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the reader where it is not likely to be bumped out of alignment. Encompass 4
Readers should not directly face each other or be positioned back-to-back.
For a pole mount installation, install the reader as high as possible so that you can
point the reader down to control the read zone and minimize interference in the
adjacent lane.
Tag Placement
Reader location determines tag placement in the windshield. Overhead readers
require a center-mounted tag; readers on the side of the lane require that tags are
placed on the nearest side of the windshield.
Site Layout, Lane Type, and Traffic Flow
It is important to know the configuration of the site and its proximity to other sites
in order to develop a correct site plan as well as a workable frequency plan. Will
the lanes be AVI only, or will the lanes also have ticket machines, proximity
readers, or other in-lane equipment?
The number of lanes at the site, how they are grouped, and number of total entry
and exit points determine the number of readers required and the distance
between readers. You must determine the lane widths and the distance between
adjacent lanes, taking into account any island/barrier width. TransCore
recommends that, for the Encompass 4, the lane width with barrier be at least 12
feet.
Interfaces to External Loops, Gates or Converters
For the best lane layout and transaction framing, the distance from the entry loop
to the reader should normally be no more than about 8 feet with the distance from
the reader to the gate arm not exceeding an additional 3 to 4 feet. In most cases,
the reader will be positioned before the gate.
With this defined read area (frame), it is very difficult for a non-tagged vehicle to sit
in front of the gate and be admitted by a following car (the following car won’t be
read). As well, if the first vehicle is valid, then subsequent vehicles will not be able
to follow.
If the read zone is much larger than the distance referenced above, then a
following car may be read and allow a non-tagged vehicle to enter the facility.
Bigger isn’t always better; in RFID systems, long range can create a problem.
The readers are typically configured to be loop activated (on by presence) but may
be set to have RF on continuously. The choice depends on traffic volume and
possible interaction with the other in-lane components.
Frequency Plan
The Encompass 4 Reader FCC-approved frequency band is 911.75 to 919.75
MHz. Because of this relatively narrow frequency band, it requires careful planning
to maintain the desired 2 MHz frequency separation between adjacent readers.
If readers are spread out within a facility (readers ½ mile or so apart), and loops
are used, then frequencies may be reused. Special circumstances may
necessitate use of multiplexers, especially in installations exceeding 20 readers.
The illustration below shows frequency separation for 4 lanes.
