SmarTrunk ST-2112C Service Manual

ST-2112C (400Mhz ~ 470Mhz)

UHF FM DIGITAL TRANSCEIVER

SERVICE MANUAL

SmarTrunk Systems, INC.

ST-2112C SM R1.2

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

Table of Contents

1. Specifications: ............................................................................................................................... 5

2. ST-2112 EXPLODED VIEW .............................................................................................................. 6

3. ST-2112 SIMPLIFIED DIAGRAM ..................................................................................................... 7

4. - ST-2112 RF DESCRIPTION ................................................................................................................ 8

4.1. Circuit Configuration ................................................................................................................. 9

4.2. Receiver System ........................................................................................................................ 9

4.2.1. Front-end RF Receiver ........................................................................................................... 9

4.2.2. ANALOG Audio Processing .................................................................................................... 9

4.2.3. Virtual Squelch Circuit ........................................................................................................... 9

4.2.4. Virtual VOLUME CONTROL .................................................................................................. 10

4.2.5. Sub audio signaling ............................................................................................................. 10

4.2.6. ANALOG AUDIBLE SIGNALING ............................................................................................. 10

4.2.7. DIGITAL AUDIO PROCESSING .............................................................................................. 10

4.3. Transmitter System ................................................................................................................. 11

4.3.1. ANALOG TX SIGNAL ............................................................................................................. 11

4.3.2. DIGITAL TX AUDIO: .............................................................................................................. 11

4.3.3. Drive and Final Amplifier Stages ......................................................................................... 11

4.3.4. Automatic Transmit Power Control .................................................................................... 12

5. RC-2112 ALIGNMENT .................................................................................................................. 13

5.1. Introduction ............................................................................................................................ 13

5.2. ALIGNMENT:............................................................................................................................ 13

5.3. Alignment Procedure .............................................................................................................. 14

5.3.1. GENERAL ALIGNMENT CONSIDERATIONS: .......................................................................... 14

5.4. MAIN RADIO ALIGNMENT ....................................................................................................... 15

5.5. TRANSMITTER ALIGNMENT: ................................................................................................... 15

5.5.1. Main Clock alignment: ........................................................................................................ 16

5.5.2. Transmit Power alignment: ................................................................................................. 17

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

5.5.2.1. High POWER LEVEL ALIGNMENT ..................................................................................... 17

5.5.2.2. Mid POWER LEVEL ALIGNMENT ...................................................................................... 18

5.5.2.3. LOW POWER LEVEL ALIGNMENT .................................................................................... 18

5.5.3. ANALOG MAXIMUM DEVIATION ........................................................................................ 18

5.5.4. Modulation Gain alignment: ............................................................................................... 18

5.5.5. FDMA DATA MODULATION alignment: .............................................................................. 19

5.5.6. TDMA DATA MODULATION alignment: .............................................................................. 20

5.5.7. EIA tones Level Alignment: ................................................................................................. 20

5.5.8. DTMF signaling level alignment: ......................................................................................... 20

5.5.9. DCS signaling alignment: ..................................................................................................... 21

5.5.10. CTCSS signaling alignment .................................................................................................. 21

5.5.11. FSK signaling alignment: ..................................................................................................... 22

5.6. RECEIVER ALIGNMENT ............................................................................................................ 23

5.6.1. DISCRIMINATOR GAIN ......................................................................................................... 23

6. COMPLEMENTARY RADIO ALIGNMENT ...................................................................................... 24

6.1. BATTERY WARNING LEVEL ...................................................................................................... 24

7. COMPLIMENTARY USER ALIGNMENT ......................................................................................... 25

7.1. OPTION ALIGNMENT: .............................................................................................................. 25

7.1.1. ANALOG Microphone gain: ................................................................................................. 25

7.1.2. ANALOG External Mic Gain: ................................................................................................ 25

7.1.3. ANALOG AGC ...................................................................................................................... 26

7.1.4. DIGITAL AGC ........................................................................................................................ 26

7.1.5. MINIMUM VOLUME LEVEL: ................................................................................................ 27

7.1.6. SQUELCH LEVEL: .................................................................................................................. 27

7.1.7. DISABLE RF POWER ............................................................................................................. 27

8. RADIO APPEARANCE ALIGNMENT .............................................................................................. 28

8.1. DISPLAYS AND LEDS: ............................................................................................................... 28

8.1.1. Auto backlight delay alignment: ......................................................................................... 28

8.1.2. Power on Text: .................................................................................................................... 28

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

8.1.3. Leds: .................................................................................................................................... 29

8.2. Tones ....................................................................................................................................... 29

8.3. ANNUNCIATION ...................................................................................................................... 29

