HF/SSB antenna inside Dyneema lifelines

[Jammer]

Backstay antennas have a number of limitations, among them dependence on a large tuner, dependence on a ground plate, and overall cost.

I am thinking of replacing my lifelines with Dyneema and running conductors of suitable length down the center of the dyneena to serve as center fed, half-wave antennas. On my vessel the feedpoint would be under the amidships boarding gate with insulated wire coming up on standoffs on either side of the gate before entering the Dyneema and running fore and aft.

For the 40 meter ham band and 8 Mhz marine band, realistically, on a 38' boat, loading coils will be required, or a tuner. If using a tuner, it should be possible to run ladder line to eliminate the losses associated with coax and the requirement for a balun at the antenna feed point. If using loading coils, they would go roughly at the midpoint and be suspended from the line. I would try to do them without any connections, for example by using magnet wire for the antenna and just having it come out of the Dyneema braid, wound around the coil form, then reentering the Dyneema braid to go on its way.


My main interest is middle distances just beyond VHF range where NVIS provides most of the signal. A lifeline antenna will mostly radiate vertically, which is perfect for NVIS. Great way to talk with someone 80 miles away and over a couple of islands or peninsulas.


For 80m/4Mhz the best I can come up with is to put the feedpoint at the stern and run elements inside the Dyneema on each side of the boat, going under the deck at the amidships boarding gates then back up into the Dyneema to the bow. There would have to be loading coils for this to work. I am not sure it would transmit well enough to be worth doing.

Higher frequencies are relatively easy since the lengths are shorter. Could do some frequencies on port, others on starboard; some on upper lifeline, some on lower lifeline, to the extent operation on higher bands is a goal.

I would think a modest tuner would probably be required to get to the edges of each band. If designing for a limited number of bands rather than the "whole world" it should be possible to wire everything in parallel and avoid the need for an antenna switch.

Advice and experiences welcome.

[S/V Illusion]

Worth the effort?

You still need a tuner and ground while losing the advantage of a typical diagonal antenna (sloper) radiation pattern. Additionally, you would need to do an RF field calculation to ensure the crew isn’t exposed to excessive RF while surrounded by the antenna.

[Jammer]

Originally Posted by S/V Illusion

Worth the effort?

You still need a tuner and ground

A center-fed half-wave dipole does not require, or benefit from, a ground.


Because these antennas are tuned to be a pretty close match, they ask much less of the tuner, which means that a smaller, lighter, simpler, and far less expensive tuner can be used than, say, a $600 AT-140.

Additionally, you would need to do an RF field calculation to ensure the crew isn’t exposed to excessive RF while surrounded by the antenna.

I was waiting for that. I've done the math on this before, and usually 3 feet puts you on the safe side of the (very conservative) FCC exposure limits at 100 watts, with a half wave dipole, below 10 MHz and a little ways above that. Between 20-30 MHz, 6 feet.


A 6 watt VHF handheld with an aftermarket, longer antenna will put you over the exposure limit when you use it, because it's 8" away from your body and VHF is more hazardous than HF and the standards reflect that. So will many 25 watt VHF installations where the antenna is not well above crew.

[S/V Illusion]

Originally Posted by Jammer

A center-fed half-wave dipole does not require, or benefit from, a ground.

Any antenna including a dipole can and often does require a tuner over it’s designed band limits particularly as described in your plan in such close proximity to other metal. And when used with any ‘solid state’ radio, SWR or impedance mismatch will cut back RF output. It doesn’t care if the mismatch is from a dipole or a long wire.

Because these antennas are tuned to be a pretty close match, they ask much less of the tuner, which means that a smaller, lighter, simpler, and far less expensive tuner can be used than, say, a $600 AT-140.

Loss in a small tuner can be significant compared with a higher rated one because they aren’t true LC networks. Plus the cost difference between a small and larger tuner can be trivial.

I was waiting for that. I've done the math on this before, and usually 3 feet puts you on the safe side of the (very conservative) FCC exposure limits at 100 watts, with a half wave dipole, below 10 MHz and a little ways above that. Between 20-30 MHz, 6 feet.


.

Apples/oranges. Unless you calculated being surrounded by the antenna on all sides, the analogy fails.

Seems like a long way to go to reinvent the wheel.

