

5
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
THEORY OF
OPERATION
MT-3 FM TRANSMITTER
MAINBOARD
General
Switch SW1 on the Front Panel Board is a
double pole, double throw (DPDT) switch that
controls the operation of the transmitter.
When SW1 is in the OFF position the transmitter
is turned off; however, +13.8 VDC is still
present on the transmitter mainboard as the
+13.8 VDC supply is not switched. When SW1
is in the KEYED position, +9.5 VDC is supplied
to the transmitter circuitry and the transmitter
is continuously keyed on. When SW1 is in the
NORM position, +9.5 VDC is supplied to the
transmitter circuitry and the transmitter can
be keyed from any of the several Push-To-Talk
inputs.

Theory of Operation
6
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Transmitter Push-To-Talk
All three of the Push-To-Talk (PTT) inputs that
key the transmitter are active low (< +2 VDC).
One PTT input is on the front panel microphone
connector. The other two PTT inputs: PTT
WTO (PTT with Time-Out-Timer) and PTT
NTO (PTT No Time-Out-Timer) are on the
backplane connector of the transmitter board.
If required, the microphone’s PTT input can be
congured to activate the transmitter’s Time-
Out-Timer (TOT). An isolated PTT input can be
made available by installing an optional relay
(RELAY1) and conguring jumpers J1 to J4 so
that the relay controls the PTT circuitry.
Microphone PTT
Jumper J1 on the Front Panel Board congures
the microphone’s PTT input (MIC PTT) to
either bypass or activate the transmitter’s TOT.
Installing surface mount jumper J1 in the ‘X’
position (default) selects the MIC PTT NTO
line, which bypasses the TOT. Installing surface
mount jumper J1 to the ‘Y’ position selects
the MIC PTT WTO line, which activates the
transmitter’s TOT. When SW1 is in the KEYED
position, the MIC PTT NTO line is automatically
grounded.
PTT With Time-Out-Timer
Pins B10 and Z10 of the backplane connector
are the PTT WTO input. When the PTT WTO
signal, which is normally high, falls below
+2.0 VDC, the transmitter is keyed. The
transmitter is disabled when the PTT WTO input
rises above +2.3 VDC or if the TOT’s time-out
period is exceeded. If the time-out period is
exceeded, the PTT WTO input must go high
(> +2.3 VDC) and then low again in order to
re-key the transmitter.
The PTT WTO threshold of approximately
+2 VDC (0.3 VDC hysteresis) is set by U1a, R1,
R2, R3, R4, R9 and R10 while diodes D1 and
D2 provide over-voltage protection for U1a. The
PTT WTO signal output from U1a is ‘AND’ed
with the MIC PTT WTO by U2a. When either the
PTT WTO or the MIC PTT WTO is activated,
the output of U2a goes low, which triggers the
transmitter’s TOT located on the FM Audio
Processor. The TOT’s output is ‘AND’ed with the
MIC PTT NTO signal (U2c) and the PTT NTO
signal (U2d).
When any one of the preceding three signals
(TOT’s output, MIC PTT NTO, PTT NTO) go low,
the transmitter is activated by transistors Q1 to
Q7 which switch power to the various modules.
PTT No Time-Out-Timer
Pins B14 and Z14 of the backplane connector
are the PTT NTO input. When the PTT NTO
signal, which is normally high, falls below
+2.0 VDC, the transmitter is keyed. As
long as the PTT NTO signal remains below
+2.0 VDC, the transmitter will remain keyed.
The transmitter is disabled when the PTT NTO
signal rises above +2.3 VDC.
The PTT NTO threshold of approximately
+2 VDC (0.3 VDC hysteresis) is set by U1b, R5,
R6, R7, R8, R9 and R10 while diodes D3 and
D4 provide over-voltage protection for U1b. The
PTT NTO signal is ‘AND’ed with the output of
U2c (MIC PTT NTO signal ‘AND’ed with the TOT
output) by U2d. When the output of U2d goes
low, transistors Q1 to Q7 activate the transmitter,
which switch power to the various modules.
PTT Relay
The transmitter’s PTT circuitry can be
completely isolated by installing RELAY1.
Jumpers J1 to J5 congure the relay to provide
an isolated PTT input for either the PTT WTO
line or PTT NTO line. Energizing the relay
enables the isolated PTT input. The transmitter
board will accept any of the Aromat TF2E line
relays. These relays are DPDT, single side
stable, and have coil voltages ranging from
+3 VDC to +48 VDC. Only one set of relay
contacts is used to activate the PTT circuitry.
To congure the isolated input for PTT WTO
operation, jumpers J2, J3 and J4 must be in the
‘Y’ position. In this mode, pins B10 and Z10 no
longer function as the PTT WTO input; however,
pins B14 and Z14 continue to function as the
normal PTT NTO input.
To congure the isolated input for PTT NTO
operation, jumpers J2, J3 and J4 must be in the
‘X’ position. In this mode, pins B14 and Z14 no
longer function as the PTT NTO input; however,
pins B10 and Z10 continue to function as the
normal PTT WTO input.

