Ritron RIT20-250 220 MHz TRANSCEIVER User Manual dtxmanual

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RIT20 250 User Manual

USERS MANUAL

TYPE OF EXHIBIT:USERS MANUAL

FCC PART: 2.1033(c)(3)

MANUFACTURER:RITRON, Inc.

505 West Carmel Drive

Carmel, IN 46032

MODEL:DTX-254

TYPE OF UNIT:220 MHz Transceiver Module

FCC ID: AIERIT20-250

DATE: December 23, 2004

RITRON, INC. PRELIMINARY 12-04

RITRON MODELS DTX-154, 254 & DTX-454

PROGRAMMABLE

FM TRANSCEIVER MODULES

MAINTENANCE & OPERATING

MANUAL

FOR USE ONLY BY AUTHORIZED SERVICE/MAINTENANCE PERSONNEL

TABLE OF CONTENTS

IDTX-154/254/454 MODULES

1INTRODUCTION

1.1 GENERAL

1.2 MODEL IDENTIFICATION

1.3 FCC REGULATIONS

2MODELS DTX-154, DTX-254 AND DTX-454 SPECIFICATIONS

2.1 GENERAL

2.2 TRANSMITTER

2.3 RECEIVER

3DTX-154/254/454 INPUT/OUTPUT CONNECTOR

4ACCESSORIES

5OPERATION

5.1 CHANNEL SELECTION

5.2 POWER SUPPLY VOLTAGE

5.3 DUTY CYCLE/KEY-DOWN LIMITATIONS

5.4 OPERATING MODES

5.5 RNET COMPATIBILITY MODE

6PROGRAMMING

6.1 PC PROGRAMMING KIT

6.2 LOADING THE PROGRAMMING SOFTWARE

6.3 COMPUTER SOFTWARE COPYRIGHTS

6.4 USING THE PROGRAMMING SOFTWARE

6.5 PROGRAMMER MENUS

II DTX-154/254/454 STAND-ALONE RF BOARD

7DTX RF BOARD DIMENSIONS

8RF BOARD J102 INPUT/OUTPUT

9DTX SYNTHESIZER LOADING

III MAINTENANCE

10 IMPORTANT MAINTENANCE INFORMATION

11 THEORY OF OPERATION

11.1 DTX-154/254 RF BOARD

11.2 DTX-454 RF BOARD

11.3 CONTROL/LOADER BOARD

12 HARDWARE OPTIONS

12.1 CONTROL/LOADER BOARD OPTIONS

12.2 RF BOARD OPTIONS-STAND-ALONE OR PART OF DTX MODULE

12.3 RF BOARD OPTIONS-STAND-ALONE ONLY

13 ALIGNMENT

13.1 REQUIRED TEST EQUIPMENT

13.2 ALIGNMENT PROCEDURE

13.3 RF BOARD INTERNAL ADJUSTMENTS

14 ACTIVE COMPONENT VOLTAGE CHART

14.1 DTX-154/254 RF BOARD

14.2 DTX-454 RF BOARD

14.3 CONTROL/LOADER BOARD

15 SCHEMATIC DIAGRAMS

IDTX-154/254/454 MODULES

1INTRODUCTION

1.1 GENERAL

The RITRON DTX-154/254/454 modules are programmable 2-way radios, which operate either in

the VHF, 220 MHz or UHF professional FM communications bands. Each of eight channels can

be programmed to contain a unique set of operating frequencies. The DTX-154/254/454 module

is made up of two PC boards, an RF board and a control/loader board. These two boards are

enclosed in a metal case with two connectors on one end; a 50 ohm BNC connector for connection

to an antenna and a DB-15 sub-miniature connector for power and control input/output.

In addition, the RF board is available as a stand-alone unit for system integrators. The RF board

as sold as a stand-alone item has a few more hardware options than when installed and sold as part

of a module. See section 11 for details on the hardware options.

1.2 MODEL IDENTIFICATION

The part number system for the DTX-154/254/454 module is as follows:

The module has a part number in the form of “DTX-A54-BCDEF”

Where:

A is the major frequency band designator:

1=VHF

2=220 MHz

4=UHF

B is the sub-band designator:

G=136-162 for VHF and 400-420 for UHF

A=420-440

B=430-450

O=148-174 for VHF, 217-245 MHz for 220 MHz band, and 450-470 for UHF

C=470-490

T=490-512

C is the connector designator:

B=BNC connector

D designates the IF bandwidth:

N=narrow

W=wide

E designates the maximum power level:

3=3 watts

6=6 watts

9=10 watts

F designates whether the control/loader board has a regulator and if so, at what current level:

D=no regulator; the unit must operate at +7.5 VDC and is limited to either 3 or 6 watts

max.

L=low current regulator; the power module is not regulated. Used for 10 watt version

only.

I=high current regulator; the unit operates from 10-15 volts at either 3 or 6 watts max.

Example: A DTX-454-OBN6I would be a UHF module for operation between 450 and 470 MHz

with a BNC RF connector, narrow (12.5 kHz channel spacing) IF bandwidth, 6 watts maximum

output power, and an internal regulator to allow operation from 10 to 15 volts.

The part number system for a stand-alone RF board is the same as that for a module except that

“F” designator (regulator option) does not exist and a “-DD” is appended at the end.

Note that the RF board inside a module is not exactly the same as the corresponding stand-alone

RF board. There are a number of components and jumper options on the stand-alone board that

are not necessary when mated to the RITRON DTX control/loader board.

1.3 FCC REGULATIONS

1.3.1 LICENSING

The FCC requires that the radio owner obtain a station license for his radio before using the

equipment to transmit, but does not require an operating license or permit. The station licensee is

responsible for proper operation and maintenance of his radio equipment, and for ensuring that

transmitter power, frequency and deviation are within the limits specified by the station license.

This includes checking the transmitter frequency and deviation periodically using appropriate

methods.

1.3.2 EQUIPMENT AUTHORIZATION

The unit is certified for transmission of either voice or data signals when aligned according to the

alignment procedure for the proper bandwidth and when operated as a complete unit in the metal

case. Operation of the RF board as a stand-alone unit or in combination with any other equipment,

in any mode outside the alignment procedure, or with the clipper filter electronically disabled will

require the filing of a new type acceptance application with the FCC by the user.

1.3.3 SAFETY STANDARDS

The FCC, with its action in General Docket 79-144, March 13, 1985, adopted a safety standard for

human exposure to radio frequency electromagnetic energy emitted by FCC regulated equipment.

The DTX-154 has been evaluated for compliance with the maximum exposure limits for RF

energy at the maximum power rating of the unit and with the only antenna sold for use with this

product by RITRON. To ensure compliance with the General Population/Uncontrolled maximum

exposure limits, please observe the following:

When the Ritron RAM-1545 remote magnetic mount antenna is used, mount the antenna in a

location that will ensure that all persons will be at least 19 inches (49 cm) away from the antenna.

Antennas other than the Ritron RAM-1545 must be tested with the DTX-154 for RF exposure

compliance in the environment in which it is to be used per the FCC’s OET Bulletin 65, Edition

97-01 or Industry Canada RSS-102.

The DTX-254 has been evaluated for compliance with the maximum exposure limits for RF

energy at the maximum power rating of the unit with a common unity gain quarterwave magnetic

mount mobile antenna. To ensure compliance with the General Population/Uncontrolled

maximum exposure limits, please observe the following:

When the quarterwave remote magnetic mount antenna is used, mount the antenna in a location

that will ensure that all persons will be at least 26 inches (67 cm) away from the antenna.

Antennas other than a quarterwave magnetic mount antenna must be tested with the DTX-254 for

RF exposure compliance in the environment in which it is to be used per the FCC’s OET Bulletin

65, Edition 97-01 or Industry Canada RSS-102.

