Location-based scanning (LBS) allows you to control which systems/sites and channel groups are scanned based on your exact location. This frees you from having to manually enable and disable systems or channel groups as you change location.
To explain the operation simply, LBS uses the scanners lockout function to control what is scanned based on your location. It unlocks systems, sites, or channel groups when you are inside a the element's radius. When you exit the radius, the element is temporarily locked out. Since the element is temporarily locked out, all elements are scanned when you first power on the scanner, until the GPS gets a location fix and starts reporting coordinates.
To use Location-Based scanning, you need to have the following:
- the location for the center point for each system/site or channel group you want to control
- the radius or distance from the center point you want to set as the range for each system/site or channel group
- if you are scanning while traveling, you may want to include the heading (direction) of travel
- some type of mapping method. If you don't want to use paper maps, you might try a mapping software (such as Microsoft® Streets and Trips or Delorme® Street Atlas) that allows you to draw markings and overlays on maps.
- a GPS receiver with a serial data output (NMEA)
There are many different approaches you can use to determine where to place a center point for a system/site or channel group. The two most common are the geopolitical approach and the antenna-centric approach. For large trunked systems, you may find that a combination of these two approaches works best.
The Geopolitical Approach
With the geopolitical approach, you want the scanner to turn on the system/site or channel group at the limit of relevance rather than reception. This approach is useful for scanning targets that have a well-defined jurisdiction and their transmission are only relevant when you are within that jurisdiction.
To use the geopolitical approach, find the geographical center of the scanning target's territory (whether city, county, district, precinct, or other agency jurisdiction), and set these coordinates as your center point location. Then, adjust the range or radius to cover the boundaries of that target.
To use this method, use your chosen mapping application to zoom out so that the entire target is visible, then, draw a circle that just covers the targets boundaries. Adjust the size of the circle to the nearest 1/2 mile increment.
Depending on the shape of the territory, you may have to choose between a lot of overlap or not covering the entire area: jurisdiction, you might end up with a large amount of overlap. You'll have to decide which radius that best suits your application.
For example, if your territory is a city, you'll have a lot of "extra" area if you use one single location:
On the other hand, if you sub-divide the area, you may end up with areas that are not covered:
The Antenna-Centric Approach
Using an antenna-centric approach, you set the physical antenna location as the system/sites center point and the antenna's actual reach as the range.
Finding an antenna location
You can find the physical location of antennas using the databases available at Radio Reference
or the FCC's Antenna Structure Registration site. Both sites list the latitude, longitude, and height of the antenna, and both sites can map the exact location for you. (Radio Reference
is more user-friendly, so it's easier to find what you're looking for.)
Combining for Efficiency
Because many trunked systems have both multiple antenna sites and multiple agencies with differing geographic boundaries, you may want to combine the approaches:
- Use the antenna centric approach at the site level: set the geographic coordinates of the antenna as the central location for each site.
- Use the geopolitical approach at the channel group level. Within the same system, set up a channel group for each agency, and set the central point of the agency territory as the group location.
With both approaches combined into a single system, the scanner will now seamlessly switch between antenna sites as needed to keep the scanner tuning only to those sites you can receive well, and will also turn channel groups on and off as you relocate to different jurisdictions.
Connecting a GPS receiverProgramming locations