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TX RX Systems Inc. Manual 7-9487-3 05/05/11 Page 27

2) For an MCU style system connect the spectrum

analyzer to one of the output ports of the multi-
coupler,  see  figure  25.  For  the  CMU  style  sys-
tem  connect  the  spectrum  analyzer  to  the  RF
Output  port  on  the  rear  of  the  unit,  see  figure
26.

3) Setup the spectrum analyzer as follows;

Span = 700 - 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 33.5

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 33.5
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 28

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;

Caution

During this test on-air sig-

nals will NOT pass through to the
station receivers.

1) The signal generator and SINAD meter (or bit

error rate meter if appropriate) should be con-
nected to the system as shown in

Figure 29

for