Content

1Scope ..................................................................................................................................................3Theory ......................................................................................................................... 3234HD Video Formats ..............................................................................................................................3
2.1 SDI (Serial Digital Interface) - The Ideal Transport Interface ...................................................3
2.2 1080p - Why a Higher Capacity Interface Is Required .............................................................3Return Loss.........................................................................................................................................3
3.1 What Is Return Loss? ...............................................................................................................3
3.2 About Return Loss ....................................................................................................................3
3.3 How To Measure Return Loss ..................................................................................................4Timing Jitter ........................................................................................................................................4
4.1 What Is Jitter? ...........................................................................................................................4
4.2 Wander, Timing Jitter................................................................................................................4
4.3 About Timing Jitter....................................................................................................................4
4.4 How To Measure Timing Jitter..................................................................................................4Measurements ............................................................................................................ 556Return Loss.........................................................................................................................................55.1 Measurement Setup .................................................................................................................55.2 Measurement Conditions..........................................................................................................55.3 Measurement Results...............................................................................................................55.4 Conclusion ................................................................................................................................6Timing Jitter ........................................................................................................................................6
6.1 Measurement Setup .................................................................................................................66.2 Measurement Conditions..........................................................................................................66.3 Measurement Results...............................................................................................................76.4 Conclusion ................................................................................................................................8Neutrik AG
Im alten Riet 1439494 Schaan
Liechtenstein
Author: Wolfgang Schwarz© Copyright 2009 Neutrik AG.
All rights reserved.

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Especially the opportunity to reuse the existing
infrastructure has been one of the critical success factors for SDI and is characterized by theability of the interface to evolve over time, while
retaining the use of the existing cable installation,
patch panels, and BNC connectors.
The so far latest step of evolution for the serial
digital interface was the introduction of the1080p/60 video image.

1 Scope
Based on the increasing demands of high resolution video formats, and high data rates coming
along with it, more and more interest is focusedon transmission lines (connectors, cables) andtheir response to high frequency signals. Broadcasters are facing the challenge of making theirstudios, OB vans etc. future-proof with regards
to HD1080p and thus would like to ensure that
their equipment will provide reliable performance.
Return Loss and Jitter are identified to be thekey characteristics in judging compliance withhigh resolution standards.

2.2

Among the obvious reason of higher resolution
and hence the opportunity to display video material more realistic, 1080p provides an additional
major advantage:

We, Neutrik AG, as one of the leading manufacturers of BNC connectors, decided to accomodate the evolution of HD formats and to test ourproducts with regards to the enhanced requirements. Theory on Return Loss and Timing Jitterand corresponding measurement results are thebasis of this paper.

1080i and 720p, the two original HD formats are
not ideally compatible. If deciding to go for one
format, it is quite possible that a customer will
request the material in the other format. Actually,
the conversion between 1080i and 720p, or viceversa, is problematic, and may cause pixelizationand other undesirable artifacts.
By shooting in 1080p/60 respectively 1080p/50,
the higher frame rate HD image of 1080p/60 canbe easily converted into either 1080i or 720p withno artifacts.

THEORY
2 HD Video Formats

Thus, 1080p/60 provides the ability to offer a
product in 1080i or 720p formats with no loss ofimage quality, and also introducing an extended
life of material, as it will still be available whenthe 1080p distribution format emerges.

At present the two common formats for HD video
in the professional broadcast and production
world are 720p/30 (a progressive format with
720 active lines progressively scanned at a rateof 30 frames/sec) and 1080i/60 (an interlacedformat with 1080 active lines alternately scanned
at a rate of 60 fields/sec). Both formats are usually distributed over a high-definition serial digitalinterface (HD-SDI) at a data rate of 1,5 Gbit/sec.
The next step in the search for the ultimate picture resolution is 1080p/60 which requires 3Gbit/sec and thus twice the distribution data rateof 720p/30 & 1080i/60. Following the earlier established formats, 1080p/60* is distributed overHD-SDI.

