Handbook for Sound Engineers

424 Chapter 14

BNC 50: connectors are often used to terminate
digital video lines. This is probably acceptable if only
one or two connectors are used. However, if more
connectors are used, 75: connectors are required to
eliminate RL. Connectors should exhibit a stable 75:
impedance out to 2.25 GHz, the third harmonic of
750 MHz.

14.12 Radio Guide Designations

From the late 1930s the U.S. Army and Navy began to
classify different cables by their constructions. Since the
intent of these high-frequency cables, both coaxes and
twisted pairs, was to guide radio frequency signals, they
carried the designation RG for radio guide.
There is no correlation between the number assigned
and any construction factor of the cable. Thus an RG-8
came after an RG-7 and before an RG-9, but could be
completely different and unrelated designs. For all
intents and purposes, the number simply represents the
page number in a book of designs. The point was to get
a specific cable design, with predictable performance,
when ordered for military applications.

As cable designs changed, with new materials and
manufacturing techniques, variations on the original RG
designs began to be manufactured. Some of these were
specific targeted improvement, such as a special jacket
on an existing design. These variations are noted by an
additional letter on the designation. Thus RG-58C
would be the third variant on the design of RG-58.
The test procedure for many of these military cables
is often long, complicated, and expensive. For the
commercial user of these cables, this is a needless

expense. So many manufacturers began to make cables

that were identical to the original RG specification

except for testing. These were then designated utility

grade and a slash plus the letter U is placed at the end.

RG-58C/U is the utility version of RG-58C, identical in

construction but not in testing.

Often the word type is included in the RG designa-

tion. This indicates that the cable under consideration is

based on one of the earlier military standards but differs

from the original design in some significant way. At this

point, all the designation is telling the installer is that

the cable falls into a family of cables. It might indicate

the size of the center conductor, the impedance, and

some aspects of construction, with the key word being

might.

By the time the RG system approached RG-500,

with blocks of numbers abandoned in earlier designs,

the system became so unwieldy and unworkable that the

military abandoned it in the 1970s and instituted

MIL-C-17 (Army) and JAN C-17 (Navy) designations

that continue to this day. RG-6, for instance, is found

under MIL-C-17G.

14.13 Velocity of Propagation

Velocity of propagation, abbreviated Vp , is the ratio of

the speed of transmission through the cable versus the

speed of light in free space, about 186,282 miles per sec-

ond (mi/s) or 299,792,458 meters per second (m/s). For

simplicity, this is usually rounded up to 300,000,000

meters per second (m/s). Velocity of propagation is a

good indication of the quality of the cable. Solid poly-

ethylene has a Vp of 66%. Chemically formed foam has a

Table 14-26. SMPTE Serial Digital Performance Specifications

SMPTE 259 SMPTE 292M

Level A Level B Level C Level D Level D Level L

Parameter NTSC 4fsc

Composite

PAL 4fsc

Composite

525/625

Component

525/625

Component

1920 × 1080

Interlaced

1280 × 720

Progressive

Data Rate in Mbps (clock) 143 177 270 360 1485 1485

½ Clock Rate in MHz 71.5 88.5 135 180 742.5 742.5

Signal Amplitude (p-p) 800 mV 800 mV 800 mV 800 mV 800 mV 800 mV

dc Offset (volts) 0 ±0.5 0 ±0.5 0 ±0.5 0 ±0.5 0 ±0.5 0 ±0.5

Rise/Fall Time Max. (ns) 1.50 1.50 1.50 1.5 0.27 0.27

Rise/Fall Time Min. (ns) 0.40 0.40 0.40 0.40 – –

Rise/Fall Time Differential (ns) 0.5 0.5 0.5 0.5 0.10 0.10

% Overshoot Max. 10 10 10 10 10 10

Timing Jitter (ns) 1.40 1.13 0.74 0.56 0.67 0.67

Alignment Jitter (ns) 1.40 1.13 0.74 0.56 0.13 0.13