Section 5 Troubleshooting; Problems And Potential Solutions; Rfi, Hum, Clicks, Or Buzzes; Unexpectedly Quiet On-Air Levels - Orban OPTIMOD-FM 5500 Operation Manual

OPTIMOD-FM DIGITAL
Section 5
Troubleshooting

Problems and Potential Solutions

Always verify that the problem is not the source material being fed to the 5500, or
in other parts of the system.

RFI, Hum, Clicks, or Buzzes

A grounding problem is likely. Review the information on grounding on page 2-10.
The 5500 has been designed with very substantial RFI suppression on its analog and
digital input and output ports, and on the AC line input. It will usually operate adja-
cent to high-powered transmitters without difficulty. In the most unusual circum-
stances, it may be necessary to reposition the unit to reduce RF interference, and/or
to reposition its input and output cables to reduce RF pickup on their shields.
Particularly if you are using a long run of coaxial cable between the 5500 and the
exciter, a ground loop may inject noise into the exciter's composite input — espe-
cially if the exciter's input is unbalanced. The Orban CIT25 Composite Isolation Trans-
former can almost always cure this problem.
The AES3 inputs and output are transformer-coupled and have very good resistance
to RFI. If you have RFI problems and are using analog connections on either the in-
put or output, using digital connections will almost certainly eliminate the RFI.

Unexpectedly Quiet On-Air Levels

The ITU412 multiplex power controller may have been turned on accidentally. See
step 20 on page 2-21.
The 5500 may be in stand-alone stereo encoder mode. The on-air preset determines
this.
The 5500 may not be controlling peak modulation as desired. See the next topic be-
low.

Poor Peak Modulation Control

First, check whether the final clipper is active (step 6 on page 2-31). If you are using
the analog or digital output to drive the transmitter, make sure that this output is
not receiving the M signal (step (8.B) on page 2-33).
ONITOR
TROUBLESHOOTING
5-1