The drive to higher data rates and thus clock
frequencies (SMPTE standard1 specify that theclock frequency will equal the signal bit rate**)has focused increasing interest on Return Loss
and Timing Jitter.
** The unit interval of a 270 Mb/sec SD-SDI signal equals
one period of a 270 MHz clock or 3.7 ns.
The unit interval of a 1.485 Gb/sec HD-SDI signal equals
673 ps or one period of a 1.485 GHz clock. Hence, the unitof a 2.97 Gb/sec high frame rate HD-SDI signal equals
336.7 ps or one period of a 2.97 GHz clock.

* Please note that when this paper mentions 1080p/60, the50-frame alternative 1080p/50, preferred in Europe, is also
included.

2.1

3 Return Loss

SDI (Serial Digital Interface) - The
Ideal Transport Interface

3.1

Ability to transport uncompressed signals
Low latency
Cost-effective implementation
Robustness and reliability
Seamless interoperability
Reuse of existing infrastructure

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What Is Return Loss?

Return loss is signal attenuation caused by impedance variations in the structure of a cable orassociated connectors. These variations cause
the signal to reflect (return) back to the source.
At lower frequencies, return loss is a minor effect; at frequencies above 50 MHz, it can have asignificant effect. At frequencies used for highdefinition video, 3000 MHz and higher, it is amajor, even critical factor.

SD and HD SDI have become the ubiquitousinterface standards within the professional
broadcast industry, and the success of the SDI is
broadly justified due to a number of specificcharacteristics:
•
•
•
•
•
•

1080p - Why a Higher Capacity Interface Is Required

3.2

About Return Loss

With the introduction of HD signals coming alongwith higher data rates and thus increased clock

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frequencies the impedance of BNC connectorsbecame more important than ever.
Every deviate impedance has a negative influence on the "return loss“ / "VSWR“ (VoltageStanding Wave Ratio) which are importantmeasurements for reflected signals in a transmission line.
Especially on high frequencies - as they occur
when transmitting high frame rate HD signals(typical transmission @ 4.5 GHz) - an impedance mismatch results in a lot of return loss.

3.3

4.3

Timing jitter has always degraded electrical systems, but the drive to higher data rates and lower
logic swings has focused increasing interest andconcern on it.
Impedance discontinuities through connectors
and transmission lines as well as attenuation,
cross talk, and noise coupling contribute to jitter.
In all of the above cases, the jitter effect is due tosome form of signal distortion and cannot becompletely eliminated. Thus, the jitter introduced
from these effects can be considered systematicand cumulative (arithmetically additive).

How To Measure Return Loss

Return loss is measured by the help of a Network Analyzer. The analyzer is set to nominal
cable impedance (e.g. 75 Ω) and the tested cable is terminated with a 75 Ω load. A signal isintroduced to the cable and the reflected signal
is measured.

4.4

What Is Jitter?

4.4.1 The Eye Diagram4

This simple and intuitive definition is provided by
the SONET specification2:“Jitter is defined as the short-term variations of adigital signal’s significant instants from their ideal
positions in time.”
Ideally, the time interval between transitions in
an SDI signal should equal an integer multiple ofthe unit interval. In real systems, however, thetransitions in an SDI signal can vary from theirideal locations in time. This variation is calledtime interval error (TIE), commonly referred to asjitter. This timing variation can be induced by avariety of frequency, amplitude, and phaserelated effects.

4.2

Figure 1

An eye diagram is created when many shortsegments of a waveform are superimposed suchthat the nominal edge locations and voltage levels are aligned, as suggested in stylized Figure 1(Colours have been used to show how the individual waveform segments are composed into aneye diagram).
The waveform segments may be adjacent ones,
as shown in the figure, or may be taken from
more widely spaced samples of the signal.

