Midland SD-250, User Manual, Page: 8 / 20

Rev. 0B
7
Pin Outs
1
5
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.
TTL level
0V = Tx
o/c = Rx
I/P
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