User Guide
Contents
Introduction 2
Preparing for use 2
Unpacking and inspection 3
Description of modem 3
External Connections 3
Pin Outs 4
Channel Selection 5
Operation
Transmit/Receive Operation
Serial Commands
Status Indicators
Programming 5
Installation 5
Antennas 5
Power sources 6
Cabling 7
Fixing 7
Safety and general information 10
Warranty and repairs 12
Care of the equipment 12
Disposal / Recycling 12
Introduction
The SD225 range is a 1 to 5 Watt PMR data modem at VHF and UHF frequencies
The SD225 is housed in a rugged cast-aluminium box sealed to IEC 529 (IP54) making it suitable for a wide range of mobile and fixed applications.
All SD225 modem units meet the essential requirements of the relevant directives. In order to maintain this compliance the installation and safety information must be
adhered to at all times.
• The SD225 modem must only be installed where unintentional contact cannot be made. The surface of the device may be hot to touch under certain transmit
conditions. The SD225 is not designed for permanent transmission. If prolonged transmission periods are used, the unit will become hot and will require an
additional heatsink to be fitted.
• When fitting the modem into a fixed installation, care must be taken in the routing of all cabling such that the insulation cannot become damaged.
• The recommended supply sources for use with the SD225 are a standard 12V / 2A dc supply, but is capable of operating in the range 9V - 18V.
Preparing for use
Unpacking and inspection
Unpack the modem and check that you have received the following items:
• SD225 modem
• User Guide (this document)
If any of these items are missing, please contact your supplier.
Description of modem
The SD225 is a network free, point to point data radio that offers great flexibility in varied applications where wireless data or voice communication is needed.
It can be used as a transparent radio, with no internal modem fitted, to allow users to facilitate the use of their own modem and protocol. The correct signal levels need to
be used with the use of separate control lines, see the pin out table below.
The SD225 can also be fitted with a Bell 202/V23 modem (1200 baud rate). The internal modem allows communication with a pc using RS 232 for the data and control
lines. For further details, please refer to the modem manual.
SD225 has standard radio features available which are associated with a private radio. This includes CTCSS and DCS, software controlled squelch, time out timer
options and busy channel lockout as listed below (not all available with option modem fitted). There is a microphone input and speaker output to allow speech to be
transmitted and received.
Features
• Compact and rugged die cast box
• Resistant to dirt, dust and water ingress (IP54 rated)
• Network free, point to point communication
• 1/5 watt programmable output power
• Synthesised operation with 16 channel capability
• SAT when used with Bell 202/V23 modem or speech
• Programmable 12.5 / 25kHz channel spacing
• External modem / Direct FM
• Internal modem options available: Bell 202/V23
• ‘Busy’ output (can be set active high or low)
• 9 – 18 volt supply input
• Busy Channel lockout
• Time out timer
External Connections
1. HD 9-way d-type (data, control signals and power supply)
2. BNC antenna connector
PIN Outs
DB-9 PIN OUT table with input and output levels
Pin No. Function Description Signal Type I/O
1
link option
1
link option
2
link option
2
link option
3 PTT In
4 Ground Ground connection to chassis of the radio. 0V (Chassis)
5 +Ve Power connection: +12 Volts nominal
6 Busy
7
8 Program : WRITE/
9 SPEAKER OUT Audio output from the audio amplifier.
Data modulation
IN
(used with an ext.
modem)
RS 232 data IN Input to Bell 202/V23 modem
Data unfiltered
OUT
(RX disc)
RS 232 Data OUT Output from Bell 202/V23 modem
(Tx Key) /
Program: READ
(CD)
MIC IN /
Serial command
A/c coupled signal directly injected to MOD through
data low pass filter without pre-emphasis.
Link 409 fitted. Link 412 not fitted
Link 409 not fitted and link412 fitted
Discriminator audio from the D-200. Unprocessed AF
signal (prior to tone filtering and de-emphasis)
Link 413 fitted and link 414 not fitted.
Link 413 not fitted and link 414 fitted
Signal, which keys the transmitter. Is an active low
signal with an internal pull up resistor. If required can
be converted to active high using link options.
Note: If the option modem board is installed, a
jumper board can select RS-232 signal levels. See
Modem manual
Program : READ used for outputting programming
data from mode
Logic level output to indicate presence of a carrier.
(If required, link changes enable the busy line to be
active high)
Note: If the option modem board is installed, a
jumper board can select RS-232 signal levels. See
Modem manual
Audio signal that is filtered (high pass and preemph) then follows same route as data mod through
LPF. Sub-audio tone is mixed with audio after the
LPF.
Used for inputting programming data and use of
serial command
Filtered by tone-filter and de-emphasis circuit.