Theory of Operation 7
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
PTT Output
Pin B24 on the backplane connector is an open
drain output (Q9), which is pulled low anytime
the transmitter is keyed and the synthesizer is
locked. An N-channel MOSFET Q9 is capable of
sinking currents up to two amps and is activated
by Q8, which is activated by the Qualied PTT
signal (JS2-6) of the synthesizer module. The
Qualied PTT signal also controls the LED
ENA line for diode D1 on the front panel board
and enable line for the MT-3 Amplier Module
(JP1-1).
PTT Voltage Switching
The PTT voltage switching circuitry is comprised
of transistors Q1 through Q7 and the associated
resistors. The base of Q1 is driven by the output
of U2d, which is the combined PTT signal from
all of the PTT inputs. When the transmitter
is keyed, Q1 is turned off and subsequently
transistors Q3, Q4 and Q6 are turned on.
Transistors Q3, Q4 and Q6 provide three
separate functions:
Q3 Provides the active low signal for the
synthesizer module PTT input.
Q4 Turns on Q5, which turns on the
+9.5 VDC Switched supply.
Q6 Turns on Q7, which turns on the
+9.5 VDC PTT Switched supply.
The +9.5 VDC Switched supply (Q5) can also be
activated by installing jumper J6 or by externally
grounding the TX Standby Line (pins B12 and
Z12). The +9.5 VDC PTT Switched supply and
the +9.5 VDC Switched supply both provide
+9.5 VDC but, depending on how jumpers J6,
J7 and J18 are congured, the transmitter’s
standby mode will change.
Front Panel Board
The Front Panel Board is attached to the MT-3
FM Transmitter Mainboard and is used to mount
the front panel switch, diode and microphone
connector. The main purpose of the board is to
eliminate a wiring harness for the front panel
components. Jumper J1, located on the rear of
the circuit board, is used to select whether or
not the MIC PTT line activates the transmitter’s
TOT. Jumper J2 is used to select whether or not
RX Audio or 13.8 Volt is supplied to Pin 4 of the
microphone.
J1 X position MIC PTT NTO – no time-out-
timer (factory setting)
Y position MIC PTT WTO with time-out-
timer
J2 X position RX Audio enabled to MIC-4 pin
(factory setting)
Y position +13.8 Volts
supplied to MIC-4 pin

Theory of Operation
8
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Transmitter Standby Modes
The MT-3 series transmitters have eight different standby modes that trade off standby current
consumption for start-up speed.
Three jumpers are found on the transmitter mainboard:
J6 Continuously enables the +9.5 VDC switched supply.
J7 Selects the power source for the FM Audio Processor.
J18 Selects the enable line for the Synthesizer module.
Additionally, there is a jumper on the FM Audio Processor Board:
JU36 Determines the power source for the dual compression ampliers.
If JU36 is not installed on the FM Audio Processor, both microphone and balanced audio
compression ampliers will be disabled, eliminating the use of the front panel microphone jack
for local microphone operations. With this conguration, the balanced audio is routed around the
compression circuitry via JU11 (installed) with JU1 and JU2 removed.
Mode Condition Table
Mode # J6 J7 J18
Synthesizer/
Osc. State
Audio Processor State
(8 V Switched)
Audio Processor
Compression JU36
1a OUT Y Y PTT Switched PTT Switched Switched +8.0 V (X)
1b OUT Y Y PTT Switched PTT Switched Continuous 9.5 V (Y)
1c OUT Y Y PTT Switched PTT Switched Disabled (Not Installed)
2a IN Y X Always Enabled PTT Switched Switched +8.0 V (X)
2b IN Y X Always Enabled PTT Switched Continuous 9.5 V (Y)
2c IN Y X Always Enabled PTT Switched Disabled (Not Installed)
3IN X Y PTT Switched Always Enabled Doesn’t Matter
4IN X X Always Enabled Always Enabled Doesn’t Matter