The DTX-454 has been evaluated for compliance with the maximum exposure limits for RF

energy at the maximum power rating of the unit and with the only antenna sold for use with this

product by RITRON. To ensure compliance with the General Population/Uncontrolled maximum

exposure limits, please observe the following:

When the Ritron RAM-45 remote magnetic mount antenna is used, mount the antenna in a

location that will ensure that all persons will be at least 21 inches (53 cm) away from the antenna.

Antennas other than the Ritron RAM-45 must be tested with the DTX-454 for RF exposure

compliance in the environment in which it is to be used per the FCC’s OET Bulletin 65, Edition

97-01 or Industry Canada RSS-102.

2MODELS DTX-154/254/454 SPECIFICATIONS

DTX-154 DTX-254 DTX-454

2.1 GENERAL

FCC Identifier AIERIT12-150 AIERIT20-250 AIERIT11-450

FCC Rule Parts 22, 74, 90 90 22, 74, 90, 95

Industry Canada Identifier 1084A-DTX154 1084A-DTX254 1084A-DTX454

Frequency Range 136-162 MHz 217-245MHz 400-420 MHz

148-174 MHz 420-440 MHz*

430-450 MHz*

450-470 MHz

470-490 MHz*

490-512 MHz*

Number of Channels 888

Transmit/Receive Spacing 26 MHz max. 28 MHz max. 20 MHz max.

Mode of Operation Simplex/half Duplex

Frequency Control PLL Synthesizer

Channel Increment (Synthesizer step size) 2.5 kHz 2.5/3.125 kHz 5/6.25 kHz

Emissions Bandwidth

Narrow Mode 11 kHz 11 kHz 11 kHz

Wide Mode 16 kHz 16 kHz (FCC) 16 kHz

Frequency Stability (-30 to +55 °C) 1.5 ppm 1.0 ppm 1.5 ppm

Supply Voltage

3 and 6 watt versions

w/o internal regulator 7.5 VDC 7.5 VDC 7.5 VDC

w internal regulator 11-16 VDC 11-16 VDC 11-16 VDC

10 watt version N/A N/A 11-16 VDC

RF Input/Output Connector BNC standard

Power/Data Interface 15 pin subminiature D type

Maximum Dimensions (L x W x H) 3.6” x 2.3” x 1.0” including connectors

Weight 6 oz.

* Not Available Yet

DTX-154 DTX-254 DTX-454

2.2 TRANSMITTER

Operating Bandwidth 26 MHz 28 MHz 20 MHz

RF Output Power(internally adjustable)

3 watt version N/A N/A 1 to 3 watts

6 watt version 1 to 6 watts 1 to 6 watts 1 to 6 watts

10 watt version N/A N/A 1 to 10 watts

Duty Cycle 5 to 100 % depending upon voltage and power level

RF Load Impedance 50 ohms

Modulation Distortion (per TIA/EIA 603) 5 % max.

Frequency Response (+1/-3 dB ref 1 kHz)

At MIC IN (ref pre-emphasis curve) 50 Hz to 2500 Hz

At AUX IN w/o pre-emphasis 50 Hz to 2700 Hz

Transmitter Attack Time: 15 ms max

Spurious and Harmonics -20 dBm max.

FM Hum and Noise (per TIA/EIA 603)

12.5 kHz channel operation 40 dB min.

25 kHz channel operation 45 dB min.

Group Delay Variation (50-2500 Hz) 5 us max.

Current Drain

1 watt 1.0 A max. 1.0 A max. 1.0 A max.

3 watts 1.6 A max. 1.6 A max. 1.6 A max.

6 watts 2.4 A max. 2.4 A max. 2.4 A max.

10 watts @ 13.5 V N/A N/A 2.4 A max.

AUX IN adjustment range (60% rated dev.)

w pre-emphasis (@ 1 kHz) 200 to 1000 mV rms

flat 40 to 300 mV rms

DTX-154 DTX-254 DTX-454

2.3 RECEIVER

Operating Bandwidth 26 MHz 28 MHz 20 MHz

Sensitivity (12 SINAD w de-emphasis) 0.30 uV (-117.5 dBm)

RF Input Impedance 50 ohms

Adjacent Channel Selectivity

+/- 12.5 kHz w narrow IF 60 dB min.

+/- 25 kHz w wide IF 70 dB min.

Spurious and Image Rejection 70 dB min.

Intermodulation Rejection 67 dB min.

FM Hum and Noise (per TIA/EIA 603)

12.5 kHz channel operation 35 dB min.

25 kHz channel operation 40 dB min.

Conducted Spurious -57 dBm max.

Receive Attack Time (transmit to receive) 15 ms max.

Noise Squelch Attack Time 13 ms max.

RSSI Squelch Attack Time 5 ms max.

Audio Distortion (per TIA/EIA 603) 5 % max.

Audio Response at AUX OUT (+1/-3 dB, ref 1 kHz)

12.5 kHz channel operation 100 Hz to 3.5 kHz

25 kHz channel operation 100 Hz to 5 kHz

Group Delay Variation (100-3500 Hz) 20 us max.

Receive Current Drain 80 mA max. 80 mA max. 75 mA max.

AUX OUT Adjustment Range

w de-emphasis (@ 1 kHz) 50 to 500 mV rms open circuit

flat 250 to 1800 mV rms open circuit

AUDIO OUT Adjustment Range (@ 1 kHz) 400 to 1750 mV rms

3DTX-154/254/454 INPUT/OUTPUT CONNECTOR

Connector Pinout

Pin Number Name Description Comments

1CS0 Channel Select low bit

2CS1 Channel Select mid bit

3CS2 Channel Select high bit

4MIC IN Microphone Input Input for microphone type

signals to be transmitted.

Signals at this input are

pre-emphasized, limited,

and filtered.

5CSN High/Low Power or Channel 1/2

6RAW SUPPLY Power Supply Input Positive Supply voltage

input.

7AUX IN Auxiliary Input Wideband input for data.

8AUX OUT Auxiliary Output Wideband output for data.

9PGN IN/OUT Programming I/O External programmer

connects here.

10. CTS Clear to Send Active high when

transmitter can accept

modulation.

11. RX MON Monitor Breaks squelch in receive.

12. AUDIO OUT Audio PA Output Output of audio PA.

13. DCD Carrier Detect Carrier detect output.

14. PTT/RTS Push to Talk Activates transmitter.

15. GND Ground Negative supply point and

reference for all inputs.

Pinout Description

Pin Number Description

1CS0-Least significant bit of the channel select lines. Active high 5 volt

TTL/CMOS level. Internal 10 kΩ pull-up to +5 volts.

2CS1-Mid bit of the channel select lines. Active high 5 volt TTL/CMOS level.

Internal 10 kΩ pull-up to +5 volts.

3CS2-Most significant bit of the channel select lines. Active high 5 volt

TTL/CMOS level. Internal 10 kΩ pull-up to +5 volts.

Channel CS2 CS1 CS0

1 0 0 0

2 0 0 1

3 0 1 0

4 0 1 1

5 1 0 0

6 1 0 1

7 1 1 0

8 1 1 1

0 = Logic low

1 = Logic high

Note: Due to the internal pull-up resistors, the unit defaults to channel 8 if the

channel pins are left open (unconnected).

4MIC IN-Microphone input. This input accepts microphone type input signals

for transmit. The signal is amplified, passed through the clipper and the clipper

filter and then to the RF board. This input can be programmed to be disabled

(muted) if desired.

5CSN-When enabled through programming, this input selects between channels 1

and 2. This input is TTL/CMOS level type input with a logic low required for

channel 1 and a logic high required for channel 2. Internal 10 kΩ pull-up to +5

volts.

6RAW SUPPLY- The positive supply voltage for the unit is supplied through this

pin. The actual supply voltage required depends upon model type. Ensure that

the correct supply voltage per the given model is used.

7AUX IN-This is the broadband input for modulation. The gain through this

input to the modulator is programmable, as is the use of pre-emphasis. This

signal passes the clipper and clipper filter.

8AUX OUT-This is the broadband output of the receiver. The gain from the

receiver to the output is programmable, as is the use of de-emphasis. The choice

of AC or DC coupling from the RF board discriminator is also programmable.

