Additional Features 9
OUTPUT LEVEL
The SCT4860 provides a +40 dBmV QAM output level that
is desirable when transcoders are combined with analog
modulators that have +45 dBmV output level. The
SCT4860 output level can be turned down as much as
15 dB if a lower level is desired. Each SCT4860’s RF
output level can be read out on the PS151 power supply
LCD when that unit is selected, or via the RS232 remote
connection.
Because some operators may not have test equipment
designed to measure QAM power levels, and analog
meters may be grossly inaccurate if a QAM signal is read,
the SCT4860 has a CW output mode that can be useful
for measuring/adjusting the output level of the transcoder
with any meter that measures CW carrier power. A
special QAM instrument is not required. No input signal is
required for this measurement. The CW carrier power is
equal to the QAM power level that will result when the unit
is returned to a normal QAM modulation mode.
IMPORTANT NOTE: When the SCT4860 is placed in the
continuous wave (CW) mode, the output carrier frequency
will be at the center of the output channel. It will not be
located at the NTSC video carrier frequency. Adjust test
equipment accordingly to obtain an accurate result.
The PC control software allows all transcoders to be
easily switched to the CW mode at one time for set up
purposes. After any level tweaks are made, they can all
be switched back to normal mode at one time. It is also
possible to individually select a single transcoder to be
switched to the CW mode, if desired. In a typical leveling
process, the output of the headend is monitored after the
final combiner and all analog channel levels are set to the
desired level. Then, with the SCT4860s all set for CW
output, the SCT4860 CW carrier levels can be all
tweaked to a desired level (usually 6 to 10 dB) below the
analog video carrier levels. When switched back to
normal mode, the SCT4860s will all be outputting QAM
channel powers equal to the CW powers set up.
RAIN FADE LOGIC
When the rain fade feature is enabled, the transcoder will
mute its RF output whenever the input S/N drops below a
fixed threshold that is determined by FEC type. This logic
is always enabled in the DISHScan mode.
STANDBY MODE
The SCT4860 has a standby output mode which turns off
the RF output. This can be used when it is desirable to
keep a backup unit on line. The standby mode can be
selected via the OUTPUT menu.
POWER SUPPLY
The SCT4860 requires multiple power supply voltages
that are all obtained from the Drake model PS151 power
supply module. The PS151 mounts in the RMT150 rack
tray along with one to ten SCT4860 (or other similar
Drake models) transcoders. The PS151 buffers and
distributes the RS232 remote control data from its DB9,
RS232 INPUT connector to up to ten transcoders and to
the DB9, RS232 OUTPUT connector. Multiple PS151s
can be ‘daisy chained’ via the DB9 INPUT and OUTPUT
connectors to allow control of up to 70 transcoder
modules with a single connection to a PC.
The PS151 operates over a wide range of AC input
voltages from 90 VAC to 264 VAC. The USA version has
an attached 3 wire line cord. Power consumption from the
AC line will be around 150 W maximum with ten
transcoders installed. In many cases, the power will below
this level.
RS232 REMOTE CONTROL AND MONITORING
The SCT4860 provides for remote control and/or
monitoring of all transcoder parameter settings. It is
possible to view all of the current parameter settings
including the output level setting for each transcoder. It is
also possible to remotely monitor the SNR level and the
baud rate. The transcoder parameter settings may be
uploaded to a PC file for saving on the PC or a new
parameter configuration from the PC file can be down-
loaded to the SCT4860. A single parameter may be
adjusted if desired. It is possible to put all transcoders in
or out of CW mode with a single command. A unit may be
placed in or taken out of the standby mode. A password
can be assigned to prevent unauthorized changes to
parameter settings but the present settings can be read
out remotely without entering the password. Further
details on the RS232 control program are provided with
the instructions included with the CDROM containing the
control program (shipped with your PS151 power supply).
The previously described remote interface is accom-
plished by connecting an RS232 interface cable between
the PS151 power supply DB9 INPUT connector and a PC
serial port. The required program is supplied by Drake
with the PS151 power supply. This setup will allow
RS232 interfacing to up to ten SCT4860 transcoders
connected to the PS151. When more than one tray of
transcoders is used, the OUTPUT DB9 connector on the
PS151 can be used to link to a second PS151 as well as
a PS150 (SCT1860s) or a PS100 (SCT860s) in the same
headend. Use a DB9 to DB9 RS232 jumper cable from
the OUTPUT of the first supply to the INPUT of the
second supply. You can extend this to additional supplies
as long as the total number of PS151s to control does not
exceed 7 (70 SCT1860/2860/3860/4860s) and the
number of SCT860s does not exceed 64.
