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Installed in the SH-3H SeaKing helicopter as well as the P3 Orion, the On Top Position Indicator (OTPI) was a VHF receiver system capable of providing relative bearing information from the aircraft to any of the 31 different channels of sonobuoys launched across the suspected path of a submerged submarine. It was used in conjunction with direction finding equipment with the system consisting of:
UHF antenna - This was common to both the UHF/DF and the OTPI systems of the aircraft and located behind a protective cover aft of the electronics compartment on the bottom of the fuselage.
AM-3969 amplifier - The radio frequency amplifier was designed to amplify the received signals and pass them to the receiver for processing. It was located on the upper shelf of the electronics compartment.
R-1047A/A receiver - The receiver enabled the selection of any sonobuoy channel and used received signal strength to tune the ARA-25 antenna to its maximum signal position. It was located on the upper shelf of the electronics compartment. and had a frequency range 162 to 174 MHz FM.
C3540 Control Unit - Controling the receiver it enabled channel selection between each sonar buoy.
Indicators - OTPI bearing information was displayed on the number one needle of the pilot, co-pilot and TACCO's BDHI (Bearing Distance Horizontal Indicator)
The controls on the C3540 consisted of the following:
Press for Control Button - (This was not used in the SeaKing aircraft)
Channel Knob - The rotary dual-range switch enabled the selection of the desired sonobuoy channels.
OFF/1-16/17-3 - In addition to being a power switch, this control selected either the low or high range of sonobuoy channels.
Signal Intensity Lamp - (Disabled in the SeaKing aircraft).
Operating procedures for the OTPI were as follows:
- Pilot selects either T/R and G or T/R on the UHF radio remote control panel;
- Set OFF/1-16/17-31 switch to desired range.
- Set channel knob to desired channel.
- Select UHF/TAC on BDHI selector panel; and
- Number one pointer will indicate the bearing to the sonobuoy.
Here is an extremely informative youtube video of the launch and activation of one of the SSQ-801E BARRA Sonobuoy deployment which are an updated version to those carried by the SeaKing and later SeaHawk helicopters: https://www.youtube.com/watch?v=eidMDdMK38s
This Seaking Helicopter Instrument comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in aircraft cockpit.
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Your Seaking C3540 OPTI VHF Receiver, Original Recovery Curios Warbird Collectable includes:
- Original Warbird instrument
- Highly detailed hand-built and airbrushed 1/72 plastic scale model of the aircraft,*
- Hand-crafted and beautifully finished 100yr, Far North Queensland Mango Wood display stand
- Detailed, 2-sided, printed and laminated Instrument Fact Sheet detailing aircraft and instrument
- Removable Magnetic Display Arm
*An upgrade to the larger and more detailed 1/48 scale model is also available in the hand-built and airbrushed plastic version for an additional $45 (Click on the 1/48 scale option)
Both the 1/72 & 1/48 scale hand-built and airbrushed plastic models are available with canopy and doors 'open or closed' with a choice of two Squadron markings and camouflage.
Upon order placement you will receive an email asking for your preferred configuration.
Your complete Recovery Curios Original Instrument Collectable is securely packed and delivery normally takes between 3 - 4 weeks approx.
Did you fly, crew or maintain a Seaking or have a friend, colleague or family member who did? Check out our PERSONALISED ORIGINAL INSTRUMENT COLLECTABLE OPTION here.