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PS Engineering Audio System Installations Theory and Practices
Disclaimer • • • Your PS Engineering Dealer is responsible for the product installation. – Refer specific interface questions and procure any special tools or additional installation supplies from the PS Engineering retail dealer. – All PS Engineering dealers have an FAA Certified Repair Station with at least a Limited Radio Rating, and are qualified to make these installations. If the installation is not performed by a PS Engineering dealer or a custom wire harness is not purchased, the warranty is VOID Installation of an intercom in a certified aircraft in accordance with regulations may require specific knowledge, experience and tools. – FAR 65. 81 (b) A certificated mechanic may not exercise the privileges of his certificate and rating unless he understands the current instructions of the manufacturer, and the maintenance manuals, for the specific operation concerned. This presentation does not contain basic information about crimping, soldering, or fundamental assembly techniques. These skills are required to fabricate a wiring harness. Either the PS Engineering authorized dealer or PS Engineering can make a custom harness for you for products made by PS Engineering.
Why can’t we help with installation questions? • We don’t have the expertise. We have never performed an installation, so we must rely on avionics shops that have the knowledge and tools to perform installs. • We don’t have the necessary resources to provide the technical support necessary to aid in installations. • To assure proper installation, we have trained our dealers about the specifics about our products. This assures that we will not have warranty costs associated with improperly installed products
Applicability • This presentation applies to: – Intercom Installation – The intercom portion of audio panel installation • This does not apply to: – Radio Interface to Audio Panels – Any other avionics installation – Any wiring practice not specifically addressed
Topics 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Overview Tools and Hardware Required Theory of shielding and overall harnesses The interface for the intercom Building the Harness for the intercom How to properly make shield terminations The Intercom Installation How to ground the harnesses Entertainment interface Troubleshooting
Overview • Build Harness for Installation • Create Wire Harness per the Wiring Diagram located in the Installation Manual • Route cables to the mounted mic and headphone jacks throughout aircraft • Route cables to the music and telephone inputs as necessary • Connect audio panel/intercom to power and ground • Verify power and ground continuity • Mechanically Install Audio Panel/Intercom in panel – Note: If installing Intercom, Install Auxiliary Microphone and Headphone Jacks • These are the jacks that will connect directly to either the single radio or to the audio panel. • Test these jacks using a headset and in-line PTT switch to assure you can hear and transmit over the radio
Tools and Hardware Required Tools • • • Wire Strippers (Ideal Strip Master) Wire Cutters Crimping Tool (Palatine PA 1440) Soldering Station (WTCPT) Drill Philips Screwdriver #1
Molex Crimping tool (PMA 6000/70 00 Series) Use “A” Strip 18 -24 AWG Crimping tool for PMA 8000/9000 series (High Density)
Hardware Jacks • Three types – Microphone, Headphone (mono and stereo) • Mono Phones (1/4”) – 2 Conductor • Stereo Phones (1/4”) – 3 Conductor • Microphone (mic) jacks – Note, the mic jack has a smaller opening than the headphone jacks – 3 conductor – Smaller inside diameter
Wire • All wire must be aircraft grade – Tefzel insulation for flammability requirements – Single conductor must meet MIL-STD 22759 – Multiple Conductor must be shielded, and meet MIL-STD 27500 – Microphone and stereo headphones must be 3 conductor with shield. – Mono headphone must be 2 -conductor with shield – Never use the shield to carry signals or grounds
Wire Marking • Identification markings should be placed at each end of the wire and at 15 -inch maximum intervals along the length of the wire. • Wires less than 3 inches long need not be identified. • Wires 3 to 7 inches in length should be identified approximately at the center.
Raychem Solder Sleeves – Heat evenly until the blue and white rings melt, and provide a plug on each end. avoid overheating the wire. – Watch the wire/braid connection to see the solder fully wetting the connection.
Theory of shielding and overall harnesses Shielding • Shield grounded at one end keeps RF out because undesired currents can’t flow. • Braided shields grounded at one end create a Faraday RF shield. • Stray signals seek a low impedance (Z) path to ground. The properly terminated braid shield provides that path.
Schematic Representation This shows some typical shielding schematics. Notice how in the top schematic the low is connected to a unit pin. In some PS Engineering installations, to save space, the low side is connected to the shield ground AT THE UNIT. This is NOT the same as using the shield as the audio low. The number of solid wires that pass trough the ungrounded end of the shield signifies the number of conductors in the cable.
The Aircraft RFI/EMI Jungle • Countless sources of RFI/EMI Energy – – – Comm radios Electric motors (flaps, trim, blower) Switches Alternators & generators Strobes & beacons Other audio systems • Any and all will create noise in the audio system – Unless you follow manufacturer’s installation instructions
Audio Low • Return path for audio signals – Older avionics may not have a dedicated audio low – use chassis ground at radio/audio panel • Never use a shield as current carrying wire. All shields must remain un-terminated at the jack end. • Never use airframe ground as audio return path
Ground Do and Ground Don’t • DO ground shields at one end ONLY • DO tie shields together at ONE (1) end – Almost always the signal SOURCE • Don’t ground the jacks mechanically • Don’t ground both ends of shield set – even for different systems • Don’t use the shield as an audio return wire • Don’t EVER run mic and headphone audio in same shield (it will squeal!).
