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Posts: 67

« on: June 02, 2003, 07:14:10 PM »

I have been operating Maritime Mobile region two for
past seven years and have operated in Bahamas with cga recip.   comments about other instals and equip, I use ICOM 706 and Icom at 120 tuner and have 100 percent backup on equip,,, also use airmail and winlink for e-mail and am quite impressed about the system,,,,the
antenna is a 45 foot backstay and many many many sq feet of bronze window screen in the hull tied to the tuner.....comments, ideas, critics,,,?Huh?

Posts: 10248


« Reply #1 on: June 03, 2003, 08:58:27 AM »

If it were mine, I wouldn't use the AT120, I'd use the AH-4. The AT120 is designed for coax fed antennas and does not have the matching range of the AH-4 which is designed for applications like yours. Other than that, you've covered the bases.

Alan, KØBG


Posts: 939

« Reply #2 on: June 08, 2003, 01:46:55 PM »

Well, if you've been doing it for 7 years and it's working fine for you.........then the old saying, "If it aint broke, Don't fix it!..." comes to my mind....
(but I've always got a few ideas...see below)

Regarding the AT-120....
Alan, K0BG, the AT-120 is a Maritime/Commercial remote automatic antenna coupler (aka, "remote tuner"), designed for "end-fed wire antennas"....It is NOT a limited range "coax-type" ham radio tuner......

The AT-120 is an older version of the AT-130 (which has now been replaced by the AT-140).....
Although the VERY early versions of the AT-120, were only desined for 2mhz - 23mhz....they "might" work thru 30mhz, depending on your antenna/ground system...
The later versions of the AT-120 were designed to cover 2-30mhz....
And the "ham radio version" of this later AT-120, was the AH-2.......which of course has now been superceded by the AH-4......(But, while the AH-4 is is NOT the same as the AT-130/140.....which are designed for 150 watts Continuous Duty operations, on board ocean going vessels, and are much more rugged / weather resistant....)

Although it is "old", the AT-120 is in fact a very good, rugged coupler (tuner), with a very good quality weather-proof cabinet......

Okay, onto the important stuff......
If you're looking for some advice on how to make your set-up better.......then I've got a quick idea/comment for you...
A REAL, LOW Impedance RF Ground connection from your coupler (tuner), to the sea water (such as a "DynaPlate", or connecting your ground screen to your bronze thru-hulls, etc.) will certainly improve your antenna's ground plane......

This has been tested (real world testing, by on-air signal reports, AND using RF ampmeter on the backstay antenna) by many......Including Gordon West, who wrote a fairly detailed article about this.......If I can find it, I'll forward the magazine/issue info to you, But I honestly don't remember it it was in Sail or Cruising World......

The "old standard" of using 100 sq. ft. of copper mesh/screen (or other similar conductive screen such as bronze, etc.) was NOT, and IS NOT really based on any real world experience, NOR was it based on HF ground planes needed on sailboats in salt water....
This "100 sq.ft. rule" has been told, retold, repeated, and written about SO much that it is thought of as "fact" by most........(even Icom wrote about using this as an acceptable RF Ground Plane, in some of their Marine HF Installation instructions..)
BUT, in truth it is NOT......
The complete history of this "rule" is not only too long to go into here, but some of the details escape me at the moment...Hi, hi....
But the jist of this myth is:
In the early 60's, "someone" put together a "spec", which was then accepted by the "experts" (including the FCC, who I believe even included questions about it in one test for one of the commercial Radiotelephone and/or Radiotelegraph licenses).....
This "spec" said that 100 sq. ft. of conductive copper mesh, placed against the inside of a non-conductive hull (wood or fibergalss), below the waterline, will allow sufficient coupling to the water, to be used as an effective RF Ground Plane for use on 2mhz AM DSB Maritime Radiotelephones.......

Whether you believe that story or not, please believe that a short length (less than 10' - 12') of 3" to 6" wide copper strap correctly attached to only one bronze thru-hull fitting, provides a much better RF Ground Plane for ALL HF communications on board sailboats so equipped.....(as long as the thru-hull is NOT coated with many layers of bottom paint, marine growth, etc......)
And, while the use of a dedicated, submerged RF Ground Plate (i.e. "DynaPlate"), does actually provide an even further improvement over just using a single thru-hull connection......The difference between the "DynaPlate" and single thru-hull RF Ground connection is not as large as the difference between the "100 sq. ft. ground screen" and just about any "Low Impedance" DIRECT sea water connection.....

Just for your information, (I'm NOT boasting here) in addition to almost 25 years in ham radio (HF, VHF, UHF), I have been an avid offshore sailor for about 30 years.......
AND I also have about 30 years of experience in operating, installing, troubleshooting, etc. Marine HF radios, couplers/tuners, antennas, etc......
(Yes, my experience goes way back to the old days of crystal controlled transceivers, "motorized" / fixed-tuned remote antenna couplers, etc....)

Ira, I wish you good luck and fair winds!!!
John,   KA4WJA

P.S.  You might want to check out the "elmers" forum here on I like the idea of specific forums for spocific issuses....I myself (and I suspect others, as well) do NOT have the time peruse all of these forums, except once a month, or even less often......
SO, I find myself simply reading/answering questions mainly in the "ELmers" forum......
It's kind of a "catch-all" for anyone wanting info on anything ham-related......

Posts: 67

« Reply #3 on: June 08, 2003, 05:09:51 PM »

thanks for the comments, interesting to get ideas and suggestions from other hams..
I also have a icom at 130 tuner (backup to the 120)
and both tuners tune the backstay from 160 meters thru 10 meters,  It was interesting to work the boston 10 meter repeater from the bahamas with a cga call,,,,ye gads and little fishes talk about a pile up from europe
had 122 contacts in less than forty minutes, all thru the repeater... all this was done with the 706 and the at 120..  i also have the bronze screen tied to the engine with copper tape.  this 'grounding system' has
been evolving over 7 yrs.  I am a firm believer in
the fact that dynaplates are good for the people that
sell dynaplates. but for actual operation, well, i am just not so sure.  we are tied to water thru shaft, and prop in as much as the engine is also part of the
"bulk" part of ground (so is a 2X5X3 monel water tank
buried in the keel)
Gorden West used our boat "Pelago" as a example of
"how to do it" in a recent edition of Nuts and Volts
magazine....always wondered how the ah 4 would work on
maritime 2182 or 2670, cuz the at 120 and 130 sure work good on em....
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