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Two electrical / radio specific Q's

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Two electrical / radio specific Q's

Postby Crisp » Mon Dec 20, 2010 12:01 am

Hi all,

This is Ben Brigham, long lost creator of the Sir Frankie Crisp....crisp...crisp... (see "Subregatta 2001" video) How's everyone doing?
I had some down-time recently and started working on new guts for the Crisp. Since I have no idea when this project will conclude I won't make any promises for an article quite yet. (phrased as an apology, reads like a promise)

But maybe someone can help me get two steps closer to that goal. Got two questions; one electrical, one radio, both about how H20 affects them.

1.) Conventional wisdom holds that as long as the water is fresh & clean, there is no risk of shorting a lead-acid (or any ) battery across its leads when the battery is immersed, period. While I assume that wisdom still holds, has anyone tested that theory to see when 'close' becomes too-close? My battery leads are spaced more than 1" apart, so I'm not concerned there. But what about connectors where the spacing is less than 1/4"? Same situation? Does fresh water basically behave like rubber, regardless of distance?

2.) Obviously someone's addressed the proper way of getting a radio antenna out of the WTC and up a mast without difficulty. My old WTC used an electrically-isolated brass nut/bolt through the endcap, and that seems fine but it's a great deal more metal added to that antenna wire. Antennas of specific frequencies are supposed to be of specific lengths, and thus 'more is usually not better' and 'less is certainly not better' when it comes to antenna length. So is there any rule-of-thumb or empirical way of determining optimal antenna length for a given frequency once it's been sent through a bulkhead via brass nut/bolt? Or do submarine applications on surface frequency ranges make it totally not worth worrying about? Just asking this before I commit scissors-to-wire. There is no 'undo' button for that step.

Many thanks! I aim to hit the SF regatta in 2011!!!! Huzzaaaah!!!
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Re: Two electrical / radio specific Q's

Postby Wheelerdealer » Mon Dec 20, 2010 2:28 pm

1) There will always be some conduction but it will minimal. Still I have always insulates the positive terminal out of habit. I use bullet connecters and slide a short piece of silicone fuel tubing over them to waterproof it.

2) I have never taken my antennae out of the WTC. Seem to work just fine. Most antennaes seem to be 1/8 wave length long (for the 40mhz frequency I use) . I would stick with that or go for 1/4 wavelength if you have very long model (somewhere to lay it all out with out coiling)
Whaddya mean, I need a license to do that?!
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Re: Two electrical / radio specific Q's

Postby JWLaRue » Mon Dec 20, 2010 6:31 pm

Hi Ben,

I've been running all of my subs with the batteries in mini-dive modules that are either 1-inch or 1.5-inches in diameter.....with the battery terminals exposed to the surrounding water. The terminals are no more than 3/4-inch apart.

Some of the positive terminal parts do corrode away (really electrolysis) over time, so I just replace the brass washers and nuts about every 2 years. The stainless steel threaded posts have not shown any damage.

I prefert this to covering the terminals with silicone since it gives me more flexibilty to take things apart if/when needed.

Rohr 1.....Los!
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Re: Two electrical / radio specific Q's

Postby Crisp » Sat Dec 25, 2010 11:55 pm

Thanks Jim & Jeff, greatly appreciated!
(and sorry for posting in the wrong forum like a total knob) :oops:
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