Theory of Operation 9
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
The actual current and start-up time depend
on the oscillator source and amplier module.
The current and start-up times given below
are representative values intended only as
guidelines. For further information, refer to the
appropriate modular instruction manuals for
specic oscillator and amplier types.
Standby Mode Selection Table
Mode # Standby Current Turn-on Time
1a 14 mA 150 mS
1b 21 mA 10 mS
1c 14 mA 10 mS
2a 166 mA 150 mS
2b 173 mA 10 mS
2c 167 mA 10 mS
3 29 mA 10 mS
4 181 mA 10 mS
NOTE: Standby Current is the total current
drawn by the synthesizer and FM Audio
Processor from the +9.5 VDC supply.
FM Audio Processor Total Current Consumption
Compression
Conguration
Audio Processor
Current Draw
Keyed / Unkeyed
Compression enabled (JU36 X) 15 mA / 0.45 mA
Compression and microphone
disabled (JU36 Open)
9.2 mA / 0.45 mA
Compression enabled (JU36 Y) 15 mA / 9.2 mA
Audio Circuits
The FM Audio Processor performs audio signal
conditioning (e.g., limiting, ltering and pre-
emphasis). The transmitter mainboard routes
the audio lines from the backplane connector to
the audio processor and then to the synthesizer.
The audio lines routed to the audio processor
are two subtone inputs (backplane pins B22
and Z24), a direct modulation input (pin Z28), a
squelched / at audio input (pin Z20), a 600 Ω
balanced input (pins B18 and Z18), and an audio
control line (pin Z22). The audio processor’s
balanced input pins are isolated from pins B18
and Z18 by a transformer (T1).
Two audio outputs from the FM Audio Processor
are routed to the synthesizer modules.
Microphone Audio
Normally the microphone audio is sent from
the attached transmitter, however the MIC IN
and MIC OUT lines can be congured on the
transmitter mainboard such that the microphone
audio modulates a different transmitter. The
conguration of the MIC IN (pin Z4) and MIC
OUT (pin B4) lines on the MT-3 FM Transmitter
Mainboard are controlled by jumpers J16
and J17 respectively. Jumper J16 selects the
audio source for the FM Audio Processor’s
microphone input. Jumper J17 is used to enable
or disable the MIC OUT line. Normally the
transmitter’s microphone is selected (J16 in the
X position) and the MIC OUT line is enabled
(J17 is installed).
Received Audio
Pin B20 is the audio input from the transmitter’s
corresponding receiver. The default setting for
this line is to have it AC coupled (Jumper J9 is
out) and directly connected to the front panel
board RX AUDIO line.
Channel Selection
Synthesized Transmitter
Seven backplane connections are used to
communicate with the synthesizer unit. Pins
D28, D30 and D32 are used (in house) to
program the synthesizer. Channel select lines
CSEL 0 (least signicant bit) through CSEL 3
(most signicant bit), which are available at
pins D20, D22, D24 and D26, are used once
the synthesizer is programmed to select one of
16 channels. If the channel select lines are all
low (Channel 1) the channel for the synthesizer
is read from switches FSW1 (most signicant),
FSW2, FSW3 and FSW4 (least signicant);
otherwise one of 15 pre-programmed
frequencies is selected. Refer to the channel
designation tables (manual IM20-VT3H040CT)
to set the operating frequency.

Theory of Operation
10
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Amplier Circuits
The MT-3 series Amplier has six connections that are cabled to the transmitter board:
+13.8 VDC•
+9.5 VDC•
Enable•
Forward Power Sense•
Reverse Power Sense•
Ground•
The +13.8 VDC supply (JP1-3) is always on while the +9.5 VDC supply (JP1-2) is always switched by
a PTT signal. The enable line (JP1-1) is active low and is controlled by the Qualied PTT signal from
the synthesizer module.
Jumpers J12, J13, J14 and J15 are used to congure the amplier’s forward and reverse power sense
lines (JP1-4 and JP1-5). Normally jumpers J13, J14 and J15 are in the X position, which directly
connects the amplier’s forward and reverse power sense lines to the backplane connector (pins B26
and Z26 respectively).
The forward and reverse power sense lines from the amplier can be open collector or linear outputs
depending on how they are congured in the amplier module. In open collector conguration, the
lines are active low, that is, the output will go low when a “fail” condition is detected. If both lines from
the amplier module are congured as open collector outputs, the power sense lines can be ‘OR’ed
together to make a general fail indicator (jumper J12 in, jumpers J13, J14 and J15 in the Y position).
The Fail Indicator is also an open collector output; however, the Fail Indicator is active high (the
output goes high when a “fail” condition is detected). When the transmitter is congured with the
general fail indicator option, pin Z26 (VSWR reverse) is not used and pin B26 becomes the Fail
Indicator output.