Wander, Timing Jitter

The jitter spectrum in an actual SDI signal generally contains a range of spectral components.
The recovered clock will generally track spectral
components below the clock recovery bandwidth, but will not track spectral components
above this bandwidth.
Hence, the impact of jitter on decoding depends
on both the jitter’s amplitude and its frequency
components. This has led to a frequency-basedclassification of jitter.

Unit Interval(UI)
IdealSampling
PointJitter

Conventionally, the term “jitter” refers to shortterm time interval error, i.e. spectral components
above some low frequency threshold. For SDI
signals, the SMPTE standards set this thresholdat 10 Hz and refer to spectral components above
this frequency as timing jitter.
The term wander refers to long-term time intervalerror. For SDI signals, components in the jitter
spectrum below 10 Hz are classified as wander.

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How To Measure Timing Jitter

Various methods to measure and estimate peakpeak jitter are common in industry.
We decided to use the eye diagram, which is ageneral tool for jitter measurement, since it gives
insight into the amplitude behavior of the waveform as well as the timing behavior.

4 Timing Jitter
4.1

About Timing Jitter

JitterFigure 2

Colored eye diagrams are used to indicate thedensity of waveform samples at any given pointof the display. Figure 2 shows such a color density display for a waveform that exhibits several
types of noise.
As the jitter on a signal increases, the eye becomes less open, either horizontally, vertically orboth. The eye is said to be closed when no open
area remains in the center of the diagram.

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MEASUREMENTS
5 Return Loss
5.1

Measurement Setup

Figure 3

5.2

Measurement Conditions

Return loss measurement has been carried out with Neutrik NBNC75BTU11 75 Ω BNC connectors.
To compare the results of the Neutrik connectors, we have chosen the BNC connectors of a European
manufacturer (Standard series & HD optimized series), whose products are widely spread in broadcast applications across Europe, as reference.
All tested cable assemblies have been terminated with 20 m of the well-known Belden 1694A 75 Ωcoax cable.
a) Single cable (length 20m) with both ends terminated for connector evaluation
DUTSMPTE 424M3 specifies a return loss of better than 10 dB between 1.485 GHz and 3 GHz and better
than 15 dB from 5 MHz to 1.485 GHz (values below SMPTE limits are indicated red in Figure 4).
All test specimens were sweep tested up to 4.5 GHz.

5.3

Measurement Results

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5.4Conclusion

The cable assembly with the Neutrik rearTWIST® 75 Ω BNC Connectors offer at least 15 dB returnloss budget with respect to SMPTE 424M requirements. This is a minimum of 7 dB more return loss
budget compared to European manufactured products.
To achieve this outstanding result every Neutrik BNC connector has been adapted to the measurements of a small group of cables, this guarantees the best possible performance and a minimized
return loss.
Neutrik BNC connectors feature a true 75 Ω design that meet the stringent requirements of high frame
rate HDTV and sustain consistent impedance at high frequencies up to 4.5 GHz.
The higher the frequencies the more pronounced is the "skin effect“, which means that the energymoves to the outside of the conductor. Therefore, the plating of outer and centre contacts is more
important than for audio connectors with low frequencies - both contacts of Neutrik BNC connectors
are gold plated.

6 Timing Jitter
6.1

Measurement Setup

Figure 5

6.2

Measurement Conditions

For jitter measurements we nominated the Neutrik NBNC75BTU11 75 Ω BNC connector. To judge theresults of the Neutrik connectors, we have chosen the BNC connectors of a European manufacturer(Standard series & HD optimized series), whose products are widely spread in broadcast applications
across Europe, as reference.
All tested cable assemblies have been terminated with 1m of the well-known Belden 1694A 75 Ω coaxcable.
a) Single cable (length 1m) with both ends terminated for connector evaluation
DUTb) 10 pcs of cables (length 1m each) connected in series via adapters to exhibit the influence of several connections as they typically occur on broadcast applications when patching signal leads
DUT…8x DUT…

DUT

SMPTE publishes standards, recommended practices (RP), and engineering guidelines (EG) for thevideo industry. SMPTE 424M, SMPTE RP184, SMPTE RP194 were considered in the actual Jitter
Measurement.

