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From: Jeff -(JEFFCROES) TO: ALL
Date Posted: 202001-13-2 11:57:00
Message:
Body:
Hi to all, today I'm having a strange problem on G1 23, On HBOW ch 102, quality is around 25, but on ch 100 it's only around 10, west feeds have higher raeding than the east feeds, I don't understand this because those channels are on the same transponder but with different quality reading, any idea !

Jeffrey


From: trackerlee -(LEETRACKER02) TO: Jeff
Date Posted: 202001-14-2 3:20:00
Message:
Body:
If you notice that the Bitstream for 100 is "I" and 102 is "Q".

From: Jeff -(JEFFCROES) TO: trackerlee
Date Posted: 202001-14-2 4:25:00
Message:
Body:
Can you please explain about the bitstream?

Thank you


From: 1notmike -(NTDWS) TO: Jeff
Date Posted: 202001-14-2 4:33:00
Message:
Body:
GI requires that the digital datastream on a transponder be split up when the datastream is higher than 15MB/s
At 29.27MS/s and 3/4 FEC the effective speed of the data stream is >15MB/s.

Click the glossary below for more.


From: Jeff -(JEFFCROES) TO: 1notmike
Date Posted: 202001-14-2 4:37:00
Message:
Body:
Thank you for your help, will check your link.

From: Rod Hewitt -(RODHEWITT) TO: 1notmike
Date Posted: 202001-14-2 3:28:00
Message:
Body:
If I may, a little more technical info.

DCII (like DVB and DSS) uses QPSK modulation which results in two bits being sent per time period. When these are recovered by the receiver, there are two lines coming from the front end, the I and Q components.

In some DCII formats (and all DVB), the I and Q bits are shifted into parallel in order, i.e. they are combined so that their order in a byte is IQIQIQIQ.

Some DCII formats split the I & Q into two different transport streams so that the reconstructed bytes are IIIIIIII or QQQQQQQQ. This was apparently done because DCII has been around for a long time and I would imagine that some component in the DCII system couldn't handle the data rate of combining the two phases and so they split the stream into two, halfing the bitrate.

In split mode, there really are two transport streams - each with its own PAT/PMT plus the DCII extensions like the VCT and TDT. These DCII extensions are what's responsible for tying the two transport streams from each of the phases together so that they appear to be one set of channels.

Needless to say, GI has gotten around the problem since there are now QPSK carriers running 29.27Msps in combined mode.

A little correction on your bitrate math:

29.27MSps = 58.54Mbps (b = bit, B = byte)
58.54Mbps * (188/204) = 53.94Mbps (this is the Reed-Solomon coding overhead)
53.94Mbps * 0.75 = 40.46Mbps (3/4 FEC coding overhead)
40.46Mbps / 8 = 5.05MBps (not that Bytes really matter in the comminications world - everything is though of in bits)

Regards,
Rod