Theory of Operation 11
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Time-Out-Timer Circuitry
The MT-3 FM Transmitter also has an
associated programmable push-to-talk
(PTT) time-out-timer (TOT) circuitry on the
transmitter mainboard. The TOT circuitry
is powered via J34 from the continuous
+9.5 VDC supply and is programmable for
various time-out periods.
The TOT input trigger (enabled by J33) is
normally high and in this state the timer is
disabled. When the input trigger level falls
below +2.0 VDC, the timer is activated, the
TOT output trigger (enabled by J35) is pulled
low and the transmitter is keyed. If the input
trigger rises above +2.4 VDC or if the time-
out period is exceeded, the output trigger will
go high, disabling the transmitter. If the time-
out period is exceeded, the TOT input trigger
must go high and then low again in order to
re-key the transmitter.
The time-out duration is jumper selectable
from 1 second to 8 hours (see Table 1).
The positions of the jumpers are on the
top (through-hole component) side of the
transmitter mainboard.
J32 J31 J29 J28 J26 J27 Minutes
I I I I I I 0.01
I I I I I N/I 0.01
I I I I N/I I 0.01
I I I N/I I I 0.01
I I I N/I I N/I 0.02
I I N/I I I I 0.02
I I I N/I N/I I 0.03
I I N/I I I N/I 0.04
I I N/I N/I I I 0.05
I I N/I I N/I I 0.06
I I N/I N/I I N/I 0.08
I N/I I I I I 0.10
I I N/I N/I N/I I 0.12
I N/I I I I N/I 0.15
I N/I I N/I I I 0.19
I N/I I I N/I I 0.23
I N/I I N/I I N/I 0.31
I N/I N/I I I I 0.38
I N/I I N/I N/I I 0.47
I N/I N/I I I N/I 0.62
I N/I N/I N/I I I 0.75
I N/I N/I I N/I I 0.94
I N/I N/I N/I I N/I 1.25
N/I I I I I I 1.5
I N/I N/I N/I N/I I 1.88
N/I I I I I N/I 2.5
N/I I I N/I I I 3.0
N/I I I I N/I I 3.75
N/I I I N/I I N/I 5.0
N/I I N/I I I I 6.0
N/I I I N/I N/I I 7.5
N/I I N/I I I N/I 10
N/I I N/I N/I I I 12
N/I I N/I I N/I I 15
N/I I N/I N/I I N/I 20
N/I N/I I I I I 24
N/I I N/I N/I N/I I 30
N/I N/I I I I N/I 40
N/I N/I I N/I I I 48
N/I N/I I I N/I I 60
N/I N/I I N/I I N/I 80
N/I N/I N/I I I I 96
N/I N/I I N/I N/I I 120
N/I N/I N/I I I N/I 160
N/I N/I N/I N/I I I 192
N/I N/I N/I I N/I I 240
N/I N/I N/I N/I I N/I 320
N/I N/I N/I N/I N/I I 480
N/I = Not Installed
I = Installed
Bold text represents default settings.
TABLE 1: Time-out Jumper Settings and Duration

Theory of Operation
12
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
FM AUDIO PROCESSOR
Introduction
The FM Audio Processor is a versatile circuit
board that can provide several types of audio
processing for voice or data transmission (see
Figure 1).
Bandwidth Table
Term Channel Spacing
Rated
System Deviation
Wide band (WB) 25 kHz or 30 kHz ±5.00 kHz
Features include:
• Automatic level control using a compression
amplier with a 25 dB dynamic range
• Limiter and splatter lter that removes noise
and harmonics
• Selectable pre-emphasis or at audio
response
• Temperature compensated audio output
• Ability to transmit data and voice switched
by a single control line
• Multiple jumpers that can be congured
to allow maximum exibility in routing
signals from inputs to outputs and disabling
selected circuits to reduce operating current
• Dual microphone and balanced audio
compression circuits
• On-board multi-congurable temperature
compensation to correct for changes in
transmitter deviation over temperature
caused by changing characteristics of
synthesizers and oscillators
• A single chip 10th Order Linear Phase Low
Pass Splatter Filter for increased cut-off
attenuation responses
• Separate voice and direct modulation
outputs, each individually congurable
• Direct modulation input for LTR®, DCS,
paging and other digital modulations that
require very low frequency modulation to the
synthesizer module
• Multiple audio inputs for various audio lter
or modulation congurations
NOTE: If dual mode CTCSS and LTR® / DCS
is desired in the same transmitter, it may
be possible with dual port modulation
synthesizers. It is not feasible with single
port modulation synthesizers. These
synthesizers are characterized by the
lack of a modulation port in their VCO
circuit. Contact the Daniels factory for
further details.
A continuous +9.5 VDC supply and a switched
+8.0 VDC supply are required to power the
module which is normally supplied by the
transmitter mainboard.
The FM Audio Processor’s balanced input
pins are isolated by a transformer (T1) on the
transmitter mainboard. Two audio outputs
from the FM Audio Processor are routed to the
synthesizer module.