9. ST-2112 SCHEMATIC ................................................................................................................... 32

10. ST-2112 FROM BOARD SCHEMATIC ............................................................................................ 33

11 ST-2112 COMPONENT LOCATOR (TOP LAYER) ............................................................................... 34

12 ST-2112 COMPONENT LOCATOR (BOTTOM LAYER) ....................................................................... 35

13 ST-2112 PCB TOP LAYER .................................................................................................................. 36

14 ST-2112 PCB BOTTOM LAYER .......................................................................................................... 37

15 ST-2112 PCB GROUND LAYER ......................................................................................................... 38

16 ST-2112 PCB POWER LAYER ............................................................................................................ 39

17 ST-2112 FRONT BOARD COMPONENT LOCATOR (TOP LAYER) ....................................................... 40

18 ST-2112 FRONT BOARD COMPONENT LOCATOR (BOTTOM LAYER)............................................... 41

19 ST-2112C BOM ................................................................................................................................ 42

20 ST-2112 KEYBOARD & DISPLAY BOM .............................................................................................. 52

21 ACCESSORY PORT: ........................................................................................................................... 53

22 ST-2112 SERVICE MANUAL REVISIONS ........................................................................................... 55

1. Specifications:

SPECIFICATION

ST-2112C

GENERAL

Frequency Range [Mhz]

400 TO 470

Channels

512

Groups/Banks

Power [Vdc]

6.4 to 8.8

Dimensions [mm]

130(H)x36(D)x52(W)

Weight [gr] (oz)

320 - (11.3)

Temperature range

- 30 °C ~ 60 °C (-22°F ~ +140°F)

Signaling

51 CTCSS tones / 183 DCS tones / 65534 SDR IDs

Reverse Burst

Display

128x64 (supports international characters)

Emergency call

Yes

GPS

Option

Channel Scan

Yes

BCLO / BTLO

Yes

Power Saver control

Yes

TOT

Yes

Radio Kill/Alive

Yes

Adjustable Power Selection

Auto + H/M/L

Key lock

Yes

Adjustable Squelch Level

16 Step

Password

Yes

Key Function selection

Yes

TRANSMIT

MAX RF power

4 W

Frequency Stability

>1PPM

Bandwidth [Khz]

6.25/12.5/25

Adjacent Channel Power

-65dBC (typ)

SNR

45dB typ

Analog harmonic distortion

3% typ (AF 1Khz, 60% deviation)

Data transmit rate

2400/4800/9600 bps

Max frequency deviation

2.5Khz@12.5Khz BW/5Khz@25Khz BW

Analog Modulation type

11K0F3E, 25K0F3E

TDMA Emissions

8K30F7E, 8K30F7D

FDMA Digital emissions

6K25F1E, 6K25F1D, 8K30F1E, 8K30F1D, 8K30F1W

Ext. Mic. Impedance

600 Ohms

RECEIVER

Analog Sensitivity

0.25uV (12dB Sinad)

Digital Sensitivity

0.25uV (3% BER)

Image rejection

60dB typ

Adjacent Channel selectivity

65dB typ @25KHz BW

HUM and NOISE ratio

45dB

Speaker Audio Power

External audio power

Specifications subject to change without notice or obligation

2. ST-2112 EXPLODED VIEW

ST-2112V

Jack Chang

Daniel Martin

2 . ST-2112 EXPLODED VIEW

3. ST-2112 SIMPLIFIED DIAGRAM

LPF

Ant Sw D1/D3

Final

AMP

Power

Detection

Driver

Buffer

AMP

TX CTRL

[U3]

CLOCK

[Y1]

POWER

CTRL

[U2]

FLASH

MEMORY

[U4]

RAM

MEMORY

[U7]

DISPLAY

GPS

G-SENSOR

PWM

KEYBOARD

SIDE KEYS

USB

SERIAL

PORT

Main Processor

[U8]

Radio

Audio Processor

Modem

[U5]

VOCODER

[U6]

CLOCK

[Y2]

MIC

AMP

[U12]

AUDIO

[U10]

CLOCK

[Y3]

JP2

Notes:

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

4. - ST-2112 RF DESCRIPTION

4.1. Circuit Configuration

The receiver is a single receiver with built-in DSP fully integrated.

Incoming signals from the antenna, after passing through LPF filter, are fed direct to the DSP down converter to get the baseband voice from 0Hz to 3500Hz.

Demodulated signals are filtered and conditioned onto a second DSP based filter, which also includes a high efficiency 4FSK modem.

For digital demodulation, the recovered data is fed into a vocoder, which converts the data to voice.

