American Fibertek RR-94882SL - Manual (Page 10)

10
RS485 OFFSET BIAS
The RS485 specification requires receivers to detect input signals down to 200mVp-p of voltage
level. In many cases this can cause systems to be sensitive to noise on the data wires. In an
effort to eliminate the effects of low levels of noise, some manufacturers of equipment that
communicate using RS485 have introduced a small voltage bias to the data lines. This is
usually accomplished using a 470 Ohm resistance to +5V on the positive line and 470 Ohm
resistance to ground on the negative line. When used in conjunction with the appropriate
termination resistors referred to in the previous section, this introduces about a 300 mV offset,
improving noise immunity.
RT-980 SERIES STATUS INDICATORS
Each of the RT-980 series transmitters provides the following front panel LED status indicators
to aid in installation and troubleshooting:
VIDEO 1 THROUGH VIDEO 8
A bi-color LED indicator is provided for the each of the eight video inputs to the RT-980 series
transmitters. Video status associated with each of these LED’s is summarized below.
Video Presence LED Video Status
Green Proper Input Video Present
Red Input Video Not Detected