User's Manual

Chapter 4 Operation

Reading Mode Performance Enhancement Features

This section describes three MMI performance enhancement features that are often

employed to achieve a greater read success in certain situations. These features are the

GEO mode of interrogation, Dynamic Interrogation Window, and Frequency Scan. The

interrogation mode and the Dynamic Interrogation option may be enabled or disabled at

any time through the System Setup menu contained within the Tools command. The

interrogation mode may also be changed by pressing the backspace key while in Reading

mode. The Frequency Scan option is controlled from the Frequency Control menu within

the Tools command.

GEO Mode

As described in the Reading mode section, the GEO mode is similar to L/L mode in that

it uses the Lat/Lon locations of transponders to determine whether or not they should be

interrogated. However, it differs by also including in the interrogation window any

transponder that does not have a Lat/Lon coordinate. This most often occurs as new

transponders are added to an existing route. Most utilities do not have a means of

assigning a Lat/Lon coordinate at the time the transponder data is added to the route. As

a result, any new and uninitialized transponder would never be read while in L/L mode,

which is the primary mode of interrogation. Ordinarily, such transponders would have to

be read using FIFO mode, which would require the operator to be aware of where each

uninitialized transponder was located, and then switch interrogation modes until the

desired uninitialized transponder reading was obtained. On all but the smallest routes,

this need to constantly change interrogation modes would prove too unproductive to be

practical.

It is when a small number of uninitialized transponders are mixed into the route, that

GEO mode is used. GEO gets its name since transponders without coordinates are

geocoded as they are read. Geocoding is simply an action that assigns a Lat/Lon

coordinate to an object. Since the MMI records Lat/Lon information for each transponder

as it is read, once a read occurs there now exists an approximate Lat/Lon coordinate for

that transponder that may be used the next time that transponder is uploaded to the MMI.

Because the recorded Lat/Lon coordinate is the position where the MMI obtained the

reading, and not where the transponder is actually located, an additional restriction is

placed on the transponder before its reading is accepted. Each time a transponder reply is

received, a measure of its signal strength is recorded. The signal strength is proportional

to the distance to the transponder. As the MMI moves closer to the transponder, the

received signal strength increases. Therefore, the goal is to ensure that an uninitialized

transponder is read in GEO mode at a shorter range than normal. This ensures that the

recorded Lat/Lon coordinate will be effective the next time the transponder is read using

its new coordinates. To force this range restriction, a minimum signal strength

requirement is set in the System Setup menu that will be applied only to uninitialized

transponders being read in GEO mode. Other transponders with Lat/Lon coordinates, as

well as any transponder in FIFO mode will not face this restriction. Any transponder