[Jim Cate]

When used over land, dipole antennae do better when elevated well above ground. would t his not affect the useful radiation from such a lifeline mounting only a few feet above the sea water?

Jim

[Jammer]

Originally Posted by Jim Cate

When used over land, dipole antennae do better when elevated well above ground. would t his not affect the useful radiation from such a lifeline mounting only a few feet above the sea water?

Good question. Over land, dipole antenna have a high takeoff angle when installed close to the ground. I would expect this to be true, also, over seawater. To what extent it is true over fresh water (I am in the Great Lakes) is unclear.


As you're probably aware, a high takeoff angle is considered undesirable in ham radio circles because it reduces the maximum usable frequency (MUF), which is a function of angle of incidence. Even when using a frequency below the MUF, the strength of the received signal is reduced at DX because more "hops" are required. In ham radio circles, power radiated vertically is considered "wasted" and antennas prone to high takeoff angles are characterized as "cloud warmers."


But half-wave dipoles mounted low to the ground are the preferred antenna for short- and mid-distance communications using NVIS techniques, in part because of the high takeoff angle. The idea with NVIS is to use lower frequencies that will reflect from the F-layer to provide communications with high path reliability up to several hundred miles, without a skip zone, and without line-of-sight limitations. That matches my goals for HF -- I would like something that will work reliably beyond VHF range but don't necessarily want to talk to people on the other side of the world.


There is an excellent NVIS article here: https://kv5r.com/ham-radio/nvis-antennas/

[stormalong]

Originally Posted by Jim Cate

When used over land, dipole antennae do better when elevated well above ground. would t his not affect the useful radiation from such a lifeline mounting only a few feet above the sea water?

Jim

Originally Posted by Jammer

Good question. Over land, dipole antenna have a high takeoff angle when installed close to the ground. I would expect this to be true, also, over seawater. To what extent it is true over fresh water (I am in the Great Lakes) is unclear.


As you're probably aware, a high takeoff angle is considered undesirable in ham radio circles because it reduces the maximum usable frequency (MUF), which is a function of angle of incidence. Even when using a frequency below the MUF, the strength of the received signal is reduced at DX because more "hops" are required. In ham radio circles, power radiated vertically is considered "wasted" and antennas prone to high takeoff angles are characterized as "cloud warmers."


But half-wave dipoles mounted low to the ground are the preferred antenna for short- and mid-distance communications using NVIS techniques, in part because of the high takeoff angle. The idea with NVIS is to use lower frequencies that will reflect from the F-layer to provide communications with high path reliability up to several hundred miles, without a skip zone, and without line-of-sight limitations. That matches my goals for HF -- I would like something that will work reliably beyond VHF range but don't necessarily want to talk to people on the other side of the world.


There is an excellent NVIS article here: https://kv5r.com/ham-radio/nvis-antennas/

This is the point. Dipole antenna are best at least half a wavelength above ground. For HF on a boat you are not interested in short range communications. That is what VHF is for. You will loose most of your radiated energy into the ground (water in this case). Stick with the backstay and counterpoise. Or you can hoist an inverted V on a halyard. But handling the amount of feedline and the acute angle of the two halves of the dipole are issues.

[S/V Illusion]

Slopers and inverted V antennas are inherently NVIS antennas in part because of their design. Neither produces low take-off angle. In fact, the major lobes of both configurations are above 35degrees and greater.

Predicting relative performance is pretty simple to model with any of the public domain modeling programs. Although I didn’t bother trying, I would be astonished the proposed configuration is of any benefit and suggest you do this prior to making the effort.

[Jammer]

Originally Posted by S/V Illusion

Predicting relative performance is pretty simple to model with any of the public domain modeling programs. Although I didn’t bother trying, I would be astonished the proposed configuration is of any benefit and suggest you do this prior to making the effort.

I've done it and also have both types of antennas installed at my house, where I have experimented.


A 43' 1/4 wave vertical performs extremely poorly without a fantastic ground plane, which I don't have at my house, and which I don't have on my boat on Lake Superior (freshwater). The center-fed half wave does much better, even though it's "too low."


Modeling bears some of this out although it's hard to model a bad ground plane with the NEC-5 and similar free programs. There are also some considerable losses in tuner, with a backstay antenna, since there is no attempt to make it resonant. Exactly how bad these are is hard to model but it's easy to lose 5 dB at 40 meters even if you're doing everything right.



