[PSUBS-MAILIST] coax

[Sean T. Stevenson via Personal_Submersibles]

Provided you are using a common monopole (whip) antenna and not a dipole or something fancy, the radio antenna will typically use one "hot" conductor (the coax core) to excite the antenna element, and connect the coax shield to a conductive ground plane (your hull / car body / etc.) immediately beneath and at right angles to the antenna. You only need a single core penetrator for this, but the coax shield ideally will be terminated to the penetrator in a way which completely surrounds the core without gaps (360° termination), as opposed to breaking out the shield and terminating it to a single point at the hull or penetrator. Passing the coax through a compression fitting accomplishes much the same thing, as the ground plane connection would simply be made at the antenna mount outside the hull, or you could not connect the shield to a ground plane and feed a dipole antenna instead.

Video signals are a different story, as the video feed is a differential signal of typically much lower power than an antenna feed, and uses the coax for noise immunity. You wouldn't connect the shield of a video feed to the hull under any circumstances.

Sean


On January 25, 2017 3:10:45 PM MST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Brian, that is not true, I have done this many times with my log
>salvage ROV's.  I ran 350 feet of coax through a penetrator and to my
>camcorder.  Perfect video and audio.Works perfect!Hank 
>
>On Wednesday, January 25, 2017 11:56 AM, Brian Cox via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>
>Hank,  When you interrupt the shielding like that it messes up the wave
>propagation .    Emile,  Do those fitting essentially just squeeze the
>cable really tight?   Is there a manufacturer that is recommended?   My
>cable is 200 thousandths ( 5mm) diameter thick, and is RG59     I guess
>I could just thread the cable through without cutting into it?
>No?  Brian   
>
>--- personal_submersibles at psubs.org wrote:
>
>From: hank pronk via Personal_Submersibles
><personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org>
>Subject: Re: [PSUBS-MAILIST] coax
>Date: Wed, 25 Jan 2017 18:35:25 +0000 (UTC)
>
>Brian,I have made a two wire penetrator for coax, just but an adaptor
>that goes from coax to two wires.  Emile's plan is less work
>though.Hank 
>
>On Wednesday, January 25, 2017 5:45 AM, hank pronk via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>
>I was very surprised to receive a phone call on my cell sealed up
>inside Gamma.Hank 
>
>On Wednesday, January 25, 2017 4:46 AM, Brian Cox via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>
>Hi All,                  Been installing my ship to shore VHF marine
>radio.  what is a good way to run the coax thru without having to get
>the manufactured connectors,  Those things are kind of pricey !   
>  Brian
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