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Re: Serial D-1 Jitter
Several things you might look at:
1. Is it possible that the foam core of some of these cables has
been smashed or deformed. This will case reflections. In rare
cases, a tight bend radius in the cable dressing can cause
reflections, depending upon the cable type and outer jacket
Where we all have rolled over video cable in the NTSC past with
heavy equipment, it's strictly a NO NO in a serial digital plant.
2. Are you using "self Normalizing" patch panels. Debate has
been raging for years over the pro's and con's of using self -
normalizing patch panels vs. non - normalizing with "hair pins"
for 270mb/s video. I have used both.
Critics of self - normalizing say that over time and non-use
(inserting a patch card in a patch jack) can cause the self -
normalizing contact to corrode or become dirty, thus inducing
distortions in the transmission chain.
3. Are all of your cable, connectors, patch panels, truly 75
ohm? If you started with a NTSC analog house and slowly migrated
to serial digital was there a chance older transmission hardware
was re - used. For years we all used, at on time or another, 50
ohm connectors and in some cased patch panels. This was of no
concern when signals only went out to 10mhz. Now with signal
going out to 270 mhz, it's critical.
4. The most obvious is, how long are your cable runs? Maximum
length without reclocking will vary from cable types. I've run
Belden 1505A out to 300 meter with a successful packet recovery,
however my recommendation is "don't try this at home!" ... that's
really pushing your luck.
5. You stated that you were using a GVG (I assume Series 7000)
serial digital router. This router (at least the one I put in
some years ago) reclocks on the input. You will note in the 7000
specifications, that it will pass signals up to 360mb/s. This
360mb/s spec. was for provisions for increasing luminance
resolution to 18mhz sampling for 16:9. However, the trade off is
"More Jitter" vs. adhering to 270mb/s, at least with today's
current chip-sets. This condition is true even if the signal is
The pro's and con's of 18mhz luminance sampling is beyond the
scope of this discussion.
6. One last item: would any of this trouble be associated when
using a DVR-2100/OS. If you are reclocking while using the 2100
in off speed operation, that signal comes out serially at a
"nonstandard" data rate. Some devices tolerate it better than
With a cable of known reliable 270mb/s performance, try
bypassing your patch panel, or try a whole different cable path
and see if the jitter performance changes or is consistent.
More more info I recommend an article in the August 1992 SMPTE
Journal written by Takeo Eguchi, from our Sony Atsugi
Technologly Center, titled:
"Pathological Check Codes for Serial Digital Interface Systems".
We may have an all serial digital pathway now, but it is still
susceptible to analog degradation. The good news is that when
the signal performance is marginal at best, visually it's still
"great", when it steps over that fine, sometimes invisible line,
it "catastrophically fails".
Hope this has been helpful.
Sony Digital Production Systems
______________________________ Reply Separator _________________________________
Subject: Serial D-1 Jitter
Author: telecine at xyzoom.alegria.com at sonycom
Date: 1/24/96 1:36 PM
Subject: Time: 12:56 PM
OFFICE MEMO Serial D-1 Jitter Date: 1/24/96
Dear fellow Telecine Group members,
We have a pretty big GVG serial router for our D-1 signals here ( 96x96 ).
Some of those signals are derived from Parallel only devices such as
Digiscan-4 Ranks or older Accom DNR's and are serialized using Miranda
parallel to serial converters. Others are from devices with direct serial
outputs such as DaVinci 8:8:8 Processors. Some of the signals exhibit very
little jitter when measured on the AAVS Digital Signal Analyser but others
have up to about 1.60 ns of jitter which sometimes causes failure of the
signals intermittently. The jitter doesn't seem to be related to any class of
device, some Miranda derived signals are low jitter, others are high. What
has been the experience of some of the rest of you with dealing with this sort