Tait TEL0049, TEL0048 User Manual

Page 1

M850-00

Part C T856 Transmitter & T857 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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T856/857 General Information

C1.1

1 T856/857 General Information

This section provides a brief description of the T856 transmitter and T857 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

1.2.6.1

1.2.6.2

1.2.6.3

1.3 Product Codes 1.13

1.4 T856 Standard Product Range 1.14

1.5 T857 Standard Product Range 1.15

Specifications

Introduction General RF Section Audio Processor

Inputs Modulation Characteristics CTCSS

Microcontroller Test Standards

European Telecommunication Standard DTI CEPT Recommendation T/R-24-01 Telecommunications Industry Association

1.8

1.9

1.10

1.11

1.12

Figure Title Page

1.1 T856 Main Circuit Block Identification 1.4

1.2 T856 Front Panel Controls 1.4

1.3 T857 Main Circuit Block Identification 1.6

1.4 T857 Front Panel Controls 1.6

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1.1 Introduction

T856/857 General Information

C1.7

The T856 is a synthesised, microprocessor controlled FM base station transmitter designed for single or multichannel operation in the 400 to 520MHz frequency range with a standard power output of 25W. The RF section of the transmitter comprises a frequency synthesiser which provides 100mW 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 T856 in case operating temperatures exceed acceptable levels.

The T857 is a synthesised, microprocessor controlled FM base station exciter designed for single or multichannel operation in the 400 to 520MHz frequency range standard power output of only 1W, the exciter is designed for use with the T858 50W or T859 100W power amplifiers. The RF section of the exciter comprises a frequency synthesiser which provides 100mW 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.

. With a

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 T856 and T857 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 400-520MHz frequency range, the T856 and T857 have an 8MHz switching range (see Section 1.2.3 and Section 3.1).

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T856/857 General Information

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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 Section 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:

Transmit - T856 .. 5.5A (typical)

- T857 .. 750mA

Standby - T856 .. 165mA (typical)

- T857 .. 150mA (typical)

Operating Temperature Range .. -20°C to +60°C

1. Additional channels may be factory programmed. Contact your nearest Tait Dealer or Customer Service Organisation.

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T856/857 General Information

Dimensions:

Height .. 183mm Width .. 60mm Length .. 322mm

Weight .. 2.1kg

C1.9

Time-Out Timer (optional) .. 0 to 5 minutes

adjustable in 10 sec-

ond steps

Tail Timer .. 0 to 5 seconds adjustable in 100ms

steps

Transmit Key Time .. <30ms

Transmit Lockout Timer .. 0 to 1 minute adjustable in 10 second

steps

1.2.3 RF Section

Frequency Range .. 400-520MHz (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 .. ±1ppm, -20°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 Switching .. complies with ETS 300 113

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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C1.10

Transmitter Side Band Noise: (no modulation, 15kHz bandwidth)

Intermodulation .. -40dBc with interfering signal of

T856 Mismatch Capability:

Radiated Spurious Emissions:

T856/857 General Information

At ±25kHz .. -95dBc At ±1MHz .. -105dBc

-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 1GHz to 4GHz

Standby .. -57dBm to 1GHz

-47dBm 1GHz to 4GHz

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Conducted Spurious Emissions: (T856 Only)

Transmit .. -36dBm to 1GHz

-30dBm 1GHz to 4GHz

Standby .. -57dBm to 1GHz

-47dBm 1GHz to 4GHz

Power Output:

T856 - Rated Power .. 25W (see Duty Cycle)

- Range Of Adjustment .. 5-25W

T857 .. 1W ±300mW

Duty Cycle (T856 Only) .. 100% @ 25W at +25°C

.. 25% @ 25W at +60°C .. 100% @ 10W at +40°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

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Microphone Input:

Impedance .. 600 ohms Sensitivity (60% modulation @ 1kHz)-

With Compressor .. -70dBm Without Compressor .. -50dBm

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

T856/857 General Information

.. 300Hz to 2.55kHz (NB)

pre-emphasis characteristic

C1.11

Above Limiting Response .. within +1, -2dB of a flat response

(ref. 1kHz)

Distortion .. 2% max.

Hum And Noise:

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%

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T856/857 General Information

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1.2.5 Microcontroller

Auxiliary Ports:

Open Drain Type .. capable of sinking 2.25mA via 2k2Ω

max. .. 5V

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 T850 Series II product code provide information about the model, type and options fitted, according to the conventions described below.

The following explanation of T850 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:

T85X

-XX-XXXX T855 receiver T856 25W transmitter T857 exciter T858 50W power amplifier T859 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: T85X-X

The second digit in the Type group indicates the channel spacing: T85X-XX

X-XXXX ’1’ for 400-440MHz

’2’ for 440-480MHz ’3’ for 480-520MHz

-XXXX ’0’ for wide bandwidth (25kHz) ’3’ for mid bandwidth (20kHz) ’5’ for narrow bandwidth (12.5kHz) ’6’ for United States market only

Options

T85X-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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T856/857 General Information

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1.4 T856 Standard Product Range

The following table lists the range of standard T856 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) 400-440

Deviation (kHz) 2.5 2.5 4 5

TCXO ±1ppm -20°C to +60°C

Transmitter Type: T856- 16-0000

Frequency Range (MHz) 440-480

Deviation (kHz) 2.5 2.5 4 5

TCXO ±1ppm -20°C to +60°C

Transmitter Type: T856- 26-0000a25-0000 23-0000 20-0000

Frequency Range (MHz) 480-520

Deviation 2.5 2.5 5

TXCO ±1ppm -20° to +60°C

Transmitter Type: T856- 36-0000a35-0000 30-0000

a. United States market only.

Caution:

T856-1X-XXXX Product Types

••••

15-0000 13-0000 10-0000

••••

•••

The 406 to 406.1MHz frequency range is reserved worldwide for use by Distress Beacons. Do

not program transmitters to operate in this fre-

quency range.

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 T857 Standard Product Range

The following table lists the range of standard T857 types (i.e. no options fitted and cyclic keying disabled) available at the time this manual was published. Consult your nearest Tait Dealer or Customer Service Organisation for more information.

Frequency Range (MHz) 400-440

Deviation (kHz) 2.5 2.5 4 5

TCXO ±1ppm -20°C to +60°C

Exciter Type: T857- 16-0000

Frequency Range (MHz) 440-480

Deviation (kHz) 2.5 2.5 4 5

TCXO ±1ppm -20°C to +60°C

Exciter Type: T857- 26-0000

Frequency Range (MHz) 480-520

Deviation 2.5 2.5 5

TXCO ±1ppm -20° to +60°C

Exciter Type: T857- 36-0000

a. United States market only.

Caution:

T857-1X-XXXX Product Types

••••

15-0000 13-0000 10-0000

••••

25-0000 23-0000 20-0000

•••

35-0000 30-0000

The 406 to 406.1MHz frequency range is reserved worldwide for use by Distress Beacons.

Do not program exciters to operate in this frequency

range.

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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T856/857 Circuit Operation

C2.1

2 T856/857 Circuit Operation

This section provides a basic description of the circuit operation of the T856 transmitter and T857 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

2.8

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 T856 Drive Amplifier & PA 2.12

2.9 T857 Exciter Drive Amplifier 2.13

General Audio Inputs Keying Inputs Compressor (Automatic Level Control (ALC)) Outputs To Modulators

2.8

2.9

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C2.2

T856/857 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

T856 High Level Block Diagram T857 High Level Block Diagram T856/857 Microcontroller Block Diagram T856/857 Synthesiser Block Diagram T856/857 Two Point Modulation T856/857 Audio Processor Block Diagram T856/857 Power Supply & Regulators Block Diagram T856/857 Transmit Timers

2.3

2.4

2.5

2.6

2.8

2.10

2.11

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T856/857 Circuit Operation

C2.3

2.1 Introduction

The individual circuit blocks which make up the T856 and T857 are:

• synthesiser

•VCO

• audio processor

• drive amplifier

• power amplifier (T856 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 (T856) or 6.3 (T857) 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

Switch

Time

Delay

Time

Delay

Figure 2.1 T856 High Level Block Diagram

Switch

Time

Delay

Synthesiser

Audio

Processor

+22dBm

Lock Detect

Gate

Exciter Output

(+30dBm to

+33dBm)

Drive Amp.

Ramp

Gen.

Time

Delay

Switching

Control

Directional

Coupler

Low Pass

Filter

Low Pass

Filter

Exciter Output

(+28dBm to

+31dBm)

PA Control Signal (via exciter RF coax)

Transmitter Output (25W)

VCO

Tx Reg

Time

Delay

VCO

Figure 2.2 T857 High Level Block Diagram

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C2.4

T856/857 Circuit Operation

2.2 Microcontroller

(Refer to the microcontroller circuit diagram (sheet 8) in Section 6.2 or 6.3.)

M850-00

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 T856/857 Microcontroller Block Diagram

Overall system control of the T856/857 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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T856/857 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

ref

Controller

Phase

Detector

Programmable

Divider

Charge

Pump

Loop Filter

Prescaler

64/65

Modulation

VCO

VCO Buffer

Divider Buffer

VCO PCB

Output

Buffer

Figure 2.4 T856/857 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

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, Q790) 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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T856/857 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.

Deviation

TCXO VCO

Frequency

Figure 2.5 T856/857 Two Point Modulation

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T856/857 Circuit Operation

C2.7

2.4 VCO

(Refer to the VCO circuit diagram in Part E.)

