Tait TEL0047 User Manual
M830-00
CI
Part C T836 Transmitter & T837 Exciter
This part of the manual is divided into six sections, as listed below. There is a detailed
table of contents at the start of each section.
Section Title
1 General Information
2 Circuit Operation
3 Initial Tuning & Adjustment
4 Functional Testing
5 Fault Finding
6 PCB Information
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T836/837 General Information
C1.1
1 T836/837 General Information
This section provides a brief description of the T836 transmitter and T837 exciter, along
with detailed specifications and a list of types available.
The following topics are covered in this section.
Section Title Page
1.1 Introduction 1.7
1.2
1.2.1
1.2.2
1.2.3
1.2.4
1.2.4.1
1.2.4.2
1.2.4.3
1.2.5
1.2.6
1.3 Product Codes 1.13
1.4 T836 Standard Product Range 1.14
1.5 T837 Standard Product Range 1.15
Specifications
Introduction
General
RF Section
Audio Processor
Inputs
Modulation Characteristics
CTCSS
Microcontroller
Test Standards
1.8
1.8
1.8
1.9
1.10
1.10
1.10
1.11
1.12
1.12
Figure Title Page
1.1 T836 Main Circuit Block Identification 1.4
1.2 T836 Front Panel Controls 1.4
1.3 T837 Main Circuit Block Identification 1.6
1.4 T837 Front Panel Controls 1.6
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1.1 Introduction
T836/837 General Information
C1.7
The T836 is a synthesised, microprocessor controlled FM base station transmitter
designed for single or multichannel operation in the 136 to 174MHz frequency range
with a standard power output of 25W. The RF section of the transmitter comprises a frequency synthesiser which provides 170mW of frequency modulated RF drive to a two
stage, wide band output driver followed by a 25W power amplifier. A thermal shutdown feature is provided in the T836 in case operating temperatures exceed acceptable
levels.
The T837 is a synthesised, microprocessor controlled FM base station exciter designed
for single or multichannel operation in the 136 to 174MHz frequency range
standard power output of only 800mW, the exciter is designed for use with the T838
50W or T839 100W power amplifiers. The RF section of the exciter comprises a frequency synthesiser which provides 170mW of frequency modulated RF drive to a two
stage, wide band output amplifier.
A wide selection of audio characteristics may be obtained from the audio processor.
Optional circuit blocks are an audio compressor and a pre-emphasis stage. They can be
bypassed or linked to one or both audio inputs, and then back into the remaining audio
circuitry in almost any combination. All audio processor options are link selectable.
The synthesiser frequency is programmed via the serial communications port. Eight
channel select lines are accessible via an optional D-range connector (D-range 2 T800-03-0000) at the rear of the set.
1
. With a
1
All components except those of the VCO are mounted on a single PCB. This is secured
to a die-cast chassis which is divided into compartments to individually shield each section of circuitry. Access to both sides of the main circuit board is obtained by removing
each of the chassis lids. There is provision within the chassis to mount small option
PCBs.
The front panel controls include line sensitivity, microphone socket and carrier switch.
This switch turns on the carrier (unmodulated) as an aid to servicing.
The T836 and T837 are both 60mm wide and each occupies a single space in a Tait rack
frame, which has the ability to accommodate up to seven standard modules.
1. Although capable of operating over the 136-174MHz frequency range, the T836 and
T837 have an 8MHz switching range (see Section 1.2.3 and Section 3.1).
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1.2 Specifications
1.2.1 Introduction
The performance figures given are minimum figures, unless otherwise indicated, for
equipment tuned with the maximum switching range and operating at standard room
temperature (+22°C to +28°C) and standard test voltage (13.8V DC).
Where applicable, the test methods used to obtain the following performance figures are
those described in the EIA and ETS specifications. However, there are several parameters for which performance according to the CEPT specification is given. Refer to Sec-
tion 1.2.6 for details of test standards.
