BIRD 424-86A-03, Инструкция по установке и эксплуатации

Страница: 20 / 36

TX RX Systems Inc. Manual 7-9322-5 08/09/06 Page 14
“>” symbol next to the MODE menu change the
mode using the enter button. For additional
testing while in modes 0 or 1 the active amplifier
in the TTA can be changed also. Move the “>”
to the LNA menu and select either the A or B
amplifier. Note that mode 2 does not allow
amplifier selection.
4) Exit the menu mode and return to normal oper-
ation by pressing down the A/B amplifier select
switch. The system will reset itself to mode 0
with amplifier A active. This is the default mode
of operation.
Test Port Sensitivity with Dummy load (Mode 1)
Place the system into Test Port Mode 1. During
this test a 50 ohm load is switched into the input of
the tower top preselector. The equipment is con-
nected as shown in
Figure 10 . For future reference
record the length and type of diagnostic cable
used. The same length and type of diagnostic
cable should be used when performing all post
installation tests. (
Small diameter coaxial cable
used for diagnostic connections has relatively high
signal loss per foot at 800 MHz and higher. If differ-
ent cable lengths are used when making tests, it
will contribute to significant variability of the mea-
sured levels
).
• Record the test port sensitivity on the data
sheet.
This value represents the best possible sensitivity
measured though the test port and is always lower
than the value obtained in the Installed Sensitivity
test by a factor of approximately -30 dB which is
the coupling loss of the sampling port built into the
preselector in the tower box (the coupling loss can
vary from TTA to TTA by a factor of -28 to -32 dB).
Test Port Sensitivity with Antenna (Mode 0)
• Place the system into Test Port Mode 0. This is
the normal default mode of operation for the
system and connects the antenna to the input
of the preselector. The equipment is connected
as shown in
Figure 11 .
Test
Port
12 dB SINAD
Signal Generator
RX
MCA
RF
Out
FRX MHz
3 KHz dev
1 KHz
Generator to test port
= Effective sensitivity
Enter on front panel
Daughter
Board
Input
Diagnostic
Cable
Antenna
Sampler
Port Output
Preselector
Input
Switch
Output
Switch
Main Test Ant
Figure 11 : Measuring test port sensitivity with antenna connected
(sensitivity less than or equal to sensitivity using a dummy load).