Single-point Grounding • A designated ground on the unit or system for connecting all shield and circuit grounds. • Designed to accept RFI and EMI and pass safely around the signal paths. • Any change in ground potential is felt identically by all subsystems, and ignored.
Block Diagram COM radio or Audio Panel Aircraft Radio Headphone , Microphone, & PTT
For the Intercom installs, Auxiliary Jacks • These are a REQUIRED part of any intercom installation. It where the Intercom is connected to the radio(s) • Mechanical and Electrically interface assures failsafe operation. – Bypass intercom – Use if intercom is removed – Essential part of troubleshooting
AUX Jacks Schematic (for intercom installations)
Building the Harness • Strip outer jacket • Comb out braid and fold back over jacket • Create a drain wire for the shield: – Using heat activated LC-3 Raychem sleeves, insert a stripped “drain” wire between ring and braid. • Connect drain wire of the shielded cable to appropriate ground point: – If necessary, daisy-chain to other “drain” wires, or connect to designated ground pin
Wire Shield Orange Tracer Blue Tracer White PS Engineering Harness Conventions Microphone White – Ring – Mic Audio Blue – Barrel – Mic Audio Low Orange – Tip – Radio P-T-T Headphone or Music White – Tip – Audio (Rt) Blue – Barrel – Audio Low Orange – Tip – Audio (Lt)
Termination Complete Solder melted and flowed Seals melted Heat Shrink conforms
Crimp Strip 1/16” (depth of middle band) Verify good crimp by pulling on the wire.
Insert and Close
Jack Wiring • Mono Headphone – Connect Audio Hi to tip – Connect Audio Low to barrel – Do NOT connect shield • Stereo Headphone – – Connect Audio Right Hi to tip Connect Audio Left Hi to ring Connect Audio Low to barrel Do NOT connect shield • Microphone – – – Connect Push-to-Talk (Radio P-T-T) to tip Connect mic audio to ring Connect mic low to barrel Connect low side of P-T-T to barrel Do NOT connect shield
Anatomy of a Jack Tip Mic Jack 0. 205” ID Phones Jack 0. 250” ID Ring Stereo Jack or Mic Jack Layout Schematic View (3 conductor) Tip Ground (Barrel) Tip Ring Ground (Barrel) Ring Shield
Jack/Plug Contacts Barrel Ring Tip
Hardware Installation • Connect pilot, copilot and passenger jacks. – Verify correct intercom operation, talk between all seats and test all modes. • Make connection between intercom and existing (AUX) headphone and microphone jacks connected to radio/audio panel
Checkout Procedure • With audio panel/intercom off, test Fail. Safe system by transmitting and receiving on radio from Pilot Headset positon • Turn intercom on – Verify that the radio is not keyed • Test radio receive and transmit on pilot and copilot. Test intercom ISO and Crew function (if present). • Secure unit, harness and jacks.
Fail-Safe • Connects pilot headphone and microphone to radio through a relay contact in closed position • In fail safe when off, or power removed at breaker. • In stereo installation, radio audio will be in one ear only • Verify fail-safe on initial installation – If it doesn’t work, the installation is wired incorrectly
Intercom Installation • Drill 6 holes – 2 knobs – Switch – LED (if equipped) – 2 mounting screws
Jack Installation • Drill 15/32” (0. 450”) hole for each jack • Place flat insulating washer on jack and insert from rear. • Place shoulder washer on jack so shoulder fits into the hole. • Add nut and tighten. – Be sure that the jack barrel does not contact the metal airframe. – Be sure that no part of a headphone jack touches a microphone jack
Sidetone • Audio signal from COM radio of transmission – Designed to help person regulate voice – In PS System it is passed through from the COM • Where did it go? – Not present in some Cessna systems • Separate sidetone output on some radios – Can be lost through Radio Frequency Interference (RFI) caused by improper shielding
Entertainment Inputs • One input on standard intercoms • Two inputs on units with crew mode – Second input active only in crew mode • Requires a minimum audio level 1 V p-p (Line Level) compatible with portable devices – Do NOT USE speaker levels from automotive units • Input jacks should not be grounded – Install in plastic panel
Unswitched Inputs • Only Available in PM 3000, P/N 11931 A – Two inputs for alert audio, warnings etc. • NO unswitched inputs on other models – Kluge installations are unapproved – Some COM receivers have aux inputs
Installation Troubleshooting Symptom Possible Cause Excessive electrical Noise in intercom Mic and or headphone jacks touching ground. Incorrect shield connection Intercom partially keys when turned on Mic jack miswired Failsafe doesn’t provide headphone audio Stereo headphone jack miswired No sidetone Not provided on com phones output Mic and or headphone jacks touching ground. Incorrect shield connection Audio squeal when volume on intercom turned up Mic and headphone signals crossed, or running in same shield Noise in system that goes away when radio or intercom active Music source introducing noise Music jack is grounded Intercom audio in one ear only Stereo headset to stereo in mono installation