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[Articles Home]  [Add Article]  

A Simple Delta Loop Antenna for Smaller Vessels

from Patrick Bryant, N8QH on March 2, 2013
View comments about this article!

The long time standard antenna for sailing vessels is the insulated backstay antenna. These work very well on vessels that are large enough to offer a ground plane that is a substantial portion of a quarter wave at the lowest expected operating frequency. The ground plane is usually accomplished either by connecting to a conductive hull - or in the case of fiberglass hulls - with a wire mesh laid below the waterline that establishes capacitive coupling to the sea.

But with smaller vessels, as is the case with my 26 foot Pearson Ariel, the length of the vessel is insufficient to provide a good counterpoise at longer wavelengths. My vessel is only 18.5 feet long at the water line – just slightly longer than a quarter wave at 20 meters. To operate efficiently at 30, 40, 80 and 160 meters, I needed another solution.

There are also some serious disadvantages to the conventional insulated backstay antenna:

1) it requires the installation of insulators in the backstay which operates at high mechanical tension. If an insulator fails, you can lose the mast (a very inconvenient experience at sea). The insulators themselves require at least four swaged connections, which are also vulnerable to failure.

2) The insulated backstay has no DC continuity to the rest of the vessel, making anything connected to the antenna vulnerable to lightning damage.

3) The antenna “tuner” (correctly called a coupler) may not be able to tune the antenna when its length approximates a half wave or multiple of half waves because an end-fed half wave antenna presents infinite impedance at its feed point. If the objective is to operate on ALL of the Ham bands, and on ALL of the maritime bands (which are interspersed between the Ham bands), then choosing the correct length of the backstay antenna presents a daunting problem. A loop antenna, on the other hand, presents much more moderate excursions in its impedance up and down the bands.

I’ve been operating a Delta Loop antenna as illustrated for over two years with very good success. It is tuneable from 1.7 to 30 MHz, with no gaps. There is complete DC continuity between all of the antenna elements, negating the need for lightning suppression (I trail a zinc plate at the backstay chain plate during thunderstorm activity and whenever at the dock). And the biggest advantage, in my estimation, is the fact that no modifications whatsoever need to be made to the sailing rig.

Member Comments:
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A Simple Delta Loop Antenna for Smaller Vessels  
by K7AAT on March 2, 2013 Mail this to a friend!

Nice article, even though I am not a sailor. I'd like to see the boat drawings a bit better. Any chance of posting a larger / higher resolution picture?
 
A Simple Delta Loop Antenna for Smaller Vessels  
by W1JKA on March 3, 2013 Mail this to a friend!
Very interesting article,right up my maritime alley.I also had to improvise when I downsized to a(pdracer.com)#728 where I was limited to making a 20M inverted U supported in the middle atop my 16 Ft. mast.Needless to say it works best when on the hard or at dockside.
 
Instructions For Building This Antenna  
by TANAKASAN on March 3, 2013 Mail this to a friend!
1) Take one boat................ :)

As a landlubber this isn't of much interest however I'm sure that those with salt water running through their veins will have fun.

Tanakasan
 
A Simple Delta Loop Antenna for Smaller Vessels  
by N6JSX on March 3, 2013 Mail this to a friend!
Are you dragging a wire in the water to make a salt water ground connection for the tuner/system? Or is your whole RF system free floating against the chassis of the tuner/radio/battery/motor?

Delron isolators should have the strength/isolation you require. But I'm not sure about the wear with the constant sail tensions when tacking, pitching & rolling. May need metal inserts to isolate the rub wear and minimize direct contact to the Delron.
 
A Simple Delta Loop Antenna for Smaller Vessels  
by VA7CPC on March 3, 2013 Mail this to a friend!
A "delta loop" is electrically continuous from one end to the other.

If I understand your diagram, the antenna runs:

. . . from tuner "hot" (forward end of cabin) to
. . . . bottom of forestay;

. . . along forestay to masthead;

. . . [mast is "live" -- connected to antenna]

. . . from masthead down the backstay;

. . . forward, _inside the hull_, to the tuner
. . . . . "ground" terminal.

That's an interesting configuration! Labelling the part inside the hull as "ground plane" is confusing -- it's part of the loop!

If I understand it right, the whole rig is a part of the antenna, because _everything_ (including shrouds) is connected to the mast.

