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INTRODUCTION
ORBAN MODEL 9300
Sag is a result of inadequate steady-state regulation. It causes the conventional car-
rier shift that is seen on a modulation monitor. Good transmitter engineering prac-
tice usually limits this shift to -5% (which corresponds to about 0.5dB — not a highly
significant loudness loss).
A more serious problem is dynamic carrier shift, or bounce. This has been known to
cause up to 3dB loudness loss. Resonances in the power supply's LC filter network
usually cause it. Any LC network has a resonant frequency. In order to achieve rea-
sonable efficiency, the power supply filter network must be underdamped. There-
fore, high modulation excites this resonance, which can cause overmodulation on
the low-voltage peaks of the resonance.
Curing bounce is not straightforward because of the requirement that the power
supply filter smooth the DC sufficiently to achieve low hum. One approach that has
been employed is use of a 12-phase power supply. Upon rectification, the ripple
component of the DC is down about -40dB without filtering. A single-capacitor filter
can thus be used, eliminating the filter inductor as a potential source of resonance
with the capacitor.
Other sources of resonance include the modulation reactor and modulation trans-
former in conventional plate-modulated transmitters. Such transmitters will not
greatly benefit from a 12-phase power supply.
The newer generations of transmitters employ switching modulation techniques to
control bounce far better than do older plate-modulated designs. The latest trans-
mitters using digital modulation techniques have even better performance and most
are essentially transparent.
Pre-1965 Transmitters
Some older transmitters were under-designed by today's standards because modern
audio processing techniques to increase average modulation had not yet been de-
veloped and because the designers of those transmitters assumed that average
power demands on the modulator would be relatively small. If you have a transmit-
ter designed before 1965, you should monitor it carefully to make sure that
OPTIMOD-AM processing is not overheating the modulation transformer, the modu-
lation reactor, or the power supply. The high-frequency boost performed by
OPTIMOD-AM can cause unusually high voltages in the final amplifier, which could
cause arcing and/or component breakdown (although the latter is very rare).
There are no simple cures for such problems. Pre-1965 transmitters usually require
substantial modification, including the addition of heavier-duty components and
perhaps a completely new power supply for the modulator alone. Because of dra-
matic improvements in transmitter design since these transmitters were built, we
recommend that such transmitters be replaced. The latest solid-state transmitters
sound audibly better on-air and their higher efficiency substantially reduces operat-
ing power costs.
Summary of Contents for OPTIMOD-AM 9300
Page 1: ...Operating Manual OPTIMOD AM 9300 Digital Audio Processor Version 2 0 Software...
Page 7: ...Operating Manual OPTIMOD AM 9300 Digital Audio Processor Version 2 0 Software...
Page 178: ...3 46 OPERATION ORBAN MODEL 9300...
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Page 221: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 21...
Page 222: ...6 22 TECHNICAL DATA ORBAN MODEL 9300 CONTROL BOARD PARTS LOCATOR...
Page 228: ...6 28 TECHNICAL DATA ORBAN MODEL 9300...
Page 229: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 29 I O DSP BOARD LEFT AND RIGHT ANALOG INPUTS...
Page 230: ...6 30 TECHNICAL DATA ORBAN MODEL 9300 I O DSP BOARD ANALOG OUTPUTS...
Page 231: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 31...
Page 238: ...6 38 TECHNICAL DATA ORBAN MODEL 9300 FRONT VIEW REAR VIEW FRONT PANEL PARTS LOCATOR DIAGRAM...
