Bird Technologies 429-83H-01 Series-Manual - Manual (Page 22)

TX RX Systems Inc. Manual 7-9439-6 09/03/09 Page 14
Interference and IM Considerations
Although TX RX Systems, Inc. TTA systems are
designed for maximum interference immunity,
there are many factors that can lead to harmful
interference when using a tower-mounted ampli-
fier. It is highly recommended that the receiving
and transmitting antennas be vertically separated
to maximize antenna isolation.
Although most 700/800 MHz transmitters are con-
nected to their antenna through a combiner, it is
quite likely that the combiner does not have
enough transmitter noise filtering to prevent desen-
sitization of the receivers unless there is significant
antenna space isolation. Large values of antenna
isolation are most easily realized when the anten-
nas are separated vertically. This antenna isolation
also helps reduce the possibility of intermodulation
interference in the receiving system.
One other important factor that can strongly con-
tribute to interference problems is excessive gain,
ahead of the receiver. Excessive gain can cause
overdrive to the station receivers when strong sig-
nals are present, making them more prone to inter-
modulation or carrier desensitization problems.
R eceiver pream pl if ier s s hould no t be use d
because the receiver multicoupler, which is incor-
porated in the MCU, serves this purpose.
FEEDLINE DATA
As part of the installation process you will need to
determine the cable losses for your main and test
transmission lines. These loss values can be deter-
mined by sweeping the cables or they can be
looked up from the cable manufactures specifica-
tions. For your system these values will be fixed
once the cable type is chosen and cut to length.
Once you have determined the main and test line
cable loss for your system this information can be
recorded in system memory for future reference in
the Feedline Data menu selection. To save the
cable loss values in memory perform the following
steps.
1) From the default display press the DOWN
ARROW button on the front panel to scroll
through the menu choices until you reach the
FEEDLINE DATA menu.
2) With the FEEDLINE DATA menu displayed
press the ENTER button to step down to the
MAIN LINE LOSS sub-menu.
3) Use the UP and DOWN ARROW buttons to set
the main line loss to the desired value. This
storage register works in a forward loop fash-
ion, starting at 0.0 and increasing to 9.9. A but-
ton press after 9.9 returns the setting back to 0.
Figure 14: Alarm terminals. Normally open or normally closed screw terminals are available.
Model 429-83H-01-M-48 shown.
DC Power Cord used in model 429-83H-01-M-48
(Red is -48 Volts and Black is common)
AC Cord used in model 429-83H-01-M
Test Cable
connects here
Main Cable
connects here
Ground
(double-shielded)
CAT-5e Cable
connects here
Alarm Terminals
T h e g r o u n d l u g
must be connected
t o t h e e q u i p m e n t
rack master ground
bar with a pigtail.