Details of test methods and the conditions which apply for Type Approval testing in all
countries can be obtained from Tait Electronics Ltd.
The terms "wide bandwidth", "mid bandwidth" and "narrow bandwidth" used in this
and following sections are defined in the following table.
Channel Spacing
Wide Bandwidth 25kHz ±5.0kHz 15.0kHz
Mid Bandwidth 20kHz ±4.0kHz 12.0kHz
Narrow Bandwidth 12.5kHz ±2.5kHz 7.5kHz
Modulation
100% Deviation
Receiver
IF Bandwidth
1.2.2 General
Number Of Channels .. 128 (standard)
Supply Voltage:
Operating Voltage .. 10.8 to 16V DC
Standard Test Voltage .. 13.8V DC
Polarity .. negative earth only
Polarity Protection .. crowbar diode
Line Keying Supply (if required) .. -50V DC
Supply Current:
1
Transmit - T836 .. 4.5A (typical)
- T837 .. 600mA
Standby .. 150mA (typical)
Operating Temperature Range .. -30°C to +60°C
1. Additional channels may be factory programmed. Contact your nearest Tait Dealer or
Customer Service Organisation.
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T836/837 General Information
Dimensions:
Height .. 183mm
Width .. 60mm
Length .. 320mm
Weight .. 2.1kg
C1.9
Time-Out Timer (optional) .. 0 to 5 minutes
1
adjustable in 10 sec-
ond steps
Tail Timer .. 0 to 5 seconds adjustable in 100ms
2
steps
Transmit Key Time .. <30ms
Transmit Lockout Timer .. 0 to 1 minute adjustable in 10 second
steps
1.2.3 RF Section
Frequency Range .. 136-174MHz (refer to Section 1.4 and
Section 1.5)
Modulation Type .. FM
Frequency Increment .. 5 or 6.25kHz
Switching Range .. 8MHz (i.e. ±4MHz from the centre
frequency)
Load Impedance .. 50 ohms
Frequency Stability .. ±2.5ppm, -30°C to +60°C
(see also Section 1.4 and Section 1.5)
Adjacent Channel Power (full deviation):
Wide Bandwidth (WB) .. -75dBc
(±25kHz/15kHz B/W)
Mid Bandwidth (MB) .. -70dBc
(±20kHz/12kHz B/W)
Narrow Bandwidth (NB) .. -65dBc
(±12.5kHz/7.5kHz B/W)
Transmitter Side Band Noise:
(no modulation, 15kHz bandwidth)
At ±25kHz .. -95dBc
At ±1MHz .. -105dBc
1. Adjustable from 0 to 10 minutes in PGM800Win version 2.12 and later.
2. Adjustable in 20ms steps in PGM800Win version 2.12 and later.
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Intermodulation .. -40dBc with interfering signal of
T836 Mismatch Capability:
Radiated Spurious Emissions:
Conducted Spurious Emissions: (T836 Only)
T836/837 General Information
-30dBc
.. -70dBc with 25dB isolation
& interfering signal of -30dBc
(PA with output isolator)
Ruggedness .. refer to your nearest Tait Dealer or
Customer Service Organisation
Stability .. 3:1 VSWR (all phase angles)
Transmit .. -36dBm to 1GHz
-30dBm to 4GHz
Standby .. -57dBm to 1GHz
-47dBm to 4GHz
Transmit .. -36dBm to 1GHz
-30dBm to 4GHz
Standby .. -57dBm to 1GHz
-47dBm to 4GHz
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Power Output:
T836 - Rated Power .. 25W
- Range Of Adjustment .. 5-25W
T837 .. 800mW ±200mW
Duty Cycle (T836 Only) .. 100% @ 25W at +25°C
.. 30% @ 25W at +60°C
.. 100% @ 10W at +60°C
1.2.4 Audio Processor
1.2.4.1 Inputs
Inputs Available .. line, microphone and CTCSS
Line Input:
Impedance .. 600 ohms (balanced)
Sensitivity (60% modulation @ 1kHz)-
With Compressor .. -50dBm
Without Compressor .. -30dBm
Microphone Input:
Impedance .. 600 ohms
Sensitivity (60% modulation @ 1kHz)-
With Compressor .. -70dBm
Without Compressor .. -50dBm
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1.2.4.2 Modulation Characteristics
