H34222
VHF Antenna Installation 500
23-21-11Page 402 Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 15/68
VHF ANTENNA - INSPECTION/CHECK
1. General
A. The following bonding check should be conducted any time that a VHF antenna has been reinstalled (Ref 23-21-11 R/I).
2. Equipment and Materials
A. Bonding Meter (Ref 20-22-01)
3. Check VHF Antenna Bonding
A. Measure dc resistance between antenna base and fuselage structure per 20-22-01. Resistance should not exceed 0.1 ohm.
500
Feb 20/85 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 23-21-11 Page 601
SELCAL SYSTEM - DESCRIPTION AND OPERATION
1. General
A. Two identical selcal (selective calling) systems are installed in the airplane. A four-tone alert signal from a ground station, is sent to an airplane VHF or HF system and is detected by the selcal system. The selcal system alerts the crew members by means of a light and a chime whenever a message is to be received on one of the communication systems.
B. The selcal systems are composed of a decoder, chime, and selcal control panel. The decoder is located in electronic equipment rack (E2-2). The chime is enclosed within the aural warning unit on the forward right side of the control stand. The selcal control panel is installed on the pilots aft overhead panel. See Fig. 1 for the component locations.
C. Selcal system No. 1 obtains 28 volts dc from switched electronics bus No. 1 on circuit breaker panel P18. Selcal system No. 2 obtains 28 volts dc from switched electronics bus No. 2 on circuit breaker panel P6.
2. Control Panel
A. On GJ B-2509 thru B-2510 and B-2524, the control panel has two indicator lights and a PUSH-TO-RESET button Selcal-1 indicator light will come on when decoder unit No. 1 is activated; and selcal-2 light responds to decoder unit No. 2. When pressed the PUSH-TO-RESET button deactivates both decoders simultaneously.
B. On GJ B-2501 thru B-2503, the control panel has two indicator lights, a selector switch for Selcal-2, and a RESET button. Selcal-1 is connected to VHF-1 system and Selcal-2 can be switched between the HF and VHF-2 systems. The RESET button deactivates both decoders simultaneously.
C. On GJ ALL EXCEPT B-2501 thru B-2503 and B-2509 thru B-2510, the control panel has two indicator lights, PRESS TO RESET buttons, selector switches, and a MARKER selector switch. Each selcal decoder can be switched between the HF-1, HF-2, VHF-1, and VHF-2 systems. The PRESS TO RESET buttons allow each decoder to be deactivated individuality.
3. Dual Selcal Module
A. The dual selcal module consists of two separate decoder units in a common case. One unit is connected to HF No. 1 and VHF No. 1 system receivers; the other is connected to HF No. 2 and VHF No. 2 system receivers. Each unit consists of an audio amplifier, dc amplifier, control relays and vibrasponder resonant reed assemblies (Fig. 2).
B. The decoder unit audio amplifier consists primarily of two stages of amplification followed by push-pull power amplifier. The power amplifier is capacitively coupled to the coils of 12 vibrasponders (resonant reed assemblies). When a tone signal is received, the signal is amplified and fed to the coils of the vibrasponders. An AGC circuit is provided to maintain proper drive for the vibrasponders.
C. The dc amplifier consists of the vibrasponder contactors, filter network and an amplifier. When the proper combination of tones is impressed on the vibrasponders, the vibrasponder reeds vibrate and complete the circuit through the reed contacts to the filter network and amplifier. When the amplifier is operating a circuit is completed through a decoder relay. When the decoder relay is closed, a voltage is applied to the coil of the relay causing it to effectively latch closed.
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