The VCO transistor (Q1) operates in a common emitter configuration, with an LC tank circuit coupled between its gate and drain to provide the feedback necessary for oscillation. The VCO control voltage from the loop filter (IC750) is applied to the varicaps (D1-D2) to facilitate tuning within an 8MHz band of frequencies. A trimcap (C6) is used for coarse tuning of the VCO. The output from the oscillator circuit drives a cascode amplifier stage (Q2, Q3) which supplies +10dBm (typically) to a further stage of amplification, Q5. This is the final amplifier on the VCO PCB, and delivers +20dBm (typically) to the exciter drive amplifier.

A low level "sniff" is taken from the input to Q5 and used to drive the divider buffer for the synthesiser (IC740).

The VCO operates at the actual output frequency of the exciter, i.e. there are no multiplier stages. It is modulated by superimposing the audio signal onto the control voltage and by phase modulating the reference signal.

2.4.1 VCO Supply

The VCO is supplied from two switched +9V supplies under the control of the Tx-Reg. supply.

The VCO and buffer amplifier are supplied from one +9V switched supply by Q540 via the C multiplier (Q550, C530 on the T856 and C550 on the T857).

The output amplifier is supplied from the other +9V supply by Q520, Q530, and Q510.

A delay circuit holds the VCO on for a short time after the Tx-Reg. supply has been switched off. This is to allow the RF power circuits (both exciter and PA) to ramp down in the correct manner before the VCO is switched off.

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C2.8

T856/857 Circuit Operation

2.5 Audio Processor

(Refer to the audio processor circuit diagram (sheet 2) in Section 6.2 or 6.3.)

Carrier

M850-00

Opto-Key

Tx Key

PTT

Microphone

Input

Line Input

Constant Current Sink

Opto-coupler

Microphone

Pre-amp.

Audio 1 Audio 2

Link

34 5

PL205

Compressor

Pre-

emphasis

mic.

Inputs

line

Multiplexer

Output

Inhibit

Output

6 4

Link

PL210

Figure 2.6 T856/857 Audio Processor Block Diagram

Tx Enable

Link

PL215

Link

PL220

Buffer

Output

To VCO

Limiter

Set Deviation

Digital Pot. (EPOT)

Low Pass Filter

Ref. Mod. Adjust

Digital Pot. (EPOT)

Integrator

Ref. Mod.

CTCSS

2.5.1 General

The audio processor comprises several link selectable circuit blocks which may be configured in a variety of combinations to suit individual requirements. The pre-emphasis network and compressor may be linked individually or cascaded between either or both audio inputs and the limiter.

Refer to Section 3.5.1 for linking details.

2.5.2 Audio Inputs

Two audio inputs are available: one from a 600 ohm balanced (or unbalanced) line, and the other from a local microphone. The microphone signal is passed first to a pre-amplifier (Q210) and ultimately to a multiplexer (IC240), but in between may pass through the compressor (depending on the linking details). The line transformer is also connected to the multiplexer and is disabled by the microphone PTT switch.

A third input for external CTCSS tones is also provided.

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C2.9

2.5.3 Keying Inputs

There are four ways to key the exciter:

• pulling the Tx-Key line low (pin 13 on D-range 1 [PL100]) at the rear of the set);

• pushing the "Carrier" button on the front panel - this will inhibit all audio;

• using the PTT button on the local microphone, disabling audio from the line;

• via the opto-key inputs (pins 11 and 12 on D-range 1 [PL100]) when electrical isolation is required. This features a constant current sink (Q270) to ensure reliable activation of the opto-coupler (IC250) at low keying voltages.

2.5.4 Compress or (Automatic Level Control (ALC))

The input signal is fed via a current controlled attenuator (Q230, Q220) to a high gain stage (IC230) from which the output signal is taken. This signal is passed to a comparator (IC230) which toggles whenever the audio signal exceeds a DC threshold determined by RV220. Thus, the comparator produces a square wave whose mark-space ratio is determined by the amplitude of the audio signal. This square wave pumps up the reservoir capacitor (C233) which controls the attenuator (Q230, Q220), thus completing the feedback loop.

The compression level is set by adjustment of the comparator threshold (RV220).

Note:

Although the high dynamic range of the compressor allows the use of very low audio signal levels, such conditions will be accompanied by a degradation of the signal-to-noise ratio. Very low audio input levels should therefore be avoided where possible.

2.5.5 Outputs To Modulators

The output signal from the limiter (IC210, IC230) is summed with a CTCSS tone at a summing amplifier (IC260). The signal is then low pass filtered (IC260) and split to supply the two modulators.

Since the VCO modulator is a true frequency modulator, its audio is simply buffered (IC260). The reference modulator, however, is a phase modulator and its audio must first be integrated (IC210).

It is vital that the audio levels to the modulators are accurately set,

other. Hence the inclusion of level adjustment in the reference modulator path. Once

set, adjustments to absolute deviation may be made only by IC220, a 256-step 10k electronic potentiometer (EPOT), which is controlled 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 adjusting the absolute deviation level.

relative to each

Page 28

C2.10

T856/857 Circuit Operation

2.6 Power Supply & Regulator Circuits

(Refer to the regulators circuit diagram (sheet 6) in Section 6.2 or 6.3.)

+9V

Buffer

Tx Enable

Micro-

controller

Power

Switch

Tx Reg.

M850-00

13.8V Nom. From Rear

D-Range

Crowbar

Diode

13.8V Nom.

Reg

Amp

5V 5V Dig9V 20V

Switching

5V Dig

Reg

Watchdog

Timer

LVI

Figure 2.7 T856/857 Power Supply & Regulators Block Diagram

The T856 and T857 are designed to operate from a 10.8-16V DC supply (13.8V nominal). A 5.3V regulator (IC630) runs directly from the 13.8V rail, driving much of the synthesiser circuitry. It is also used as the reference for a DC amplifier (IC640, Q630, Q620) which provides a medium current capability 9V supply. The T856 has a regulator (IC370) which produces 9V for use in the exciter and audio circuits.

A switching power supply (Q660, Q670) runs from the 9V supply and provides a low current capability +20V supply. This is used to drive the synthesiser loop filter (IC750), giving a VCO control voltage range of up to 20V.

Ultimate control of the transmitter is via the Tx-Reg. supply, switched from 9V by Q610. This is enabled via the Tx-Enable signal from the audio processor, and microprocessor.

µP

µP Reset

A crowbar diode is fitted for protection against connection to a power supply of incorrect polarity. It also provides transient overvoltage protection.

Note:

A fuse must be fitted in the power supply line for the diode to provide effective protection.

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Page 29

M850-00

T856/857 Circuit Operation

C2.11

2.7 Transmi t Time rs

The transmit tail timer, transmit timeout timer and transmit lockout timer can all be set from PGM800Win. The fields for setting these are found on the system information page. These three timers operate as follows (refer also to Figure 2.8):

Timer Function Adjustment

Transmit Tail Sets the tail time during which the

transmitter stays keyed after the external key source has been removed.

Transmit Timeout Sets the maximum continuous trans-

mission time. Once the timer has timed out, the transmitter must be keyed again, unless prevented by the transmit lockout timer.

Transmit Lockout Sets the period of time that must

elapse after a timeout before the transmitter can re-transmit. Once the timer has timed out, the transmitter can be keyed again.

a. Adjustable in 20ms steps in PGM800Win version 2.12 and later. b. Adjustable from 0 to 600 seconds in PGM800Win version 2.12 and later.

Tx-Enable

Tx-Reg.

0-5 seconds in 100ms

steps

0-300 seconds

in 10

second steps

0-60 seconds in 10 second steps

Tail Time

Tx-Reg.

Lockout Time

Timeout

Time

Figure 2.8 T856/857 Transmit Timers

Page 30

C2.12

T856/857 Circuit Operation

M850-00

2.8 T856 Drive Amplifier & PA

(Refer to Figure 2.1 and the exciter and PA circuit diagrams (sheets 3 & 4) in Section 6.2.)

The output power of the PA is maintained at a constant level via a power control loop applied to the two-stage, wide band exciter amplifier (Q350, Q355). The forward and reverse RF power levels are sensed via a dual directional coupler and detector diodes (D440, D420 in the PA cavity). The detected DC signals are buffered (IC330 pins 3 & 5) and then summed with the ’power control’ level and fed to the control integrator (IC350 pin 6). The output control voltage is buffered by Q310 and Q315, and applied to the collector of the wide band exciter amplifier.

Note:

To reduce the spurious output level when the synthesiser is out-of-lock, the Tx-Reg. and Lock-Detect signals are gated to inhibit the PA control circuit and to switch off the RF signal at the input to the drive amplifier. This is achieved by a PIN switch attenuator (D340, D380, D360).

Cyclic keying control is provided by additional circuitry consisting of several time delay, ramp and gate stages:

This is to allow the RF power circuits (both exciter and PA) to ramp up and down in a controlled manner so that minimal adjacent channel interference is generated during the transition.

The output of the wide band amplifier is approximately 1W (+30dBm) for an input of 100mW (+20dBm) from the VCO, when the power control is set to maximum.

Forward and reflected power signals are summed so that, under high VSWR, the power control will turn the output RF level down.

• Q325, IC350 power ramping

• Q355, Q325 Tx-Reg. and Lock-Detect

• Q335, Q340, Q345 delay and PIN switch drive.

gate

A temperature sensor (R481) is provided so that the RF output power can be reduced to a preset level when a set temperature is exceeded. This is a protection circuit (IC350 pin 1, Q320) to prevent overheating, as the unit is to Section 1.2.3 for duty cycle specifications).

#R517, #R518 and #R519 form an attenuator to provide good VCO/exciter isolation as well as the correct exciter drive level.

