Midland SD-250 User manual

SD-250
User Guide

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Contents
Introduction --- 2
Preparing for use
Unpacking and inspection --- 3
Description of modem --- 4
Features --- 5
External Connections --- 6
Pin Outs --- 7
Operation
Channel Selection --- 9
Transmit/Receive Operation --- 10
Serial Commands --- 10
Status Indicators --- 12
Programming --- 13
Installation
Antennas --- 14
Power sources --- 14
Cabling --- 15
Fixing --- 15
Safety and general information --- 16
Warranty and repairs --- 18
Care of the equipment --- 18
Disposal / Recycling --- 18

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Introduction
The SD250 range is a 1 to 6 Watts RF data module at VHF and UHF frequencies.
The SD250 is housed in a rugged cast-aluminum box sealed to IEC 529 (IP54)
making it suitable for a wide range of mobile and fixed applications.
All SD250 RF data module 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 SD250 RF data module 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 SD250 is not designed for permanent transmission. If
prolonged transmission periods are used, the unit will become hot and will
require an additional heat-sink to be fitted.
• When fitting the module 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 SD250 is a standard 12V /
2A dc supply, but is capable of operating in the range 9V - 18V.

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Preparing for use
Unpacking and inspection
Unpack the modem and check that you have received the following items:
• SD250 RF data module
• User Guide (this document)
If any of these items are missing, please contact your supplier.

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Description of modem
The SD250 is a network free, point to point RF data module 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 SD250 can also be fitted with below a few different modems
• Bell 202 / V.23 modem (1200 baud rate)
• FFSK modem (4800 baud rate)
• GMSK modem (9600 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.
SD250 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.

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Features
• Compact and rugged die cast box
• Resistant to dirt, dust and water ingress (IP54 rated)
• Network free, point to point communication
• 1 / 6 watt programmable output power
• Synthesized operation with 16 channel capability
• SAT when used with Bell 202 / V.23 and FFSK modem or speech
• Programmable 12.5 / 25kHz channel spacing
• External modem / Direct FM
• Internal modem options available: Bell 202 / V.23, FFSK, GMSK
• ‘Busy’ output (can be set active high or low)
• 9 – 18 volt supply input
• Busy Channel lockout
• Time out timer

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External Connections
1. HD 9-way d-type (data, control signals and power supply)
2. BNC antenna connector

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Pin Outs
15
96
Busy Detect
Mic Input
Prog. Data Input
Speaker Output
Mod. Input (Data)
Demod. Output (Data)
PTT / Prog. Data Output
GND
B+
DB-9 PIN OUT table with input and output levels
D-Type
Pin No. Function Description Signal Type Input/ Output
Data modulation IN
(Tx Mod)
Default : AC coupled signal directly injected
to MOD through data low pass filter without
pre-emphasis.
Direct Modulation(includes POCSAG) : DC
coupled signal directly injected to MOD. No
data filter and pre-emphasis on signal path.
Direct FM MOD. is selected by PC program.
Link 409 fitted. Link 412 not fitted.
Default :Analog signal
1KHz audio at 60%
peak system deviation
input level =
100 to 120mVrms
Direct FM : TTL level
1
RS 232 data IN Input to Bell 202/V23, FFSK, GMSK modem.
Link 409 not fitted and link412 fitted. RS-232 level (option) +12V = Tx
-12V = Rx
I/P
Data unfiltered OUT
(RX disc) Discriminator audio from the SD-250. This is the unprocessed AF signal prior to tone
filtering and de-emphasis.
Link 413 fitted and link 414 not fitted.
Analog signal
1KHz audio at 60%
peak system deviation
produces
200 to 300mVrms
2
RS 232 data OUT Output from Bell 202/V23, FFSK, GMSK
modem.
Link 413 not fitted and link 414 fitted
RS-232 level (option)
+12V = Tx
-12V = Rx
O/P
3 PTT In (Tx Key)
/
Signal, which keys the transmitter, is an
active low input with an internal pull up
resistor. If required, the pin can be converted
to active high using link options.
TTLlevel
0V = Tx
o/c = Rx
I/P
/