Analogue signal
1KHz audio at 60% peak
dev. input level =100 to
120mVrms
RS232 level I/P
Analogue signal
1KHz audio at 60% peak
dev. produces
200 to 300mVrms
RS 232 levels O/P
TTL level
0V = Tx
open cct = Rx
RS-232 level (option)
+12V = Tx
-12V = Rx
TTL level (RS 232
converter in cable
9v-18v extreme
TTL level
0V = carrier
5V = no carrier
RS-232 level (option)
+12V = carrier
-12V = no carrier
1KHz audio at 60% peak
system deviation
input level =
6 to 8Vrms
TTL level (RS232 converter
in cable)
1KHz audio at 60% peak
dev. produces nominal
1Vrms @ 8Ω
I/P
O/P
I/P
1/P
O/P
I/P
I/P
O/P
Operation
Channel Selection
Channels are selected by the use of internal switches and can be set as shown below. The top 4 screws will need to be removed to gain access to the switches, care
must be taken to avoid any damage which could invalidate the warranty. The channel can also be changed by a serial command inputted from the external control
system.
Figure: Setting of channel selector switch for each channel
Transmit/Receive Operation
The SD225 is put into transmit/receive either by using TTL levels, RS 232 levels or serial command, depending on the application and modem set up.
When the radio is used with no internal modem, TTL levels (pin 3 on DB9) can be used. The default condition is active low for transmit, and active high, or not
connected, for receive. It is possible to alter the polarity of this control signal by adding components, refer to the pin out table for details.
If an internal modem is fitted the levels used need to be RS232 and a jumper board needs to be incorporated in the correct position to allow correct operation, see
modem manual.
The TX serial command (see later for further details) can also put the radio into transmit, until the rx serial command is received (pin 8 of DB9).
Serial Commands
The modem can be controlled by using the serial command (pin 8) , sending commands to the radio such as PTT or change channel
The format for these commands (asynchronous) are:
• baud rate: 4800 bit/sec
• Data Bit: 8 bit, non parity
• Stop Bit: 1 bit
• MSB first transmission
Each serial command consists of 3 bytes. The first byte is the command, the second is data required by the command and the third is the check sum to validate
contents
Byte0
ST 1st Byte (command) SP
Byte1
ST 2nd Byte (data) SP
Byte2
ST 3rd Byte (check Sum) SP
Transmit command and data (To SD225)
Mode Transmit command (byte0) Transmit Data (byte1)
1. Channel Change 0 x 64 0x??*: required channel (0x64 + channel)
2.
RTX Mode Send
4 Modem test mode 0x75 0x78 : enable test data
*?? = number of required channel
0 x 61 R(0x72) : Rx mode
T(0x74) : Tx mode
0x79 : disable test data
Check sum (byte2)
Transmit command + data
(0x61+0x72)
(0x61+0x74)
(0x75 + 0x78)
(0x75 + 0x79)
Receive Command and data (response from SD225)
Mode
1 Process Complete commands 0xaa
If byte2 and the sum of byte0 and byte1 are the same, the SD225 will send ACK (acknowledge) and execute command. If this is not the case, then the SD225 sends
NACK (not acknowledge).
User would go into next step if receives ACK data. If user receives Nack data, user should send command again.
Example) To change from 1
st
received data are same, radio sends ACK and changes to 2
Transmit Command
(byte0)
0x55
Channel to 2nd Channel, the change command is: ( 0x64,0x02 , ( 0x64 + 0x2 )) to Radio. If Byte2 and sum of Byte0 and Byte1 among
Transmit data (byte1) Check sum (byte2):
Transmit command + data
ACK
NACK
nd
channel. If not, radio would send Nack data
Status indicators
The LED indicates the current status of the radio and if an external speaker is connected to pin 9 of the DB-15, audible tones can be heard under certain fault conditions.
The details are shown below:
STATUS DESCRIPTION LED COLOUR AUDIBLE TONE
NORMAL
WARNING
PROGRAM
SQUELCH
PROGRAM MODE
POWER ON Green-Orange-Red
Busy Channel Orange
Correct Call (with SAT) Green
Transmit Red
Transmit Not Allowed
Busy Channel lockout Two Green flashes Single Beep Tone
Time out Time One Green flash
Before 5S T-O-T One Green flash Single Beep Tone
EEPROM Error One Orange flash
Out of lock Four Yellow flashes
Communication error with Modem
MCU
Transmit Hang on time - Single Beep Tone
Read Mode Red LED flashes
Write Mode Green LED flashes
Initial data load Green-orange-red
Open Squelch Mode Three Green flashes
Close Squelch Mode Two Green flashes
Save Squelch Mode One Green flash
Green LED flash
Programming
The data modem is a pc programmable modem. The parameters available for programming include:
• Frequency, channel spacing and sub-audible tones on a per channel basis
• Standard radio settings such as power save mode, scan, tx lockout, tx timeout
• Squelch enable
• Modem options when the Bell 202/V23 is fitted, such as data settings (flow control, block size etc) and timings.