Theory of Operation 13
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
FM Audio Processor Block Diagram
Splatter
Filter
Pre-
emphasis
Select
Pre-
emphasis
Select
Compression
Amp
Compression
Amp
Limiter/Summing
Amplifier
Buffer
+4 V
Regulator
+4 V
Pre-
emphasis
Select
Auxillary
Buffer
Amp
Tx Audio
Control
Audio
Switch 1
Audio
Switch 2
Regular Modulation
Buffer
Subtone
1
3 KHz
Direct Modulation
Offset Buffer
TCVCXO
Modulation Buffer
Offset
TCVCXO
DC Level
Adjust
Reg Mod
Out
Low Freq
Out
Inverting Amp
Coupling
Select
2 Port
Polarity
Select
JU35
JU34
Tx Audio
Control
3dB
Narrow
Band
Pad
JU14
JU26
JU27
JU30
JU43
JU28
JU25
49K9
49K9
P1-3
R2
U1A
U1B
P1-1
R31
Tone
Digital
Input
P2-1
Balanced
Input
Microphone
Input
U3A
U3B
U2A
U2C
U2D
P2-2
R48
R42
U5
U6
Q1
Direct
Modulation
Input
P4-3
U2B
R87
P4-4
P4-2
P3-1
U3C
U3D
P4-1
JU4
Subtone
2JU13
R36
JU12
JU11
B0232
*
FIGURE 1

Theory of Operation
14
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Factory Conguration
The FM Audio Processor is factory congured as follows:
Parameter Specication
Maximum Deviation ±5.0 kHz
Microphone Input • 1 kHz signal at -10 dBm gives ±60% rated system deviation
• 1 kHz signal compression set at ±84% rated system deviation
Audio Balanced Input • 1 kHz tone at -8 dBm gives pre-emphasis response ±60% rated
system deviation
• 1 kHz signal compression set at ±84% rated system deviation
Subtone Input 1 100 Hz tone at -18 dBm gives ±500 Hz
All Other Audio Inputs Disabled
Interconnection Pin Layout Diagram
PCB
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
P1P2P4P3
Balanced Input
END VIEW
Mic Inp u t
Subtone Inp ut 1
+8V
+9.5V
Low Frequen cy
Direct Mod Output
Voice
And Subto ne
Output -8
dBm
-10
dBm
-18
dBm
Surface Mou nt Si de
0
dBm
B0312
FIGURE 2
For the interconnections and functions of the FM Audio Processor external connections, see
Figure 2. Connectors P1, P2, P3, and P4 are four-pin audio processor headers soldered directly to
the transmitter mainboard. For troubleshooting isolation, the audio processor could be unsoldered
from the mainboard and analyzed. Power and I/O connections, as well as their expected levels, are
shown in this diagram.

