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Old 27-02-2010, 01:29   #1
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Insulated Backstay vs Solar-Array Gaposis

HI from S/V Nomadness...

Bit of an odd antenna theory question, and I could probably answer this with an evening spent on a much-needed refresher in the ARRL books. But I bet someone here has already dealt with this.

I have twin backstays on my Amazon 44, one of which is insulated and connected to an Icom 802 in a pretty traditional configuration (including a big mica capacitor for RF ground to my steel hull, but that belongs in a different thread).

I'm in the process of adding a 480-watt PV array, split half-and-half fore and aft of my radar arch. The forward half is constrained by the backstays and boom end, so includes a notch with an inch or so of clearance for the stays (wild guess on how much needed to avoid mechanical interference on various points of sail). The structure is stainless, and is insulated where there is potential for the backstay to make contact as things sag, stretch, bend, or get leaned upon.

All good so far, but I'm wondering if there is a potential impedance bump, so to speak... I can't quite picture what the impressed RF will do with this big metal hole. It is approximately 4 feet up from the bottom insulator and the GTO-15 connection, which is perhaps that much again from the actual start of the active element (the output of the tuner). Of course, this is just a second instance of the radiating element passing through something metallic, given the steel deck, and that is no big deal, so I'm probably worrying needlessly.

My gut feel is that the tuner will just deal, and any distortion of the radiation pattern is just a fact of life, not really important... the high-voltage end is up near the masthead.

Any RF gurus wish to corroborate this assumption, or raise any cautions I should consider? Just making sure I'm not introducing a problem...

Thanks and 73,
Steve
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Old 27-02-2010, 03:35   #2
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Hello Steve,
The antenna section of the backstay :- how long ? The part that passes though the radar arch, how is this insulated ?
As an aside, the 23ft Shakespeare vertical whip works extremely well on a steel boat.
Richard
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Old 27-02-2010, 10:31   #3
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HI Richard...

Not sure of element length... the air draft is about 60 feet. Insulation through the panel plane (not the arch) is PVC tube slipped long-ago over the backstay for human safety, though I'll provide a soft interface on the stainless side also.

I may allow for a whip as well - no shortage of counterpoise!

Steve
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Old 27-02-2010, 12:10   #4
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Steve,

Not to worry. I'm sure that on your boat you have some REAL things to worry about :-)

73,

Bill
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Old 27-02-2010, 12:17   #5
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Bill - *grin* - thought so.

Thanks.
Steve
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Old 27-02-2010, 13:01   #6
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Steve,
Same here. No worries.
I ran my backstay through a 2" piece of PVC where it went through a homemade hot water recirculation panel in my PV array. The ICOM 735 never gave me a bit of trouble, and the AT120 tuner was always happy. It drove the chainplate directly with a single insulator at the top.
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Old 27-02-2010, 13:21   #7
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Sounds good - and I'd love to see that hot-water system! I'm just working on my Isotherm installation now.

Cheers from OH Marina,
Steve
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Old 27-02-2010, 20:09   #8
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Quote:
Originally Posted by Microship View Post
Sounds good - and I'd love to see that hot-water system! I'm just working on my Isotherm installation now.

Cheers from OH Marina,
Steve
I posted something about it on a thread here somewhere.
Stop by sometime and I'll show you pictures. It was on our previous boat which, after we sold it was sailed back to Mexico.

Steve B.
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Old 27-02-2010, 20:15   #9
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I'll nose around; I'd enjoy seeing what you did. On this Saturday evening, I'm doing the classic boat thang... standing on my head in acoustically enclosed echoing space, squinting in bad light and flying sawdust, ruining my hearing with a jigsaw, cutting a hole close enough to a bulkhead to be awkward, then following that with plumbing hacks adjacent to live AC wiring. Do we know how to party, or what?

But then I stand back on the dock in that magic bit of light between a dreary day and sunset, and it's all worth it:
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Old 27-02-2010, 20:25   #10
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Steve,

I found it.
Message # 68
Only Solar
---------------------------------------------------------------------

Here's what we did for hot water on "Grey Max". our cruising mono.

The panel was home made. It was designed to fit in a solar array so it was about 26"x50". The backstay went through a hole in the panel.
Acrylic was suspended on short nylon spacers above a copper tubing parallel array and 1" of foam made up the bottom.

An aluminum angle frame held it all together.

A differential controller sensed the panel and the hot water tank temperatures. Whenever the panel was hotter than the tank, a 12 volt March magnetic drive pump circulated the water. We always had hot water.

Steve B.
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Old 28-02-2010, 13:53   #11
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Very elegant, Steve - thanks for the link. I'm just installing an Isotemp slim square water heater, and it has provision for using the engine cooling loop in addition to AC (750 watts). I'm going to try a solar heater with isolated working fluid using that same loop (instead of engine).
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Old 28-02-2010, 17:24   #12
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I just recirculated the pressurized water. I put a burp valve at the top of the system and had to periodically purge the air. It only took a few seconds, but you should have heard the comments from nearby boats! "What the heck is that?? You have WATER squirting out of your SOLAR PANELS !!!"
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Old 01-03-2010, 11:50   #13
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"Thar she blows!" I think mine will need a circulation pump, since I don't see a way to drive it convectively as a closed loop if the heat source is at the top (though I think you solved that problem by having it in the pressure water loop).

OK, this is straying a little off the RF topic... I should probably post over in the plumbing forum!

Fair winds,
Steve
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