Orban Optimod-AM 9400 Operating Manual Download

Page: 220 / 295

5-4

TROUBLESHOOTING ORBAN

MODEL

9400

important to drive the 9400 with professional levels (more than 0 dBu reference
level) to achieve adequately low noise. (Clipping occurs at +27 dBu.)

The 9400's AES3 input is capable of receiving words of up to 24 bits. A 24-bit word
has a dynamic range of approximately 144 dB. The 9400's digital input will thus
never limit the unit's noise performance even with very high amounts of compres-
sion.

If an analog studio-to-transmitter link (STL) is used to pass unprocessed audio to the
9400, the STL's noise level can severely limit the overall noise performance of the
system because compression in the 9400 can exaggerate the STL noise. For example,
the overload-to-noise ratio of a typical analog microwave STL may only be 70-75 dB.
In this case, it is wise to use the Orban 8200ST Studio AGC to perform the AGC func-
tion prior to the STL transmitter and to control the STL's peak modulation. This will
optimize the signal-to-noise ratio of the entire transmission system. An uncom-
pressed digital STL will perform much better than any analog STL. (See

Studio-

Transmitter Link,

starting on page 1-11.)

Shrill, Harsh Sound

This problem can be caused by excessively high settings of the HF EQ control It can
also be caused (or at least exaggerated) by a transmitter with substantial distortion,
particularly at higher modulating frequencies

Dull Sound

A narrowband antenna that truncates higher modulating frequencies is the most
likely cause. Inappropriately low settings of the HF EQ control can also cause it.

In addition, bear in mind that most analog AM receivers have less than 3 kHz audio
bandwidth so they will inevitably sound dull compared to full-bandwidth media.

Excessive Occupied Bandwidth

The active transmission preset determines the maximum audio bandwidth at the
9400’s output. (This can be reduced within a User Preset, but not increased higher
than the setting in the active transmission preset.)

The 9400 has very tight spectral control that significantly exceeds the requirements
of all international regulatory authorities, including the FCC and ITU-R. Because its
processing is entirely determined by DSP software, there is very little that can go
wrong with the 9400 that will increase its output bandwidth without causing an all-
out failure of the unit.

If a spectrum analyzer determines that the 9400 is creating excessive bandwidth by
itself, the likely culprits are the output D/A converter and the output line amplifier.
However, a far more likely cause is a misbehaving transmitter Any problem in the
transmitter that causes audio distortion will also increase occupied bandwidth Flat
tubes are particularly suspect.

Some older designs (like out-phasing modulation schemes) are notorious for causing
out-of-band radiation when processing audio with substantial pre-emphasis, like
that supplied by the 9400. After the out-phasing transmitter's exciter has been care-

Orban Optimod-AM 9400, Operating Manual

Search results

Summary of Contents for Optimod-AM 9400

Reviews:

Related manuals for Optimod-AM 9400

Brands by name

Popular brands