The coupling at the output of this pin is AC coupled, however. It can be

converted to DC coupling with internal hardware modifications.

9PGN IN/OUT-Connect via RITRON DTXP-PCPK PC Programming Kit to

computer for programming the unit.

10 CTS-Clear-To-Send output from the unit which indicates that the unit is

transmitting a carrier at the correct frequency and power level and is ready to

accept an input signal to be transmitted. This output would normally become

true in response to a PTT RTS (see pin 14 description below) activation. The

polarity of this output can be programmed. The output is active low 5 volt logic

with an internal 10 k ohm pull-up to 5 volts. It can source up to 10 mA when

low.

11 RX MON-This input breaks the squelch on the receiver i.e. allows for

monitoring the channel even when a signal not strong enough to break squelch is

present. Input levels are TTL/CMOS; polarity may be programmed. Internal 10

kΩ pull-up to +5 volts.

12 AUDIO OUT-This is the output of the audio power amplifier. This output can

drive up to ½ watt in to an 8 ohm load. This output can be enabled and its gain

controlled by programming.

13 DCD-Carrier detect output. This output becomes true when a signal strong

enough to exceed the programmed squelch threshold is present. This output is

not affected by the RX MON input. The polarity can be programmed. The

output is active low 5 volt logic with an internal 10 kΩ pull-up to +5 volts. It

can source up to 10 mA when low.

14 PTT/RTS-Push to Talk/Request to Send. This input commands the unit to

transmit. Input levels are TTL/CMOS; polarity may be programmed. Internal

10 kΩ pull-up to +5 volts.

15 GND-System ground. All signals and voltages are referenced to this input. The

negative side of the power supply should connect here.

4ACCESSORIES

Note: Programming kits are for use by authorized service/maintenance personnel only.

The Programming Kit for DTX-154/254/454 radios (via compatible computer) is model DTXP-

PCKT. It includes:

1) Programming software diskettes, 3.5” (qty 2).

2) 1 25 pin PC to 6 pin modular adapter cable with built-in interface circuitry.

3) 1 modular adapter to DB-15 connector cable with power cable.

Factory programming of channels and features is also optional. Contact the factory for details.

5OPERATION

5.1 CHANNEL SELECTION

The DTX module supports eight channels. The desired channel is chosen via pins 1,2, and 3 of

the 15 pin connector as shown:

Channel Pin 3 Pin 2 Pin 1

1 0 0 0

2 0 0 1

3 0 1 0

4 0 1 1

5 1 0 0

6 1 0 1

7 1 1 0

8 1 1 1

0 = Logic low

1 = Logic high

A logic low is a voltage level below 1 volt while a logic high is a voltage level above 3.5 volts.

These three pins have an internal 10 kΩ pull-up resistor to + 5 volts. Therefore, any pin left

unconnected will assume a logic high state. Do NOT apply voltages outside the range of 0 to +5

volts to these pins.

A change in the channel selection in receive will cause the receiver to operate on the new channel.

In transmit, however, the channel selection is only checked upon a push-to-talk activation.

Changes in channel during transmit will not change the transmit operating channel of the unit until

the unit is cycled from transmit to receive and back to transmit.

5.2 POWER SUPPLY VOLTAGE

Pin 6 is the positive supply input to the unit. The type of module determines the actual voltage

that should be applied to this pin. One should be absolutely sure of the proper voltage and current

requirements before applying power.

Three voltages are used within the unit; +5 volts for the processor and logic circuits along with

most of the receiver, +7.5 volts for the transmitter driver stages, and the supply voltage for the RF

power module which depends upon which module is used.

The VHF and 220 MHz units and the 3 and 6-watt UHF units use 7.5 volt RF power modules.

Two supply voltage options are available for these units depending upon whether the

control/loader board has a regulator installed. If a regulator is not installed, the voltage should be

7.5 volts +/-10 %. This voltage should be “clean” and preferably regulated since the RF power

module is powered directly from this source. Variations in voltage will cause variations in

transmitted output power. Conversely, if the control/loader board has a regulator installed, the

supply voltage can be at any voltage between 10 and about 15 volts. Although the use of the

regulator allows flexibility in terms of supply voltage, because of the amount of heat generated by

the regulator, significant duty cycle/key down limitations may apply (see below).

The RF power module in the 10 watt UHF unit requires at least 12 volts to achieve 10 watts,

although voltages as high as 15 may be used. Since the module is powered directly from this

voltage, the supply should be “clean” and, preferably, regulated. The output power will vary with

supply voltage. The 7.5 volts required for the transmitter driver stages is developed by a regulator,

but since the current requirements are limited, the regulator is not a factor in determining the duty

cycle/key down limits.

5.3 DUTY CYCLE/KEY-DOWN LIMITATIONS

The major heat generating components within the module such as the RF power amplifier and

voltage regulator (if used) have maximum temperature limits that should not be exceeded. In

addition, the temperature within the module itself must be kept below the maximum temperature

of the reference oscillator. As a result, depending upon power, supply voltage, and temperature,

limits upon the average transmit duty cycle and the maximum continuous transmitter on time

exist. These limits are summarized below for operation in still air:

Temperature (°C) Duty Cycle (%) Key-Down Time (s)

w/o internal regulator:

3 watt RF output 25 100 30

60 15 5

6 watt RF output 25 80 30

60 10 5

10 watt RF output @ 13.5 V 25 30 15

60 5 5

w internal regulator

3 watt RF output 25 50 20

60 5 5

6 watt RF output 25 30 15

60 5 5

Blowing air across the unit and/or adding heat sinks can significantly improve the duty cycle/key-

down times, especially in units without the internal regulator.

5.4 OPERATING MODES

5.4.1 RECEIVE

Carrier Detect and Squelch Operation

The DTX is a transceiver; i.e. it can receive and transmit, although not at the same time. A carrier

detect system exists within the unit to detect the presence of a carrier which controls the logic state

of the DCD (data carrier detect) output. The RF levels at which this output changes state are

programmable. In addition, the unit may be programmed such that the audio outputs, AUDIO

OUT and AUX OUT, are muted (squelched) in conjunction with DCD operation. In units where

squelch operation has been enabled, the RX MON input can be used to override a squelched

condition. The DCD output is not affected by the RX MON operation.

Receiver Audio Outputs

Two receiver audio outputs are present on the DTX module. The AUX OUT is general purpose

output which can have pre-emphasis enabled or bypassed. Its gain can be controlled and its output

is designed to drive 600 Ω loads. The coupling from the discriminator on the RF board may be set

to AC or DC by the programmer. The output stage is AC coupled, but can be modified for DC

coupling. See the maintenance section of the manual for details on this modification. The

AUDIO OUT is always de-emphasized, but its gain can be programmed. In addition, transmit

sidetone can be programmed as an option, if desired. This output can drive 8 Ω speaker-type

loads.

5.4.2 TRANSMIT

PTT Operation

The transmitter is activated by placing the PTT/RTS (Push-To-Talk/Request-To-Send) input in its

true state. This state is programmable. If the unit is to operate in simplex (transmitter and receiver

on the same frequency), one should check for activity on the channel before transmitting. This can

be done by checking the state of the DCD output. In addition, the unit can be programmed so that

transmit operation is inhibited if the DCD threshold has been exceeded.

CTS Output

The CTS (Clear To Send) output goes to its true state when the unit has powered up the

transmitter, is locked on the correct transmit frequency, and is ready to accept modulation. This

output may be used to signal a modem to start transmitting data. If this output is not used, to

avoid loosing data, a delay of at least 15 ms is required between PTT/RTS activation and the

application of data.

Transmitter Audio Inputs

Two audio inputs are available on the DTX module. The AUX IN is a general-purpose input that

can have pre-emphasis enabled or bypassed and its gain can be controlled through programming.