At 80 and 160 meters, the difference in performance is huge, because the vertical antenna is too short, leading to a low radiation resistance and large losses in the tuner.

[S/V Illusion]

Originally Posted by Jammer

I'm not sure what you're trying to say. The performance of half-wave antennas is widely understood, no modeling required, unless you're suggesting that I try to model the rig, stanchions, toerail, etc.


The only interesting question is whether to use the surface of the water as the ground or the lakebed. The water in Lake Superior does not conduct electricity as well as the ocean.


My goal is not to build an antenna that performs better than a backstay antenna in the ocean. My goal is to build an antenna that will perform better (and cost less) on Lake Superior where a ground plate is useless and where the goal is medium distances.

Sorry if I wasn’t clear - antenna performance modeling is pretty simple to use and quite precise in its depiction of radiation pattern affected by various variables you plug into the model such as ground (water) proximity, geometry of the antenna, proximity to roof (read - deck), other objects and elevation of course.

I understand your goal. What I doubt is what you describe would perform better than the traditional types chosen based on their all-around performance on boats after decades of experience.

Parenthetically, your signal will never ‘see’ the lakebed. The water surface will reflect RF or absorb RF depending on proximity.

[team karst]

It is worth a try. I have used an extension cord on deck and made hf contacts out of state. You might also research mag loops. May do better than very low dipoles. Btw, my 23’ whip does very well into midwest, texas and SoCal from bahamas. But that’s tunerville and 20m.

[Jammer]

Originally Posted by S/V Illusion

I understand your goal. What I doubt is what you describe would perform better than the traditional types chosen based on their all-around performance on boats after decades of experience.

Nobody chose a backstay antenna for all-around performance.

Backstay antennas are used because they integrate with the rig without adding windage or getting in the way of the sails, and because they don't need to be taken down when not in use. All that is important. The use of a backstay also predates the availability of nonconductive lifeline material, which provides an opportunity that has been IMO insufficiently explored.


Improvements in materials provide an opportunity for innovation.

[S/V Illusion]

Originally Posted by Jammer

Nobody chose a backstay antenna for all-around performance.

Backstay antennas are used because they integrate with the rig without adding windage or getting in the way of the sails, and because they don't need to be taken down when not in use. All that is important. The use of a backstay also predates the availability of nonconductive lifeline material, which provides an opportunity that has been IMO insufficiently explored.


Improvements in materials provide an opportunity for innovation.

It’s your time to waste so have at it. Inverted V antennas have been in wide and effective use for decades; hardly a boating compromise phenomenon.

Innovation is always a good thing but only when the principles are sound. That’s what modeling tells you.

You asked, I offered my perspective based on decades of antenna design and testing and you dismiss it. Have fun.

[MicHughV]

On my first boat...ketch rigged...I made up a long wire antenna from 1/8" cable from the transom up to the mizzen mast.
Yes, off course, there was a tuner at the base of the wire.
I never, ever had a problem either transmitting or receiving on any frequencies, so I don't understand the issue you describe.
On my next boat, I had the typical insulated backstay. As before, reception and transmission was excellent, whether close by or 1,000's of miles away.
A large tuner..ha ha....funny....my tuner was no bigger than a shoebox and it was out of sight, located in a spot where it lived happily ever after.

[Jammer]

Originally Posted by S/V Illusion

It’s your time to waste so have at it. Inverted V antennas have been in wide and effective use for decades; hardly a boating compromise phenomenon.

Innovation is always a good thing but only when the principles are sound. That’s what modeling tells you.

You asked, I offered my perspective based on decades of antenna design and testing and you dismiss it. Have fun.

I know the theory and the history too and am not new at this. I see the value of the models but also understand their limitations especially in a complex environment. As other posters have pointed out upthread there is some history of successful use of on-deck, near-deck, and centerpoint-hoisted inverted Vs that are not particularly far above deck. They lack popularity not because they are ineffective but because they are inconvenient.



I am surprised at the negativity of some of your replies.


Getting performance at least as good as the backstay antenna system, as installed, real world, on most sailboats is a low bar to clear. In many cases, these antennas work because QRP works, especially when both receivers are in remote areas away from noise sources and there's an ocean in between them with a fantastic ground plane.