The attenuator (#R395, #R396 and #R397) aids in producing the correct exciter drive level to the PA over the three frequency ranges.

The RF output from the exciter is fed to the driver stage (Q410) and then to the final (Q420). DC is fed to the final via a low pass filter with special low frequency decoupling. CV475 tunes the output matching across the entire band.

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not rated for continuous operation (refer

Page 31

M850-00

T856/857 Circuit Operation

C2.13

2.9 T857 Exciter Drive Amplifier

(Refer to Figure 2.2 and the exciter circuit diagram (sheet 3) in Section 6.3.)

A two-stage, wide band amplifier (Q304, Q305) provides an output level of approximately 1W (+30dBm) for an input of 100mW (+20dBm) from the VCO. IC300 pin 1, Q302, and Q303 provide a 9V regulated supply for the exciter.

To reduce the spurious output level when the synthesiser is out-of-lock, the Tx-Reg. and Lock-Detect signals are gated to inhibit the exciter control circuit and to switch off the RF signal at the input to the drive amplifier. This is achieved by a PIN switch attenuator (D201, D202, D203).

Cyclic keying control is provided by additional circuitry consisting of several time delay, ramp and gate stages:

• Q301, Q302, Q303, IC300 power ramping

• Q310, Q311 Tx-Reg. and Lock-Detect

• Q306, Q307, Q308, Q309 delay and PIN switch drive.

This is to allow the RF power circuits (both exciter and PA) to ramp up and down in a controlled manner so that minimal adjacent channel interference is generated during the transition.

R517, R518 and R519 form a 3dB attenuator to provide good VCO/drive amplifier isolation as well as the correct exciter drive level

Note:

The exciter provides a DC control signal to the PA via the RF coax. This is injected via L314.

gate

Page 32

C2.14

T856/857 Circuit Operation

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Page 33

M850-00

T856/857 Initial Tuning & Adjustment

3 T856/857 Initial Tuning & Adjustment

C3.1

Caution:

The following section describes both short and full tuning and adjustment procedures and provides information on:

• channel programming

• selecting required audio links

• synthesiser alignment

• PA alignment (T856 only)

• modulator adjustment

• limiter adjustment

• setting line level

• compressor adjustment

• timer adjustment.

Note:

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.

Refer to Figure 4.4 and Figure 4.5 which show the location of the main tuning and adjustment controls. Refer also 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.

Section Title Page

3.1 Introduction 3.3

3.2 Channel Programming 3.3

3.3 Test Equipment Required 3.4

3.4

3.4.1

3.4.2

3.4.3

3.4.4

3.4.5

Short Tuning Procedure

Introduction Synthesiser Alignment Output Power Adjustment (T856 Only) Two Point Modulation Adjustment CTCSS Encoder (If Used)

3.5

3.6

3.7

3.4.6

3.4.7

FM Deviation (Limiter) Adjustment Line-in Level Adjustment

3.7

Page 34

C3.2

T856/857 Initial Tuning & Adjustment

Section Title Page

M850-00

3.5

3.5.1

3.5.2

3.6 Synthesiser Alignment 3.9

3.7 PA Alignment (T856 Only) 3.10

3.8 Thermal Shutdown (T856 Only) 3.10

3.9

3.9.1

3.9.2

3.9.3

3.9.4

3.9.5

3.9.6

3.9.6.1

3.9.6.2

3.9.6.3

Audio Processor Links

Link Details Typical Options

Audio Processor & CTCSS

Two Point Modulation Modulator Adjustment CTCSS Encoder (If Used) Limiter Adjustment Line Level Without Compressor Compressor

Compressor On Line Input Only Compressor On Microphone Input Only Compressor On Both Line & Microphone Inputs

3.8

3.11

3.12

3.13

3.14

Figure Title Page

3.1

3.2

T856/857 Test Equipment Set-up With T800-01-0010 T856/857 Test Equipment Set-up Without T800-01-0010

3.4

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Page 35

M850-00

3.1 Introduction

T856/857 Initial Tuning & Adjustment

C3.3

When you receive your T856 transmitter or T857 exciter it will be run up and working on a particular frequency (the "default channel") that is within the 8MHz switching range (i.e. ±4MHz from the factory programmed frequency), you should only need to reprogram the transmitter/exciter with the PGM800Win software (refer to the PGM800Win programming kit and Section 3.2 below).

However, if you want to switch to a frequency outside the 8MHz switching range, you will have to reprogram and re-tune the transmitter/exciter to ensure correct operation. In this case you should carry out the short tuning procedure described in Section 3.4.

If you have carried out repairs or other major adjustments, you must carry out the full tuning and adjustment procedure described in this section (except for Section 3.4).

. If you want to switch to a frequency

3.2 Channel Programming

You can program up to 128 channel frequencies into the transmitter/exciter’s EEPROM memory (IC820) by using the PGM800Win software package and an IBM also use PGM800Win to select the transmitter/exciter’s current operating frequency (or "default channel").

 PC. You can

If the transmitter/exciter is installed in a rack frame, you can program it via the programming port in the speaker panel. However, you can also program the transmitter/ exciter before it is installed in a rack frame as follows:

• by using a T800-01-0010 calibration test unit;

• via D-range 1;

• via D-range 2 (standard T800-03-0000 auxiliary D-range only);

• via SK805 (internal Micromatch connector).

If you do not use the T800-01-0010, you will have to connect the PC to the transmitter/ exciter via a module programming interface (such as the T800-01-0004).

For a full description of the channel programming procedure, refer to the PGM800Win programming software user’s manual.

Note:

When an auxiliary D-range kit (D-range 2 - T800-03-0000) is fitted, you can also select a channel with an external switch, such as the DIP switch on the rack frame backplane PCB. Refer to Part C in the T800 Series Ancillary Equipment Service Manual (M800-00-101 or later issue) or consult your nearest Tait Dealer or Customer Service Organisation for further details.

1. Use the "Read Module" function in PGM800Win to find out what the default channel is.

Page 36

C3.4

T856/857 Initial Tuning & Adjustment

3.3 Test Equipment Required

You will need the following test equipment:

• computer with PGM800Win installed

• T800 programming kit

• module programming interface (e.g. T800-01-0004 - optional)

• 13.8V power supply

• digital multimeter

• audio signal generator

• RF power meter

M850-00

• audio voltmeter x 2 or RF test set (optional)

• modulation meter

• oscilloscope (digital preferred)

• 20dB or 40dB pad

• T800-01-0010 calibration test unit (optional)

Figure 3.1 and Figure 3.2 show typical test equipment set-ups.

PSU

Audio

Generator

PGM800Win

+13.8V

-Ve

Ω600

Audio

Voltmeter

Line I/P

CTCSS I/P

T800

Calibration

Test Unit

Exciter/

Transmitter

Figure 3.1 T856/857 Test Equipment Set-up With T800-01-0010

20dB pad: exciter 40dB pad: transmitter

RF O/P

RF Power

Meter

Audio

Voltmeter

Frequency

Counter

AF O/P

Modulation

Meter

Oscilloscope

PSU

Audio

Generator

PGM800Win

+13.8V

-Ve

Ω600

Audio

Voltmeter

Line I/P

CTCSS I/P

Exciter/

Transmitter

Serial

via module programming interface (e.g. T800-01-0004)

Com

40dB pad: transmitter

RF O/P

Key

20dB pad: exciter

RF Power

Meter

Audio

Voltmeter

Frequency

Counter

AF O/P

Modulation

Meter

Oscilloscope

Figure 3.2 T856/857 Test Equipment Set-up Without T800-01-0010

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Page 37

M850-00

T856/857 Initial Tuning & Adjustment

C3.5

3.4 Short Tuning Procedure

Use this procedure only if you want to reprogram the T856/857 to a frequency outside the 8MHz switching range and do not intend to carry out any other major adjustments or repairs.

3.4.1 Introduction

Reprogram the operating frequency as described in the PGM800Win programming kit (refer to Section 3.2).

Remove the top cover (nearest the handle).

Set up the test equipment as described in Section 3.3.

Set the links in the audio processor section as required (refer to Section 3.5).

3.4.2 Synthesiser Alignm ent

• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-

ures the synthesiser loop voltage).

• Key the transmitter by earthing the Tx-Key line.

• Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V.

Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V on the middle channel. If there is no middle channel, tune C6 so that the channels

are symmetrically placed around a loop voltage of 10V. All channels should lie within the upper and lower limits

of 16V and 3V respectively. Do not attempt to program channels with a greater fre-

quency separation than the specified switching range of 8MHz.

3.4.3 Outpu t Power Adjustment (T856 Only)

Connect an RF power meter with suitable attenuation to the output socket and key the transmitter.

Turn RV310 (power control) fully clockwise.

Tune #CV475 (output power trim) for maximum output power and check that this is >30W.

Adjust RV310 for the required output power (between 5 and 25W).

Readjust #CV475 to reduce the supply current by up to 0.5A.

Page 38

C3.6

T856/857 Initial Tuning & Adjustment

3.4.4 Two Point Modulation Adjustment

M850-00

Note 1:

Note 2:

Note 3:

Note 4:

1. Inject an audio signal of 300Hz 1.5V rms (+5dBm) into the CTCSS input (D-range

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

The reference modulation and limiter adjustments are controlled by 256step electronic potentiometers (EPOTs), which are adjusted via the “Reference Modulation” and “Deviation” settings in PGM800Win. This allows the two point modulation and deviation settings to be adjusted for each channel.

To optimise the modulation response across the switching range, repeat steps 1-4 below for each channel that will be used (usually needed only for data applications). In applications where the modulation response is less critical (e.g. voice use only), carry out steps 1-4 below on the middle channel and use the “EPOT Fill” option other channels.

