NAV antenna balun mystery

I am replacing the antenna wiring in my 1960 C310D as the coax is original … I have the dipole cat whiskers which are mounted to the vertical stab cap which is fiberglass … when I removed the fiberglass stab cap and disconnected the BNC connector I noticed there was no ground wire from the balun box to the airframe (on a previous 310 B I had noticed it had a ground from the balun box to the airframe) … when I removed the coax it appeared to have a coax balun as well – meaning 18” down from the BNC connector there was a 6” piece of coax with its shield tied to the feed shield … to my understanding if this was actually a true coax balun then it would be looped and the shield would feed directly to the antenna (no BNC) … a friend saw this and said it might be a ground plane …

Two questions – (1) should the balun box in the stab cap be grounded to the airframe and (2) is the old coax correct – I suspect this is a left over from a previous install … Attachment not found. Attachment not found. Attachment not found.

Any help and insight would be appreciated …

Comments

  • Scott ShererScott Sherer COO Forum Moderator
    Thanks for writing, let me run this by our A&P Erich Rempert. Please stand by

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Scott ShererScott Sherer COO Forum Moderator
    Hi again, I need some assistance from you. Can you please email the photos to me at scotts@jonespublishing.com ? That will make it easier to get a good answer.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Pictures are on their way to you ... thank you ...
  • Scott ShererScott Sherer COO Forum Moderator
    Ok, I have them. Please stand by. :)

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Scott ShererScott Sherer COO Forum Moderator
    Ok, your questions and photos have been forwarded to our A&P Erich Rempert, who's also an avionics tech. I'll let you know as soon as I hear from him.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Scott ShererScott Sherer COO Forum Moderator
    Here's a response from Erich:

    It seems the antenna is not wired properly. If it's using a balun, the balun should feed the antenna as shown in the picture. The Bnc would be OK if it was not in between the antenna and balun, meaning to disconnect the balun / antenna assembly. I'm not sure on the ground wire, I'd look at an installation drawing for the antenna if you can find one. It seems to me if my memory serves me correctly, I have seen a ground strap on others but I'm sure it depends on the antenna.

    I would re work the antenna as shown in your diagram and connect it to the feed coax with a BNC so it can be removed with the antenna and then try it. If it doesn't work, add the ground strap later and re test.



    ~Erich Rempert, A&P Consultant

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Thank you ... I've seen a similar C310 which had the balun box with a straight coax and it also had a ground wire on it to the airframe ... this coax appears to have been the original balun and then cut and a BNC added and the metal balun box added at a later time ... I installed new coax and but have not run a ground wire yet ... I will test things out once I put the plane back together (extensive annual) and get her in the air ... then determine if the ground is needed ... thank you for the feedback ...

    Dusty
  • Scott ShererScott Sherer COO Forum Moderator
    Sounds like you're slowly making progress. Good luck and thanks for the update.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

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