Bird Technologies 429-83H-01 Series-Manual - Manual (Page 27)

TX RX Systems Inc. Manual 7-9439-6 09/03/09 Page 19
preselector is not adequately performing its job
and must be changed.
3) All Other Frequencies - The receiver is
designed to monitor very low signals and there
must be a minimum amount of undesired
energy exposure. The preselector has very
sharp selectivity and must reduce all carriers
outside the bandwidth below -75 dBm except as
indicated above.
Procedure for Spectral Analysis
Spectral analysis will verify the signals arriving at
the receiver as well as validate the TTA Net Gain
adjustment. To perform a spectral analysis of the
site follow the steps listed below.
1) Make sure programmable attenuators are prop-
erly adjusted.
2) Connect the spectrum analyzer to one of the
output ports of the multicoupler.
3) Setup the spectrum analyzer as follows;
Span = 700 to 800 MHz
Resolution = 50 KHz
RF Attenuation = 0 dBm
Reference Level = -20 dBm
Peak (Max) Hold = ON
4) Monitor the spectrum for 5 minutes (during
peak hours).
OPERATIONAL TESTS
(SENSITIVITY AND DEGRADATION)
Before sensitivity and degradation can be verified,
attenuation adjustments and spectrum analysis
must be performed. If these are not correct, the
sensitivity and degradation may appear out of tol-
erance.
The sensitivity tests will measure the full range of
performance from the maximum achievable to real-
world performance in the presence of RF noise.
These tests are absolutely necessary, not only to
insure proper performance, but also to serve as a
bench mark for future evaluations and trouble-
shooting.
Two types of sensitivity measurements will need to
be made, Static and Effective. Static sensitivity is
measured without the presence of site noise while
the Effective sensitivity measurement includes site
noise. The difference between the two is the sys-
tem degradation.
Front Panel Test Port
The front panel BNC test port is connected to the
tower box through the test line allowing signals
generated at ground level to be injected into an iso-
lated 45 dB port at the input of each tower top
amplifier circuit board. The test port feature pro-
vides a convenient means of performing static sen-
sitivity tests of the system.
Tower Top Amplifier Inputs
Under normal operating conditions RF signals pass
from the antenna to the inputs of the tower top
amplifier. In addition, the input of each tower top
amplifier can also be switched to an internal 50
Ohm load for testing purposes. The front panel test
port remains connected (through its isolated 45 dB
input) to the tower top amplifiers regardless of
whether the amplifiers input is connected to the
antenna or the internal load. This allows system
sensitivity testing to be done with and without site
noise being coupled into the system through the
antenna.
Static System Sensitivity
Static sensitivity is the maximum sensitivity achiev-
able because any possible interfering signals are
blocked from entering the LNA while static sensitiv-
ity is measured. To determine the Static system
sensitivity the signal level into the first amplifier
must be known. The easiest way to achieve this is
to inject a test signal into the Test Port (located on
the front panel of the base unit) and measure the
BER or SINAD of the test receiver. The static sys-
tem sensitivity can only be measured while the
active tower-top LNA is connected to the internal
load. Once you have made the measurement the
actual static system sensitivity can be calculated.
Figure 17 shows the formula for calculating the
actual static system sensitivity as well as a worked
through example.
Measuring Static Sensitivity
(Load Connected)
To test the static system sensitivity through the test
port with the internal load connected to the ampli-
fier perform the following steps;