INSTALLATION IN THE SCT860
Looking at the SCT860 from the front panel, observe the right side of the unit.
Remove the three top screws as shown, three side screws, and three bottom screws holding the
right side of the case.
Remove the right side and then lay the transcoder on a flat surface laying on its left side.
Locate the 36 pin interface connector and remove the 11 jumpers that are in place. Keep these
jumpers for future use in case the 100-2365 board is ever removed.
Remove the original screw at location A.
Screw the standoff spacer, that is included with the option board, into the hole at location A.
Carefully remove the 100-2369 board from its static protection package.
Position the board as indicated and plug it into the 36 pin connector.
Reinstall the screw to fasten the Option Board to the spacer. Replace the right side cover and
screws.
FIRMWARE UPDATE REQUIRED
Install the "Fixed" version of the SCT860 operating firmware. This is provided on the included floppy
disk. Download via the RS-232 interface on the PS100. This firmware is also available on the CD-
ROM included with the PS100.
OPERATION
Follow the instructions in the SCT860 instruction manual. Now that the 100-2365 board is installed,
the FIXED clock option may be selected and the output BD RATE (baud rate which is the symbol
rate) may be set. The original AUTO clock mode is still selectable, if desired.
Installation / Operation 2
INTRODUCTION
The 100-2365 board is used to add a fixed,
programmable, clock option to the SCT860
transcoder. Why is this needed? When the
standard SCT860 demodulates the satellite
signal and recovers the MPEG2 transport
stream, the data rate of this stream has been
determined at the satellite uplink. This data
rate, the FEC mode, required guard bands,
etc. have all been carefully selected to
optimize the use of a 27 MHz wide satellite
transponder and a 6 MHz wide 64 QAM
CATV channel. The resulting design
provides a transport stream bit rate of around
27 Mb/s. This bit rate results in a 64 QAM
symbol or baud rate of 5.057 MS/s. This rate
completely fills the 6 MHz channel. The
standard SCT860 does not modify the
transport stream and thus performs the
desired translation from the satellite channel
to the terrestrial QAM channel producing the
output rate as described above. Drake labels
this mode the ‘Auto Clock’ mode as the
output rate is automatically determined by
the received input signal data rate.
Sometimes there are reasons for the satellite
uplink to use a different data rate than that
which produces the 5.057 MS/sec, 64 QAM
data rate. For example, if 36 MHz wide
transponders are used, not all of the satellite
bandwidth is being utilized with only a
27 Mbps bit rate - a higher satellite rate is
possible to make maximum use of the
satellite bandwidth. If the satellite rate is
increased to make optimum use of the wider
satellite transponder, after transcoding, the
resulting output signal would exceed the
maximum 6 MHz CATV channel bandwidth. If
priority is given to utilizing all of the satellite
bandwidth then a higher order of CATV
modulation, such as 256 QAM, must be used
to accommodate the additional data rate on
the QAM output side OR some of the excess
data must either be deleted or split so as to
deliver it in two CATV channels.
3 TOP SCREWS
1
TM
Model 100-2365 Fixed Clock/Null Packet Stuffing Option Board (SCT860)
When it is not desirable to go to 256 QAM
modulation, one possibility, if some of the
information is not needed at any one receiver, is
to encode the uplinked signal such that all bits
from any one program source are coded to only
bits of the Q channel or the I channel. Then it is
possible to demodulate the satellite signal at the
transcoder and use only the I or Q side (SCT860
Split-I or Split-Q mode). The resulting data rate is
then below the available maximum capacity with
64 QAM modulation. The standard SCT860, in
auto clock mode, would output the resulting
reduced symbol rate signal at a symbol rate below
the 5.057 MS/s maximum rate but, unfortunately,
many set top boxes will only sync to the 5.057
maximum rate. This is where the 100-2365 board
is used. This option allows the user to select a
‘Fixed Clock’ mode. The desired output symbol
rate (such as 5.057 MS/s) can be programmed.
The 100-2365 option will then add MPEG2 null
packets to the transport stream (sometimes called
‘null packet stuffing’) as needed to increase the
symbol rate to the one programmed. The set top
box will just ignore the extra null packets.
By using two SCT860 transcoders with the
100-2365 option to receive the same satellite
transcoder (using split mode) and setting one for
the ‘Split-I’ mode and one for the ‘Split-Q’ mode,
the entire satellite payload can be split between
two different CATV 64 QAM channels thus
transcoding all of the satellite program services. It
is necessary for the signal to be uplinked in the
split mode in order for this process to work.
REMOVE 11 JUMPERS FROM THE 36 PIN CONNECTOR
LOCATION A
PLUG INTERFACE
HEADER INTO 36 PIN
CONNECTOR
TIGHTEN SCREW
INTO SPACER
