DRAKE SCT4860 Buku Petunjuk - Halaman 9

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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.

Additional Features

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.