Analog voice from the analog path or the analog voice recovered from the vocoder, are fed into an audio power amplifier.

Transmit signal frequency is generated by integrated VCO and PLL. RF frequency generated by the integrated RF chip is amplified into a 3-step amplifier then filtered by a low pass filter to be applied to the antenna.

4.2. Receiver System

4.2.1. Front-end RF Receiver

Incoming RF signals from the antenna are delivered to the Receiver Unit and pass through a Low-pass filter, antenna switching

diode, and then fed to the receiver (U1) passing through a limiter BPF.

4.2.2. ANALOG Audio Processing

The RF signal is tuned by U1, which includes a base band DSP audio processing, recovering flat audio from DC up to 3500 hz.

The detected audio is amplified, filtered and conditioned inside of U5 which also includes a deemphasize filtering shape for received audio signals

The output of the filtered and conditioned audio is delivered to an audio power amplifier (U10) then to the speaker passing through the external audio connector switch.

4.2.3. Virtual Squelch Circuit

S/N ratio is measured by the receiver (U1) as the result of the analysis of the signal and the noise of the carrier. The output is sent to the main processor as a digital frame, which is analyzed by radio firmware, removing noise then qualifying the signal level. If the signal level is higher than the

LPF

SWITCH

PROTECTION

FILTER

RECEIVER

[U1]

RECEIVER

[U1]

AUDIO

PROCESSOR

[U5]

AMPLIFIER

[U10]

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

expected for the current programmed squelch threshold, then the processor analyzes the expected signaling programmed on the current channel table. In case of not any signaling is required, or the signal has been detected, the processor ask to the audio processor (U5) to open the audio path, unmuting the audio amplifier (U10).

4.2.4. Virtual VOLUME CONTROL

The potentiometer position (RV1) is measured by one analog to digital converter on the audio processor (U5), and then the information is reported to the main processor. The firmware immediately adjusts the audio processor path gain to get the appropriate overall circuitry volume control. Minimum volume, emergency and private audio level are controlled only by software overriding the information received from the DAC on U5.

4.2.5. Sub audio signaling

Received sub audio signaling like CTCSS and DCS are received and processed by the receiver (U1) then detected on the audio processor (U5). Once decoded, the sub audio signaling is reported to the processor where the firmware compares it with the value programmed into the current channel programming.

If the received signaling matches the channel programming, then the main processor (U8) requests the

audio processor (U5) to open the audio patch.

4.2.6. ANALOG AUDIBLE SIGNALING

DTMF signals, MDC1200 and tone signals are processed and decoded by the audio processor (U5). Decoded information or received tone is reported to the main processor (U8).

4.2.7. DIGITAL AUDIO PROCESSING

Digital received information is processed by the receiver DSP (U1)

then delivered to the audio processor (U5), which includes a high speed (4FSK) modem. Data decoded by the modem is transferred to the main processor (U8) which de-encrypts the information, checks the integrity, corrects the wrong bits and extract the audio information form the received frame.

The portion of the data received, error free, is moved to the vocoder (U6).

The vocoder re-builds the audio from the compressed data then applies filter it, adjust the volume

RECEIVER

[U1]

AUDIO

PROCESSOR

[U5]

AMPLIFIER

[U10]

MAIN

PROCESSOR

[U8]

VOCODER

U6]

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

and fed it to the audio power amplifier (U10).

4.3. Transmitter System

4.3.1. ANALOG TX SIGNAL

The AF signal from the internal microphone (MK1) or external microphone (J5) are processed as differential signal, then it is conditioned and transformed into common mode by the microphone pre-amplifier (U12).

The result of the conditioned inband filtered signal is fed to the Audio Processor (U5), which provides audio compander, emphasize, limitation, encryption, etc.

The high audio band of the signal from 300 to 3500 Hz are directly fed to the transmitter (U1), which performs a direct modulation of a generated carrier.

Low frequency signaling audio are fed directly to Y1 VC TXCO main clock generator and U1 with a corresponding balance controlled by software.

4.3.2. DIGITAL TX AUDIO:

The AF signal from the internal

microphone (MK1) or external microphone (J5) are fed directly to the vocoder chip (U6) which perform the data codification, delivering the digitized and encoded audio as digital frames which are processed by the Main Processor U8, which add a FEC (Frame Error Correction), encrypt the information and add the user related information as user ID, etc.

The final data frame is fed to the Audio Processor (U5) which has a built in modem, which operates for FDMA or TDMA signals, controlling the modulation of the Transmitter (U1) through the VC TXCO for DC to low frequencies and the direct modulation for higher frequencies.