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Program: Read Note: If the option modem board is installed,
a resistor link can select RS-232 signal
levels. See Modem manual
Program : READ used for outputting
programming data from mode
RS-232 level (option)
+12V = Tx
-12V = Rx
TTL level only for
radio program
O/P
4 Ground Ground connection to chassis of the radio. 0V (Chassis)
5 B+ Power supply input (Nominal 12V) 9.0V – 18.0V DC
6 Busy
(CD) 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 resistor link can select RS-232 signal
levels. See Modem manual.
TTLlevel
0V = carrier
5V = no carrier
RS-232 level (option)
+12V = carrier
-12V = no carrier
O/P
7 Microphone filtered
audio IN Audio signal that is filtered (high pass and pre-emphasis) then follows same route as
data mod through LPF. Sub-audio tone is
mixed with audio after the LPF.
Audio
1KHz audio at 60%
peak system deviation
input level =
6 to 8Vrms
I/P
8 Program: Write /
Serial command Used for inputting programming data and use of serial command. TTLlevel I/P
9 Speaker filtered
OUT Audio output from the audio amplifier. Filtered by tone-filter and de-emphasis
circuit.
1KHz audio at 60%
peak dev. produces
Nominal 1Vrms @ 8Ω
O/P

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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.
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1
16
234
5678
9101112
151413
CHANNEL NO.
SWITCH POSITION
Figure: Setting of channel selector switch for each channel

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Transmit/Receive Operation
The SD250 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 resistor link
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 RF data module 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: 9600 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

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Byte0
Start bit 1st 8-Bits (Command) Stop bit
Byte1
Start bit 2nd 8-Bits (Data) Stop bit
Byte2
Start bit 3rd 8-Bits (Check Sum) Stop bit
Available Command and Data format
Mode Command
(1st 8-Bits)
Data
( 2nd 8-Bits)
Check sum ( 3rd 8-Bits )
: Command + Data
1. Channel Change 0x64 0xXX :Current channel ( 0x64 + Channel )
2. RTX Mode Selection 0x61 R(0x72) : Rx mode
T(0x74) : TX mode
( 0x61+ 0x72 )
( 0x61+ 0x74 )
3. Modem test mode 0x75 0x78 : Enable test data
0x79 : Disable test data
( 0x75 + 0x78 )
( 0x75 + 0x79 )
GMSK 0x7a 0x00 : Disable
0x01 : Enable
( 0x7a + 0x00 )
( 0x7a + 0x01 )
0x7c 0x00 : Disable
0x01 : Enable Mark data
( 0x7c + 0x00 )
( 0x7c + 0x01 )
4.
Modem
alignment
mode
FFSK
&
AFSK 0x7e 0x00 : Disable
0x01 : Enable Space data
( 0x7e + 0x00 )
( 0x7e + 0x01 )
5. Radio Reset 0x86 0x01 ( 0x86 + 0x01 )
example) In order to change channel from 1 to 2,
0x64, 0x02, ( 0x64 + 0x2 ) should be applied to Radio in order.
Note) To clear memory buffer for serial command in Micro-controller, its 3 bytes
buffer should be filled up. On getting 3 consecutive bytes, MCU automatically
decides its correct action and then clear its memory immediately.

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Status indicators
The LED indicates the current status of the radio and if an external speaker is
connected to pin 9 of the DB-9, audible tones can be heard under certain fault
conditions.
The details are shown below:
STATUS DESCRIPTION LED COLOR AUDIBLETONE
POWER ON Gren-Orange-Red
Busy Channel Yellow
Correct Call Green
Transmit Red
NORMAL
Transmit Not Allowed
Normal Scan Mode Green LED flashes
Scan Delete One Red flash
SCANNING
ScanAll Delete Two Red flashes
Busy Channel lockout Two Green flashes Single Beep Tone
Time outTime One Green flash
Before 5S T-O-T One Green flash Single Beep Tone
EEPROM Error One Yellow flash
Unlock Four Yellow flashes
Communication error with Modem
MCU
Green LED flashes
WARNING
Transmit Hang on time - Single Beep Tone
Read Mode Red LED flashes
PROGRAM Write Mode Green LED flashes
Open Squelch Mode Three Green flashes
Close Squelch Mode Two Green flashes
Save Squelch Mode One Green flash
SQUELCH
PROGRAM MODE
Initial Data Load One Green flash

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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 / V.23, FFSK, GMSK is fitted, such as data
settings (flow control, block size etc) and timings.
The pc program also allows for squelch adjustments and calibration

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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

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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 SD250 is securely fixed to a surface, either directly, or
with a suitable bracket. The fixing hole center 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 SD250 is fixed by cable ties to any wiring
looms.

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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 minimize 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 centers 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.

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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.

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Warranty and repairs
The SD250 is a low maintenance device. Once installed it requires no ongoing
maintenance.
In the event that your SD250 RF data module needs repair, return your radio to
an authorized 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 SD250 RF data module 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 SD250 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 authorized recycling centre or contact your supplier.
FCC warnings:

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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.