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1.6.4.9 Two-Pulse Beacon Interrogation and Codes
The transmitter of the RT-1601 sends an interrogation signal to the ground-based beacon
transponders when the BCN B mode is selected on the display. All of the ground beacons that
receive the signal reply by sending a two-pulse signal back to the aircraft. All beacons operate at the
same frequency. Each beacon transponder in a given area is assigned a different code (spacing
between the two pulses) that they emit upon each interrogation.
All of the responding beacons within the area of the display will appear on the indicator screen. Each
beacon location will appear as two short curved lines on the screen. The two curved lines will be
spaced corresponding to the pulse spacing from the transponder.
The first pulse received from the transponder generates the curved line closest to the aircraft as the
antenna scans the beacon. The actual beacon location will be at the center of this curved line.
There is a delay between the time that the beacon transponder receives a radar pulse and then sends a
reply (first of two pulses). The delay time will affect the beacon range location on the display, and is
usually adjustable on the beacon.
If the transponder delay is too long, the beacon will appear farther away than it actually is. If the
transponder delay is less, the beacon will appear closer on the screen than it actua1ly is.
Note
+ Refer to the beacon transponder manual for
correct delay adjustment.
The PUSH CODE button on the radar control panel permits identifying each beacon displayed.
Repeatedly pressing the button will sequence through 9 beacon codes. The spacing between the two
pulses of a beacon's reply determines the beacon’s code (see Table 1.6-4).
Assume you are looking for a beacon with pulse spacing of 6.0 miles. This beacon signal is coded
"B3" on the display. To find the beacon proceed as follows.
(a) Turn on the system and press the BCN mode button.
(b) Observe that the word B1 appears on the display.
Table 1.6-4. Typical Two-Pulse Beacon Transponder Pulse Spacing
SPACING SPACING
BETWEEN BETWEEN
CODE BEACON PULSES CODE BEACON PULSES
DISPLAYED (IN MILES) DISPLAYED (IN MILES)
1 3.6 to 4.3 6 8.3 to 9.3
2 4.4 to 5.3 7 9.3 to 10.3
3 5.3 to 6.3 8 10.3 to 11.3
4 6.3 to 7.3 9 11.3 to 13.0
5 7.3 to 8.3
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