How does one know if one is in a simulcast system? Is there a map?
Without knowing your location, I'll use a site in Hit Factor's state for illustration.
Let's use Detroit. It's on the statewide system,
MPSCS.
Here's the Detroit site on MPSCS.
In this case, it is labeled simulcast, but that is not always the case.
Click on the name, Detroit City Simulcast which gets you to this page:
Michigan's Public Safety Communications System (MPSCS) Site: Detroit City Simulcast Details
www.radioreference.com
The site page shows that there are ten sites being used.
To see the tower locations, click on the small page icon at the lower corner of the map.
That gets you to a page with the tower
locations.
Depending on exactly you are located when trying to monitor a simulcast site, the multiple tower sites all use the same set of frequencies, transmitting the same voice traffic at the same time. But since these towers are at varying distances from your monitoring location, those signals arrive at your scanner out of synch, with enough variation to hinder the scanner's ability to receive it. The Uniden SDS series scanners, and the Unication pager have internal circuitry that handles that. Other scanners do not. But location is the key here. If you are very close to one specific tower, like a quarter mile or less, that close, strong, signal might be enough to override the other out of synch transmissions from other locations.
For more on simulcast, see this Wiki page:
Simulcast digital distortion - The RadioReference Wiki