Section 3: Operation
NetClock/GTP Instruction Manual
Page 3-23
3.4
REMOTE OUTPUT USAGE
The Remote Output provide a continuous once-per-second time data stream in
RS-485 levels. RS-485 is a balanced differential transmission, which offers
exceptional noise immunity, long cable runs and multiple loading. These
characteristics make RS-485 ideal for distributing time data throughout a facility.
The Remote Output can drive 32 devices over cable lengths up to 4000 feet.
Spectracom manufactures wall clocks, talking clocks, NTP time providers, RS-
485 to RS-232 converters and radio link products that utilize the RS-485 data
stream as an input. Figures 3-8 and 3-9 illustrate typical RS-485 time data bus
interconnections. Follow the guidelines listed below when constructing the RS-
485 data bus.
3.4.1 RS-485
Guidelines
Cable selection
: Low capacitance, shielded twisted pair cable is recommended
for installations where the RS-485 cable length is expected to exceed 1500 feet.
Table 3-5 suggests some manufacturers and part numbers for extended distance
cables. These cables are specifically designed for RS-422 or RS-485
applications; they have a braided copper shield, nominal impedance of 120
ohms, and a capacitance of 12 to 16 picofarads per foot.
RS-485 cable may be purchased from Spectracom. Specify part number
CW04xxx, where xxx equals the length in feet.
MANUFACTURER
PART NUMBER
Belden Wire and Cable Company
1-800-BELDEN-1
9841
Carol Cable Company
606-572-8000
C0841
National Wire and Cable Corp.
232-225-5611
D-210-1
TABLE 3-5 CABLE SOURCES FOR RS-485 LINES OVER 1500 FEET
