Appendix B - Antennas; Overview - Mantracourt T24-ACMi-SA User Manual

Appendix B - Antennas

Overview

Radio performance at microwave wavelengths is very dependent upon the operating environment; any structure
within the operating region of the radios will give rise to three effects:
Obscuration. Obscuration will result in reduced range and occurs when an obstruction masks the line-of-sight
between radios.
Aberrations to the horizontal and vertical space patterns. Distortion of these patterns may occur if structures
or objects are placed in the near or intermediate field of the antenna. The effect will be to distort the coverage
patterns, adversely affecting range and link quality.
Reflection. Any object placed in line-of-sight of the transmit antenna will result in signals arriving at the receiver
by an indirect path. Degradation of performance due to reflection (multipath effects) appears as reduced range or
poor link quality.
Any of the above will reduce RSSI figures, an increase in the packet loss rate and in extreme cases complete loss
of signal. Fortunately, if consideration is given to these effects at the integration stage then a good quality link
will be obtained.
Guidelines for product design:
When selecting materials for product enclosures, preference should be given to fibreglass, light coloured ABS or
Polypropylene (Dark colours can sometimes be achieved with the addition of carbon which can attenuate the
radio signal); at the wavelength of 2.4GHz radio other materials will adversely affect the signal by attenuation,
refraction or change in polarisation.
If the application demands that the radio is fitted inside a metal enclosure then ensure that the specified
clearances are maintained around the antenna and design in a fibreglass RF window at least as large as the
clearance dimensions but ideally as large as possible.
RA24i radios fitted inside a product should be oriented so that the chip antenna will be vertical when the product
is in its normal operating position.
Guidelines for installation:
When planning installations ensure that line-of–sight between nodes is maintained and that objects or structures
are kept at least one metre away from antennae wherever possible.
To avoid poor link quality between a RA24i radio and a handheld module ensure that the RA24i is mounted so
that the chip antenna is vertical. Improvement may also be obtained by altering the height above ground of the
RA24i; a small increase or reduction in antenna elevation will often improve reception.
Range underwater is only 100 mm or so depending on packet rate. Best performance underwater is obtained by
using low packet rates and immersing water-proofed antennae rather than water-tight enclosures containing the
antennae.
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T24 Telemetry User Manual