SHEARWATER AVIATION MUSEUM

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  • AIRCRAFT OPERATING INSTRUCTIONS
  • PART 1 – GENERAL DESCRIPTION – AIRCRAFT AND SYSTEMS
  • Section 11 – Navigational Aids
  • DIRECTION FINDER (DF) (AN/ARA-25)

    • ARA Selector Panel

    The selector panel has eight push-button switches in two horizontal rows of four. The four switches in the lower row are not interrelated. They are push-on, push-off switches whose individual functions are illuminated in the top half of the switch. The lower half of the switch illuminates when the switch is selected on. These switches are:

    a. UHF SQL. Provides the ability to disable the UHF squelch system which, when activated, will be indicated by OUT in the lower half of the switch.

    b. DF RNG. Allows the range or sensitivity of the direction finder system to be decreased by switching out the broad band RF amplifier. This will dampen the oscillations of the No.1 BDHI needle, allowing for a more accurate on top homing, and when activated will be indicated by SHORT illuminated in the lower half of the switch.

    c. UHF ANT. Allows selection of the lower or upper UHF antenna. When off, the lower antenna is selected. When pushed on, the upper antenna is selected and is indicated by UPPER being illuminated in the lower half of the switch.

    d. ARA 25. Controls power to extract and interpret information received from the UHF, VHF/AM, VHF/FM and OTPI systems for visual display on the BDHIs. When depressed the lower half of the switch indicates ON.

    The top four switches are push-on type which, when pressed, will select the direction finder system to the facility indicated on that switch. When pressed ON, the bottom half of the switch will illuminate to indicate which radio is connected to the direction finder system. The direction finder facility is disconnected from a radio by selecting it to another radio. The four buttons are:

    a. UHF. Allows direction finding of UHF receiver signals.

    b. OTPI. Allows direction finding of sonobuoys.

    c. VHF/FM. Allows direction finding of VHF/FM receiver signals.

    d. VHF/AM. Allows direction finding of VHF/AM receiver signals. The ARA 25 antenna is not designed to handle the VHF AM frequency band. Therefore the VHF AM/DF function is unreliable and should not be relied on for navigational information.

    A 100 Hz tone will be heard when a received signal is processed by the direction finder system from any of the UHF, VHF/FM or VHF/AM radios.

    Figure 1-11-15 ARA Selector Panel (DF)