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