Orban OPTIMOD-FM 8600S, Operating Manual

Page: 50 / 354

1-24
INTRODUCTION ORBAN MODEL 8600S
In the analog radio processing chain, the BS.1770 meter and Safety Limiter are cali-
brated per EBU Tech 3344
6
, Section 5.9. This calls for a 1 kHz sinewave at –23 LUFS to
produce an FM carrier deviation of
±
10 kHz without pilot tone. This corresponds to
13.33% modulation without pilot tone. This calibration includes 50
µ
s transmission
preemphasis. The loudness meter is calibrated so that “0” corresponds to the setting
of the
BS.1770
LOUDNESS
C
ONTROL
T
HRESHOLD control in
I
NPUT
/O
UTPUT
> U
TILITY .
Built-in Calibrated Line-up Tones
To facilitate matching the output level of the 8600S to the transmission system that
it is driving, the 8600S contains an adjustable test tone oscillator that produces sine
waves at 8600S’s (analog or digital) left, right and composite outputs. The frequency
and modulation level of the line-up tones can be adjusted from the front panel (as
described in
Test Modes starting on page 3-84).
The stereo encoder is calibrated so that 100% left or right modulation will provide
100% modulation of the stereo composite signal, including pilot tone but excluding
any SCA subcarriers.
The pilot tone stereo system has an interleaving property, which means that the ste-
reo composite modulation is approximately equal to the higher of the left or right
channels. Because the pilot tone is phase-synchronous with the stereo subcarrier, the
composite modulation will increase about 2.7% when the modulation is changed
from pure single-channel to L+R modulation while the peak audio level is held con-
stant.
When the 8600S’s left/right analog output is switched to
F
LAT , a de-emphasis filter is
inserted between output of the 8600S’s audio processing and its line output. Thus,
as the frequency of the Test Tone is changed, the level at the 8600S’s line output will
follow the selected de-emphasis curve. In most cases, the pre-emphasis filter in the
driven equipment will undo the effect of the 8600S’s internal de-emphasis, so the
8600S’s output level should be adjusted such that the tone produces 100% modula-
tion of the transmission link as measured after the link’s pre-emphasis filter. At
100Hz, switching the de-emphasis out or in will have negligible effect on the level
appearing at the 8600S’s left and right audio outputs.
You can adjust the frequency and modulation level of the built-in line-up tone. You
can use the front panel, the PC Control software, or the opto-isolated remote con-
trol interface ports to activate the Test Tone.
Built-in Calibrated Bypass Test Mode
A
BYPASS
Test Mode is available to transparently pass line-up tones generated ear-
lier in the system. It will also pass program material, with no gain reduction or pro-
tection against overmodulation. It can transparently pass any line-up tone applied
to its input up to about 130% output modulation, at which point clipping may oc-
cur.
6
EBU – TECH 3344: “Practical guidelines for distribution systems in accordance with
EBU R 128; Supplementary information for EBU R 128,” available for free download.
Use a search engine to find the latest version.