Antennas - Microhard Systems IP-921 Operating Manual

7.0 Installation
Direct human contact with
the antenna is potentially
unhealthy when a Spectra
920A is generating
energy. Always ensure that
the Spectra 920A equipment
is powered down (off) during
installation.
© Microhard Systems Inc.

7.2.1 Antennas

The two most common types of antenna are the omnidirectional
('omni') and directional (Yagi).
An omni typically has 3-6dBi gain and spreads its energy in
all directions (hence the name 'omnidirectional').
'pattern' of the energy field is in the shape of a donut, with
the antenna mounted vertically at the centre. This vertical-
mounted antenna produces a signal which is vertically
'polarized'.
A Yagi has a more focused antenna pattern, which results
RF
in greater gain: commonly, 6-12dBi. The pattern of a Yagi
is in the shape of a large raindrop in the direction in which
the antenna is pointed. If the elements of the Yagi are per-
pendicular to the ground (most common orientation) the
radiated signal will be vertically polarized; if parallel to the
ground, the polarization is horizontal.
The network topology, application, and path calculation are all
taken into consideration when selecting the various antenna types
to be used in a radio network deployment.
In a long-range PTP network, Yagi antennas should be considered.
There antennas will provide for the most focused ‗RF connection'
between the two sites.
In a PMP network where remotes are located in all directions from
the Master, the Master site will have an omni so that it can commu-
nicate with all remotes; the remotes, however, may all employ Yagi
antennas ‗pointed at' the Master.
Typically a Repeater site will employ an omni such that it can read-
ily receive an RF transmission from one direction and be able to
readily transmit it in another.
If an application involves remotes which are not stationary (e.g. mo-
bile application), all sites would likely use omni antennas so that
wherever the units may be, there should be antenna pattern cover-
age.
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