CALAMP WIRELESS NETWORKS INC. MCUB5R Manual Do Utilizador

This is a 4-digit value, including the leading mi-
nus sign, expressed in dBm with a typical accu-
racy of +/- 2dB. For example, a value of -090
indicates a signal strength of -90 dBm.

 

Displays the strength of the last valid data signal
received by the connected Integra-TR unit. The
format described in the Remote RSSI section
above applies.

 

Typical values of RSSI will be in the range of
-110 dBm to -60 dBm, with higher values (i.e.
less negative values) indicating a stronger sig-
nal.

 

Reliability of data reception depends largely on
signal strength. Good design practice calls for a
minimum 30 dB “fade margin”, based on a
threshold reception level of -107 dBm (1 uV) at
speed of 9600 b/s. Experience indicates that this
will give about 99.5% reliability.

 

Some representative performance values for
9600 b/s operation are given below. These val-
ues assume that the units are correctly aligned
and installed in a quiet location. Environments
with high electrical or RF noise levels will re-
quire an increase in the numbers shown to
achieve a given level of reliability.

 

-100 dBm. Approximately 50% reliability.

Fading may cause frequent data loss.

 

-90 dBm. Approximately 90% reliability. Fad-

ing will cause occasional data loss.

 

-80 dBm. Approximately 99% reliability. Rea-

sonable tolerance to most fading.

 

-70 dBm. Approximately 99.9% reliability with

high tolerance to fading.

 

If RSSI values drops seasonally, the most likely
cause is tree foliage, which can interfere with
radio transmissions during the spring and sum-
mer.

 

Approximate measure of transmit power. This is
a 4 digit value in  watts rounded to the nearest

tenth.  Note that this is an approximate value
that should be used for trend monitoring
only. It does not compare in accuracy with val-
ues obtained by a standard wattmeter.

 

The values returned are approximate and should
not be regarded as an absolute indicator of per-
formance. For example, a unit that shows a for-
ward power of 4.5 watts may actually measure
at 5.0 watts on a lab quality wattmeter. For this
reason, these values should not be used to indi-
cate that a unit is out of spec or to compare one
unit to another.

 

 

Therefore, the following conditions are worthy
of investigation.

1.  Forward power output drops or rises by

more than 10% from its established value.
Reflected power remains low.

2.  This indicates that the transmitter may need

alignment or that a component may be in
need of replacement.

3.  Forward power output drops by more than

10% from its established value. Reflected
power shows an increase.

This indicates a possible antenna or feedline
problem that affects SWR (Standing Wave
Ratio).

 

Approximate measure of reverse (reflected)
power. The value is returned differently for on-
line and offline diagnostics:

 

Online: The value returned is 0 if reverse power
is within acceptable limits, 1 if reverse power is
too high. The threshold is set to approximately
1/4 of the forward power value.

 

Offline: Value is in watts to the nearest tenth.
This value is intended as an indication of an-
tenna problems and will normally be used for
trend monitoring. Ideally it should close to be