Wiring Headset Jacks

Discussion in 'Avionics and Upgrades' started by hamer, Apr 4, 2019.

  1. hamer

    hamer Pre-takeoff checklist

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    Is there any reason (or regulation) that people typically use a two conductor and three conductor shielded wire for the headset jacks rather than using a single 5 conductor shielded wire? The shields all terminate together, but I guess having all 5 conductors twisted together might not be ideal?

    Thanks for the input.
     
  2. Dana

    Dana Line Up and Wait

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    Backwards compatibility with existing avionics. Some newer headsets, like those from Lynx and Comtronics, have a single cord/plug, but require an adapter to connect to existing standard radios. Such things are popular for ultralights and experimentals.

    The standare two plug setup dates back to telephone switchboard hardware of the 1930s, using components that were readily available back then.
     
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  3. bnt83

    bnt83 Final Approach PoA Supporter

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    For one thing 5 conductor shielded wire at a reasonable cost doesn’t exist, at least not in 24 gauge.

    Second,if you have crosstalk/noise using a 5 conductor shielded cable have fun rewiring it

    Third, with typical intercoms every seat doesn't have a phone wire that runs all the way back to the audio panel. In fact, typically all passenger phone jacks are wired in series. Pilot and copilot phones are wired in parallel
     
    Last edited: Apr 4, 2019
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  4. asicer

    asicer En-Route

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    Not sure I understand you correctly. Electrically speaking, it's not obvious to me how jacks wired in series would work or how a parallel circuit could be isolated. Do you really mean to say that pax are wired daisy-chain while pilot/copilot are wired home-run?
     
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  5. bnt83

    bnt83 Final Approach PoA Supporter

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    Correct

    upload_2019-4-4_9-10-34.png
     
  6. asicer

    asicer En-Route

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  7. AK737pilot

    AK737pilot Pre-Flight

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    I seem to remember reading somewhere that the audio wires and mic wires shouldn’t be in the same shield to prevent introducing noise....

    Yep, just looked it up, PS Engineering says “Don’t EVER run mic and headphone audio in the same shield (it will squeal!).


    Sent from my iPhone using Tapatalk
     
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  8. hamer

    hamer Pre-takeoff checklist

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    The radio I'm looking to hook up has discrete Pilot/Copilot, so I'll be running two sets of wires.

    Thanks guys. This is reason enough for me.
     
  9. Rob58

    Rob58 Pre-takeoff checklist

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    I have also read that the cable shields for the audio circuits should be isolated from the airframe ground... any opinion on this?
     
  10. Dan Thomas

    Dan Thomas Final Approach

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    That diagram shows the pax phones and mics all wired in parallel.
     
  11. Dan Thomas

    Dan Thomas Final Approach

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    They should be grounded at the audio panel end, and ungrounded at the jacks. The jacks themselves should be mounted with insulating washers. If they're grounded, or if the shields are grounded at both ends, airframe currents run through them and can cause noise in the headsets.

    Antenna shielding is grounded at both ends.
     
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  12. Rob58

    Rob58 Pre-takeoff checklist

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    Makes perfect sense... thanks for the explanation!