M
IDIAN
E
LECTRONICS
I
NCORPORATED
P
AGE
4
TDM-1 v 1.0
5-12-00
I
NSTALLATION
I
NSTRUCTIONS
Installation Note:
Midian products utilize CMOS integrated circuits, which are susceptible to damage from high
static charges. Be sure to follow standard antistatic procedures when handling, including using grounded workstations
and soldering irons and wearing grounding bracelets.
Wire
Function
Instructions
RJ-11 Connector (radio)
Black
Ground
Connect to ground point in the radio. Can usually be connected to the mic jack.
Red
5.5 - 16 VDC
Connect to switched B+ in radio. Can usually be connected to the mic jack.
White
COR/COS (Carrier
Detect) In or
CTCSS Detect
Connect to point in Squelch or CTCSS circuit that changes logic level between 0 and 5 volts DC
when carrier is received. This is usually not available on the mic jack. A jumper can be connected
from the COR circuit to a spare pin on the mic jack. The COR wire is not mandatory. It prevents the
TDM-1 from producing garbage data on voice or squelch noise. The COR wire could be programm ed
for positive polarity and then shorted to the PTT wire. When the unit is transmitting the COR will
see a busy and no data will be decoded. In full duplex operation the COR wire can be omitted. The
TDM-1 ships with the carrier detect input set for positive polarity (5V =carrier detected).
If
necessary, re-program the COR polarity via the menu system.
Yellow
RX Tone Data In
Connect to a receive audio point in receiver, preferably to a point with a fixed audio level (before the
volume control). Can usually be connected to the mic jack but be careful to set volume control and
mark it. It will also be necessary to set the RX level pot R6 for proper level (0.5 to 2.0 Vpp at
pin 4 of IC-2). If using the radio’s volume control this pot could be set to perhaps mid-range and
then the radio’s volume control set to the optimal level and marked or somehow prevented from
being moved.
Blue
TX Tone Data Out
Connect to modulator circuit – usually at the mic jack. Using TX level pot R7 set the modulation
on wide band to be about 3-3.5 kHz of modulation. On narrow band systems set the modulation
from 1.5 to 1.8 kHz. Sending a data file during this time will key the transmitter and generate tone
data modulation.
Green
PTT out
Connect to the radio’s PTT circuit. TDM-1 now has control of PTT and will key the radio whenever data is being
transmitted. Can usually be connected to the mic jack.
DB25 Connector P2 (DTE)
P2-7
Ground
Picks up computer or DTE ground.
P2-5
Clear to Send
Applies Clear to Send (CTS) to the computer or DTE.
P2-3
RX Data
Applies RX data to the computer or DTE.
P2-2
TX Data
Picks up transmit data from the computer or DTE.
NOTE:
Be sure to adjust the audio input and output level pots as described above. This will require opening the DB-
25 shell.
MODEM SETTINGS:
Any device connected to the RS-2332 port of this modem must be configured for
1200 baud, 8
data bits, 1 stop bit, and no parity
. Hardware flow control should be enabled if available. The modem is configured
as an RS-232 DCE device and therefore must be connected to a DTE device. See description of DTE at the end of
this manual for more information.
OPTIONAL SQUELCH OUTPUT:
Pins 1 or 20 of IC-1 may be connected to customer supplied circuitry to squelch
the radio speaker while data is being received by the modem. Pin 20 goes high while data is being received, pin 1
goes low. Squelch outputs are activated as soon as a character is received by the modem. They are deactivated
when COR drops. Please note that voice or noise on the channel could be interpreted as data and cause the squelch
outputs to activate.
Warning:
These pins are unprotected microprocessor outputs. Customer supplied circuitry must
include current limiting and transistor buffering to protect the outputs. Failure to do say may damage the
microprocessor and void the warranty.
ERROR REDUCTION:
Using the COR/COS/CTCSS lead can help minimize falsing on voice or noise. The TDM -1 will
receive data at a 12 dB SINAD point with numerous errors. Quieting the radio to about 17 dB will give little or no
errors. Most manufacturers will set the squelch point of their radios to about 12 dB SINAD. We recommend tightening
the squelch adjustment to 17 dB SINAD so that the radio will not unsquelch on a weak, noisy signal. Most radios have
a 12 dB SINAD point for about .25
µ
V of sensitivity. At 17 dB SINAD the receiver will have about .3
µ
V of sensitivity.
This should give virtually error-free data. Fully quieting the radio at or above .5
µ
V of sensitivity is recommended.