But I may be wrong about the connectivity.

I decided to spend around $600 for a set of Sta-Lok backstay insulators, and use a more-or-less conventional setup. But my boat is 36' long, so I have room for reasonable counterpoise wires along the toerails.

Thanks for the article --

. Charles / "Right Galah" / Morgan 36 Out Island
 
A Simple Delta Loop Antenna for Smaller Vessels  
by W3TTT on March 5, 2013 Mail this to a friend!
From the diagram, it looks like the antenna tuner feedline connects to the forestay, mast, and backstay. Isn't your forestay grounded where it connects to the foresprit?
If the forestay is not grounded at the connection to the foresprit, then you have the same issue as if you connected to the backstay, that is, an insulator.
I see two loops, the forestay to the mast to ground, and the forestay to the backstay to ground.
If you ground the far end of an antenna, isn't it really a Beverage?
 
A Simple Delta Loop Antenna for Smaller Vessels  
by K5WRN on March 7, 2013 Mail this to a friend!
I have a passion for sailing as well and hope to own my own boat someday. I too would like to see a higher resolution picture. Though that may lead to even more questions (o:

Thanks for the great article.

73 - K5WRN
 
A Simple Delta Loop Antenna for Smaller Vessels  
by K4FMX on March 7, 2013 Mail this to a friend!
The problem with an antenna on a boat is getting a proper ground. Ground screens, radials, copper strap etc. laid in the hull usually don't work well. The easiest is to connect to the sea water is via a ground plate on the outside of the hull and or bonding the prop shaft and thru hulls that are close.

Sea water skin effect is very high and it does not take much metal in the water to have an affective ground.
Where most people have problems with ground systems in boats is where they place the tuner. It needs to be as close to your sea water ground as you can get it.

The antenna starts at your ground.
Remember that your ground lead to the tuner will be part of the antenna and so will all the cables going to the tuner and they will radiate in the boat where you don't want RF if you have any ground lead length.
Placing the tuner close to ground will limit RF on the coax and control cables. Even though your antenna lead may have to run under the deck to reach the tuner, it is better than having things energized with RF that you don't want.

73
Gary K4FMX

 
A Simple Delta Loop Antenna for Smaller Vessels  
by N8BOA on March 8, 2013 Mail this to a friend!
I have a S2 26ft that needs a rig in it I have thought of the same solution however I was thinking of using a gamma match thus the back stay would be at "dc" ground. This would require a parallel wire running with the back stay. Thinking the antenna coupler would fine a gunning solution. . Great article and merging of two great hobbies
N8BOA
 
A Simple Delta Loop Antenna for Smaller Vessels  
by TTOMAS59 on March 12, 2013 Mail this to a friend!
I figured out the article - loop & a sloop!
 
A Simple Delta Loop Antenna for Smaller Vessels  
by TTOMAS59 on March 12, 2013 Mail this to a friend!
A sloop loop that doesn't droop is no dupe.
 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by GW3OQK on March 14, 2013 Mail this to a friend!
Looks simple (when I'm not doing it) and practical because you are not modifying the standing rigging and the fibreglass boat acts as a big insulator. It looks complex electronically with the mast shorting out the after delta. I expect someone will analyze it shoreside and say its ng, but you have proved otherwise.


Experimenting with antennas is great and they always seem to radiate.I wonder what it would be like if you put the tuner into the wire going to the mast.
73
Andrew (ex MN)

 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by N8QH on March 15, 2013 Mail this to a friend!
Nope. The only connection to the water is a zinc plate that I submerge from the stern, connected to the backstay chainplate, when I'm either docked or caught out on the water during a thunderstorm (a rarity here in California). The zinc plate has no appreciable affect on the antenna (it doesn't help or hurt propagation).

The whole idea was to construct an antenna with a minimum of complexity and no modification of the sailboat's rigging, with nothing trailed behind the boat (to hang up on kelp or crab pots), no through-hull connections (which increase vulnerability to water ingress) and full DC continuity of the rig (for static/lightning suppression).
 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by N8QH on March 15, 2013 Mail this to a friend!
You are correct the the "ground" is part of the loop. I labeled it such because it is also the common potential for the DC supply.

It's unfortunate and confusing that we've inherited the electrical term "ground" at all since, ground is something you try to avoid ever touching with the bottom of a boat.
 
