pinch more info
scanner are available; and up grades to some of the old ones too
Digital Simulcasting
As the new APCO-25 scanners make their way into hobbyist's hands, there are reports that they don't work correctly while monitoring some simulcast systems. (
Simulcast just means that the same information is transmitted from more than one repeater at the same time, allowing users across a wide geographic area to all hear the same messages.) The symptoms are mainly the inability hear an entire transmission. The first second or two of voice is heard, which then trails off to silence.
To add to your list of acronyms, there is another type of modulation scheme that's used with some multi-site Project 25 systems. Linear Simulcast Modulation (LSM) is a trademarked term for a form of CQPSK that provides a way for receivers to properly handle multiple identical transmissions. It's just different enough that the regular C4FM processing doesn't work correctly.
Because no Phase II systems are currently in operation, the developers at Uniden and GRE didn't expect an immediate need to handle this type of modulation. However, several municipalities are using LSM/CQPSK modulation for simulcast, including Phoenix and Mesa in Arizona; the greater Twin Cities area of Minnesota; Hamilton County in southwest Ohio; and Austin and Travis County in Texas.
If you live near any of these areas, or monitor systems that are "pure" APCO-25 with simulcasting, you may want to wait until Radio Shack has an upgrade for the PRO-96. As described in the August
Tracking the Trunks column, the Radio Shack PRO-96 (built by GRE) was designed to accept updates to the "DSP Application" portion of the scanner through the use of flash upgrades. This kind of flexibility allows production problems and bugs to be corrected without the need to buy a new scanner or replace circuit boards. In this case, an upgrade can also add new features and capabilities.
Radio Shack is expected to provide a firmware update that will give the scanner the ability to process LSM transmissions. As of this writing there's no release date for such an update, or whether there will be a cost involved. There may be a way to have the upgrade done at your local Radio Shack store, or to download the upgrade from Radio Shack's web site. We'll keep you posted as we get more details.
No word yet from Uniden on a fix for their scanners, although they have a new pair of scanners in the works to compete with the PRO-96.
Digital Diversity of APCO 