Frequency Response .. flat or pre-emphasised (optional)
(below limiting)
Line And Microphone Inputs:
Pre-emphasised Response-
Bandwidth .. 300Hz to 3kHz (WB & MB)
Below Limiting .. within +1, -3dB of a 6dB/octave
Flat Response .. within +1, -2dB of output at 1kHz
Above Limiting Response .. within +1, -2dB of a flat response
Distortion .. 2%
Hum And Noise:
T836/837 General Information
.. 300Hz to 2.55kHz (NB)
pre-emphasis characteristic
(ref. 1kHz)
C1.11
Wide Bandwidth .. -55dB (300Hz to 3kHz [EIA]) typical
Mid Bandwidth .. -54dB (CEPT)
Narrow Bandwidth .. -50dB (CEPT)
Compressor (optional):
Attack Time .. 10ms
Decay Time .. 800ms
Range .. 50dB
1.2.4.3 CTCSS
Standard Tones .. all 37 EIA group A, B and C tones
plus 13 commonly used tones
Frequency Error .. 0.08% max.
(from EIA tones)
Generated Tone Distortion .. 1.2% max.
Generated Tone Flatness .. flat across 67 to 250.3Hz to within 1dB
Modulation Level .. adjustable
Modulated Distortion .. <5%
1.2.5 Microcontroller
Auxiliary Ports:
Open Drain Type .. capable of sinking 2.25mA via 2k2Ω
max. .. 5V
V
ds
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1.2.6 Test Standards
Where applicable, this equipment is tested in accordance with the following standards.
1.2.6.1 European Te lecommunication Standard
ETS 300 086 January 1991
Radio equipment and systems; land mobile service; technical characteristics and test
conditions for radio equipment with an internal or external RF connector intended primarily for analogue speech.
ETS 300 113 March 1996
Radio equipment and systems; land mobile service; technical characteristics and test
conditions for radio equipment intended for the transmission of data (and speech) and
having an antenna connector.
ETS 300 219 October 1993
Radio equipment and systems; land mobile service; technical characteristics and test
conditions for radio equipment transmitting signals to initiate a specific response in the
receiver.
ETS 300 279 February 1996
Radio equipment and systems; electromagnetic compatibility (EMC) standard for private land mobile radio (PMR) and ancillary equipment (speech and/or non-speech).
1.2.6.2 DTI CEPT Recommendation T/R-24-01
Annex I: 1988
Technical characteristics and test conditions for radio equipment in the land mobile
service intended primarily for analogue speech.
Annex II: 1988
Technical characteristics of radio equipment in the land mobile service with regard to
quality and stability of transmission.
1.2.6.3 Telecommunications Industry Association
ANSI/TIA/EIA-603-1992
Land mobile FM or PM communications equipment measurement and performance
standards.
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C1.13
1.3 Product Codes
The three groups of digits in the T830 Series II product code provide information about
the model, type and options fitted, according to the conventions described below.
The following explanation of T830 Series II product codes is not intended to suggest that
any combination of features is necessarily available in any one product. Consult your
nearest Tait Dealer or Customer Service Organisation for more information regarding
the availability of specific models, types and options.
Model
The Model group indicates the basic function of the product, as follows:
T83X
-XX-XXXX T835 receiver
T836 25W transmitter
T837 exciter
T838 50W power amplifier
T839 100W power amplifier
Type
The Type group uses two digits to indicate the basic RF configuration of the product.