The input impedance is greater than 50 kΩ and is capacitive coupled with a lower roll-off

frequency of about 25 Hz. The MIC IN input is fixed gain input designed for connection to a

standard electret or dynamic microphone. About 25 mV rms of input signal at 1 kHz will produce

60 % of maximum deviation. The signal at this input is pre-emphasized. The signals at both

inputs pass through the modulation limiter and post-limiter filter.

High/Low Power

If RNet compatibility mode is not programmed into the unit, high and low power levels can be

programmed into the unit on a channel by channel basis. High power is selected by placing the

CSN input at a logic high state. Placing the CSN input at a logic low state chooses low power.

The CSN input has an internal pull-up resistor; it will assume the high state i.e. high power when

left unconnected.

Specialized Modem Operation

Modems designed to achieve the highest data rates possible in a radio channel may require a direct

DC connection to the modulation path and the removal of the limiter-filter. In order to receive

FCC Type Acceptance, the DTX module must either be tested and approved with a specific

modem connected to the transmitter, or a modulation limiter and limiter-filter must always be

present in the transmit modulator audio path with the modulation inputs AC coupled. To allow for

the most flexibility for the end user, the unit was type accepted as a stand-alone unit. It is

possible, with hardware modifications and special programming software (not supplied with the

unit), to DC couple the AUX IN input and/or defeat the limiter-filter. The modulation limiter

would still be in place, but the deviation of the DTX module could be set such that the modulation

limit within the DTX module is never reached. The deviation would be set by the modem level

and the AUX IN gain setting. The end user/system integrator would then bear the responsibility of

obtaining type acceptance or operating in a frequency band where type acceptance is not required.

Contact RITRON for details. Note: Most modems will connect directly to the DTX without

requiring any special modifications or programming.

Antenna Placement

The DTX module is enclosed in a metal housing for RF shielding. However, RF emitting sources

located very close (less than 12 inches) to the unit can at times affect its operation. It is not

recommended that an antenna be connected directly to the module’s BNC connector unless the RF

output power is set for less than 1 watt or the module is placed within another RF tight enclosure.

5.5 RNET COMPATIBILITY MODE

The DTX module can be programmed to mimic some of the behavior of the RNet 450 radio. In

the RNet compatibility mode, the CSN input is used as a channel selector line. A logic low selects

channel 1 while a logic high selects channel 2. The channel select lines, CS0, CS1, and CS2 have

no effect. Also, the DCD output is held in its true state during transmit. It would normally be

false in transmit.

6PROGRAMMING

To program the DTX Module, the RITRON PC Programming Kit, DTXP-PCKT, must be used.

6.1 PC PROGRAMMING KIT

The user should install the programming software on the host computer. The RITRON adapter

cables connect the radio to a computer’s serial communications port. Once the cables are hooked

up, the user runs the programmer software. This program transfers data between radio and

computer memory.

6.1.1 PROGRAMMING KIT CONTENTS AND REQUIREMENTS

The RITRON Programming Kit includes the following:

1. Programming software that is contained on two diskettes.

2. PC to radio adapter cable, which is terminated at one end with a DB-25F connector and at the

other end with a modular plug. The DB-25 connector plugs into the computer’s serial port,

the modular plug into an adapter.

3. The adapter for use with the DTX Plus series of radios. This adapter mates the modular plug

to a DB-15M plug for connection to the radio. The adapter also includes wires for powering

the unit. The red wire is for positive voltage, the black for negative. Insure that the correct

voltage is applied to the unit.

The Programmer Kit requires a PC compatible computer with Windows 95 or later operating

system installed. The computer must have an RS-232 serial port available. A hard disk drive is

also required.

6.2 LOADING THE PROGRAMMER SOFTWARE

Insert disk one of the two disk set in the floppy disk drive. View the contents of the floppy disk

and double click on the install.exe file. Follow the instructions as they appear on the screen

including the prompt to insert the second disk. At the conclusion of the installation procedure, the

programming software will be resident on the user’s host computer.

6.3 COMPUTER SOFTWARE COPYRIGHTS

The RITRON, Inc. products described in this manual include copyrighted RITRON, Inc. computer

programs. Laws in the United States and other countries grant to RITRON, Inc. certain exclusive

rights in its copyrighted computer programs, including the exclusive right to distribute copies of

the programs, make reproductions of the programs, and prepare derivative works based on the

programs. Accordingly, any computer programs contained in RITRON, Inc. products may not be

copied or reproduced in any manner without the express written permission of RITRON, Inc. The

purchase of RITRON, Inc. products does not grant any license or rights under the copyrights or

other intellectual property of RITRON, Inc. except for the non-exclusive, royalty fee license to use

that arises in the sale of a product, or as addressed in a written agreement between RITRON, Inc.

and the purchaser of RITRON, Inc. products.

6.4 USING THE PROGRAMMING SOFTWARE

Upon starting the programming software, a screen will appear with three buttons at the top,

Program Radio, Programmer Configuration, and Exit. Program radio moves the user to the

program radio menus which are described below. Programmer configuration is used to select the

appropriate serial port and password (if desired). A few notes about using the programming

software:

• Moving from menu item to menu item and from screen to screen may take from 1 to 7 or 8

seconds. Some commands require that the entire contents of the radio’s memory be accessed.

An hourglass symbol may or may not be present for some or all of that time.

• If the programmer acts as if it is accepting commands, but the radio does not appear to be

responding, exit the programmer and start over. A power glitch on the radio during the

middle of a programming session can cause a serial communications conflict.

• The adjustments on the alignment menu are somewhat slower than changes in settings on the

settings menu. More computations and radio memory communications are required on the

alignment items.

6.5 PROGRAMMER MENUS

The DTX Programmer has four menus or pages, selectable via tabs at the top of each page, which

are always visible. These pages are:

1. Frequency Selection-Used to program the channel frequencies of the radio.

2. Settings-Used to set programmable features/functions of the radio.

3. Alignment-Used to align and set the internal digital potentiometers in the radio. Information

on the use of this page is found in the Maintenance section of the manual.

4. Restore EEPROM-Used to program the unit with a set of previously saved frequency and

setting values.

5. Summary-Used to summarize on one page the model, settings, and alignment information.

6.5.1 FREQUENCY SELECTION

The Frequency page has fields for the transmit and receive frequencies for each channel. Channel

information can be entered by clicking on the appropriate box and entering the desired frequency.

The frequency chosen must be within the operating range of the radio and on a frequency for

which the synthesizer is capable of channeling i.e. for VHF, divisible by 2.5 kHz and for UHF,

divisible by 5 or 6.25 kHz. When the RNET compatibility mode is chosen via the settings menu,

only channel one and two are available for programming.

6.5.2 SETTINGS

The Settings page allows for programming various parameters of the radio. These are detailed

below:

Microphone Mute-Allows the signal path from the MIC IN (microphone input) to be muted. If the

microphone input is not to be used, the “mute” function should be selected. Factory default is for

the microphone to be muted.

TX Pre-emphasis-Allows for the signal path from AUX IN to be either pre-emphasized or flat.

Most applications where the AUX IN input is used work best with a flat response. Factory default

is flat response.

RX De-emphasis-Allows for the signal path from the discriminator to the AUX OUT to be either

de-emphasized or flat. Most applications where the AUX OUT output is used work best with a

flat response. Factory default is for flat response.

Busy Channel Lockout-Prevents the transmitter from activating when the carrier detect output is

true. Used to prevent interference on a channel where activity already exists. Not normally

enabled in half duplex operation since the transmit and receive channels are not on the same

frequency. Factory default is for this function to be off.

Squelch Enable-Allows the receive audio paths to be muted when the carrier detect output is false.

Used to prevent the output of noise from the audio outputs when no signal is present. Due to the

finite squelch attack time, some high-speed modems work best with unsquelched audio. The

factory default is for this function to be set for never mute.

DCD Output Logic Level-Allows the setting of the polarity of the DCD (Data Carrier Detect)

output. Active high means that the true state is a logic high while active low means that the true

state is logic low. Normal setting is active high. The factory default is active high.

