7;5;6\VWHPV,QF
Manual 7-9547-1 12/09/14 Page 30
Hardware Problems
Two of the most common reasons for TTA alarms
are direct lightning strikes and vandalism. Even
though the system is designed with redundancy so
that likely-to-fail components have backups, it is
possible to shut the system down, especially if a
common component such as a transmission line or
antenna is damaged.
LIGHTNING & LIGHTNING ARRESTERS
The tower box uses three lightning arresters: one
on the antenna port, one for the main transmission
line and one for the test line. Although no practical
amount of protection can prevent catastrophic fail-
ure as the result of a direct hit, the lightning arrest-
ers are very effective in preventing damage from
nearby strikes and smaller direct hits. Lightning
arresters do not last forever and can eventually fail,
especially after a strong hit. A damaged arrester
can cause low gain with known-good A & B amplifi-
ers. An arrester with lightning damage will exhibit
increased insertion loss, poor return loss and may
appear as a DC short on the main or test lines.
VANDALISM
Damage to the TTA caused by hunters or target-
shooters in remote locations is not uncommon.
Penetrating bullets may open or short transmission
lines. Operating voltages are applied to the tower
top box by the main transmission line. In addition,
the main transmission line carries RF, tower box
operating voltage, and serial communications, so
serious damage to this cable can prevent system
operation. The system will operate normally if the
test transmission line becomes damaged but there
will be a loss of system testing and an alarm will be
continuously set.
AC Line Fuse (110 VAC model)
A failure of the power supply will obviously shut the
tower amplifier down because of high signal loss
through the tower box and control unit. The power
supply is located on the control unit chassis and
has a replaceable 250 volt, 2 amp fuse for the AC
line. The supply has a green status LED located on
the power supply assembly next to the connectors
which illuminates when the supply is turned on.
The 48 VDC model uses a DC-DC conver ter
instead of a power supply assembly.
Loss of Sensitivity (Intermittent / Continuous)
Individual Receive Channel(s) affected
All Receive Channels affected
Intermittent
Continuous
Intermittent
Continuous
Measure Sensitivity
Measure Sensitivity
Measure Sensitivity
Measure Sensitivity
Small to moderate loss of
sensitivity
Small to severe loss of
sensitivity
Small to moderate loss of
sensitivity
Small to severe loss of
sensitivity
Do spectrum analysis
Do spectrum analysis
Do spectrum analysis
Do spectrum analysis
Two or more carriers > 35 dBm
when desense occurs
On-channel TX stuck on and
visible in spectrum.
One carrier > 35 dBm when
desense occurs then Carrier
Desense Interference likely.
Possible Alarm condition
Other-channel modulation
heard in FM system or dropouts
in digital system
Defective cable / connector /
Receiver
Carrier(s) < 35 dBm when
desense occurs then Transmit-
ter Noise Interference likely.
Check operation with amplifier
A and B. Failed amplifier gives
low sensitivity on 1 amplifier
only.
Intermodulation Interference
likely
If operation is the same on
amplifier A or B, Defective com-
mon component is likely
Table 7
: Troubleshooting Guide for TTA systems with degraded performance. Shaded blocks indicate common possible cause.
