HF alternatives to backstay antennas.

[Jammer]

Thank you all for the ideas and advice.

Originally Posted by smallFry

Jammer, does your Hunter have a steel compression post stepped to the keel? If so, your mast and rig are probably electrically continuous with your keel through the tabernacle.

There is a compression post. She's a water ballasted boat shaped like a bathtub with a centerboard, no keel.

[caffel]

I sailed 25,000 miles with a 15' coax fed masthead vertical using all 4 elements of the standing rigging as counterpoise/ground plane. This gave good performance to the SEAnet all the way across the Indian Ocean.
The great thing about a sailboat is that there are so many 'hoist it up and try' opportunities. If I were to do it all again I'd get or make a vertical and send it up the mains'l track for a trial run and then commit to the masthead bracket for it.
KC3LZR

[K1MGY]

Originally Posted by David B

Just one more thing to consider - if your mast falls over, so do your antennas. Always good to have a back-up you can at least temporarily clamp to your pushpit (or in your case, even better - your arch).

In an emergency such as loss of mast I wonder if a balloon carrying a wire antenna aloft would be a good backup?

[Jammer]

Originally Posted by K1MGY

In an emergency such as loss of mast I wonder if a balloon carrying a wire antenna aloft would be a good backup?

Usually people talk about using kites. There are fishing kites made that are said to be a good fit. I've never tried it.

[Double-Wide]

I had very good luck with something called a “Rope Antenna “. It was a piece of nylon double braid that had replaced the rope core with a piece of copper wire. It was sold online. I attached it to the top of the mast and ran it down to the rail just aft of the shrouds. It worked great throughout the Bahamas.

[Talbot]

I have a cat with no backstay, but sweptback shrouds. My aerial is on one of my shrouds.
There are advantages for this. My Antenna Tuner Unit is fitted right by the stay, so the distance between aerial and ATU is minimal. The radio M802 is also close to the ATU.

[Mike Burch]

Right now we are just coming off the bottom of the eleven-year sunspot cycle, which means that HF propagation is rubbish, and will remain so for a year or two yet. Therefore we require the least inefficient antenna possible.

We want the signal to take off as close to horizontal as possible, and that means a vertical antenna. Any vertical antenna (other than a dipole, and if you have a tall enough rig for a dipole at HF you won't be reading this) is only half an antenna. The other half is the image of that antenna half in the ground—which in the case of a yacht is that perfect conductor, the ocean.

Therefore the "earth"connection is as important as whatever wire you string up. By far the best earth is a sintered bronze earth plate—a thing about 6" x 2 " x 1/2", having an actual surface area of 6 square metres, and consisting of thousands of tiny bronze spheres sintered together, and mounted outside the hull well below the waterline. It should be connected to the antenna tuner by the shortest possible length of wide copper foil. (RF energy travels only on the surface of a conductor, so we want surface area, not cross-sectional area, in an RF conductor. This is known as "skin effect". Foil has much greater surface area than the same amount of copper made into a circular wire.)

My ketch had a split back-stay for the main, so I used the starboard main cap shroud, fitting an insulator a couple of feet from the top, and passing it through a Tufnol tube to isolate it from the spreader. Rather than feeding the chainplate, I took a copper wire from above the turnbuckle down though the deck to the tuner, being careful to moisture-proof the connection between stainless and copper. It wasn't ideal, having the aluminium mast so close, but it was always available, and when the propagation gods were smiling I could (just!) work England from the South Pacific.

[Jon Hacking]

Originally Posted by Jammer

... My Hunter 26 doesn't have a backstay -- the fractional rig has a forestay with a roller furler on it, and swept-back shrouds, upper and lower. What is the most reasonable antenna to use on a boat like this?

As a cat without a backstay, we run a wire up to our uppermost spreader, about 3' ahead of the cap-shrouds. I try to use fairly thick wire, like the outer shield of a bit of coax. This insulation isn't really up to the voltages I can generate, but nobody's out holding the antenna while I'm xmitting.

So my tuner (manual to stbd, auto to port) is mounted inside, near the bottom of where the wire comes down. Each tuner has a ground-plate under it, with 2" wide copper strap between the plate & the grounding studs. Drill a small hole through the hull a bit below the toe-rail to feed the insulated wire out (& a bit of sealant to keep water out) & run it up towards the spreader. The top of the wire has a few feet of 1/8" parachute cord as insulation, & that cord is what is tied to the top spreader. I tie a bit more light cord to the antenna lower down, & tension it down to a life-line. I try to keep the wires a few inches from conductive members like stanchions & toe-rails.

I also like the idea of using the whole rig. One thing I've found is that the rest of my rigging makes my signal somewhat directional, & a full-rig antenna would probably get rid of that. But I don't think it would work well if waves were lapping the chain-plates, or other variable or intermittent grounding forces were at work.

[Michael Cobbe]

[QUOTE=Jim Cate;3262413]Well, you could do what I've done for the last 34 years: use the whole, uninsulated rig. On our previous boat I fed the backstay chainplate below decks, and on this boat the port shroud chainplate. I use a manual MFJ tuner and it works on all the HF bands. I've tried it with the mast base grounded and floating, noted little difference in perceived performance, but the tuning is slightly different.




If whole the rig isn't inslulated then all of it will be live, as will anything else connected, if you hold any of it you will cook your hand from inside to out. It is not good idea.

[Sailmonkey]

Originally Posted by Michael Cobbe

[
If whole the rig isn't inslulated then all of it will be live, as will anything else connected, if you hold any of it you will cook your hand from inside to out. It is not good idea.

True, but the same hold true for the normal insulated back stay antenna too. Hang out near the stern with your hand on the GTO feeder line and you’ll cook as well.

[waterman46]

Originally Posted by Michael Cobbe

If whole the rig isn't inslulated then all of it will be live, as will anything else connected, if you hold any of it you will cook your hand from inside to out. It is not good idea.

Couple of exaggerations in last few posts about effects of HF RF on human body at the power levels we are using (<200W).
RF at this frequency and power level does not "cook" from the inside out. It passes around, not through, your body without damage. At these wavelengths, your body is too small of an object to receive energy in the sense that it would cook from the inside out.

What you could actually experience if you touched an *uninsulated* antenna near the tuner would be an RF "burn". This is a surface burn like you'd get if you touched a hot pan.

[Jim Cate]

Originally Posted by waterman46

Couple of exaggerations in last few posts about effects of HF RF on human body at the power levels we are using (<200W).
RF at this frequency and power level does not "cook" from the inside out. It passes around, not through, your body without damage. At these wavelengths, your body is too small of an object to receive energy in the sense that it would cook from the inside out.

What you could actually experience if you touched an *uninsulated* antenna near the tuner would be an RF "burn". This is a surface burn like you'd get if you touched a hot pan.

Yep, quite so!

Otherwise I'd be well done by now. And to be accurate, in the 34 years we've used this system, zero burns, electrocutions, cookings or other nasty results.

Maybe I'm just really lucky.

Jim

[Jammer]

I will point out that in my misspent youth (tm) I got an RF burn on my finger that took several weeks to heal. It was from a defective antenna connection on a 4 watt handheld, albeit at VHF.


VHF frequencies are more dangerous from any injury standpoint than any other. The 1000 watt broadcast FM transmitter I used to maintain while in college was the probably the most hazardous piece of radio gear I've worked on.