CalAmp GUARDIAN User Manual download pdf (Page 25)

2.7 TERRAIN AND SIGNAL STRENGTH

A line of sight (LOS) path between stations is highly desirable and provides the most reliable communications link in all

cases. A line of sight path can often be achieved by mounting each station antenna on a tower or other elevated

structure that raises it high enough to clear surrounding terrain and other obstructions.

The requirement for a clear transmission path depends on the distance to be covered by the system. If the system is to

cover a limited distance, say 3-5 miles, then some obstructions in the transmission path may be tolerable. For longer-

range systems, any obstruction could compromise the performance of the system, or block transmission entirely.

The signal strength (RSSI) at the receiver must exceed the receiver sensitivity by an amount known as the fade margin

to provide reliable operation under various conditions. Fade margin (expressed in dB) is the maximum tolerable

reduction in received signal strength, which still provides an acceptable signal quality. This compensates for reduced

signal strength due to multi-path, slight antenna movement or changing atmospheric losses. CalAmp recommends a 30

dB fade margin for most projects. The following table shows the RSSI versus Reliability.

Table 14 RSSI Reliability

RSSI

Reliability

-100 dBm Approximately 50% reliability. Fading may cause frequent data loss.

-90 dBm Approximately 90% reliability. Fading will cause occasional data loss

-80 dBm Approximately 99% reliability. Reasonable tolerance to most fading.

-70dBm Approximately 99.9% reliability with high tolerance to fading.

2.8 RADIO INTERFERENCE

Interference is possible in any radio system. However, since the Guardian is designed for use in a licensed system,

interference is less likely because geographic location and existing operating frequencies are normally taken into

account when allocating frequencies.

The risk of interference can be further reduced through prudent system design and configuration. Allow adequate

separation between frequencies and radio systems. Keep the following points in mind when setting up your radio

system.

a. Systems installed in lightly populated areas are least likely to encounter interference, while those in urban and

suburban areas are more likely to be affected by other devices.

b. Directional antennas should be used at the remote end of the link. They confine the transmission and reception

pattern to a comparatively narrow beam, which minimizes interference to and from stations located outside the

pattern.

c. If interference is suspected from another system, it may be helpful to use antenna polarization opposite to the

interfering system’s antennas. An additional 20 dB (or more) of attenuation to interference can be achieved by

using opposite antenna polarization.

d. Check with your CalAmp sales representative or CalAmp Technical Services for additional options. The Technical

Services group has qualified personnel to help resolve your RF issues.

Guardian™ Serial Modem or Analog Radio for Licensed Spectrum PN 001-5006-000 Rev. 3 | Page 17

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 99 100

No comments

CalAmp GUARDIAN User Manual Page 25