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Old 17-03-2008, 12:24   #1
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Mounting SSB/HF tuners above deck?

Has anyone here mounted their SSB or HF tuners above deck rather than below? My Icom AH-4 survived on shore for years mounted underneath my wood deck - about 8 feet above the mean high tide line on the harbor, 12 feet from the seawall - with nary a corrosion blemish. I'd suspect my old AT-120 (or a new AT-140) would fare the same.

Mounting it to the rail would put it right next to the insulated stay, keeping the lead short. On my boat, it would be about 8 above the waterline. I could enclose it in a vented box (or even sealed - for double protection). And I don't think that using a length of tinned battery cable to reach back into the boat for connection to the copper RF ground strap would present a problem, either.

Anyone do something similar? What were your results?
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Old 17-03-2008, 13:08   #2
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tuner was mounted outside wheelhouse on my commercial fishing boat for years with no problems, I'd say go for it
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Old 17-03-2008, 14:09   #3
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Beausoleil (and we've sure got that today...lovely!),

You could do that, but I wouldn't for a couple of reasons.

1. The length of the ground strap is more critical than that of the GTO-15 wire needed to connect to the backstay; and

2. Battery ground strap is insufficient, in either case.

Better to install the tuner underdeck, with a short run -- or none at all, depending on your copper strapping configuration -- on the ground side, and run a length of GTO-15 thru-deck to the backstay. If you had no lower insulator on the backstay, you could just connect to the backstay fitting underdeck, and use a length of PVC to cover the lower part of the backstay if you were worried about RF burns.

JMO,

Bill
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Old 17-03-2008, 14:54   #4
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reinforcing Bill's statements

Visualize that the "antenna" radiating element BEGINS at the tuner output terminal to which you attach the GTO-15 wire. The radio frequency "ground" BEGINS at the tuner "ground" terminal.

This is why the tuner should be as electrically and physically close to the seawater as possible/practical. This is why effective radiated output power from the tuner is degraded when the GTO cable is parallel to and close to stern pulpits or a backstay as it gets "dressed" up to a lower insulator, if you have one. This is why Bill's suggestion to attach the GTO wire to the backstay as soon as you can physically make the lowest connection is good. Consider, for example, using the backstay chainplate inside your lazarette to make the connection. One can install a knife switch to open/close a connection between the chainplate and a bonding or "lightning" ground or rf ground strap. If you are in a lightning storm merely close the knifeswitch. Don't worry about transmitting into a ground if you forget to open the knifeswitch because most tuners can "tune" into anything without self destructing...you just woun't be able to get out on the air.
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Old 18-03-2008, 14:18   #5
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Beausoleil (and we've sure got that today...lovely!),

Bill,

For a second there I was picturing you were sitting in the in the "beau soleil" enjoying a nice beaujoleil! The name of our boat is actually in honor of one of my distant ancestors, Joseph "Beausoleil" Broussard, a patriot or terrorist (depending on whether you took the French side or the British) who led a contingent of exiled Acadians from Nova Scotia to Louisiana back in the mid 18th century. Homage to my Cajun roots!

Rick,

As noted, my backstay (actually two backstays, one for each radio) is already insulated, so I just need to figure out the best compromise distance from the lower stays for insulating standoffs to get the GTO-15 up above the insulator. For grounding, I was going to use strapping to tie together a few bronze thruhulls. Now that I think about it, having both antenna systems "share" the same RF ground probably won't be the most efficient unless I disconnect the SSB antenna when using the ham radio and vice versa - I'm assuming that each tuner will remain "coupled" to its antenna, causing problems. I'm guessing I'll have to look into two separate RF grounds, since I'd think that even with a disconnect switch at each tuner's ground connection, there'd still be a significant amount of capacitive coupling between the two? Any ideas?

While I do have a general class ticket (KB1HTW), my areas of expertise are telephony and networking - I'm not much more than a noob when it comes to RF. Although at work I am doing some research into some advanced TCP networking over mobile wireless networks - mobile networking infrastructure stuff as opposed to networking infrastructure for mobile nodes. I wish our networks moved at a stately 8 knots rather than 400! It doesn't carry over much to what I want to do on the boat.
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Old 18-03-2008, 14:42   #6
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Beausoleil,

Wow...two backstays, each dedicated to a separate radio! What a luxury.

Do you really need to do that? One would suffice very well, and one tuner. Just switch between the ham and marine ssb radios with a common coax switch. I do on my boat, and have for many years. At home (where, indeed, we had some beau soleil yesterday but not today), I can switch between many rigs -- ham, marine, military, and commercial -- and several antennas using coax switches.

I really don't think you need to worry about separate RF grounds. One should suffice just fine....connect both tuner ground lugs to it and forget about interactive problems...not likely IMHO!

Obviously, you do NOT want to have both radios on at the same time. You could risk blowing out the front end of the "listening" one.

Have fun,

Bill
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Old 19-03-2008, 19:06   #7
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RF ground

Bill's correct. I used to work at a high power HF transmitter site that had 63 transmitters from 500W to 100kW each. With over half of them on line and transmitting it was possible to communicate half way around the world with no real RF ground problems. The transmitter and antenna site covered many acres of good RF "ground". Sharing RF grounds is not a problem as long as the RF resistance is low for each antenna and/or tuner.