4.3.3. Drive and Final Amplifier Stages

Final RF is amplified on Q2 (2SC3356) then filtered to be fed to Q3 (2SK3475) then finally amplified by Q1 (2SK3476) up to 5 watts output power.

The transmit signal then passes through the antenna switch D1 (BAR63) and is low-pass filtered to suppress harmonic spurious radiation before delivery to the antenna

AMPLIFIER

[U12]

AUDIO

PROCESSOR

[U5]

TRANSMITTER

[U1]

VC TXCO

[Y1]

AUDIO

PROCESSOR

[U5]

TRANSMITTER

[U1]

VC TXCO

[Y1]

MAIN

PROCESSOR

[U8]

VOCODER

[U6]

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

4.3.4. Automatic Transmit Power

Control

The RF power detector (RB705D) detects transmitted feedback then sends the readout to audio processor U5 (CMX-7141). Audio amplifier compares the transmitted power against the referred level stored on current channel memory adjusting the power control level generated as reference by one DAC output on the same Audio processor (U5) then amplified by U2 (MCP6241U) controlling the gate current on Q1 and Q17.

Evenly when power level is adjusted by software on three levels (Hi, Med, Lo) the power value can be adjusted to any desired value between zero and 5Watts by the alignment software.

Notes:

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

5. RC-2112 ALIGNMENT

5.1. Introduction

The ST-2112 series is carefully aligned in factory for the specified performance, across the frequency range depending for each version. Realignment should therefore not be necessary except in the event of a component failure, or altering version type.

All component replacement and service should be performed only by an authorized SmarTrunk representative, or the warranty policy may be void.

The following procedures cover the sometimes critical and tedious adjustments that are not normally required once the transceiver has left the factory.

However, if damage occurs and some parts subsequently are placed, realignment may be required. If a sudden problem occurs during normal operation, it is likely due to component failure; realignment should not be done until after the faulty component has been replaced.

We recommend that servicing be performed only by authorized SmarTrunk service technicians who are experienced with the circuitry and fully equipped for repair and align. Therefore, if a fault is suspected, contact the dealer from whom the transceiver was purchased for instructions regarding repair. Authorized Smartrunk service technicians realign all circuits and make complete performance checks to

ensure compliance with factory specifications after replacing any faulty components.

Those who do undertake any of the following alignments are cautioned to proceed at their own risk.

Problems caused by unauthorized attempts at realignment are not covered by the warranty policy. Also, SmarTrunk reserves the right to change circuits and alignment procedures in the interest of improved performance, without notifying owners.

Under no circumstances should any alignment be attempted unless the normal function and operation of the transceiver are clearly understood, the cause of the malfunction has been clearly pinpointed and any faulty components replaced, and realignment determined to be absolutely necessary.

5.2. ALIGNMENT:

The following test equipment (and thorough familiarity with its correct use) is necessary for complete realignment. Correction of problems caused by misalignment resulting from use of improper test equipment is not covered under the warranty policy.

While most steps do not require all of the equipment listed, the interactions of some adjustments may require that more complex adjustments be performed afterwards. Do not attempt to perform only a single step unless it is clearly isolated electrically from

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

all other steps. Have all test equipment ready before beginning, and follow all of the steps in a section in the order presented.

Required Test Equipment

 RF Signal Generator with

calibrated output level at 1 GHz

 Deviation Meter (linear

detector)

 In-line Wattmeter with 5 %

accuracy at 1 GHz

 50 Ohm RF Dummy Load

with power rating 10W at 1 GHz

 8 Ohm AF Dummy Load

(Attention: Audio output is BTL output)

 Regulated DC Power Supply

(standard 7.5 V DC, 3 A)

 Frequency Counter with 0.2

ppm accuracy at 1GHz

 Audio Generator  AC Voltmeter  DC Voltmeter  UHF Sampling Coupler  IBM PC / compatible

Computer with Microsoft® Windows® XP or later operating system

 SmarTrunk SDR

Programming software (version 1.0.2 or later)

 USB A/B Programming Cable

5.3. Alignment Procedure

Alignment Preparation & Precautions

A 50-Ohm RF Dummy Load and inline wattmeter must be connected to the main antenna jack in all procedures that request for

transmission, except where specified otherwise. Correct alignment is not possible with an antenna.

After completing one-step, read the following steps to determine whether the same test equipment will be required. If not, remove the test equipment (except dummy load and wattmeter, if connected) before proceeding.

Correct alignment requires that the ambient temperature be the same as that of the transceiver and test equipment, and that this temperature be held constant between 68°F and 86 °F (20°C ~ 30 °C). When the transceiver is brought into the shop from hot or cold air, it should be required to wait few minutes to come to room temperature before alignment.