The first digit in the Type group designates the frequency range:
T83X-X
The second digit in the Type group indicates the channel spacing:
T83X-XX
X-XXXX ’1’ for 136-156MHz
’2’ for 148-174MHz
-XXXX ’0’ for wide bandwidth (25kHz)
’3’ for mid bandwidth (20kHz)
’5’ for narrow bandwidth (12.5kHz)
Options
T83X-XX-XXXX The Options group uses four digits and/or letters to indicate
any options that may be fitted to the product. This includes
standard options and special options for specific customers.
’0000’ indicates a standard Tait product with no options fitted.
The large number of options precludes listing them here.
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T836/837 General Information
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1.4 T836 Standard Product Range
The following table lists the range of standard T836 types (i.e. no options fitted) available at the time this manual was published. Consult your nearest Tait Dealer or Customer Service Organisation for more information.
Frequency Range (MHz) 136-156
Deviation (kHz) 2.5 2.5 4 5
a
TCXO
Transmitter Type: T836- 16-0000
Frequency Range (MHz) 148-174
Deviation (kHz) 2.5 2.5 4 5
TCXO
Transmitter Type: T836- 26-0000b25-0000 23-0000 20-0000
±2.5ppm -30°C to +60°C
a
±2.5ppm -30°C to +60°C
• •••
b
15-0000 13-0000 10-0000
• •••
a. A TCXO with a stability of ±1ppm (0°C to +60°C) is available to suit specific
requirements. Contact your nearest authorised Tait Dealer or Customer
Service Organisation for further details.
b. United States market only.
You can identify the transmitter type by checking the product code printed on a label on
the rear of the chassis (Figure 1.1 in Part A shows typical labels). You can further verify
the transmitter type by checking the placement of an SMD resistor in the table that is
screen printed onto the PCB (refer to Section 6.1 for more details).
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C1.15
1.5 T837 Standard Product Range
The following table lists the range of standard T837 types (i.e. no options fitted) available at the time this manual was published. Consult your nearest Tait Dealer or Customer Service Organisation for more information.
Frequency Range (MHz) 136-156
Deviation (kHz) 2.5 2.5 4 5
a
TCXO
Exciter Type: T837- 16-0000
Frequency Range (MHz) 148-174
Deviation (kHz) 2.5 2.5 4 5
TCXO
Exciter Type: T837- 26-0000b25-0000 23-0000 20-0000
±2.5ppm -30°C to +60°C
a
±2.5ppm -30°C to +60°C
• •••
b
15-0000 13-0000 10-0000
• •••
a. A TCXO with a stability of ±1ppm (0°C to +60°C) is available to suit specific
requirements. Contact your nearest authorised Tait Dealer or Customer
Service Organisation for further details.
b. United States market only.
You can identify the exciter type by checking the product code printed on a label on the
rear of the chassis (Figure 1.1 in Part A shows typical labels). You can further verify the
exciter type by checking the placement of an SMD resistor in the table that is screen
printed onto the PCB (refer to Section 6.1 for more details).
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T836/837 Circuit Operation
C2.1
2 T836/837 Circuit Operation
This section provides a basic description of the circuit operation of the T836 transmitter
and T837 exciter.
Note:
Refer to Section 6 where the parts lists, grid reference index and diagrams will provide
detailed information on identifying and locating components and test points on the
main PCB. The parts list and diagrams for the VCO PCB are in Part E.
The following topics are covered in this section.
Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.
