Systems Ltd
Heading & Speed Data Interface
Type NT920HDI

The NT920HDI converts serial heading data received from different types of proprietary heading transmission sources (electronic compasses including GPS antenna types etc.) to the data type required by various end user brands of radars, trackplotters and heading repeaters etc. including some Navitron autopilot types. In addition, NT920HDI software version 4.0 onwards incorporates speed log pulse input facilities which are combined with heading to provide NMEA output data (VHW sentence) for use by ECDIS etc.

Input Signal types: -
: -

NMEA 0183
(0.2 - 25Hz) --»

(0.2 - 50Hz) --»

    Speed: -  --»
(200 or 400 pulses
per nautical mile)

Type NT920HDI

Click for larger image

Typically for use with electronic compass types
including GPS antenna models and / or
pulse output speed logs

Simultaneous Outputs: -
Heading: -
Navitron Autopilot data (
Not available from version NT920HDI / 2)
Navitron Serial data
Furuno (5Hz or 40Hz)
3, 6, 12, 24 Step/degree

Heading & Speed: -
NMEA 0183 (VHW)@1Hz & 3Hz with NMEA 0183 (HDT)@ 10Hz
NMEA 0183 (VHW)@ 1Hz & 3Hz with NMEA 0183 (HDM & HDG) @ 6Hz

The input signal applied to the NT920HDI can be of a single type (NMEA only or Furuno only) and will result in simultaneous output transmissions in the formats shown above.

Alternatively more than one heading input signal type can be simultaneously applied in which case the priority (preferred) input data to be accepted is installation selectable with backup (2nd choice) data immediately available in the event of principal data failure: -

Data Type
Data Type
NMEA 0183
NMEA 0183

If the priority input data fails, the NT920HDI will automatically select the 2nd source after a period of 5 seconds and will automatically revert to the preferred source as soon as data is restored.

When speed log input data is also available, this will automatically be combined with the heading output data to provide NMEA outputs in the VHW sentence format required by ECDIS etc.

The NMEA and Furuno outputs are not opto isolated and require that the associated receiver units are themselves equipped with opto isolated input stages to avoid common mode problems.

The Step by Step output is installation selectable at 3, 6, 12 or 24 steps/degree (as required) and is logic rated at 5V p.p / 2mA per step line and will in many cases require buffering with a Navitron Step Interface Box type NT925SIB.

The dedicated Navitron output ports provide autopilot heading reference information and custom serial data for use by Navitron Digital Heading Repeaters (type NT920DHR).

NT920HDI Application examples              Technical Specifications

Heading & Speed Data Interface Leaflet download (PDF)

Click for the NT920HDI PDF Manual

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