If you are using an RF test set, turn the low pass filter off and set the high pass filter to 15kHz

1 (PL100) pin 8).

before beginning this procedure.

in PGM800Win to copy the value to the

Key the transmitter by earthing the Tx-Key line.

2. Adjust the output from the audio generator to obtain ±3kHz (±2.4kHz) [±1.5kHz] deviation at 300Hz.

3. Change the input frequency to 100Hz and, using PGM800Win, adjust the value of the “Reference Modulation” EPOT setting for the current channel to obtain ±3kHz (±2.4kHz) [±1.5kHz] deviation (you can use either the mouse or up and down arrow keys).

4. Change the input frequency back to 300Hz. Repeat steps 2 and 3 above until the deviations achieved at the two input frequen-

cies are within 0.2dB of each other. You will need to do this at least four times.

5. Sweep the audio between 50 and 300Hz for peaks.

Note:

A peak between 50 and 300Hz will indicate a fault condition, i.e:

- incorrect set-up

or - modulation circuitry fault.

The specification window is ±1dB relative to 150Hz from 67 to 260Hz.

1. Use the “EDIT FILL” button on the tool bar or go to “Edit”, “Fill”, “Epot Settings” on the menu bar.

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Page 39

M850-00

T856/857 Initial Tuning & Adjustment

3.4.5 CTCSS Encoder (If Used)

Program a CTCSS tone on the default channel using PGM800Win.

If you are using an RF test set, turn off the 300Hz high pass filter.

Key the T856/857 with the front panel "Carrier" switch.

Adjust RV805 (CTCSS level adjust) to give ±500Hz (±350Hz) [±250Hz] deviation.

Set the maximum deviation as per Section 3.4.6.

3.4.6 FM Deviation (Limiter) Adjustment

C3.7

Note:

If the T856/857 will be used over the whole 8MHz switching range, you must set the deviation for each channel. However, if the module will be used on frequencies that cover only a 1MHz (or less) switching range, you can set the deviation on the middle channel and use this value for all other channels with the “EPOT Fill” option in PGM800Win.

Inject 1kHz at -10dBm into the line input (D-range 1 (PL100) pins 1 & 4; pins 2 & 3 shorted; refer to Section 2.2 of Part F).

Adjust RV210 (line sensitivity) fully clockwise and key the transmitter by earthing the Tx-Key line. Using PGM800Win, adjust the value of the “Deviation” EPOT setting for the current channel to obtain a deviation limit of ±4.7kHz (±3.8kHz) [±2.3kHz] (you can use either the mouse or up and down arrow keys).

Sweep the audio frequency from 100Hz to 4kHz and ensure that the maximum deviation does not exceed ±4.7kHz (±3.8kHz) [±2.3kHz]. Readjust “Deviation” if necessary via PGM800Win.

3.4.7 Line-in Level Adjustment

Remove the CTCSS signal (if used).

Set the injected signal at the line input to the required line level (typically -10 to

-20dBm).

Adjust RV210 (line sensitivity) to provide ±3kHz (±2.4kHz) [±1.5kHz] deviation.

Reapply the CTCSS signal (if required).

Page 40

C3.8

T856/857 Initial Tuning & Adjustment

M850-00

3.5 Audio Processor Links

3.5.1 Link Details

Use the following table to set up the audio processor to the configuration you require. You should set the audio processor links before carrying out any of the tuning and adjustment procedures. The factory settings are shown in brackets [ ].

Plug Link

1-2

PL205

PL210

PL215

PL220

a. The letters in this column and in the table in Section 3.5.2 below refer to the identification

letters screen printed onto the PCB beside each pair of pins.

[3-4]

5-6

[1-2]

3-4 5-6

1-2

[3-4]

5-6 7-8

9-10

1-2

[3-4]

5-6

G H

E F

not connected microphone pre-amp. output to compressor input microphone pre-amp. output to multiplexer input

multiplexer output to pre-emphasis input multiplexer output to limiter input multiplexer output to compressor input

not connected compressor output to multiplexer input compressor output to limiter input

compressor output to pre-emphasis input

not connected

pre-emphasis output to multiplexer input pre-emphasis output to limiter input not connected

Function

3.5.2 Typical Options

PL205 PL210 PL215 PL220

microphone pre-amp. compressed and pre-emphasised;

line input pre-emphasised (standard set-up)

microphone pre-amp. compressed and pre-emphasised;

line input unprocessed

line and microphone compressed and pre-emphasised

microphone pre-amp. compressed; line and microphone flat response

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[3-4]

3-4

5-6

3-4

[1-2]

3-4

5-6

3-4

[3-4]

7-8

3-4

[3-4]

1-2

3-4

5-6

Page 41

M850-00

T856/857 Initial Tuning & Adjustment

C3.9

3.6 Synthesiser Alignment

• Ensure that the T856/857 has been programmed with the required frequencies

using PGM800Win software.

• Single Channel Select a channel using PGM800Win.

Multichannel Select the middle channel via PGM800Win.

• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-

ures the synthesiser loop voltage).

• Key the transmitter by earthing the Tx-Key line.

Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V.

Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V on the middle channel. If there is no middle channel, tune C6 so that the channels

are symmetrically placed around a loop voltage of 10V. All channels should lie within the upper and lower limits

of 16V and 3V respectively. Do not attempt to program channels with a greater fre-

quency separation than the specified switching range (8MHz).

• Check that the exciter output power is 1W ±300mW (T857 only).

• Measure the exciter output frequency and adjust the TCXO (=IC700) trimmer if

required.

Caution:

This trimmer is susceptible to physical damage. Do not exert a downward force of more than 500g (1lb) when adjusting.

Page 42

C3.10

T856/857 Initial Tuning & Adjustment

3.7 PA Alignment (T856 Only)

Check that the exciter is connected to the PA with the coaxial link.

Connect an RF power meter to the PA output (use an appropriate attenuator as necessary).

Turn RV310 (power control) fully clockwise.

M850-00

Note:

Before the following measurement is taken, ensure the heatsink is at ambient temperature (20-25°C).

Measure and record the voltage (VL) at L481; perform this measurement at room temperature so that the NTC (R481) is close to 25°C.

Key the transmitter by earthing the Tx-Key line.

Tune #CV475 until maximum power is obtained. Check that the power exceeds 30W.

Adjust RV310 (power control) to 25W.

Readjust #CV475 to reduce the supply current by up to 0.5A.

3.8 Thermal Shutdown (T856 Only)

Key the transmitter by earthing the Tx-Key line and set the output power to 25W as described in Section 3.7.

Short L481 to ground.

Set RV330 (shutdown power level) for an output power of 5W.

Set RV320 (shutdown temperature) to 0.16VL volts (measured at IC350 pin 3), where VL is the voltage measured at L481 in Section 3.7. This sets the thermal shutdown at 85°C at NTC R481.

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T856/857 Initial Tuning & Adjustment

C3.11

3.9 Audio Processor & CTCSS

3.9.1 Two Point Modulation

The T856 and T857 utilise two point modulation to obtain a wide audio bandwidth independent of the synthesiser loop filter response. This is achieved by simultaneously frequency modulating the VCO and phase modulating the synthesiser reference frequency. The relative signal levels fed to the two modulators are quite critical and cause interaction when setting up.

Both modulating signals require readjustment when the exciter is shifted in frequency greater than the switching range (i.e.

∆F>±4MHz).

Note 1:

Note 2:

Note 3:

Note 4:

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

If you are using an RF test set, turn the low pass filter off and set the high pass filter to 15kHz

before beginning this procedure.

3.9.2 Modu lator Adjustmen t

in PGM800Win to copy the value to the

1. Inject an audio signal of 300Hz 1.5V rms (+5dBm) into the CTCSS input (D-range

1 (PL100) pin 8). Key the transmitter by earthing the Tx-Key line.

2. Adjust the output from the audio generator to obtain ±3kHz (±2.4kHz) [±1.5kHz]

deviation at 300Hz.

3. Change the input frequency to 100Hz and, using PGM800Win, adjust the value of

the “Reference Modulation” EPOT setting for the current channel to obtain ±3kHz (±2.4kHz) [±1.5kHz] deviation (you can use either the mouse or up and down arrow keys).

1. Use the “EDIT FILL” button on the tool bar or go to “Edit”, “Fill”, “Epot Settings” on the menu bar.

Page 44

C3.12

4. Change the input frequency back to 300Hz.

5. Sweep the audio between 50 and 300Hz for peaks.

T856/857 Initial Tuning & Adjustment

Repeat steps 2 and 3 above until the deviations achieved at the two input frequencies are within 0.2dB of each other. You will need to do this at least four times.

M850-00

Note:

A peak between 50 and 300Hz will indicate a fault condition, i.e:

- incorrect set-up

or - modulation circuitry fault.

The specification window is ±1dB relative to 150Hz from 67 to 260Hz.

3.9.3 CTCSS Encoder (If Used)

Program a CTCSS tone on the default channel using PGM800Win.

If you are using an RF test set, turn off the 300Hz high pass filter.

Key the T856/857 with the front panel "Carrier" switch.

Adjust RV805 (CTCSS level adjust) to give ±500Hz (±350Hz) [±250Hz] deviation.

Set the maximum deviation as per Section 3.9.4.

3.9.4 Limiter Adjustment

Note:

Set the links in the audio processor section as required (refer to Section 3.5).

Inject 1kHz at -10dBm into the line input (D-range 1 (PL100) pins 1 & 4; and pins 2 & 3 shorted; refer to Section 2.2 of Part F).

