Codan NGT 2010 RF Technical & Service Manual page 655

General information
NOTE
A remote control NGT system operates in a similar manner to a standard NGT system.
The handset, junction box and RF unit used in a remote control NGT system are standard
NGT devices. A technical description of how an NGT system operates is provided on
page 69, NGT—Technical description
Data Modem 3012 is described in the documentation provided with the product.
The operation of a remote control NGT system is distinct from other NGT systems due to
the existence of two separate CIB segments at the control and transceiver sites. The NRI
and line modem at each site operate together to connect the two CIB segments. Audio
signals between the sites are transferred via the NRIs and line modems using digital
speech coding technology. The use of digital speech coding technology for low
bandwidth communication links such as long leased lines means that equipment such as
HF data modems must be located at the transceiver site where a less processed audio
signal is available. Remote control NGT data systems require remote control junction
boxes to connect a PC at the control site with the HF data modem at the transceiver site.
The following information describes how the specific devices in a remote control NGT
system work.
NGT remote interface
The function of the NRI is to provide the interface between the CIB device (that is, the
junction box or RF unit) and the line modem at each end of the leased line. The NRI
converts between CIB (CAN serial data and TDM analog audio) and RS232 serial data
for transfer via the line modem. For correct operation of the NRI, the RS232 link
requires a minimum line speed of 9600 bps in full duplex mode. The RS232 leased line
link introduces additional system delays for both audio and control signals. Any
additional delays introduced by other link types should be minimised and kept below
50 ms. Two NRI units, in addition to the basic NGT transceiver are necessary to provide
the simplest remote control transceiver installation. The NRIs connected at the
transceiver and control sites are identical.
The NRI is powered externally by a switchmode power supply at the control site, and via
the transceiver supply at the transceiver site. The NRI supplies power to the attached line
modem, and at the control site it typically supplies power to other CIB devices.
NGT Transceiver System Technical Service Manual
The information in this section should be read in conjunction with the
block diagram 03-01108.
(2010). The operation of the line modem and HF
NRI—Brief description
261