A Simple Delta Loop Antenna for Smaller Vessels  
by KK4INT on March 19, 2013 Mail this to a friend!
Should you wear lead underwear when broadcasting? It would seem that you would be in the middle of the EMR.
 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by N8QH on April 11, 2013 Mail this to a friend!
The EMR is minimal. Considering the long wavelengths, there isn't much difference between being inside the loop and having all the RF radiating above my head from the more conventional backstay configuration. The only way to get more than a wavelength away is to sit in a dingy outside the boat.

I worked for years as broadcast engineer where the RF field was so intense that I could carry a florescent bulb around for lighting - and it would just light up in my hand. All my children seem normal, and I've survived 20 years of exposure. RF burns, on the other hand, are nasty, which is why I prefer everything down on the deck to be at RF "ground" potential with my loop antenna. With an insulated backstay configuration, the shrouds and the boom tend to act as secondary radiators, increasing the risk of RF burns.

I did have all the usual RFI issues that I had to cope with by using lots of ferrite suppressors: my PC would reboot or go goofy, and all my LED navigation lights would light up whenever I spoke into the mic using SSB. I solved all of those problems, and the issues are the same, or worse, with a backstay antenna.
 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by N8QH on April 11, 2013 Mail this to a friend!
The EMR is minimal. Considering the long wavelengths, there isn't much difference between being inside the loop and having all the RF radiating above my head from the more conventional backstay configuration. The only way to get more than a wavelength away is to sit in a dingy outside the boat.

I worked for years as broadcast engineer where the RF field was so intense that I could carry a florescent bulb around for lighting - and it would just light up in my hand. All my children seem normal, and I've survived 20 years of exposure. RF burns, on the other hand, are nasty, which is why I prefer everything down on the deck to be at RF "ground" potential with my loop antenna. With an insulated backstay configuration, the shrouds and the boom tend to act as secondary radiators, increasing the risk of RF burns.

I did have all the usual RFI issues that I had to cope with by using lots of ferrite suppressors: my PC would reboot or go goofy, and all my LED navigation lights would light up whenever I spoke into the mic using SSB. I solved all of those problems, and the issues are the same, or worse, with a backstay antenna.
 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by N8QH on April 11, 2013 Mail this to a friend!
The EMR is minimal. Considering the long wavelengths, there isn't much difference between being inside the loop and having all the RF radiating above my head from the more conventional backstay configuration. The only way to get more than a wavelength away is to sit in a dingy outside the boat.

I worked for years as broadcast engineer where the RF field was so intense that I could carry a florescent bulb around for lighting - and it would just light up in my hand. All my children seem normal, and I've survived 20 years of exposure. RF burns, on the other hand, are nasty, which is why I prefer everything down on the deck to be at RF "ground" potential with my loop antenna. With an insulated backstay configuration, the shrouds and the boom tend to act as secondary radiators, increasing the risk of RF burns.

I did have all the usual RFI issues that I had to cope with by using lots of ferrite suppressors: my PC would reboot or go goofy, and all my LED navigation lights would light up whenever I spoke into the mic using SSB. I solved all of those problems, and the issues are the same, or worse, with a backstay antenna.
 
RE: A Simple Delta Loop Antenna for Smaller Vessels  
by N8QH on April 11, 2013 Mail this to a friend!
The EMR is minimal. Considering the long wavelengths, there isn't much difference between being inside the loop and having all the RF radiating above my head from the more conventional backstay configuration. The only way to get more than a wavelength away is to sit in a dingy outside the boat.

I worked for years as broadcast engineer where the RF field was so intense that I could carry a florescent bulb around for lighting - and it would just light up in my hand. All my children seem normal, and I've survived 20 years of exposure. RF burns, on the other hand, are nasty, which is why I prefer everything down on the deck to be at RF "ground" potential with my loop antenna. With an insulated backstay configuration, the shrouds and the boom tend to act as secondary radiators, increasing the risk of RF burns.

I did have all the usual RFI issues that I had to cope with by using lots of ferrite suppressors: my PC would reboot or go goofy, and all my LED navigation lights would light up whenever I spoke into the mic using SSB. I solved all of those problems, and the issues are the same, or worse, with a backstay antenna.
 
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