Carrier Mode-Allows the programmer to set the radio to match the type of carrier detection used

by the RF board. The carrier detect mode may be either RSSI (Receive Signal Strength Indicator),

based upon carrier level or Noise, which is based upon the receive signal to noise level. RSSI

based is significantly faster than noise based systems and is usually preferred for data applications

where fast turn-around times are important. This selection must match that of the radio

hardware. It is preset at the factory to match the RF board and must not be changed unless

the RF board is modified. See the Hardware Options section under Maintenance in this manual

for details. The factory default is RSSI mode.

Audio PA TX Sidetone-When enabled, the Audio PA is turned on during transmit and has at its

output the signal to be transmitted as a sidetone. The factory default is for this function to be off.

RX Discriminator Coupling-Selects whether the coupling from the discriminator output on the RF

board is AC or DC coupled to the control/loader board. Since the audio outputs of the

control/loader board are AC coupled, this function is normally set for AC as well. For response to

DC, a hardware jumper options can be made for DC coupling at the AUX OUT. (See the

Hardware Options section under Maintenance for details on this option.) If this is done, this

function should be set for DC. The factory default is AC.

CSN Input-Selects whether RNET Compatibility mode is to be used. See section 5.5 for an

explanation of this function. Normal operation is to set this for high/low Power. The factory

default is high/low power mode.

PTT/RTS Input Logic Level-Sets the polarity of the PTT/RTS input. Normally set for active low

i.e. transmitter is activated when this input is at the logic low state. Due to the internal pull-up

resistor, setting this to active high will cause activation of the transmitter when the PTT/RTS

input is left unconnected. The factory default is active low.

CTS Output Logic Level-Sets the polarity of the CTS (Clear-To-Send) output. Setting for active

high caused the true logic state to be high. Active high is the normal setting. The factory default

is active high.

TX Timeout Timer-Allows for limits on the maximum time the transmitter may be continuously

keyed. When set, the maximum limit is set in the box. To prevent overheating and possible

damage to the unit, this is normally set on with a time of 60 seconds of less. See section 5.3 for

limits on maximum key-down times. The factory default is 60 seconds.

6.5.3 ALIGNMENT

The alignment page is used for setting the values of the digital potentiometers which are used for

aligning the unit and setting the gains of the audio paths. The unit leaves the factory already

aligned, but the user may wish to change the values of some of the input and output gain settings.

Different systems or modems may require different input and output levels. The factory default

settings for the various menu items are listed below.

Aux In (TX) Gain-Set so that without pre-emphasis (flat), 100 mv rms will produce 60 % rated

deviation. If pre-emphasis has been set, 500 mv rms at 1 kHz will produce 60 % rated deviation.

Aux Out (RX) Gain-Set so that without de-emphasis (flat), a signal with 60 % rated deviation will

product 400 mv rms into an open circuit (half this value into 600 ohms). If de-emphasis has been

set, the output level will be about 100 mv rms at 1 kHz into an open circuit.

Carrier Detect On and Carrier Detect Off-For RSSI based systems, factory set for carrier on at

about –110 dBm and carrier detect off at about –115 dBm.

TX Frequency Trim and RX Frequency Trim-factory set to be on frequency.

Audio PA Gain-Set such that a signal at 60 % rated deviation at 1 kHz will product 400 mV rms

of output level.

Deviation and Balance-Set such that the maximum deviation will fall within the regulatory

requirements and that the transmit audio response has the correct characteristics. Deviation and

Balance do not need to be adjusted after a change in programmed frequency. New values are

calculated and loaded by the programmer when a frequency is entered in the frequency menu.

Instructions for using the alignment page can be found in section 13 of this manual.

6.5.4 RESTORE EEPROM

This selection is used to load a previously saved radio configuration file to the radio connected to

the programmer. This is of benefit when a number of radios are to set to the same frequencies and

with the same switch settings.

6.5.5 SUMMARY

The summary page summarizes the information shown on the other three pages and, in addition,

includes the model and serial number of the unit.

6.5.6 SAVING A CONFIGURATION

Upon exiting the programmer via the exit button, the user will be presented with a box which

allows the saving of the current configuration. This is useful if a number of other radios are to be

programmed with the same frequencies and settings. If one does not wish to save the current

configuration, the cancel icon should be selected.

II DTX-154/254/454 STAND-ALONE RF BOARD

7DTX RF BOARD DIMENSIONS

8RF BOARD J102 INPUT/OUTPUT

Pin Number Name Description

J102-0 PWR_SET When PC board jumper R185 is installed (R186 omitted), the

voltage on this pin controls the RF output power. When R186

is installed (R185 omitted), the RF output power is controlled

by R187 on the RF board and this pin has no function. When

this pin is used, the voltage should range between about 1 and

4.5 VDC to vary the output power from 1 to 5 watts. The

relationship between output power and voltage is non-linear

and may vary as a function of operating frequency. The input

resistance at this pin is approximately 15 k-ohm.

J101-1 GND System ground. All voltages are referenced to this point.

J101-2 FB+ Power supply input for the RF PA module. Voltage at this pin

is filtered. Current drain can be as high as 2.5 amperes at full

power.

J102-3 TX_EN Active high, 5 volt CMOS logic level input used to enable the

transmitter driver stage and PA pin diodes. Timing circuitry

exists on the RF board to ramp the PA power up or down to

control keying spurious outputs.

J102-4 RX_EN Active high, 5 volt CMOS logic level input used to enable the

receiver stages and to set the VCO to the receive frequency

range.

J102-5 XCVR_EN Active high, 5 volt logic level input used to enable all stages

of the board except the PA and PA driver stages. This pin can

be used to conserve current consumption in a battery save

configuration.

J102-6 MOD_IN Modulation input for the transmitter. The modulating signal

must be superimposed upon a very stable and low noise 2.5

VDC level. Modulation sensitivity is approximately 4.5

kHz/V for the VHF versions and approximately 14 kHz/V for

the UHF versions. The input resistance is approximately 17

k-ohm. Note: The DC voltage at this pin directly controls the

frequency of the unit. Therefore, the DC voltage must be well

regulated and controlled over environmental conditions.

J102-7 LOCK_DETECT Lock detect output of the frequency synthesizer. Output is at

5 volt logic level with a low level indicating lock.

J102-8 SYN_EN Enable line for loading the synthesizer. Signal is at 5 volt

CMOS logic levels.

J102-9 SYN_DATA Data line for loading the synthesizer. Signal is at 5 volt

CMOS logic levels.

J102-10 SYN_CK Clock line for loading the synthesizer. Signal is at 5 volt

CMOS logic levels.

J102-11 +7.2V +7.2 VDC +/- 10 % input for powering all stages of the radio

except the RF PA module. Current drain is approximately 45

mA in receive and 100 mA in transmit.

J102-12 RSSI Receive signal strength indicator output. This is a high

impedance analog output, which is used to determine the

presence of a carrier. When set for RSSI mode, the output

will vary between approximately 0.5 VDC and 3.0 VDC as the

input signal level varies between –130 dBm and –70 dBm.

When set for SINAD mode, the output will vary between

approximately 2.5 VDC at 0 dB SINAD to 0.5 VDC at 20 dB

SINAD. See the Hardware Options section for details on

changing the mode. The loading on this output must be kept

above 100 k-ohm.

J102-13 DISC_OUT DC coupled discriminator output. This output is low

impedance with a modulation sensitivity of approximately 0.5

V/kHz for narrow band units and 0.25 V/kHz for wide band

units. The DC level at this pin is typically between 2 and 4

volts. The polarity can be set via hardware jumpers. See the

Hardware Options section for details.

J102-14 VCO_MOD Depending upon the hardware options, a signal at this pin can

modulate the VCO. Otherwise, the VCO gets its signal from

an on-board potentiometer from the MOD IN input. This pin

is provided to allow the modulation balance to be controlled

through an external board rather than the RF board. If this pin

is to be used, the DC level should be approximately 5 VDC

and from a low noise source. The DC voltage at this pin does

not affect the transmit frequency. The modulation sensitivity

is approximately 20 kHz/V.