Section Title Page
2.1 Introduction 2.3
2.2 Microcontroller 2.4
2.3
2.3.1
2.4
2.4.1
2.5
Synthesised Local Oscillator
Two Point Modulation
VCO
VCO Supply
Audio Processor
2.5
2.6
2.7
2.7
2.8
2.5.1
2.5.2
2.5.3
2.5.4
2.5.5
2.6 Power Supply & Regulator Circuits 2.10
2.7 Transmit Timers 2.11
2.8 T836 Drive Amplifier & PA 2.12
2.9 T837 Exciter Drive Amplifier 2.13
General
Audio Inputs
Keying Inputs
Compressor (Automatic Level Control (ALC))
Outputs To Modulators
2.8
2.8
2.9
2.9
2.9
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T836/837 Circuit Operation
Figure Title Page
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2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
T836 High Level Block Diagram
T837 High Level Block Diagram
T836/837 Microcontroller Block Diagram
T836/837 Synthesiser Block Diagram
T836/837 Two Point Modulation
T836/837 Audio Processor Block Diagram
T836/837 Power Supply & Regulators Block Diagram
T836/837 Transmit Timers
2.3
2.3
2.4
2.5
2.6
2.8
2.10
2.11
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T836/837 Circuit Operation
C2.3
2.1 Introduction
The individual circuit blocks which make up the T836 and T837 are:
• synthesiser
•VCO
• audio processor
• drive amplifier
• power amplifier (T836 only)
• voltage regulators.
Each of these circuit blocks is set in its own shielded compartment, formed as an integral part of the main chassis.
The configuration of the circuit blocks may be seen on a functional level in Figure 2.1
and Figure 2.2. Refer to the circuit diagrams in Section 6.2 (T836) or 6.3 (T837) for more
detail.
Reference
Oscillator
12.8MHz
Microphone
Line
Tx Reg
Reference
Oscillator
12.8MHz
Microphone
Transformer
Line
Transformer
Power
Control
Drive
Amp.
Ramp
Gen.
Synthesiser
Audio
Processor
+22dBm
Lock
Detect
&
Gate
PIN
Switch
Time
Delay
Time
Delay
Figure 2.1 T836 High Level Block Diagram
PIN
Switch
Time
Delay
Synthesiser
Audio
Processor
+22dBm
Lock
Detect
&
Gate
Exciter
Output
(+27dBm)
Drive
Amp.
Ramp
Gen.
PA
Time
Delay
Switching
Control
Directional
Coupler
Low Pass
Filter
Low Pass
Filter
Exciter
Output
(800mW)
PA Control Signal
(via exciter RF coax)
Transmitter
VCO
Output
(25W)
Tx Reg
Time
Delay
VCO
Figure 2.2 T837 High Level Block Diagram
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C2.4
T836/837 Circuit Operation
2.2 Microcontroller
(Refer to the microcontroller circuit diagram (sheet 8) in Section 6.2 or 6.3.)
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Watchdog
Reset
Microcontroller Cavity
Channel
Auxiliary
Output
EEPROM
Select
Port
Dual Digital
Potentiometer
Port
Synthesiser
12.8MHz
Clock
External
Serial
Port
CTCSS Tone
5V Digital
Regulator
5V Reset
Microcontroller
Converter
CTCSS
Encoder
Figure 2.3 T836/837 Microcontroller Block Diagram
Overall system control of the T836/837 is accomplished by the use of a member of the
80C51 family of microcontrollers (IC810). It runs from internal ROM and RAM, thus
leaving all four ports free for input/output functions.
Non-volatile data storage is achieved by serial communication with a 16kBit EEPROM
(IC820). This serial bus is also used by the microcontroller to program the synthesiser
(IC740) and deviation control EPOTS (IC220).
The main tasks of the microcontroller are as follows:
• program the synthesiser and EPOT;
• interface with the PGM800Win programming software at 9600 baud via the
serial communication lines on D-range 1 (PL100) & D-range 2;
• monitor channel change inputs from D-range 2;
• generate timing waveforms for CTCSS encoding;
• coordinate and implement timing control of the exciter/transmitter;
• control the front panel "Supply" LED (refer to Section 5.3).
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m
T836/837 Circuit Operation
C2.5
2.3 Synthesised Local Oscillator
(Refer to the synthesiser circuit diagram (sheet 7) in Section 6.2 or 6.3 and the VCO circuit diagram in Part E.)
