Noland Engineering DX28 User manual
MODEL DX28
Dual NMEA 0183 Expander
User Manual
The DX28 Expander is a 2-channel signal splitter/amplifier for NMEA 0183 data signals. It can be
configured as one 1-in x 8-out expander , two 1-in x 4-out expanders, or an auto-switching expander. The two
inputs are completely independent and can operate at the same or different baud rates up to 38,400. The
selectable auto-switching feature enables automatic switchover to the AUXILIARY input when signal is lost
from the PRIMARY input. A bicolor (green/red) status LED on each input shows data activity and a third LED
(yellow) provides “overcurrent” fault indication. Each input drives four independent RS-422 outputs. The
inputs use differential detectors, which are isolated from Power and Ground. The outputs are independent so that
shorting one output does not affect the others.
The DX28 consists of two 4-way expanders. For a single 8-way expander, the 2 inputs are cross connected.
To enable Auto-switching, connect the Auto terminal to GND so that all 8 outputs will pass the PRIMARY
input and ignore the AUXILIARY input. A loss of PRIMARY data for 3 seconds automatically switches to
the AUXILIARY input. When the PRIMARY signal returns, the DX28 immediately switches back to it.
The LED on each input flashes when data is received on that input, green for PRIMARY and red for
AUXILIARY. In Auto-switching mode, both input LED’s flash the same color at the same time, indicating
PRIMARY (green) or AUXILIARY (red) as active.
A third LED (yellow) is used for overcurrent indication. This LED turns on if the DX28 draws excess
current. This can occur if an output terminal is misconnected. It may also indicate an internal fault of
the DX28.
Connect the PWR, GND, and IN first. The IN+/IN- terminals connect to NMEA 0183 talkers (GPS, AIS,
etc.). For those talkers that only have one “Data Out” wire, connect it to IN- and connect IN- to GND. If
either IN- is not properly connected, unusual behavior may be observed such as faintly flashing LED(s). Verify
proper operation of the status LED’s with NMEA data present.
If Auto-switching mode is desired, ground the Auto terminal. Note that both input LED’s will be green with
PRIMARY data present or red if PRIMARY data is off for more than 3 sec. and AUXILIARY data is
present.
The RS-422 outputs have voltage on both (+) and (-) lines. The OUT- lines should not be grounded as it
causes driver circuit(s) to current limit. The figure shows two different ways the RS422 outputs connect to
listeners. Only the OUT+ terminal is used for single-ended (one-wire) listeners while both OUT+ and OUT–
terminals are used for differential (isolated) listeners
If the DX28 yellow LED comes on or flashes, it is probably because one of the RS-422 OUT- connections
is grounded at the Listener. To find the error, disconnect each OUT- terminal one at a time until the yellow LED
goes out. When the problem OUT– connection is found, leave it disconnected from that listener. If the yellow
LED flashes or stays on with all outputs disconnected, an internal fault has occurred. In some cases the unit
may still operate properly, but it may also need repair or replacement
SPECIFICATIONS
Input impedance 2K ohms
Input sensitivity 2V differential
Input baud rate 38,400 max.
Output level (RS-422) 3.5v = 500 ohms
Supply voltage 10 – 30 Vdc
No-load current < 20 ma.
Full-load current 100 ma.
Overcurrent indication > 100 ma.
Operating Temp (degC) 0 – 50
Humidity range 0 – 100% (non-condensing)
Size, weight 2.5” x 3.5” x 1.0”, 3 oz.
NoLand Engineering Inc
728 E Lincoln Ave
Suite 3
Melbourne, FL 32901
Tel: (321) 951 –7329 Fax: (321) 951-8773
http://www.nolandeng.com
email: info@ nolandeng.com