Whenever possible, alignments should be made with oscillator shields and circuit boards firmly affixed in place. Also, the test equipment must be thoroughly warmed up before beginning.

Note: Signal levels in dB referred to in the alignment procedure are based on 0 dBm EMF = 1 mV.

5.3.1. GENERAL ALIGNMENT

CONSIDERATIONS:

Evenly if the radio is powered off, the alignment software will detect it, but some of the test cannot be performed correctly.

Please be sure you turn the radio on before continue with this alignment procedure.

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

In case the battery has not enough charge, the test will be aborted by the software. Please ensure the battery has more than 50% of remaining charge to complete the test.

5.4. MAIN RADIO ALIGNMENT

Before setup any parameter, run SDR programming software then select Radio Alignment from top bar menu.

A complementary message will be displayed on the time the software detects the radio connected to USB port on the computer.

If the radio isn’t connected, then the

program will be timed out after 20 seconds.

As soon as the radio is detected, actual radio parameters are loaded.

Once the radio is connected, a new screen pops up showing all alignment parameters. The software downloads actual alignment parameters stored into radio memory, so the information displayed on each alignment step is the real value form the previous alignment.

The radio also stores in a special memory area, original values assigned in factory. You can go back to those values anytime for any particular alignment step.

In case the radio is password protected, dealer password is required to access to this alignment menu.

At any time, press to end the alignment procedure then the radio will returns to alignment menu.

For any transmit related alignment parameter, low power will be used.

5.5. TRANSMITTER ALIGNMENT:

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

7.5V Power Supply

PC compatible

On Line Wattimeter

30dB pad

Deviation Meter

Frequency Counter

Setup the test equipment as shown for transceiver alignment, apply 7.5 V DC power to the transceiver.

The RF parameters are typed on the alignment software to facilitate the alignment within all radio band avoiding special programming of the radio before start alignment procedure.

All parameters can be aligned without relationship to any other, so there is no an order to align. On this way, you can adjust only the desired parameter, avoiding to waste time realigning other parameters than required.

Before proceed to align any parameter, a desired frequency must be loaded into both TX and RX. Evenly when the radio has stable characteristics for all bandwidth, it is recommendable to align on middle of the radio working band.

5.5.1. Main Clock alignment:

To align the main clock for radio Tx and RX, please select Main Clock Alignment option Alignment screen.

Fig 12: alignment menu

Actual alignment value will be displayed on alignment slider.

Press [Start] then move the slider to reach the desired value at the time you checks the Frequency Counter to reach the desired frequency as shown on Frequency field of the alignment screen.

As soon the desired value is reached, press [Finish] to store the value on radio memory.

If you want to retrieve factory default, press [Factory] instead of [Start]. You will be asked to confirm the factory default alignment, and then if you confirm it, original values from factory will be loaded into current alignment settings.

This confirmation screen will appears any time you want to realign any parameter to Factory Default.

ST-2112C SM R 1.2 SMARTRUNK SYSTEMS, INC.

5.5.2. Transmit Power alignment:

ST-2112 has three power levels to be selected for each channel. High, medium and low power level can be aligned as per radio usage requirement.

For power alignment, you can do a fine tuning as per your desire frequency sub-band. The software lets you linearize the complete band

“cutting” the complete band into

five steps to let you focus into your frequency bands.

Even when the software has already assigned the most convenient frequency points to consider the alignment, you still can enter exactly the frequency of your interest.

5.5.2.1. High POWER LEVEL

ALIGNMENT

To align the High Power level select Power High Level.

Software automatically retrieves actual level to the alignment slider.

This level has been aligned in factory, but you still can adjust it as per your desires.

To realign, please select [Start] then move the slider or introduce the

value manually at the time you check the real transmit power on the wattmeter connected to the radio as recommended on TX alignment diagram.

As soon as [Start] is pressed, the radio start to transmit a carrier, so please verify the antenna dummy load is properly connected to avoid any damage to the transmitter.

As soon the desired value is reached, press [Finish] to store the value into radio memory.

If you want to load default High power only, keeping any other value without any change, press [Factory] instead of [Start]. A pop up window will ask you to confirm the default parameters upload to the radio power.

Press [OK] to confirm.

As descripted previously, you can manually select the frequency range to align, divided into five different sub-ranges.

You can also define the right frequency of interest to align, typing the desired one into the frequency field:

If selected frequency is not supported by radio hardware, the frequency field will be filled on red. In case the PLL is locked, then it becomes filled on green.

Please be sure that the PLL is locked as soon as you press [Start],

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SmarTrunk ST-2112C Service Manual

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