Handbook for Sound Engineers

Transmission Techniques: Wire and Cable 423

clock frequency and is acceptable because serial digital
receivers have signal recovery processing.

HD-SDI, whose cable loss is governed by SMPTE
292M, operates at a data rate of 1.5 Gbps (clock
750 MHz). The maximum cable length is specified at
20 dB signal loss at one-half the clock frequency. These
are Manchester Coded signals and the bit rate is there-
fore double the clock rate. Emerging 1080p/60 applica-
tions are covered under SMPTE 424M. The data rate is
3 Gbps (clock 1.5 GHz).

14.11.4 Receiver Quality

The quality of the receiver is important in the final per-
formance of a serial digital system. The receiver has a
greater ability to equalize and recover the signal with

SDI signals. SMPTE 292M describes the minimum
capabilities of a type A receiver and a type B receiver.
SDI receivers are considered adaptive because of their
ability to amplify, equalize, and filter the information.
Rise time is significantly affected by distance, and all
quality receivers can recover the signal from a run of
HD-SDI RG-6 (such as Belden 1694A) for a minimum
distance of 122 m (400 ft). The most important losses
that affect serial digital are rise time/fall time degrada-
tion and signal jitter. Serial digital signals normally
undergo reshaping and reclocking as they pass through
major network hubs or matrix routers.

Table 14-26 gives the specifications mandated in
SMPTE 259M and SMPTE 292M in terms of rise/fall
time performance and jitter. If the system provides this
level of performance at the end of the cable run, the SDI
receiver should be able to decode the signal.

14.11.5 Serial Digital Video

Serial digital video (SDI) falls under standards by the

Society of Motion Picture and Television Engineers

(SMPTE) and ITU and falls under the following catego-

ries:

These standards can work with standard analog
video coax cables, however, the newer digital cables
provide the more precise electrical characteristics
required for high-frequency transmission.
SDI cable utilizes a solid bare-copper
center-conductor which improves impedance stability
and reduced return loss (RL). Digital transmissions
contain both low-frequency and high-frequency signals
so it is imperative that a solid-copper center-conductor
is used rather than a copper-clad steel center conductor.
This allows the low frequencies to travel down the
center of the conductor and the high frequencies to
travel on the outside of the conductor due to the skin
effect. Since digital video consists of both low and high
frequencies, foil shields work best. All SDI cable should
be sweep tested for return loss to the third harmonic of
the fundamental frequency. For HD-SDI which is
1.485 Gb/s or has a 750 MHZ bandwidth, the cable is
swept at 2.25 GHz. RL can be no greater than 15 dB at this frequency.

Table 14-25. Comparing Coaxial Digital Formats

Standard Format Intended Use Connector

Style

Cable Type Transmission

Distance^2

Sample

Rate

Data Rate

(Mbps)

Guiding

Document

SDI serial broadcast one BNC coax^1 300 m/1000 ft 27 MHz 270 SMPTE 259

SDTI serial data transport one BNC coax^1 300 m/1000 ft variable 270 or 360 SMPTE 305

SDTV serial broadcast one BNC coax^1 300 m/1000 ft 27 MHz 3 to 8 ATSC; N53

HDTV serial broadcast one BNC coax^1 122 m/400 ft 74.25 MHz 19.4 ATSC; A/53

HD-SDI serial broadcast one BNC coax^1 122 m/400 ft 74.25 MHz 1500 SMPTE 292M

1080p/60 serial Master format one BNC coax^1 80 m/250 ft 148.5 MHz 3000 SMPTE 424M

(^1) Also implemented over fiber systems
(^2) Transmission distances may vary widely depending on cabling and the specific equipment involved.
SMPTE 259M D i g i t a l v i d e o t r a n s m i s s i o n s o f
composite NTSC 143 Mb/s (Level A)
and PAL 177 Mb/s (Level B). It also
covers 525/625 component transmis-
sions of 270 Mb/s (Level C) and
360 Mb/s (Level D).
SMPTE 292M HDTV transmissions at 1.485 Gb/s
SMPTE 344M Component widescreen transmission
of 540 Mb/s
ITU-R BT.601 International standard for PAL trans-
missions of 177 Mb/s