Figure 2-1. Encoder timing diaqram.

TM 11-6625-667-45/NAVAR 16-30APM123-2/T0 33A1-3-367-22

Figure 2-1. Encoder timing diaqram.

directional horizontal field pattern of the antenna

used to obtain these conditios. Encoder P2 pulses

are directed to the adjustable low P2 pulse modu-

helps reduce interference to and from other RF

later driver when the ISLS switch is OFF. When

systems. It is mounted in a horizontal plane on the

control panel of the test set to radiate a vertically

the ISLS switch is ON, the P2 pulse is directed

to the main modulator driver along with the P1

polarized signal. Adjustments can be made in this

plane for line-of-sight antenna alignment. Also,

and P3 pulses The transmitted RF output level

it can be adjusted for horizontal polarization. An-

is attenuated approximately 57 db by the 50-foot

tenna bandwidth is sufficient for the transmission

radiation test distance, the RF cable and attenu-

of 1,030-mc and reception of 1,090-mc signals

ator, or the RF cable, attenuator, and antenna test

Received signals travel from the antenna through

hood during umbilical tests. When preadjusted to

the PROBE jack and the normally closed con-

the RF level of 6 dbm, transponder sets with

tacts of self-test relay A15K1 to the receiver

minimum sensitivity limits of 66 dbm may be

section.

checked. Transponder sets that have minimum

b. Antenna Test Hood. When the test hood is

sensitivity limits between --53 and --72 dbm may

used with aircraft Antenna AT-884/APX-44, the

be checked by preadjusting the transmitter power

level between +4 and 15 dbm as required. The

test set L-band antenna is disconnected from the

antenna test hood and antenna perform as follows:

PROBE jack, then the test hood is connected to

this jack through the attenuator and RF cable.

a. L-Band Antenna. The L-band antenna, a

The test hood insures that maximum RF energy is

compact traveling-wave type, is used for trans-

coupled between the test set and the aircraft

mission of the interrogation signal and reception

of the signal during radiation tests. The highly

Change 3

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