Theory of Operation 15
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
Turn-on Time
Turn-on Time is the time it takes the FM Audio
Processor to output a stable audio signal to
P3-1 once the +8.0 VDC power is enabled.
The turn-on time can be virtually eliminated by
conguring the audio processor for continuous
audio standby; however, this results in
increased current consumption. Powering of the
compression amplier contributes to most of the
time delay, so transmitters congured with the
compression amplier disabled (for data or non-
compressed audio) will exhibit the fast
turn-on time. The response measurement is
made with the standard factory settings with a
1 kHz tone applied to the balanced input.
Low Frequency Modulation
The transmitter has an additional option
to address low frequency user modulation
requirements. A phase modulated bandwidth
from 0 (DC) to 100 Hz (PLL loop lter
bandwidth) allows specialized applications such
as paging or trunking where a separate low
frequency digital / analog modulation channel
is required. Low Frequency Modulation allows
external access to the low frequency modulation
capabilities of the synthesizer module. The
DIRECT MODULATION inputs on the J1 control
connector of the MT-3 Motherboard will be used
(B20 for TX A, and A20 for TX B).
Turn on Time
Mode Turn-on Time Audio Processor Standby Current
Fast turn on – higher current Approx 1 mS 15 mA
Current save – slower response Approx 150 mS 450 µA
FM Audio Processor Signals
The FM Audio Processor has six audio inputs,
two audio outputs and one audio control input.
Five of the audio inputs are used primarily for
voice and tone signals. The sixth, the Direct
Modulation Input, is used primarily for data
signals. The audio control input is used to switch
audio outputs so the transmitter can transmit
voice or data.
The audio inputs on the audio processor are:
• Dynamic microphone input
• 600 Ω balanced input
• Subtone inputs
• Auxiliary input
• Direct modulation input for data signals
FM Audio Processor Outputs
Both the audio outputs, Modulation Output
(P3-1) and Low Frequency / Direct Modulation
Output (P4-2), are gated by audio switches U5
and U6 respectively which are controlled by the
Transmit Audio Control Input (P4-4). The audio
switches can be operated complimentary to
each other so that only one source modulates
the transmitter. In standard conguration, the
Modulation Output port is used so switch U5 is
always on.

Theory of Operation
16
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
FM Audio Processor Modulation Outputs
The Modulation Output port is used by all
voice input signals. The voice inputs are
passed to U1A and U1B, a dual programmable
compressor-expander that is congured as
an automatic level control amplier. Op-Amp
U3A provides the limiting action for the audio
processor.
After the audio signals have been combined,
limited and buffered, they are ltered by a 10th
order Linear Phase Low Pass Filter (U4). The
output signal from the lter is then level adjusted
by the deviation control pot, R29, at the input
of buffer amplier U3D. In special applications,
jumper JU6 can be disabled and JU7 enabled
allowing the transmitter to be modulated directly
from the auxiliary input. External ltering may be
required since jumper JU7 bypasses the limiting
and lter circuits.
The Low Frequency / Direct Modulation Output
port has two functions depending on whether
the transmitter is synthesized. In a synthesized
transmitter, this port is used to modulate the
synthesizer reference frequency. The frequency
response of this port is typically DC to 300 Hz.
FM Audio Processor Microphone Input
The microphone input has an automatically level
controlled (ALC) pre-amplier U1 whose input
level is controlled by R2. The microphone input
level control (R2) can accommodate a -25 dBm
to 0 dBm input signal. The microphone input is
limited and ltered and is output at the standard
modulation output port. The microphone input
can have a standard 6 dB/octave pre-emphasis
response or a at-audio response, jumper JU1
at Y and X position respectively.
FM Audio Processor Balanced Input
The 600 Ω balanced input uses the ALC
pre-amplier U1B with input level control pot
(R31). The balanced input level control can
accommodate a -25 dBm to 0 dBm input. (Install
JU17 when using the lower input levels). Like
the microphone input, the balanced input is
limited and ltered and is output at the standard
modulation output port.
If no compression is required (i.e., customer
is providing their own), JU11 can be enabled
providing a path through R48 (Auxiliary Input
Level Control) to amplier U2C where pre-
emphasis or at audio can then be selected
from its output.
FM Audio Processor Auxiliary Input
The auxiliary input is a special input and does
not have an ALC. This input can be congured
for a pre-emphasis response (enable JU9 Y) or
a at-audio response (enable JU9 X). The level
for this input is set by R48. The auxiliary output
is normally summed with the voice signals by
Op-Amp U3A, limited, then ltered and output
at the standard modulation output port. The
value of R57 (Select) can be tailored for specic
applications.
When jumper JU6 is disabled and jumper JU7
is enabled, the auxiliary input can be used to
directly modulate the transmitter. Care should be
taken when directly modulating the transmitter
with the auxiliary input because the MT-3
transmitters use direct FM modulation and there
is no ltering or limiting action provided by the
auxiliary input. The input level to the auxiliary
input should be -18 dBm and can be driven by
one of three inputs:
• balanced input – JU11
• tone / digital input – JU12 X or Y enabled
• direct modulation input – through JU28
When the 600 Ω balanced input is connected
to the auxiliary input, the balanced input level
control can be used to adjust the level for the
auxiliary input.