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6.3

Measurement Results

6.3.1 Neutrik NBNC75BTU11 with Belden 1694A coax cablea)b)
DUT…8x DUT…

DUT

42.1 ps/div

42.1 ps/div

Figure 6

Figure 7

Connector type

Timing jitter pk – pk
[ps]
[UI]

DUT

Rise time[ps]

Fall time[ps]a) Neutrik NBNC75BTU1134.47

0.10126112b) Neutrik NBNC75BTU1137.71

0.11205

158

Adapter: Neutrik NBB75FG
6.3.2 European Manufacturer HD optimized product with Belden 1694A coax cablea)b)
DUT…8x DUT…

DUT

42.1 ps/div

42.1 ps/div

Figure 8

Figure 9

Connector type

Timing jitter pk – pk
[ps]
[UI]

DUT

Rise time[ps]

Fall time[ps]a) European Manufacturer HD optimized

35.26

0.10

133118b) European Manufacturer HD optimized

83.55

0.25

302233

Adapter: European Manufacturer
6.3.3 European Manufacturer Standard product with Belden 1694A coax cablea)b)
DUT…8x DUT…

DUT

42.1 ps/div

42.1 ps/div

Figure 10

Figure 11

Connector type

Timing jitter pk – pk
[ps]
[UI]

DUT

Rise time[ps]Fall time[ps]a) European Manufacturer Standard series

36.72

0.11139121b) European Manufacturer Standard series

168.83

0.50

543

280

Adapter: European Manufacturer

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6.4

Conclusion

As written in section 2.2, jitter cannot be eliminated completely.
However, in order to reduce the potential jitter to a minimum, Neutrik concentrates on getting to theheart of the problem by optimizing connectors and its material.
Transmission line Timing Jitter (Method b):
Unit Interval (UI)

0.60.5
Neutrik NBNC75BTU110.40.3European Manufacturer HD0.2

European ManufacturerStandard0.10Figure 12

Figure 12: After a signal path of 10 test cables (including 9 adapters), connected in series, the Neutrik
BNC connectors do only add 0.11 Unit Interval (UI) of jitter to the signal, whereas the compared test
specimens under the same conditions add 0.25, respectively 0.5 UI of jitter.
Actually, the Neutrik BNC connectors offer considerable jitter budget to enable longer cable runs
and/or a higher number of patch connections without causing the signal to be undeterminable.
Neutrik true 75 Ω BNC connectors deliver best performance, especially when routed signals in transmission paths spreads via a considerable number of connections (Patch Panels, Patch cords andadapters).
From their beginning, the Neutrik rearTWIST® BNC connectors were designed under stringent specifications with regards to impedance and screening. In the actual jitter measurement the Neutrik
rearTWIST® BNC again proved to have been and continue to be the best choice even for the1080p/60 higher frame rate HD data format transmission lines.

References / Literature:
1 SMPTE RP 184-2004, Specification of Jitter in Bit-Serial Digital Systems
2 Bell Communications Research, Inc (Bellcore), “Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria, TR-253-CORE”, Issue 2, Rev No. 1, December 1997
3 SMPTE 424M-2006, SMPTE Standard for Television – 3Gb/s Signal/Data Serial Interface
4 Tektronics, Guide to understanding and characterizing Timing Jitter
Additional Literature:- Stephen H. Lampen, Martin J. Van Der Burgt, and Carl W. Dole, High-Definition Cabling and Return Loss, SMPTE Motion
Imaging Journal, January 2001
- SMPTE Motion Imaging Journal, May/June 2009
- Tektronics, Understanding Jitter Measurement for Serial Digital Video Signals- LeCroy, Understanding the Choice for Jitter Calculation Method, Application brief, LeCroy- LeCroy SA Schweiz, Jitter-Messungen leicht gemacht, Electronics 17/07- M. Schnecker, Jitter Measurements in Serial Data Signals, LeCroy Corporation

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