Service manual

Guide to ASTRO™ Digital Radios
It cannot be stressed enough how important it is to keep your host and DSP firmware up-to-
date. There have been tremendous improvements in the audio quality of ASTRO™ digital (IMBE™)
transmissions since the first IMBE™ DSP codec was released in 1996. Some major law-enforcement
agencies are still using host and DSP firmware combinations dated from 1995-1997. The tone of
reproduced audio using DSP firmware version 6 and no subscriber AGC is terrible. Motorola Inc. is to be
commended for vastly improving the audio characteristics of their digital radios, but they haven’t made
enough of an effort to distribute new firmware upgrade packages to their customers at no charge.
Getting the latest firmware is highly recommended, but without the proper configuration of the
CSD (codeplug), the audio may still be inferior.
Subscriber AGC controls the audio gain of the transmitted audio. When enabled, it addresses
many issues which contribute to terrible audio on analog and digital transmissions. Loud-talkers have
their audio balanced, while quiet-talkers have their audio levels brought up. A side-effect of AGC is the
increase of background noise which may be present in the audio of quiet-talkers. Users of any radio-
system should be properly educated in the correct use of their radios; this is much more effective than
subscriber AGC. Optimizing radio-configuration and educating end-users make for a superior system.
Below are examples of how digital radios should be configured for the best-sounding
transmitted audio. Your mileage may vary; these are Motorola Inc. recommended settings.
Figure 9.1 Recommended settings for optimized subscriber AGC operation in ASTRO™ RSS.