User's Guide
Table Of Contents
- Description
- Features
- Ordering Information
- Absolute Maximum Ratings
- Electrical Specifications
- Typical Performance Graphs
- Pin Assignments
- Pin Descriptions
- Pre-Certified Module Pin Assignments
- Module Dimensions
- Theory of Operation
- Module Description
- Overview
- Addressing Modes
- Automatic Addressing
- Address Register Use
- Acknowledgements and Assured Delivery
- Frequency Hopping Spread Spectrum
- Compatibility with the 250 Series
- Networking
- Transmitting Packets
- Receiving Packets
- Using the Buffer Empty (BE) Line
- Exception Engine
- Carrier Sense Multiple Access (CSMA)
- Using the Command Response (CRESP) Line
- Using the CMD Line
- External Amplifier Control
- AES Encryption
- Using the MODE_IND Line
- Using the PB Line
- Restore Factory Defaults
- Using the Low Power Features
- The Command Data Interface
- Reading from Registers
- Writing to Registers
- Command Length Optimization
- Example Code for Encoding Read/Write Commands
- The Command Data Interface Command Set
- Typical Applications
- Usage Guidelines for FCC Compliance
- Additional Testing Requirements
- Information to the user
- Product Labeling
- FCC RF Exposure Statement
- Antenna Selection
- Castellation Version Reference Design
- Power Supply Requirements
- Antenna Considerations
- Interference Considerations
- Pad Layout
- Microstrip Details
- Board Layout Guidelines
- Helpful Application Notes from Linx
- Production Guidelines
- Hand Assembly
- Automated Assembly
- General Antenna Rules
- Common Antenna Styles
- Regulatory Considerations
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110 111
General Antenna Rules
The following general rules should help in maximizing antenna performance.
1. Proximity to objects such as a user’s hand, body or metal objects will
cause an antenna to detune. For this reason, the antenna shaft and tip
should be positioned as far away from such objects as possible.
2. Optimum performance is obtained from a ¼- or ½-wave straight whip
mounted at a right angle to the ground plane (Figure 120). In many
cases, this isn’t desirable for practical or ergonomic reasons, thus,
an alternative antenna style such as a helical, loop or patch may be
utilized and the corresponding sacrifice in performance accepted.
3. If an internal antenna is to be used, keep it away from other metal
components, particularly large items like transformers, batteries,
PCB tracks and ground planes. In many cases, the space around the
antenna is as important as the antenna itself. Objects in close proximity
to the antenna can cause direct detuning, while those farther away will
alter the antenna’s symmetry.
4. In many antenna designs, particularly ¼-wave whips, the ground plane
acts as a counterpoise, forming, in essence,
a ½-wave dipole (Figure 121). For this reason,
adequate ground plane area is essential.
The ground plane can be a metal case or
ground-fill areas on a circuit board. Ideally, it
should have a surface area less than or equal
to the overall length of the ¼-wave radiating
element. This is often not practical due to
size and configuration constraints. In these
instances, a designer must make the best use
of the area available to create as much ground
OPTIMUM
USABLE
NOT RECOMMENDED
NUT
GROUND PLANE
(MAY BE NEEDED)
CASE
Figure 120: Ground Plane Orientation
I
E
DIPOLE
ELEMENT
GROUND
PLANE
VIRTUAL λ/4
DIPOLE
λ/4
λ/4
VERTICAL λ/4 GROUNDED
ANTENNA (MARCONI)
Figure 121: Dipole Antenna
plane as possible in proximity to the base of the antenna. In cases
where the antenna is remotely located or the antenna is not in close
proximity to a circuit board, ground plane or grounded metal case, a
metal plate may be used to maximize the antenna’s performance.
5. Remove the antenna as far as possible from potential interference
sources. Any frequency of sufficient amplitude to enter the receiver’s
front end will reduce system range and can even prevent reception
entirely. Switching power supplies, oscillators or even relays can also
be significant sources of potential interference. The single best weapon
against such problems is attention to placement and layout. Filter the
module’s power supply with a high-frequency bypass capacitor. Place
adequate ground plane under potential sources of noise to shunt noise
to ground and prevent it from coupling to the RF stage. Shield noisy
board areas whenever practical.
6. In some applications, it is advantageous to place the module and
antenna away from the main equipment (Figure 122). This can avoid
interference problems and allows the antenna to be oriented for
optimum performance. Always use 50Ω coax, like RG-174, for the
remote feed.
OPTIMUM
USABLE
NOT RECOMMENDED
NUT
GROUND PLANE
(MAY BE NEEDED)
CASE
Figure 122: Remote Ground Plane