The RF resistance can be high between transmitters and the worst thing that will happen is to have RF levels appear on the chassis that could cause instrument problems which is usually merely an annoyance until you lower the RF resistance.
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Old 19-03-2008, 21:15   #8
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We have two HF radios, two antennas, a common counterpoise and external couplers - just like you are contemplating. Ten years so far and no problems with the externally mounted couplers or the common counterpoise.

The attached picture shows the couplers under white plastic covers that only provide shade and some protection from direct rain. The marine SSB is connected to the whip antenna and the Ham HF connected to a long wire (not raised in picture). We are fortunate that the entire aluminum bimini top is tied to the counterpoise sytem so that the run from the coupler to the counterpoise is 2" and the run from the coupler to the whip is 12" (the long wire is directly connected to the coupler).

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Old 19-03-2008, 21:40   #9
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Quote:
Originally Posted by Beausoleil View Post
Has anyone here mounted their SSB or HF tuners above deck rather than below? My Icom AH-4 survived on shore for years mounted underneath my wood deck - about 8 feet above the mean high tide line on the harbor, 12 feet from the seawall - with nary a corrosion blemish. I'd suspect my old AT-120 (or a new AT-140) would fare the same.

Mounting it to the rail would put it right next to the insulated stay, keeping the lead short. On my boat, it would be about 8 above the waterline. I could enclose it in a vented box (or even sealed - for double protection). And I don't think that using a length of tinned battery cable to reach back into the boat for connection to the copper RF ground strap would present a problem, either.

Anyone do something similar? What were your results?
A couple years ago I was on a 50+ foot steel ketch that had its antenna on one of the rear stays with the tuner mounted on the stern puplit railing. It was an older outdoor ICOM tuner (not the AH-4). Looked pretty weather beaten, but the skipper said he never had problems with it. He frequently took the boat between Maine and Trinidad.
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Old 19-03-2008, 21:53   #10
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Two myths

One myth relating to SSB (and HAM, of course being SSB as well) is that if one has no problem transmitting and/or recieving that one's system is "good". It may take only milli-watts of effective radiated output power to communicate half-way around the world with good conditions. With bad conditions 100kW will not work. The mistaken conclusion is that with a particular installation that works for some cases does not mean that it will work everywhere compared with well thought-out and designed RF installations.

The other myth is that any vessel short of 1/4 wavelength in all directions of RF "ground" has a "counterpoise". A counterpoise consists of a fabricated RF conductors which are "HUGE" in dimension relating to HF frequencies. For example, a counterpoise that enables transmission at 4 MHz will have radii equal to or greater than 50 or 60 feet FROM THE ANTENNA COUPLER IN ALL DIRECTIONS!. Has anyone ever seen a cruising boat for two people that has such areas (even with cats?) to create such geometry for a counterpoise?????

With small cruising vessels one creates capacitive coupling with the sea water or direct coupling with seawater, neither of which constitutes a counterpoise.
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Old 01-09-2008, 16:40   #11
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good evening, Will it work to RF ground the tuner to an ALU... framework for a hard top for the rf ground? The frame is as much as 8 feet above the sea but does have the square footage. The other issue is the whip antenna is only 2/3 above the framework. I had to get the tuner away from the engines as there was a possible computer conflict with the RF from the tuner output. I don't need 100% just enough to use the sail mail and get the weather from the pactor. I had put a plate through hull but the tuner had to be to close to the engine pc and caused a lot of headache though the ssb worked great. Thank you
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Old 01-09-2008, 16:59   #12
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Colemj;

A totally unrelated question - how well does having your wind transducer work mounted on your arch? Does the wind off of the main sail interfere? If not, how close is the main?

Im looking at adding an arch, and if possible the wind transducer on it as well.

Thanks,
Chris


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We have two HF radios, two antennas, a common counterpoise and external couplers - just like you are contemplating. Ten years so far and no problems with the externally mounted couplers or the common counterpoise.

Mark
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Old 01-09-2008, 19:44   #13
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Colemj;

A totally unrelated question - how well does having your wind transducer work mounted on your arch? Does the wind off of the main sail interfere? If not, how close is the main?

Im looking at adding an arch, and if possible the wind transducer on it as well.

Thanks,
Chris

Hi Chris,
That transducer is for a weather station and isn't the main wind instrument. Our main transducer is on the top of the mast like most boats.

Mark
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Old 01-09-2008, 19:51   #14
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good evening, Will it work to RF ground the tuner to an ALU... framework for a hard top for the rf ground? The frame is as much as 8 feet above the sea but does have the square footage. The other issue is the whip antenna is only 2/3 above the framework. I had to get the tuner away from the engines as there was a possible computer conflict with the RF from the tuner output. I don't need 100% just enough to use the sail mail and get the weather from the pactor. I had put a plate through hull but the tuner had to be to close to the engine pc and caused a lot of headache though the ssb worked great. Thank you
It will work if the coupler is located above (on) the arch so that the rf ground is electrically below it. When your lifelines are connected to the arch, they also become part of the ground system. Also, connect one of the arch legs to your plate using a piece of copper strap. Bolt the copper onto the arch leg socket bolts under the stern and lead it to the plate down along the hull. The arch itself is >100sqft and you have the additional lifelines and seawater connections. Your only issue might be the bottom 1/3 of the antenna radiating into ground and below your coupler.

Mark
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Old 02-09-2008, 06:56   #15
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I thought that might be the case - it did not look like any "regular" transducer that I have seen.

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Hi Chris,
That transducer is for a weather station and isn't the main wind instrument. Our main transducer is on the top of the mast like most boats.

Mark
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