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Author Topic: Screwdriver antenna for Maritime Mobile  (Read 650 times)
ZL4HP
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« on: June 04, 2007, 04:23:50 PM »

Hi All,
I am considering running a screwdriver antenna for Maritime Mobile use.  My Shack is some way from the back stay of the boat so to tune the back stay for more than about 200W would require a very expensive ATU.  Screwdrivers look like an option here.  Has anyone done this on an ocean going vessel and if so what were the results
73's
Paddy
ZL4HP
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K0BG
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« Reply #1 on: June 04, 2007, 06:31:06 PM »

Paddy, your assumption would only be true if your were running high power. Although I don't own it, I do have an installation in a 43 foot cat based in Ft. Pierce, Fla. An Icom AH-4 drives the starboard mainstay, very effectively.

There are other ways to use an auto coupler on board a boat. The only alternative is a decent vertical. Problem is, they require a better ground plane than an antenna longer than a quarter wave in length. Neither are ideal, but certainly better than some other alternatives.

If you provide me with a few more detail, perhaps I could be of better help.

Alan, KØBG
www.k0bg.com
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ZL4HP
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« Reply #2 on: June 04, 2007, 09:29:32 PM »

Hi Alan,
you are correct I had planed to use a linear to acheive around 500W.  The boat is a 44 foot centre cockpit so the equipment is installed around 25 feet from the feed point for the antenna.  I have an SGC 230 auto tuner which works ok for the back stay but won't handle above 150W.  I have tried using a Palstar manual tuner but due to the long feed line to the back stay (I assume) the results were not good and I had problems with RF in the boat.

Ground should be ok as the boat is steel, although I suspect this added to my problems with the manual tuner and feedline.

I had assumed that using a screwdriver would ensure there was a better match at the feedpoint and they claim to accept higher power.  

Let me know if you need any more info.  Any help would be appreciated.
73
Paddy
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K0BG
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« Reply #3 on: June 05, 2007, 05:59:40 AM »

The SG235 will handle 500 watts, and it has a built in buffer for an amp. The input for it can be run directly from an Icom or Yaesu (H-send on the Icom). The output is a switching FET and will easily handle 13.8 volts up to about 1.5 amps. It is there to protect the coupler of course, but it sure makes interfacing easy.

The main problem with driving the stay from a distance is the feed line. You really can't use coax, and a single line becomes part of the antenna leading to all sorts of RFI problems. The Palstar AT could be used, and it costs about the same as the SG235 (about $1,100 US).

Good luck with the install.

Alan, KØBG
www.k0bg.com
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AA4PB
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« Reply #4 on: June 05, 2007, 07:51:43 AM »

You might also want to consider antenna efficiency vs. transmit power. You may very well have better communications with a longer (more efficient) antenna like a backstay and 100W than you would with a less efficient screwdriver and 500W. The more efficient antenna also benefits receive as well as transmit.
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KI4TMM
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« Reply #5 on: June 07, 2007, 05:25:09 AM »

We spent several years cruising our cat Makai in the Caribe with maritime ssb (icom 802, at130, and shakespear 390 antenna) and now that I am a ham as well i looked to see about increasing our boats radio capabiltiy.  

The srewdriver style antennas looked like an interesting solution, but concerns of salt water intrusion is very high.  Not only for the conductivity issues but for wear and tear.

On the cruise we found that salt water gets into everything.  It staturates the air so anytime something breathes because of the changes in heat it would suck in salt air which would eventually cause most non marine items to fail fairly quickly and even some marine items as well.

In the case of the screwdriver which would be mounted out in the weather with driving rain, seas, and the physical abuse of being bounced around on a boat makes me wonder if they could withstand it all.  


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W3LK
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« Reply #6 on: June 07, 2007, 08:14:09 AM »

For all the reasons you listed, ANY motorized antenna is a poor choice for marine use on anything but a very temporary basis.

These are the same reasons marine antennas are enclosed in a fiberglass radome.

Lon - W3LK
Baltimore, Maryland - Soon to be Naugatuck, Connecticut
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KI4TMM
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« Reply #7 on: June 08, 2007, 04:10:04 AM »

Follow up on my above.  

I also like the idea of the ATU. In an emergency, let say a lost vertical antenna, a length of cable can be connected and run up the mast or even drapped about the boat and contact could be made.  Also carrying an inexpesive manual tuner could serve as back to the ATU.

I think this combo may prove about the same expense as a screwdriver with an easy constructed backup and providing more flexibilty.

just a thought.
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KI6IWX
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« Reply #8 on: June 29, 2007, 01:17:38 PM »

Wouldnt the HiQ marine stainless antenna be a logical choice? I was thinking ahead for next year for a fishing boat application. Now they have an antenna designed for submarines available as well - it's got to be the ultimate in intrusion protection...
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