TM 43-6625-916-12
RADAR TEST SET
0003 00
THEORY OF OPERATION - Continued
temperature, and therefore may be activated if the unit is exposed to excessive temperatures during shipping
or storage.
The external battery charger also provides for over current protection of the battery with a device that
automatically switches to a high impedance state when overloaded. The device will automatically reset when
power is disconnected and the battery removed for a period of one minute at room temperature.
ANTENNA SYSTEM
When using a flight line Test Set that communicates via RF, testing errors can result from the RF test signals
reflecting off of surrounding metal objects (such as nearby hangers or utility vehicles), or responses from
other nearby transponders. The Test Set may detect a signal from a transponder on a nearby aircraft if the
UUT transponder is defective. This could inadvertently lead an operator to believe that the UUT is a GO
when in actuality the Test Set detected a GO from the transponder on a nearby aircraft. The Test Set utilizes
several techniques to solve these problems. The Test Set has a dual pattern antenna to help prevent these
potential problems from producing invalid test results. Additionally, the Test Set applies power and receiver
sensitivity limits based on the user selected distance to help indicate the inadvertent interrogation of the
incorrect aircraft.
Operation of the TS-4530/UPM, antenna system is similar to the operation of the basic Transponder/
Interrogator system, which utilize a reply suppression pulse to inhibit the transponder from replying except
when it is in the center of the interrogation beam (Refer to Figure 3-2.). This system operates by using two
antenna patterns, with the main (sum) antenna pattern radiating the interrogation signal. A second antenna
pattern (difference) provides a low response in the main beam and higher response off to the sides, and is
used to radiate a suppression pulse (Side Lobe Suppression, or SLS pulse). If the transponder is not located
in the center of the main beam, the suppression pulse is received by the transponder at equal or greater
amplitude than the interrogation pulses and the transponder does not reply.
The TS-4530/UPM (interrogator) dual antenna system can also be used during reception of the transponder's
reply to determine if the signal came from the direction the antenna is pointed (Refer to Figure 3-2.). The TS-
4530/UPM receiver uses this method to determine if the reply source was the targeted transponder, a non-
targeted transponder, or was a reflection. If the reply signal strength is much stronger on the sum antenna
than the difference antenna, the Test Set accepts and processes the reply. If the difference antenna signal
approaches (or is greater than) the amplitude of the sum antenna signal, the reply is not accepted, and the
Test Set displays a "Fault=Angle" message. The system works equally well in screening interrogations
received outside the main (sum antenna) beam in interrogator test mode.
If a transponder passes a TS-4530/UPM test, the following conditions have been acceptable:
A.
TS-4530/UPM interrogations were accepted by the transponder. Transponder replies to TS-4530/UPM
interrogations were not suppressed by reception of the radiated SLS signal. Therefore, the transponder
was located near the center of the TS-4530/UPM's sub-antenna beam and no adjacent objects reflected
the SLS to the transponder antenna.
B.
Transponder replies were accepted by the TS-4530/UPM. Therefore, the reply signal was received
from the direction the unit was aimed and excessive reflection levels of he transponder signal were not
detected.
If the Test Set is poorly aimed, the test environment is reflective, or a surrounding transponder interfered with
the test, the TS-4530 will not pass the transponder because one of the following occurred:
A.
The transponder saw the Test Set's SLS pulse and did not reply. This could result from improper
aiming of the Test Set, or a strong reflection of the Test Set's signal. The Test Set will indicate a
transponder failure for low or no replies.
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