The pc program also allows for squelch adjustments and calibration
Installation
Antennas
It is important that any antennas are installed in a suitable location with an adequate ground plane. Ideally, multiple antennas should be separated by a minimum of a
wavelength (at the lowest frequency), whilst still retaining a good ground plane for each antenna. Therefore, for a 400MHz system, the ideal separation should be a
minimum of 0.75m, and for 150MHz system the minimum should be 2.5m.
Warning: If installing an antenna near people it is necessary to ensure the minimum separation is maintained. This particularly important where prolonged exposure is
likely.
Power sources
It is important that a “clean” source of power is used for the 12V supply to the modem
Cabling
If possible, run RF cables separately from other cables and keep RF cables apart from one another to avoid interference / coupling.
When fitting the modem into a fixed installation care must be taken in the routing of all cabling such that the insulation cannot become damaged.
Fixing
We recommend that the SD225 is securely fixed to a surface, either directly, or with a suitable bracket. The fixing hole centre dimensions are as shown.
The modem can be attached to any surface by using suitable size screws through the M3 holes in the mounting flanges.
Note: We do not recommend that the SD225 is fixed by cable ties to any wiring looms.
Safety and general information
Important information on safe and efficient use of your Radio device
Exposure to radio frequency energy
Your modem is a high power radio transceiver. When it is on, it receives and also sends out radio frequency (RF) signals. To help minimise human exposure to RF
electromagnetic energy, keep transmission time to 50% or less.
As with all radio devices, holding the antenna affects transmission quality and may cause the radio to operate at a higher power level than required. Do not hold the
antenna when the radio is in use.
Do not use radios with damaged or modified antenna, this may violate compliance with relevant international standards.
Where prolonged human exposure is likely, the minimum separation from the antenna should be 0.8m.
Electromagnetic interference/compatibility
Most modern electronic equipment is shielded from RF energy. However certain electronic equipment may not be shielded against RF signals. The modem needs to be
switched off in any facility where posted notices instruct you to do so to avoid electromagnetic interference or compatibility conflicts. Special care should be taken near
facilities such as hospitals or health care centres may be using equipment that is sensitive to external RF energy.
Medical devices (Pacemakers)
If you use any personal medical device, consult the manufacturer of your device to determine it is adequately shielded from RF energy. Your physician may be able to
assist you in obtaining this information.
Vehicles with airbags
Air bags inflate with great force. Do not place a radio in the area over an airbag or in the airbag deployment area, any radio may be propelled with great force and cause
serious injury to the occupant of the vehicle.
Potentially explosive atmospheres
Turn off your modem prior to entering any area with a potentially explosive atmosphere, unless it is a radio type especially qualified for use in such areas. Do not remove
install or charge batteries in such areas. Sparks in potentially explosive atmospheres can cause an explosion or fire resulting in bodily injury or death.
Potentially explosive atmospheres include fuelling areas such as petrol stations, below decks on boats, fuel or chemical transfer or storage facilities, vehicles using liquid
petroleum gas (such as propane or butane); areas where the air contains chemicals or particles such as grain, dust or metal powders, and any other area where you
would normally be advised to turn off your vehicle engine. Areas with potentially explosive atmospheres are often but not always posted.
Warranty and repairs
The SD225 is a low maintenance device. Once installed it requires no ongoing maintenance.
In the event that your SD225 modem needs repair, return your radio to an authorised Midland Radio supplier. Do not disassemble, modify or repair the unit unless the
work is carried out by a Midland Radio approved supplier. Incorrect assembly, modification or repair may cause irreparable damage to your unit and will invalidate any
warranty.
Care of the equipment
Do not immerse the SD225 modem in water or other fluids.
Do not use solvents or spirits for cleaning as this may cause
damage to the case materials.
Do not over tighten connection to the modem.
Disposal / Recycling
The SD225 is a Class 3 product in accordance with the Waste of Electrical and Electronic Equipment (WEEE) Directive. Disposal of this class of equipment must be
carried out through an authorised recycling centre or contact your supplier.
FCC warnings:
Published by Midland Radio Corp.
Any queries regarding information in this manual, please contact the Technical Services Group Leader at the above address.
Information provided in this document is believed correct at time of printing but is subject to change without notice.
Midland Radio will not accept liability for any loss, damage or costs howsoever caused as a result of the information provided.
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