Note: An RF board purchased as a stand-alone board has components installed to support easy

interface to external circuitry. This includes, but is not limited to, potentiometers for

setting deviation and balance, and various zero ohm jumpers. If the zero ohm jumpers

are placed in the correct position, operation with the RITRON control/loader board is

possible. An RF board which is part of a DTX module cannot as easily be integrated in a

system as a stand-alone board since the parts not required when used with the RITRON

control/loader board are not installed.

9DTX SYNTHESIZER LOADING

The following information describes the DTX-154/254/454 synthesizer programming format.

This information can be used for designing programming software for the DTX-154/254/454 RF

board when the DTX-154/254/454 control/loader board is not used.

Note: The user must obtain FCC and/or Industry Canada Certification when the RITRON RF

board is not used with the RITRON control/loader board in the DTX-154/254/454 enclosure.

The DTX-154/254/454 RF board uses a PLL (Phase Locked Loop) frequency synthesizer which

compares the phase of the outputs of two digital frequency dividers. One divider divides the VCO

(Voltage Controlled Oscillator) frequency and the other divides the reference oscillator frequency.

If the two divided outputs differ in frequency and/or phase, an error signal is generated which,

after filtering, is used to control the frequency of the VCO. The net result is that the VCO

frequency is locked to a multiple of the reference frequency (the divided down reference oscillator

frequency). To set the desired frequency, the divider values must be determined. These values are

converted to binary and become part of four control words, which must be loaded into the

synthesizer IC for proper operation. The steps for determining the frequency control part of the

words is as follows:

1. The RF R register counter value is first determined. This integer is the reference oscillator

frequency (14.4 MHz in this product) divided by desired reference frequency. The reference

frequency is 16 times the desired synthesizer step size. Typical step sizes are 2.5 kHz for VHF

and either 5 kHz or 6.25 kHz for UHF. For a 6.25 kHz step size and a 14.4 MHz reference

oscillator, the R register counter value would be 144 decimal. When converted to binary, this

value is substituted for the R in the State column in the RF_R_Register table. Note: The values

for the loop filter are based upon a 2.5 kHz step size for VHF and either a 5 kHz or 6.25 kHz step

size for UHF.

2. The RF N register counter values are then determined. This is accomplished by taking the desired

VCO frequency and dividing it by the desired synthesizer step size value used above. The

resulting integer is converted to binary. The least significant 4 bits become the value for the

FRAC_CNTR. For frequencies below 500 MHz, bit 21 (PRESC_SEL) must be set to 0 with the

next 3 significant bits of the integer used to fill in the 3 least significant bits of RF_NA_CNTR

(bits 6,7,and 8). The two most significant bits of RF_NA_CNTR (bits 9 and 10) are loaded with

0. The remaining bits of the integer are loaded into RF_NB_CNTR (bits 11 through 20). For

frequencies above 500 MHz, bit 21 (PRESC_SEL) must be set to 1 and the 4 bits following the 3

loaded into FRAC_CNTR are used for RF_NA_CNTR with the most significant bit of

RF_NA_CNTR (bit 10) set to 0. The remaining bits of the integer are loaded into RF_NB_CNTR.

3. In transmit, the VCO frequency is equal to the operating frequency. In receive, the VHF and 220

MHz units have a VCO frequency which is 43.650 MHz above the receive frequency. The VCO

in the UHF units operate 43.650 MHz below the desired receive frequency. When calculating

receive values, ensure that 43.650 MHz is either added or subtracted (depending upon whether the

unit is VHF or UHF) from the desired frequency before beginning the above calculations.

4. Example:

For a frequency of 461.750 MHz in transmit with a 6.25 kHz step size, the RF_R value is 144

decimal (14.4/0.1) or 0000 0000 1001 0000 binary. The RF_R register would therefore become

1000 0110 0000 0010 0100 0010 (MSB first). The VCO frequency divided by the step size is

73,880 decimal (461.750/0.00625) or 0001 0010 0000 1001 1000 binary. The RF_N register

would therefore become 0001 0010 0000 1000 0110 0011 binary. For 461.750 MHz receive, the

VCO frequency would be 418.100 MHz (461.750 – 43.650), which yields a divider of 66,896

decimal or 0001 0000 0101 0101 0000 binary. The RF_N register would become 0001 0000 0101

0001 0100 0011 binary.

The four registers of the synthesizer, their bit definitions, and required states are shown below:

IF-R Register

Bit Name State Comments

23 OSC 0External reference oscillator

22 FRAC 16 1Fraction = 16

21 FoLD 0RF digital lock detect

20 FoLD 1RF digital lock detect

19 FoLD 0RF digital lock detect

18 CP_GAIN_8 XDon’t care (1=IF charge pump current=8X)

17 IF_PD_POL XDon’t care (1=positive polarity on IF charge pump)

16 IF_R_CNTR XDon’t care (IF reference divider MSB)

15 IF_R_CNTR XDon’t care

14 IF_R_CNTR XDon’t care

13 IF_R_CNTR XDon’t care

12 IF_R_CNTR XDon’t care

11 IF_R_CNTR XDon’t care

10 IF_R_CNTR XDon’t care

9IF_R_CNTR XDon’t care

8IF_R_CNTR XDon’t care

7IF_R_CNTR XDon’t care

6IF_R_CNTR XDon’t care

5IF_R_CNTR XDon’t care

4IF_R_CNTR XDon’t care

3IF_R_CNTR XDon’t care

2IF_R_CNTR XDon’t care (IF reference divider LSB)

1 0 Identifies register

0 0 Identifies register

Notes:

1. The IF part of the dual synthesizer is not used. Only those bits which affect the RF part

of the synthesizer have importance.

IF_N Register

Bit Name State Comments

23 IF_CNT_RS 0Normal operation

22 PWDN_IF 1IF powered down

21 PWDN_MODE 0Asynchronous power down

20 Fastlock 1Fastlock enabled

19 Test 0Test bit-should be set to 0

18 OUT_1 XDon’t care in fastlock mode

17 OUT-0 XDon’t care in fastlock mode

16 IF_NB_CNTR XDon’t care (IF N register B counter MSB)

15 IF_NB_CNTR XDon’t care

14 IF_NB_CNTR XDon’t care

13 IF_NB_CNTR XDon’t care

12 IF_NB_CNTR XDon’t care

11 IF_NB_CNTR XDon’t care

10 IF_NB_CNTR XDon’t care

9IF_NB_CNTR XDon’t care

8IF_NB_CNTR XDon’t care

7IF_NB_CNTR XDon’t care

6IF_NB_CNTR XDon’t care

5IF_NB_CNTR XDon’t care (IF N register B counter LSB)

4IF_NA_CNTR XDon’t care (IF N register A counter MSB)

3IF_NA_CNTR XDon’t care

2IF_NA_CNTR XDon’t care (IF N register A counter LSB)

1 0 Identifies register

0 1 Identifies register

Note:

1. The IF part of the dual synthesizer is not used. Only those bits which affect the RF

portion of the synthesizer and the bits to shut down the IF portion are used.

RF_R Register

Bit Name State Comments

23 DLL_MODE 1Delay line loop calibration enabled

22 V2_EN 0Charge pump voltage doubler not enabled

21 CP_8X 0Charge pump current MSB

20 CP_4X 0Charge pump current MSB-1

19 CP_2X 0Charge pump current LSB+1

18 CP_1X 1Charge pump current LSB

17 PF_PD_PO 1Charge pump polarity is positive

16 RF_R_CNTR RRF R register counter MSB

15 RF_R_CNTR RRF R register counter

14 RF_R_CNTR RRF R register counter

13 RF_R_CNTR RRF R register counter

12 RF_R_CNTR RRF R register counter

11 RF_R_CNTR RRF R register counter

10 RF_R_CNTR RRF R register counter

9RF_R_CNTR RRF R register counter

8RF_R_CNTR RRF R register counter

7RF_R_CNTR RRF R register counter

6RF_R_CNTR RRF R register counter

5RF_R_CNTR RRF R register counter

4RF_R_CNTR RRF R register counter

3RF_R_CNTR RRF R register counter

2RF_R_CNTR RRF R register counter LSB

1 1 Identifies register

0 0 Identifies register

Notes:

1. CP_1X through CP_8X bits determine the magnitude of the charge pump current. The

values range from 100 uA for 000b to 1.6 mA for 111b in 100 uA steps. The values

shown are for 200 uA. This is consistent with the values of the loop filter used on the RF

board. For fast loading algorithms, this current may have to be changed dynamically.