Sweep the audio frequency from 100Hz to 4kHz and ensure that the maximum deviation does not exceed ±4.7kHz (±3.8kHz) [±2.3kHz]. Readjust “Deviation” if necessary via PGM800Win.

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T856/857 Initial Tuning & Adjustment

C3.13

3.9.5 Line Level Without Compressor

This section assumes that the compressor is not used. If the compressor is required, refer to Section 3.9.6.

Remove the CTCSS signal (if used).

Adjust the line sensitivity as follows:

• set the injected signal at the line input to the required line level (typically -10 to

-20dBm);

• adjust RV210 (line sensitivity) to provide ±3kHz (±2.4kHz) [±1.5kHz] devia-

tion.

Reapply the CTCSS signal (if required).

3.9.6 Compressor

The compressor may be used on the line input only, the microphone input only, or on both the line and microphone inputs. If the compressor is used, refer to one of the following sections as appropriate.

3.9.6.1 Compressor On Line Input Only

Set RV210 (line sensitivity) fully clockwise and key the transmitter by earthing the Tx-Key line.

Reduce the line level to -50dBm at 1kHz and set RV220 (compression level) fully clockwise.

Check that ±3kHz deviation (±2.4kHz) [±1.5kHz] is still available.

Slowly increase the audio input level until the demodulated waveform shows significant signs of clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation).

Adjust RV220 anticlockwise until the demodulated waveform is just clipping (approximately ±4kHz (±3.2kHz) [±2kHz] deviation).

Increase the input level to -10dBm and check that the test tone is still held just into clipping. The input line level should be typically -10 to -20dBm.

3.9.6.2 Compressor On Microphone Input Only

Key the transmitter by earthing the Tx-Key line and plug a microphone jack into the front panel socket.

Adjust RV220 (compression level) fully clockwise.

Acoustically couple the microphone to a tone box (1kHz) and close the PTT switch.

Page 46

C3.14

T856/857 Initial Tuning & Adjustment

Increase the audio level until the demodulated waveform shows significant signs of clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation).

Adjust RV220 anticlockwise until the demodulated waveform is just clipping (approximately ±4kHz (±3.2khz) [±2kHz] deviation).

Increase the audio level by 10dB and verify that the test tone is held just into clipping.

Whistle steadily into the microphone, checking that approximately ±4kHz (±3.2khz) [±2kHz] deviation is produced. The modulated waveform should be basically sinusoidal.

Speak into the microphone, checking that the modulation peaks reach about ±5kHz (±4kHz) [±2.5kHz] deviation.

As the line is to be used without compression, set RV210 (line sensitivity) as described in Section 3.9.5.

M850-00

3.9.6.3 Compressor On Both Line & Microphone Inputs

Set up as described in Section 3.9.6.1.

29/02/00 Copyright TEL

Page 47

M850-00

T856/857 Functional Testing

4 T856/857 Functional Testing

C4.1

Caution:

The following test procedures will confirm that the T856/857 has been tuned and adjusted correctly and is fully operational.

Note 1:

Note 2:

Refer to Figure 4.4 and Figure 4.5 for the location of the main tuning and adjustment controls, and to Section 3.3 for the test equipment set-up. Refer also 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.

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

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

4.1 Current Consumption 4.3

4.2 Output Power 4.3

4.3 Output Frequency 4.3

4.4 Timers 4.3

4.5 Frequency Response 4.4

4.6 Audio Level Input Sensitivity 4.7

Figure Title Page

4.1

4.2

4.3

4.4

4.5

T856/857 Transmit Timers T856/857 Pre-emphasis Response T856/857 Limiting Response T856 Main Tuning & Adjustment Controls T857 Main Tuning & Adjustment Controls

4.4

4.5

4.6

4.9

4.11

Page 48

C4.2

T856/857 Functional Testing

M850-00

31/09/98 Copyright TEL

Page 49

M850-00

T856/857 Functional Testing

4.1 Current Consumption

Connect the T856/857 to a 13.8V power supply.

Connect an RF power meter to the T856/857 output socket.

Check that the current in the 13.8V power cable is less than 150mA.

Key the T856/857 by earthing the Tx-Key line (the carrier "On" LED should light).

T856 Only: Adjust RV310 (power control) to obtain 25W output power.

Check that the current is as follows:

T856 <5.5A T857 <750mA.

C4.3

4.2 Output Power

Connect an RF power meter with suitable attenuation to the T856/857 output socket.

Key the T856/857 by earthing the Tx-Key line.

Check that:

T856 the output power adjusts to ≥25W with RV310 (power control)

turned fully clockwise

T857 the output power is 1W ±300mW.

4.3 Output Frequency

Connect the T856/857 output to a frequency counter via an attenuator pad:

T856 40dB pad T857 20dB pad.

Measure the output frequency and, if necessary, adjust the TCXO (=IC700) to trim to the nominal frequency (±100Hz).

4.4 Timers

Page 50

C4.4

T856/857 Functional Testing

Timer Function Adjustment

M850-00

Transmit Tail Sets the tail time during which the

transmitter stays keyed after the external key source has been removed.

Transmit Timeout Sets the maximum continuous trans-

mission time. Once the timer has timed out, the transmitter must be keyed again, unless prevented by the transmit lockout timer.

Transmit Lockout Sets the period of time that must

elapse after a timeout before the transmitter can re-transmit. Once the timer has timed out, the transmitter can be keyed again.

a. Adjustable in 20ms steps in PGM800Win version 2.12 and later. b. Adjustable in 20ms steps in PGM800Win version 2.12 and later.

Tx-Enable

Tx-Reg.

0-5 seconds in 100ms

steps

0-300 seconds

in 10

second steps

0-60 seconds in 10 second steps

Tail Time

Tx-Reg.

Lockout Time

Timeout

Time

Figure 4.1 T856/857 Transmit Timers

4.5 Frequency Response

If the T856/857 has been correctly adjusted, the pre-emphasis and limiting responses should closely match those shown in Figure 4.2 and Figure 4.3 respectively.

Note:

• If you are using an RF test set, turn off all filters.

• Measure the pre-emphasis response as follows:

The limits shown on these graphs should not be exceeded.

Reduce the line level to give ±1kHz (±0.8kHz) [±0.5kHz] deviation at 1kHz. Sweep the modulation frequency. The response should closely match that shown in Figure 4.2.

• Measure the limiting response as follows: Set the line level to give ±3kHz (±2.4kHz) [±1.5kHz] deviation at 1kHz.

29/02/00 Copyright TEL

Page 51

M850-00

Increase the line level 20dB and sweep the modulation frequency. The response should closely match that shown in Figure 4.3.

Wide Bandwidth

+10

+8 +6

+4 +2 +0

-2

-4

-6

-8

-10

-12

-14

-16

Modulation Level (dB ref. to dev. @ 1kHz)

-18

-20

-22

Peak + max. dev. = +1.0kHz @ 1000Hz Peak - max. dev. = -1.0kHz @ 1000Hz

T856/857 Functional Testing

C4.5

100 200 300 500 1k 2k 3k 5k 10k

Frequency (Hz)

Mid Bandwidth

The mid bandwidth graph is the same shape as the wide bandwidth graph. The deviation figures are as follows:

peak + max. deviation = +0.8kHz peak - max. deviation = -0.8kHz.

Narrow Bandwidth

Peak + max. dev. = +0.5kHz @ 1000Hz

+10

+8 +6

+4 +2 +0

-2

-4

-6

-8

-10

-12

-14

-16

Modulation Level (dB ref. to dev. @ 1kHz)

-18

-20

-22

Peak - max. dev. = -0.5kHz @ 1000Hz

100 200 300 500 1k 2k 3k 5k 10k

Frequency (Hz)

Figure 4.2 T856/857 Pre-emphasis Response

Page 52

C4.6

T856/857 Functional Testing

Wide Bandwidth

Modulation Level (dB ref. to max. dev.)

+10

-10

-12

-14

-16

-18

-20

-22

M850-00

Peak + max. dev. = +4.9kHz @ 1500Hz

Peak - max. dev. = -4.4kHz @ 2500Hz +8 +6 +4 +2 +0

-2

-4

-6

-8

Above limiting (steady-state)

10 20 30 200 1k 2k 3k 10k

100 500300 5k50

Frequency (Hz)

Mid Bandwidth

The mid bandwidth graph is the same shape as the wide bandwidth graph. The deviation figures are as follows:

peak + max. deviation = +4kHz peak - max. deviation = -4kHz.

Narrow Bandwidth

Peak + max. dev. = +2.4kHz @ 2000Hz

+10

+8 +6

+4 +2 +0

-2

-4

-6

-8

-10

-12

-14

Modulation Level (dB ref. to max. dev.)

-16

-18

-20

-22

Peak - max. dev. = -2.5kHz @ 2000Hz

Above limiting (steady-state)

10 20 30 200 1k 2k 3k 10k

100 500300 5k50

Frequency (Hz)

Figure 4.3 T856/857 Limiting Response

31/09/98 Copyright TEL

Page 53

M850-00

T856/857 Functional Testing

4.6 Audio Level Input Sensitivity

• Adjust RV210 (line sensitivity) fully clockwise.

• Check that the input sensitivities are better than those specified below:

Line Input 600 ohms, ±3kHz (±2.4kHz) [±1.5kHz] deviation at

1kHz:

with compressor -50dBm without compressor -30dBm

Microphone Input 600 ohms, ±3kHz (±2.4kHz) [±1.5kHz] deviation at

1kHz:

with compressor -75dBm without compressor -55dBm

CTCSS Input 1kHz deviation at 150Hz 500mV rms

C4.7

Note:

A degraded signal to noise ratio can be expected with the compressor selected. The extent of the degradation is dependent on the audio input level.

