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Ground it to bare metal. I make my living doing this. Coupling theory will result in very poor VSWR. I measure with mili-ohm meter. Our composite helos get metal mesh and bonding straps to ground also. Transponders are not cheap. Don't trust off the wall theories.
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* leave the rubber gasket on * make sure that my doubler isn't primed, ie down to the bare metal, at the point where the lock washer makes contact * probably NOT prime the doubler in this case, so that I get a good electrical connection between the doubler and the rest of the aircraft skin? Sounds like that's going to achieve the best results here, while allowing that rubber gasket to provide some friction. Does this sound like a good distillation? |
Sounds good. If you really want to, you can seal the base after installation but most don't need to. Depends on your environment. The transponder is a high power pulse type transmiiter. You should still have it tested and logged in airframe logs. Good luck.
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You can prime the doubler, as long as you keep paint out of the rivet holes (the rivets will make the electrical connection to the skin) and where the coax braid goes to ground. |
The ground path for that antenna is: threads of the body of the antenna>nut>toothed washer>mounting surface. The reason for the toothed washer is both for locking, and (hopefully) to bite through any insulating coating on the aluminum mounting surface. Paint a piece of scrap aluminum, drill it for the antenna, mount & torque the nut, then remove & look at the painted surface that was under that toothed washer.
Worrying about the rubber washer is getting off in the weeds, from an electrical standpoint; that side of the mount doesn't really participate in the grounding of the antenna. As others pointed out, it *is* intended to keep water out of the joint. You can use a dielectric paste (helps keep out moisture/corrosion on the back side) on the nut/washer side of the joint, but unless you live near the ocean it's probably overkill. |
I have zero experience with this... searching to learn. Could we not run a ground wire with eye connector to the thread of the antenna?
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The laws of Physics have not changed since, forever! Because something "works" doesn't mean it is correct. :cool: |
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