Equipment Description
Page 7-6
Reference Guide: SM6610, SM6615, SM6620 and SM6625 Satellite Modulators
ST.RE.E10152.2
Transport Stream De-jittering
When rate adaptation is switched off, the digital PLL referred to in
Transport Stream Rate Adaptation operates in conjunction with a FIFO
buffer to perform a de-jittering function, substantially removing any jitter
present on the incoming transport stream, such as is commonly generated
by SDH or PDH telecommunications distribution circuits. This jitter must be
removed before the DVB-S modulation process.
DVB Encoding
After rate adaptation or de-jittering, the transport stream is encoded in
accordance with ETSI standard EN 300 421 (DVB-S) or EN 301 210
(DVB-DSNG). The resulting I- and Q-channel signals are converted from
digital to analogue form and are then passed to the Output card.
PREKOR™ Dynamic Pre-correction (S13133 Card Only)
The PREKOR™ Dynamic Pre-correction function is performed after the DVB
encoding process and before digital to analogue conversion. This system
corrects non-linear magnitude and phase distortions, and group delay
distortion introduced by the uplink HPA and satellite transponder. It is of
particular benefit when using higher order modulations such as 16QAM.
The Beacon Receiver Input can be used for automatically adjusting the
level of pre-correction in response to an input voltage derived from an
external satellite beacon receiver. This facility is useful for compensating
for uplink fades when using PREKOR™ with a satellite that does not have
on-board AGC.
7.3.3 Output
Card
The Output card accepts the analogue I- and Q-channel signals from the
Baseband card and performs I & Q modulation of the carrier signal. There
are two different Output cards: the S10310 IF Output card and the S11291
L-Band Output card. The particular card fitted is dependent upon the
Modulator model. The S10310 card is fitted in the IF output models
SM6610 and SM6620. The S11291 card is fitted in the L-Band output
models SM6615 and SM6625.
S10310 IF Output Card
The S10310 card performs I & Q modulation, followed by frequency
down-conversion to the IF output frequency, amplification and output
power level control. Its output carrier frequency is tuneable over the range
50-180 MHz. Both main and monitor outputs are provided.
S11291 L-Band Output Card
The S11291 card performs direct I & Q modulation at the L-band output
frequency, followed by amplification and output power level control. Its
output carrier frequency is tuneable over the range 950-1750 MHz. Both
main and monitor outputs are provided.
A signal applied to the L-Band Input is combined with the on-board-
generated carrier at the input of the final output amplifier. This facility is
useful for combining carriers for transmission via the same uplink
equipment.