Page 54

C4.8

T856/857 Functional Testing

M850-00

31/09/98 Copyright TEL

Page 55

M850-00

T856/857 Fault Finding

5 T856/857 Fault Finding

C5.1

Caution:

The following test procedures and fault finding flow charts may be used to help locate a hardware problem, however they are by no means a complete fault finding procedure. If you still cannot trace the fault after progressing through them in a logical manner, contact your nearest Tait Dealer or Customer Service Organisation. If necessary, you can get additional technical help from Customer Support, Radio Systems Division, Tait Electronics Ltd, Christchurch, New Zealand (full contact details are on page 2).

Note 1:

Note 2:

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.

The following topics are covered in this section

Section Title Page

5.1 Visual Checks 5.3

5.2 Component Checks 5.3

5.3 Front Panel LED Indicator 5.3

5.4

5.4.1

5.4.2

5.5

5.5.1

5.5.2

5.5.3

5.5.4

5.6 PGM800Win Generated Errors 5.7

DC Checks

Power Rails VCO Locking

RF Checks

T856 Drive Power T856 PA Output Power T857 Output Power Audio And Modulation

5.4

5.5

5.6

Page 56

C5.2

T856/857 Fault Finding

Section Title Page

M850-00

5.7

5.7.1

5.7.1.1

5.7.1.2

5.7.1.3

5.7.2

5.7.3

5.7.4

5.7.5

5.7.6

5.7.7

5.8 To Replace The T856 PA Transistors (Q410 & Q420) 5.19

Fault Finding Charts

Microcontroller

Basic Checks Serial Communications

CTCSS Encode Regulator Synthesiser T856 Drive Amplifier T856 PA & Power Control T857 Exciter Drive Amplifier Audio Processor

5.8

5.9

5.10

5.11

5.12

5.15

5.16

5.17

5.18

Figure Title Page

5.1

5.2

RF Diode Probe Circuit Typical Transistor/Capacitor Spacing (Not To Scale)

5.5

5.19

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Page 57

M850-00

T856/857 Fault Finding

C5.3

5.1 Visual Checks

Remove the covers from the T856/857 and inspect the PCB for damaged or broken components, paying particular attention to the surface mounted devices (SMD's).

Check for defective solder joints. If repair or replacement is considered necessary, refer to Section 3 of Part A.

5.2 Component Checks

If you suspect a transistor is faulty, you can assess its performance by measuring the forward and reverse resistance of the junctions. Unless the device is completely desoldered, first make sure that the transistor is not shunted by some circuit resistance. Use a good quality EVM (e.g. Fluke 75) for taking the measurements (or a 20k ohm/V or better multimeter, using only the medium or low resistance ranges).

The collector current drawn by multi-junction transistors is a further guide to their performance.

If an IC is suspect, the most reliable check is to measure the DC operating voltages. Due to the catastrophic nature of most IC failures, the pin voltages will usually be markedly different from the recommended values in the presence of a fault. The recommended values can be obtained from either the circuit diagram or the component data catalogue.

5.3 Front Panel LED Indicator

The green "Supply" LED on the T856/857 front panel will flash according to the conditions described in the following table:

Flash Rate Condition

fast ( sec. on/ sec. off

approx.)

unequal ( sec. on/1 sec. off

approx.)

T856/857 is linked with

PGM800Win

microcontroller has detected an

internal communications error -

refer to Section 5.7.1

Where two or more conditions occur at the same time, the precedence is in the order shown above (i.e. T856/857 linked has the highest priority, followed by internal error).

Page 58

C5.4

T856/857 Fault Finding

M850-00

5.4 DC Checks

5.4.1 Power Rails

Refer to the test points and options diagrams in Section 6 for test point locations, and to the regulator fault finding chart (Section 5.7.2) for fault diagnosis.

Check the 13.8V (TP601) and 9V (TP602) supplies at their test points in the regulator compartment with a DMM.

Check the 5V (TP604) and 20V (TP603) rails at their respective test points in the regulator compartment.

Check that Tx-Reg. (TP305 in the exciter compartment) comes up to 8.8V when the exciter is keyed.

Check the +5V digital regulator output (TP607 in the regulator compartment).

T856 Only: Check the 9V supply (IC370 pin 1) with a DMM.

Check for short circuits.

5.4.2 VCO Locking

Key the exciter.

Using a DMM, monitor the VCO control voltage on the long lead of L1 on the VCO PCB.

If the synthesiser is locked and the VCO aligned, the voltage at this point should be between 3 and 16V.

If the VCO is not locked, refer to the synthesiser fault finding chart (Section 5.7.3).

31/09/98 Copyright TEL

Page 59

M850-00

T856/857 Fault Finding

C5.5

5.5 RF Checks

In-circuit RF levels may be measured with an RF probe on which the earth lead has been shortened to a minimum (i.e. 13mm). Refer to the circuit diagrams for typical levels.

Figure 5.1 shows a suitable RF probe circuit..

Probe

Earthing Clip

This unit is not suitable for use on high power RF circuits.

10k

1N6263

Figure 5.1 RF Diode Probe Circuit

100k

5.5.1 T856 Drive Po wer

Refer to the drive amplifier fault finding chart (Section 5.7.4).

Ensure that the VCO locks (refer to Section 5.4.2).

Connect the drive output to a power meter and key the transmitter.

Check that the exciter output power (SK310) is >1.5W.

Coax

DC to DVM or Oscilloscope

Note:

If the synthesiser is out of lock, the lock detector (synthesiser IC740 and comparator IC750) will prevent the RF signal from reaching the PA by switching the supply to the exciter amplifier (Q350, Q355).

5.5.2 T856 PA Output Power

Reconnect the drive output to the PA input.

Connect the PA to a power meter and key the transmitter.

Check that the output power is >30W with RV310 (power control) adjusted fully clockwise.

5.5.3 T857 Output Power

Refer to the exciter drive amplifier fault finding chart (Section 5.7.6).

Ensure that the VCO locks (refer to Section 5.4.2).

Page 60

C5.6

T856/857 Fault Finding

Connect the exciter output to a power meter and key the exciter.

Check that the output power is 1W ±300mW.

M850-00

Note:

5.5.4 A udio And Modulation

Refer to the audio processor fault finding chart (Section 5.7.7).

Set up the audio processor as described in Section 3.9.

Check that the demodulated RF output has the frequency response referred to in

Section 4.5 with at least ±5kHz (±4kHz) [±2.5kHz] deviation available at 1kHz

modulating frequency.

If the above result is not achieved, either the two modulators are incorrectly adjusted or a fault condition exists.

31/09/98 Copyright TEL

Page 61

M850-00

T856/857 Fault Finding

C5.7

5.6 PGM800Win Generated Errors

The following errors are those most likely to occur using PGM800Win. Refer to the PGM800Win software user’s manual for a complete list of error messages.

Channel Switch Set

The programmed default channel change was not accepted by the base station because a channel is selected externally. Try turning the external channel switch off to change the default channel in PGM800Win.

Synth Out Of Lock

The synthesiser received incorrect data, or the data was corrupted. Enter a frequency within the VCO switching range, or tune the VCO.

Internal Error

Data could not be read from the base station due to an internal error. Check for shorts or open circuits on the SDA, SCK, SYNTH and EPOT lines. The SDA, SCK and SYNTH are normally high, and the EPOT is normally low.

Write/Read To An Unlinked Module

The link to the module does not exist. Undefined error.

Page 62

C5.8

T856/857 Fault Finding

5.7 Fault Finding Charts

M850-00

Note:

The standard test point designations used in this section are as follows:

TP601 13.8V TP602 9V TP603 20V TP604 5V

5.7.1 Microcontroller (IC810)

5.7.1.1 Basic Checks

Is the 12.8MHz clock

present on IC810 pin 21

(microcontroller)?

Replace

IC810.

N Pulsing

Is pin 30

pulsing?

Check the

state of

pin 10.

High or open circuit

Low

Check IC740

(synthesiser).

Use a DSO* to check

operation of IC650

(i.e. active high

pulse at power up).

*digital storage oscilloscope

Replace

IC650.

Check state of

pins 36 to 43.

Static high/low

Replace IC810.

Pulsing

Check state

of pin 35.

Correct the fault causing pin 35 to be low/floating.

High

Low/floating

Replace

IC810.

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Page 63

M850-00

5.7.1.2 Serial Communication

T856/857 Fault Finding

C5.9

Disconnect the

pro

ramming lead.

Is IC810 pin 11 hi

(microcontroller)

Connect the programmin

lead and use PGM800Win

to read the rack/radio.

Check I/O pad P810

with a DSO*.

Does it swin

oscilloscope

Use PGM800Win

to send a POLL command to the

from

0 to 5V?

Y*digital storage

radio.

Check pin state.

Noise on pin

Check the SERIAL-COM

and AUDIO-1/2 links.

Check the transistor

interface circuitry

and/or replace the

ramming lead.

pro

Low/floatin

Check the transistor

interface circuitry.

Check IC810 pin 13

with a DSO. Is there

a response from IC810 after

a poll command is sent?

Check the transistor

interface circuitry

and/or replace the

ramming lead.

pro

Replace

IC810.

Page 64

C5.10

T856/857 Fault Finding

5.7.1.3 CTCSS Encode

M850-00

Use PGM800Win to

select a channel

with a CTCSS tone

rammed.

pro

Check IC810 pins 24, 25

& 26 (microcontroller).

Are there 5V square waves at

the CTCSS frequency?