2. The RF_R_CNTR bits are determined by the desired reference frequency which is

determined by the synthesizer step size. For the loop filter values as supplied, the step

size should be 2.5 kHz for VHF units and either 5 kHz or 6.25 kHz for UHF units.

RF_N Register

Bit Name State Comments

23 RF_CNT_RST 0Normal operation

22 PWDN_RF 0Powered up

21 PRESC_SEL 0Prescaler modulus set for 8/9 for 250-500 MHz

operation

20 RF_NB_CNTR BRF N register B counter MSB

19 RF_NB_CNTR BRF N register B counter

18 RF_NB_CNTR BRF N register B counter

17 RF_NB_CNTR BRF N register B counter

16 RF_NB_CNTR BRF N register B counter

15 RF_NB_CNTR BRF N register B counter

14 RF_NB_CNTR BRF N register B counter

13 RF_NB_CNTR BRF N register B counter

12 RF_NB_CNTR BRF N register B counter

11 RF_NB_CNTR BRF N register B counter LSB

10 RF_NA_CNTR ARF N register A counter MSB

9RF_NA_CNTR ARF N register A counter

8RF_NA_CNTR ARF N register A counter

7RF_NA_CNTR ARF N register A counter

6RF_NA_CNTR ARF N register A counter LSB

5FRAC_CNTR FRF fraction counter MSB

4FRAC_CNTR FRF fraction counter

3FRAC_CNTR FRF fraction counter

2FRAC_CNTR FRF fraction counter LSB

1 1 Identifies register

0 1 Identifies register

Note:

1. The bits for the RF_NB_CNTR, RF_NA_CNTR, and FRAC_CNTR are determined by

operating frequency and reference frequency.

2. To conserve power, the synthesizer can be powered down with the PWDN_RF bit.

The four registers are loaded using pins 8, 9, and 10 of J102. Pin 8, SYN_EN, is the synthesizer

enable line. Pin 9, SYN_DATA, is the data line and pin 10, and SYN_CK, is the clock line. Data

is clocked into the synthesizer most significant bit first and must be valid and stable on the rising

edge of the clock. The clock must be high a minimum of 10 ns and must be low a minimum of 50

ns before the next pulse. During loading, the synthesizer enable line must be held low. At the

conclusion of loading a register, the enable line must be taken high for a minimum of 50 ns. The

user should wait a minimum of 5 ms after board power up before loading the synthesizer. This

gives the power supply regulators time to reach stable voltages. More complete information

regarding the synthesizer IC may be obtained by referring to the National LMX2352 data sheet.

III MAINTENANCE

10 IMPORTANT MAINTENANCE INFORMATION

Surface Mount Repair: RITRON surface mount products require special equipment and

servicing techniques. Improper servicing techniques can cause permanent damage to the printed

circuit board and/or components, which is not covered by RITRON’s warranty. If you are not

completely familiar with surface mount component repair techniques, RITRON recommends that

you defer maintenance to qualified service personnel.

Precautions For Handling CMOS Devices: The DTX transceiver module contains

complementary metal-oxide semiconductor (CMOS) devices, which require special handling

techniques. CMOS circuits are susceptible to damage by electrostatic or high voltage charges.

Damage can be latent, with no failure appearing until weeks or months later. For this reason, take

special precautions any time you disassemble the module. Follow the precautions below, which

are even more critical in low humidity environments.

1) Storage/transport-CMOS devices that will be stored or transported must be placed in

conductive material so that all exposed leads are shorted together. CMOS devices must not

be inserted into conventional plastic “snow” or plastic trays of the type that are being used for

other semiconductors. Conductive containers are typically gray or pink in color.

2) Grounding-All CMOS devices must be placed on a grounded bench surface. The technician

that will work on the radio/CMOS circuit must be grounded before handling the radio.

Normally, the technician wears a conductive wrist strap in series with a 100 kΩ resistor to

ground.

3) Clothing-Do not wear nylon clothing while handling CMOS circuits.

4) Power Off-Remove power before connecting, removing, or soldering on a PC board that

contains CMOS devices.

5) Power/Voltage Transients-Do not insert or remove CMOS devices with power applied.

Check all power supplies to be used for testing CMOS devices, making sure that no voltage

transients are present.

6) Soldering-Use a soldering iron with a grounded tip for soldering CMOS circuitry.

7) Lead-Straightening Tools-When straightening CMOS leads, provide ground straps for the tool

used.

VCO Shield: The VCO shield is virtually impossible to remove without damaging either the PC

board or nearby components. The parts within the shield are low failure items; repair or

replacement should not be required unless the RF board is mishandled. If failure of a part within

the shield is deemed to have occurred, the RF board should be returned to RITRON for service or

replacement.

Unit Disassembly and Re-assembly:

1) Case Removal

a) Remove the two nuts at the rear of the unit. These nuts secure the rear bracket to the

case.

b) Remove the three side screws (one on one side, two on the other). These screws secure

the front bracket to the case. Removal of these screws requires a TORX T-9 driver.

c) Slide the case off the two-board assembly.

2) Board Separation

Remove the two screws that secure the control/loader board to the rear bracket. The rear

bracket stays connected to the RF board. Remove the two screws that secure the RF board to

the front bracket. The front bracket stays connected to the control/loader board. These four

screws are removed with a TORX T-9 driver. The two boards are held together by their

interconnecting header/socket. Gently pry the two boards apart at the header/socket. The RF

board is then rotated and tilted so to allow the right angle BNC connector to pass through the

hole in the front bracket.

3) Re-assembly is the reverse of assembly with the rear nuts installed before the side screws.

DO NOT OVER_TORQUE THE REAR NUTS-DAMAGE TO THE INTENAL PA DEVICE

MAY RESULT.

11 THEORY OF OPERATION

11.1 DTX-154 and DTX-254 RF BOARD

11.1.1 RECEIVER

RF amplifier and Bandpass Filters

The incoming RF signal from the input connector J101 passes backwards through the transmitter

lowpass filter and the electronic T/R switch to a three pole bandpass filter formed around L102,

L103, and L104. This filter is of Cohn type with 1.5 dB insertion loss and a bandwidth of 30

MHz. This filter is followed by a low noise amplifier stage formed around Q101. This amplifier

has a gain of about 17 dB with a noise figure of 2 dB and serves to amplify the incoming RF

signal above the noise of the following stages. Following this stage is a three pole Cohn filter

formed around L107 through L109. The characteristics of this filter are identical to that of the

first. The two filter sections are narrow enough to filter out the spurious responses of the first

mixer while wide enough to support a performance bandwidth of 26 to 28 MHz.

1st Mixer, 1st IF filters, and 1st IF Amplifier

IC101 is an active double balanced mixer which converts the incoming RF signal to the first

intermediate frequency (IF) of 43.65 MHz. This mixer has a gain of 0 dB and a noise figure of 10

dB. Its differential output is matched to the first IF filter, YF101, by L111, L112, C130, and

C140. An IF amplifier based around Q102 is used to provide gain. Its output drives another IF

filter section, YF102, which is identical to YF101. These two filters serve the double function

filtering out the spurious responses of the second mixer and, with the second IF filter, of removing

signals at the adjacent and further removed channels.