12.8MHz
Reference
Oscillator
Ref
Mod
Serial
Bus
Clk
Data
En
Fixed
Divider
/64
Phase
Modulator
FREQUENCY SYNTHESISER IC
Reference
Divider
f
ref
Controller
/R
Phase
Detector
Programmable
Charge
Divider
/N
Pump
Loop
Filter
Prescaler
64/65
Modulation
f
in
VCO
Σ
VCO Buffer
Divider Buffer
VCO PCB
Output
Buffer
Figure 2.4 T836/837 Synthesiser Block Diagram
The synthesiser (IC740) employs a phase-locked loop (PLL) to lock a voltage controlled
oscillator (VCO) to a given reference frequency. The synthesiser receives the divider
information from the control microprocessor via a 3 wire serial bus (clock, data, enable).
When the data has been latched in, the synthesiser processes the incoming signals from
the VCO buffer (f
) and the phase modulator (f
in
ref
).
A reference oscillator at 12.8MHz (IC700) is buffered (IC710 pins 3 & 4) and divided
down to 200kHz (IC730). This 200kHz square wave is then summed with the modulating audio and passed to an integrator (IC720 pins 9 & 8, Q710, Q720). This produces a
ramping waveform which is centred around a DC level determined by the incoming
audio. IC720 pins 5 & 6 perform as a comparator, ultimately producing a phase-modulated 200kHz square wave. This is followed by another phase shifting stage (IC720 pins
3 & 4, Q730, Q740), before being divided down to 6.25kHz or 5kHz within the synthesiser IC (IC740).
+22dB
L.O.
A buffered output of the VCO (Q795) is divided with a prescaler and programmable
divider which is incorporated into the synthesiser chip (IC740). This signal is compared
with the phase modulated reference signal at the phase detector (also part of the synthesiser chip). The phase detector outputs drive a balanced charge pump circuit (Q760,
Q770, Q775, Q780, Q785) and active loop filter (IC750 pins 5, 6 & 7) which produces a
DC voltage between 0V and 20V to tune the VCO. This VCO control line is further filtered to attenuate noise and other spurious signals. Note that the VCO frequency
increases with increasing control voltage.
If the synthesiser loop loses lock, a pulsed signal appears at LD (pin 2) of IC740. This
signal is filtered and buffered by IC750 pins 1, 2 & 3, producing the Lock-Detect signal
used to shut off the power supply to the drive amplifier. IC750 pin 1 is at 20V when the
synthesiser is out of lock.
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T836/837 Circuit Operation
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2.3.1 Tw o Point Modulation
Frequency modulation occurs by modulating both the VCO input and the synthesiser
reference input. This process is called two point modulation and ensures a flat modulation response from 67Hz to 3kHz (2.55kHz for narrow bandwidth).
The PLL has a fast response time, allowing a Tx key-up time of <30ms. Because of this
fast response time the PLL sees lower modulation frequencies superimposed on the
VCO as an error and corrects for it, resulting in no modulation on the carrier. At modulation frequencies greater than 300Hz the loop cannot correct fast enough and modulation is seen on the carrier. The response of the loop to VCO modulation is shown by f
in Figure 2.5 below.
To achieve low frequency modulation, the reference oscillator is also modulated so that
the phase detector of IC740 detects no frequency error under modulation. Thus, the
synthesiser loop will not attempt to correct for modulation and the audio frequency
response of the transmitter remains unaffected. The response of the loop to reference
frequency modulation is shown by f
The reference modulation is controlled by a 256-step 10k electronic potentiometer
(EPOT) which is adjustable via PGM800Win. The EPOT is made up of 256 resistive sections (representing approximately 39Ω each) which can be individually addressed by
the microcontroller. Each section can be switched in or out of circuit to achieve the
required total resistance, thus giving control of the reference modulation.
in Figure 2.5.
1
2
Deviation
ff
12
TCXO VCO
Frequency
Figure 2.5 T836/837 Two Point Modulation
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