Check IC830 pins 1, 7 & 14.

Are there 9V square waves at

the CTCSS frequency?

Check IC830 pin 8.

Is there a sine wave

at the CTCSS frequency?

Cannot select a channel

No square waves or

uneven mark/space ratio

No square waves or

uneven mark/space ratio

No tone

Check serial communications.

(See separate flow chart).

Replace IC810.

Check IC830 circuitry

and repair/replace.

Check RV805.

Distorted tone

Check the filter circuit for bias

problems and/or short circuits.

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Page 65

M850-00

5.7.2 Regulator

Check for

overheatin

components &

short circuits.

T856/857 Fault Finding

C5.11

13.8V present on IC630 pin 3?

5.3V present on IC630 pin 1?

9.0V present

on TP602?

20V present

on TP603?

+5V present on

IC610 pin 2?

Key Tx.

Check continuity

from pin 9 of

e 1.

D-ran

Replace IC630.

Check Q630,

Q620 & IC640.

Check Q660 is

switchin

approx. 150kHz.

Check R615.

Replace IC610.

8.8V present

on Tx re

on Q860 collector?

Check microcontroller

. TP305?

0V present

0.6V present on

Q860 base?

Regulators OK.

section.

Regulators OK.

Replace Q610.

Check Q860 and

associated circuitry.

Page 66

C5.12

T856/857 Fault Finding

M850-00

5.7.3 Synthesis er

Refer to the synthesiser circuit diagram (sheet 7) in Section 6 and the VCO circuit diagram in Part E.

A B

No VCO RF output.

9V present at VCO Q4/Q5?

DC V present

at Q4 & Q5?

8.3V present at VCO?

DC V present at

VCO, Q1, Q2 & Q3?

Capacitors OK?

Check for cracks,

shorts, etc.

VCO out of lock.

Check Tx reg.,

Q610 & 9V re

Check biasin

resistors, Q4 & Q5.

Check Q5 C

multiplier

(synth).

Check biasin

resistors, Q1,

Q2 & Q3.

Replace

if faulty.

+5V present at

IC700, IC710,

IC740, IC720

& IC730?

20V present

on IC750 pin 8?

9V present on

Q795 divider buffer?

DC V present

on Q795 emitter?

Does VCO trimmer

adjust for stable

control line

between 3 & 16V?

Check 5V reg. &

supply resistor

to each IC.

20V inverter

supply faulty.

Check 9V supply.

Check biasin

resistors & Q795.

Replace VCO.

Check VCO tunin

caps & trimmer.

Check #C1, #C7, #C8,

C6 & D1-D2 in VCO.

VCO trimmer

freq. ran

Is 8MHz VCO range

achieved between

Continued on the next pa

e OK? Y

3 & 16V?

VCO OK.

VCO freq. correct?

Does VCO trimmer

adjust for required

frequency ran

between 3 & 16V?

Synthesiser OK.

Recheck

pro

rammin

via PGM800Win.

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Page 67

M850-00

Continued from previous page

T856/857 Fault Finding

Check microcontroller

section (IC810).

C5.13

Replace synthesiser

(IC740).

Check phase detector output

pins (IC740 pins 3 & 4).

Are there very narrow pulses

(~50ns) at the reference frequency?

(i.e. 5kHz : 200µs period

6.25kHz : 160µs period) *See Note below.

Is the charge pump bias

voltage at the base of

Q760 & Q780 between

3.5 and 5V? (5V when locked) Y

Is the voltage on C762,

R760, and R758 9V ±0.2V?

Is the charge pump voltage

on Q790 gate between

3 and 8.5V? (6.5V ±0.2V locked)

Is the loop filter reference

voltage at C772 (+) 6.5V ±0.2V?

Check programming.

N Y

Check serial bus

when programming

i.e. clock/data/enable

activity (IC740 pins

18, 19 & 17).

Check Q760, Q780,

R766 & C765.

Check R762 & C762.

Check charge pump components

(Q775 & Q780) and Q790.

Check C772, R774, R772,

C770, R763 & Q790.

Programming and

serial bus OK?

Check phase

modulator sections:

IC720, Q710, Q720,

D710, Q730, Q740,

D720.

Check divider

IC730.

Is reference

clock present

at IC740 pin 20

(200kHz >4.5Vpp)?

Is reference

clock present

at IC730 pin 12

(200kHz >4.5Vpp)?

Is reference

clock present

at IC730 pin 1

(12.8MHz >4.0Vpp)?

Check TCXO (IC700)

and buffers (IC710).

Check loop filter components

R775, C774, C776, R510, C505, IC750. Is the supply

to IC750 +20V +4, -2V?

Check the signal path from

the VCO to synthesiser.

Measure the frequency from

the VCO at IC740 pin 11 using

a frequency counter.

Signal

Is the level >-10dBm?

Does the frequency adjust

as the VCO trimmer is

adjusted (out of lock)?

Replace synthesiser

(IC740).

No signal

Check regulator circuitry.

Check VCO.

Check divider buffer

circuit (Q795) and bias

voltages on Q795 emitter

(1.3V ±0.2V).

*Note:

When locked, both of these are very narrow (~50ns). If unlocked, one will be very narrow (~50ns), and the other wide (>15µs).

Page 68

C5.14

T856/857 Fault Finding

Noisy synth;

poor residual FM.

M850-00

VCO phase locked?

3-16V present on

control line?

Correct DC V

present on Q1 VCO?

Loop filter &

components around

op. amp. (IC750) OK?

Isolate audio

modulation on VCO;

still noisy?

Change trimmer;

still noisy?

Change Q1;

still noisy?

Go to B.

Check inductors, biasing resistors

& Q1.

Replace if faulty.

Trace audio fault.

Change TCXO;

still noisy?

Change varactors;

still noisy?

Replace VCO

assembly.

Synthesiser OK.

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Page 69

M850-00

5.7.4 T856 Drive Amplifier

Key exciter

& lock

synthesiser.

T856/857 Fault Finding

C5.15

10.5V on Q350 collector?

10.5V on Q355 collector?

>2V RF at

VCO output?

>1V RF

at R381?

>0.5V RF at Q350 base?

N Check attenuator

10.5V on Q315 collector?

Check continuity

of power rails & DC paths to Q365 & Q370.

Check VCO.

pad #R517, #R518,

#R519.

Check C355, C358,

C360, Q350, D340,

D380, D360, L320.

11.5V on

IC350 pin 7?

13.8V on

IC350 pin 8?

regulators.

Check lock det.

path back to synth. IC740, IC750, Q325.

Check temp.

shutdown

Check

circuit.

Check 9V &

13.8V supplies. Y

Check TP305

>+8V.

Check TP320

<0.6V.

>5V RF at

C362, #R395?

>1V RF at

Q355 base?

>6V RF at

Q355 collector?

Check signal

path to output

incl. output

socket (SK310).

Check Q350.

Check signal

path between

Q350 & Q355.

Check Q355.

Check Q310,

Q315 circuitry

& IC350.

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C5.16

T856/857 Fault Finding

5.7.5 T856 P A & Power Control

M850-00

Set RV320

(power adjust)

fully clockwise;

synth. locked;

key Tx.

Tx deliverin

full power

(>30W)?

Normal operating conditions:

Forward power = 4.7V approx. Reverse power = 0.7V approx. IC350 pin 6 = 2.02V IC350 pin 5 = 2V IC350 pin 7 = 8.63V

10.8V

at L310?

<2V on

IC350 pin 6?

Check drive at

SK310 >1.5W.

Refer to Drive Amp. Fault Findin

Check IC330,

Q310, Q315

+13.8V supply.

Chart.

& circuitry,

Check Q410,

Q420 & circuitry,

LP filter.

Check +13.8V at

Q410 & Q420.

Check supply

circuitry.

Turn RV310 ccw.

Check power drops to zero

slowly in a

controlled manner.

Set RV310 so that

output power = 25W;

check L310 approx. 7.5V.

Momentarily remove

Tx load. Volta

L310 decreases to

approx. 5V?

e at

Check lock det. circuit; TP305 should be >8V.

Check temp. shutdown circuit (IC350); TP320 should be <0.6V. Check Q320, RV330.

Does variation

of RV310

cause either

full power

or no power?

Power control

circuitry OK.

Check for break

in power sense

circuitry; directional

coupler D420,

D440 & circuitry.

Note:

c/w = clockwise cc/w = counterclockwise or anticlockwise

31/09/98 Copyright TEL

Page 71

M850-00

5.7.6 T857 Exciter Drive Amplifier

Key exciter &

lock synthesiser.

T856/857 Fault Finding

C5.17

9V at Q304 collector?

0.5V at Q304 base?

9V at Q305 collector?

>2V RF at

VCO output?

>1V RF at R323?

>0.5V RF at Q304 base?

9V at Q303

collector?

>4V present on

IC300 pin 1?

Check Q302

& Q303.

Check VCO.

Check attenuator pad

R517, R518, R519.

Check C314, #C315,

#C316, Q304, L305,

D201, D202, D203.

Check

power rails.

Check IC300.

>5V RF at

#C321, #R330?

>1V RF at

Q305 base?

>5V RF at

Q305 collector?

Drive amp. OK.

Check Q304.

Check signal path

between Q304 & Q305.

Check Q305.

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C5.18

T856/857 Fault Finding

5.7.7 Audio Processor

Key exciter &

lock synthesiser.

Connect 1kHz audio

to external CTCSS input.

M850-00

Check low

pass filter

stage IC260

pins 1, 2 & 3.

Does exciter

modulate?

Check alignment

of modulators.