2nd IF IC

The output of YF102 drives the mixer internal to IC102. IC102 is an integrated FM IF IC which

contains a mixer, high gain limiting IF amplifier, FM discriminator (detector), and other support

circuitry. The mixer in IC102 converts the RF signal at the first IF to the second IF of 450 kHz.

The output of the mixer exits the IC and is filtered by the second IF filter, YF103. The output of

the filter re-enters the IC and drives the high gain limiting amplifier. Because the discriminator

inside IC102 is sensitive to both amplitude and frequency modulation components, a limiter must

precede it to remove any amplitude modulation. In addition, the noise based carrier detection

system available with this product requires that the RF signal at the discriminator stay constant in

amplitude as the RF input signal level varies. The output of the limiter amplifier drives the

discriminator. The resonator for the discriminator is YF104.

Receiver Audio and Carrier Detection

The recovered audio from pin 9 of IC102 is filtered and DC shifted by IC103A and associated

components. IC103B is a simple inverter and is used to provide inverted audio for those

applications which may require it.

Two methods of carrier detection are available on this radio. One is based upon the absolute RF

signal level at IC102’s input and the other is based upon the magnitude of the ultrasonic noise on

the recovered audio. IC102 has circuitry which develops a DC current which is proportional to the

input RF signal level. Passing this current through a resistor (R123) creates a voltage which varies

from about 0.5 volts at no signal input to about 3 volts with –70 dBm at the antenna connector. In

addition, a voltage can be developed which is proportional to the amount of noise present on the

recovered audio signal. This is effected by filtering the recovered audio such that only frequencies

above the normal modulation range remain. This prevents modulation components from being

detected as noise. The filter is formed around an op-amp internal to IC102 between pins 10 and

11 and the components connected to these two pins. The filtered output at pin 11 is rectified by

Q103B and then filtered. The output varies from about 3 volts for a 0 dB SINAD signal to about

0.5 volts for a 20 dB SINAD signal.

2nd Local Oscillator

The two mixers in this radio act to produce an output signal whose frequency is equal to the

difference between the frequency present at the RF input port and the frequency at the local

oscillator port. To convert signals at the first IF frequency of 43.65 MHz to that of the second IF

at a frequency of 450 kHz, a local oscillator signal at a frequency of 43.2 MHz (43.65 – 0.45) is

used. This signal is created by tripling the output of the radio’s 14.4 MHz master reference

oscillator, Y101. Transistor Q111 acts as a frequency tripler. Its associated components are used

to bias the transistor at an harmonic rich bias point and to filter the output such that only the third

harmonic remains for use as the 2nd local oscillator.

11.1.2 VCO AND SYNTHESIZER

The synthesizer is responsible for generating the carrier in transmit and the first local oscillator in

receive. A voltage-controlled oscillator (VCO) is an oscillator whose frequency can be controlled

by an external signal. The synthesizer, almost wholly contained within IC109, divides the VCO

frequency by digital dividers and compares the result with an accurate reference. An error signal,

proportional to the frequency error is created which is routed to the frequency control input of the

VCO. This action locks the VCO to a frequency which is equal to the reference frequency

multiplied by the divider number. To set the VCO frequency, different divider numbers can be

programmed into the synthesizer. In most synthesizer designs, the divider must be an integer,

which forces the reference frequency to be equal to the synthesizer step size. The synthesizer IC

used in this radio, however, allows the use of non-integer values for the divider which in turn

allows the reference frequency to be much higher than normal. This creates a synthesizer whose

output has lower noise, lower spurious levels, and higher switching speeds. The reference

frequency is derived by digitally dividing the frequency of the 14.4 MHz master oscillator. When

locked, the VCO attains the same relative frequency stability as that of the master oscillator.

The VCO itself is a voltage follower Hartley oscillator formed around Q107. One of the elements

in the resonant circuit is a varactor diode, CR105, whose capacitance, when reverse biased, varies

as a function of the applied voltage. Since the oscillator frequency is controlled by the resonant

circuit, varying the voltage on the varactor diode effects a change in frequency. To serve as a

local oscillator for the first mixer, the VCO operates at a frequency 43.65 MHz above that of the

desired receive frequency. In receive, the VCO’s oscillating frequency range is shifted upward by

about 44 MHz by switching C191, C192, and L122 into the resonant circuit. The VCO has a

tuning range of about 40 MHz when its tuning voltage is varied between 1 and 5 volts. To

frequency modulate the VCO for transmit, another varactor diode, CR106, is lightly coupled into

the resonant circuit.

The output of the VCO is amplified to a level of about 0 dBm by Q106. Q110 with R171 and

C196 act as a very low noise power supply filter for the VCO.

11.1.3 TRANSMITTER

PA Driver Stages

The output of the VCO buffer drives Q105 through R152. The signal level at this point is about

–10 dBm. Q105 amplifies this signal to about +5 dBm. Q104 further amplifies the signal to +13

dBm, the level required by the PA module. The supply voltage to these two stages is switched on

in transmit by Q113.

PA Module, Lowpass Filter, and T/R Switch

When driven by +13 dBm, the PA module is capable of producing 6 watts or more of power at the

antenna connector. Pin 2 of the module is used for power control. The output power level can be

varied from less than 0.5 watts to full power by changing the voltage at this pin.

To reduce carrier frequency harmonics of the PA module output to acceptable levels, a lowpass

filter is inserted between the module and the antenna connector. This filter is of elliptic design and

formed around L115 and L116 and C169 through C173.

To isolate the PA module from the receiver, an electronic T/R switch is used. The switch is

formed around PIN diodes CR103 and CR104 which are turned on in transmit and are off in

receive. CR104 switches the PA module into and out of the circuit while CR103 protects and

isolates the receiver input when the radio is in transmit.

11.1.4 MISCELLANEOUS FUNCTIONS

Two on-board regulators are used to provide the 5 volts DC used by most of the circuitry in the

radio. IC107 is a low noise, low dropout regulator which provides 5 volts to all the portions of the

radio which do not get switched on or off as the radio changes from transmit to receive. This

regulator is enabled by the XCVR-EN (J102, pin 5) input. When this regulator is not enabled, the

radio is essentially powered down. IC108 is an identical regulator which supplies power to those

circuits which are to be powered-up only in receive. The regulator is enabled through IC106E and

IC106F by the RX-EN (J102, pin 4) input.

The transmitter PA module driver stages and the T/R switch are powered by +7.2 volts through

Q113. Q113 is enabled by the TX-EN (J102, pin3) input through delay and sequencing circuitry

formed around IC106 and Q112 and Q114. The sequencing circuitry delays PA turn-on until the

driver stages and T/R switches are on and delays driver stage and T/R switch shutdown until the

PA module has ramped down in power. This prevents “keyclicks” from abrupt transmitter turn-on

and turn-off.

11.2 DTX-454 RF BOARD

11.2.1 RECEIVER

RF Amplifier and Bandpass Filters

The incoming RF signal from the input connector J101 passes backwards through the transmitter

lowpass filter and the electronic T/R switch to a two pole bandpass filter formed around L101 and

L102. This filter is of Cohn type with 1.5 dB insertion loss and a bandwidth of 25 MHz. This

filter is followed by a low noise amplifier stage formed around Q101. This amplifier has a gain of

about 17 dB with a noise figure of 2 dB and serves to amplify the incoming RF signal above the

noise of the following stages. Following this stage is a four pole Cohn filter formed around L103

through L106. This filter has an insertion loss of 4 dB and a bandwidth of 25 MHz. The two filter

sections are narrow enough to filter out the spurious responses of the first mixer while wide

enough to support a performance bandwidth of 20 MHz.

1st mixer, 1st IF Filters, and 1st IF Amplifier

IC101 is an active double balanced mixer which converts the incoming RF signal to the first

intermediate frequency (IF) of 43.65 MHz. This mixer has a gain of 0 dB and a noise figure of 10

dB. Its differential output is matched to the first IF filter, YF101, by L107, L108, C128, and

C137. An IF amplifier based around Q102 is used to provide gain. Its output drives another IF