Demodulated audio

frequency response

flat between 50 & 300Hz?

Audio frequency

response IC260 pin 1 flat 300Hz

to 2kHz?

Audio frequency

response IC210

pin 8 6dB/octave

slope?

Audio superimposed

on 200kHz signal

IC720 pins 9 & 3 (synth)?

Audio output at

IC260 pin 8?

Audio output at

IC260 pin 1?

Audio output at

IC260 pin 7?

Check stage IC260

pins 5, 6 & 7.

Check integrator

IC210 pins 8, 9, & 10.

Check audio path

between integrator

& phase modulator.

Check audio path to

VCO control line.

Check buffer IC260

pins 8, 9 & 10.

Check low pass

filter stage IC260

pins 1, 2 & 3.

Demodulated audio frequency response as per

Section 4.5?

Check pre-emphasis

network IC230 pins 12,

13 & 14 &/or low pass

filter IC260 pins 1, 2 & 3.

Audio processor

OK.

200kHz clipped

triangle wave at

IC720 pins 8 & 4?

Check loop filter

(IC750, pins 5, 6 & 7)

& associated components.

Select standard

audio configuration.

Connect audio

to line input;

key exciter.

Does exciter

modulate?

Check IC720, Q710, Q720,

Q730, Q740, D710, D720, C727, C729, C724 & C725

Check Q260 is not faulty or

being turned on inadvertently.

Audio signal at

IC210 pin 14?

Audio signal at

IC230 pin 1?

Audio signal at

IC230 pin 14?

Audio signal at

IC240 pin 4?

IC240 pin 6

at 9V?

Check audio path between

limiter IC210 pin 14 &

summing amp. IC260 pin 7.

Check IC210

pins 12, 13 & 14.

Check IC230 pins 1, 2 & 3 or

audio path between pre-

emphasis network & limiter.

Check IC230 pins 12, 13 & 14

or audio path between multiplexer

& pre-emphasis network.

Check IC240 or audio

path between line trans-

former & multiplexer.

31/09/98 Copyright TEL

Page 73

M850-00

T856/857 Fault Finding

5.8 To Replace The T856 PA Transistors (Q410 & Q420)

C5.19

Caution:

Failure to comply with the following procedure can result in failure of the device due to poor heatsinking, or worse, can endanger the health of the assembler if the beryllium oxide die carrier is smashed during assembly.

As the location of certain components in the PA is critical to performance, it is important that any components removed or disturbed are refitted in

Before attempting to remove a transistor, measure the distance between the capacitors and transistor body to the nearest 0.5mm (measurement "A" in Figure 5.2) so that the capacitors can be replaced in

exactly

5.2 for the 6LFL package, however the same procedure applies for the

SOE (stud) package.

Do not apply too much heat or pressure to the PCB pads and tracks as you may damage them or lift them from the PCB, causing permanent damage to the transmitter.

exactly

the same position. These measurements are shown in Figure

the same position.

base collector

measurement A

Figure 5.2 Typical Transistor/Capacitor Spacing (Not To Scale)

Desolder and remove the components from around the transistor.

Q420 Only: Desolder and remove the two solder tags.

Desolder the transistor tabs by heating with a soldering iron and lifting away from the PCB with a screwdriver or thin stainless steel spike, then remove the device.

Page 74

C5.20

T856/857 Fault Finding

Q410 Only: Unscrew the transistor stud nut and remove the device.

Remove any excess solder from the PCB pads with solder wick.

Trim the tabs of the replacement transistor so that the device sits neatly on the PCB pads provided.

Lightly tin the underside of the transistor tabs. Remove any excess solder to leave a thin, even layer on the tabs.

Apply a small amount of heatsink compound (Dow-Corning 340 or equivalent) to the transistor mounting surface. Sufficient compound should be used to ensure an even film over the entire mounting surface.

Place the transistor on the PCB in the correct orientation and ensure the tabs are flush to the surface.

Q410 Only: Lightly solder one tab to the PCB, then torque down the retain-

ing nut to the correct torque (0.7Nm/6in.lbf.).

M850-00

Caution:

Q420 Only: Refit the solder tags.

Solder all transistor tabs to the PCB.

Replace each component in exactly the same position as noted previously.

Do not solder all the tabs before torquing down otherwise the device may be broken.

29/02/00 Copyright TEL

Page 75

M850-00

T856/857 PCB Information

6 T856/857 PCB Information

C6.1.1

Caution:

This section provides the following information on the T856 transmitter and T857 exciter:

•parts lists

• grid reference indexes

• mechanical assembly drawings

•PCB layouts

• test points & options connections drawings

• circuit diagrams.

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

Section Title IPN Page

6.1 Introduction 6.1.3

6.2 T856 Transmitter PCB 220-01397-01 6.2.1

6.3 T857 Exciter PCB 220-01398-02 220-01398-04

6.3.1

6.3.29

Page 76

C6.1.2

T856/857 PCB Information

M850-00

31/09/98 Copyright TEL

Page 77

M850-00

T856/857 PCB Information

C6.1.3

6.1 Introduction

Product Type Identification

You can identify the transmitter or exciter type by checking the product code printed on a label on the rear of the chassis (product codes are explained in Section 1.3 in this Part of the manual, and Fig-

ure 1.1 in Part A shows typical labels). You can further verify the product type by checking the

placement of an SMD resistor in the table that is screen printed onto the top side of the PCB, similar to the example drawn below. In this example, the resistor indicates that the product was built as a T856-10-XXXX.

856-30 PRODUCT TYPE 856-35 856-10 856-20 856- 856-13 856-23

PRODUCT TYPE 856-15 856-25

Note:

The only function of this resistor is to indicate the product type. It has no effect on the circuitry or operation of the transmitter or exciter.

PCB Identification

All PCBs are identified by a unique 10 digit “internal part number” (IPN), e.g. 220-01390-02, which is screen printed onto the PCB (usually on the top side), as shown in the example below:

The last 2 digits of this number define the issue status, which starts at 00 and increments through 01, 02, 03, etc. as the PCB is updated. Some issue PCBs never reach full production status and are therefore not included in this manual. A letter following the 10 digit IPN has no relevance in identifying the PCB for service purposes.

Note:

It is important that you identify which issue PCB you are working on so that you can refer to the appropriate set of PCB information.

Page 78

C6.1.4

T856/857 PCB Information

M850-00

Parts Lists

The 10 digit numbers (000-00000-00) in this Parts List are “internal part numbers” (IPNs). We can process your spare parts orders more efficiently and accurately if you quote the IPN and provide a brief description of the part.

The components listed in this parts list are divided into two main types: those with a circuit reference (e.g. C2, D1, R121, etc.) and those without (miscellaneous and mechanical).

Those with a circuit reference are grouped in alphabetical order and then in numerical order within each group. Each component entry comprises three or four columns, as shown below:

circuit reference lists components in alphanumeric order

variant column indicates that this is a variant component which is fitted only to the product type listed

description gives a brief description of the component

Internal Part Number order the component

this number

The miscellaneous and mechanical section lists the variant and common parts in IPN order.

Parts List Amendments

At the front of the parts list is the Parts List Amendments box (an example of which is shown below). This box contains a list of component changes which took place after the parts list and diagrams in this section were compiled. These changes (e.g. value changes, added/deleted components, etc.) are listed by circuit reference in alphanumeric order and supersede the information given in the parts list or diagrams. Components without circuit references are listed in IPN order. The number in brackets at the end of each entry refers to the Tait internal Change Order document.

IPN of new component

Parts List Amendments

R306 Changed from 180Ω to 560Ω (036-13560-00) to increase sensitivity (71003).

Change Order

number

circuit reference

or IPN

31/09/98 Copyright TEL

description

of change

Page 79

M850-00

T856/857 PCB Information

C6.1.5

Variant Components

A variant component is one that has the same circuit reference but different value or specification in different product types. Where two products share the same PCB, the term “variant” is also used to describe components unplaced in one product. Variant components have a character prefix, such as “&”, “=” or “#”, before the circuit reference (e.g. &R100).

The table below explains the variant prefixes used in T800 Series II products:

If the variant prefix is. . . the component will. . .

& change according to channel spacing

= change according to frequency stability

# change according to frequency range

% change or be placed/unplaced for special applications

be unplaced in one product (where two products share the same PCB)

Grid Reference Index

This section contains a component grid reference index to help you find components and labelled pads on the PCB layouts and circuit diagrams. This index lists the components and pads in alphanumeric order, along with the appropriate alphanumeric grid references, as shown below:

PCB layout components listed in alphanumeric order

reference

circuit diagram

reference

component location on the sheet

sheet number

component location on the layer

layer number 1 = top side layer 2 = bottom side layer

Page 80

C6.1.6

t s

T856/857 PCB Information

M850-00

Using CAD Circuit Diagrams

Reading a CAD circuit diagram is similar to reading a road map, in that both have an alphanumeric border. The circuit diagrams in this manual use letters to represent the horizontal axis, and numbers for the vertical axis. These circuit diagram “grid references” are useful in following a circuit that is spread over two or more sheets.

When a line representing part of the circuitry is discontinued, a reference will be given at the end of the line to indicate where the rest of the circuitry is located, as shown below. The first digit refers to the sheet number and the last two characters refer to the location on that sheet of the continuation of the circuit (e.g. 1R3).

hese grid references

how where the circuit

is continued

DISCRIMINATOR

1R3 2R9 2R9 8A2

IF-SIG

4R4

%R338

100

C301

4N7

C369 100P

L310 33U

C371

10U

R339 100K

R303

31/09/98 Copyright TEL

Tait TEL0049, TEL0048 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual