The advantages of a Delta Loop antenna

[Cpt Pat]

Originally Posted by belizesailor

Re cat rigging. No backstay, and forestay hard to integrate into this configuration, but you could do a similar loop incorporating both side stays and mast or a single side stay and the mast. Should work the same as a small boat rig if the stay/wave lengths work out...right?

I believe it should. In fact, for 10 meters and 6 meters on my tiny boat, I use a loop comprised of one lower shroud to the mast as a second loop and tune with my Kenwood's internal tuner. If you scale that up to a larger boat, it should work fine.

[klaus53123]

Dear Pat,

first of all many thanks for posting this very helpful information. Until now I have not considered to have Loop type antenna installed. My brain was limited to the well known backstay solution.

I own a Cat which I bought second hand. It already has one isolated back stay, the second one not yet isolated. The length of the mast is about 14m, the two backstays (rusnning from the mast top to inner side of the sugar cubes are about 17 m. If I would get rid of the isolatd back stay could I place the tuner close to one back stay and feed through the plate, interconnect the stays and the mast as counterpoise and feed the ground at the mast? I would than realize two triangles (mast, stay,counterpoise or conterpoise, stay1, stay 2). What kind of bandwidth would you expect? I am using the CG 3000 tuner.

Another question about corrosion: If you connect your mast to a copper line, is there not a severe risk of corrosion due to the highly different potential of the two metals?

Many thanks
Klaus

[Cpt Pat]

Originally Posted by klaus53123

Dear Pat,

first of all many thanks for posting this very helpful information. Until now I have not considered to have Loop type antenna installed. My brain was limited to the well known backstay solution.

I own a Cat which I bought second hand. It already has one isolated back stay, the second one not yet isolated. The length of the mast is about 14m, the two backstays (rusnning from the mast top to inner side of the sugar cubes are about 17 m. If I would get rid of the isolatd back stay could I place the tuner close to one back stay and feed through the plate, interconnect the stays and the mast as counterpoise and feed the ground at the mast? I would than realize two triangles (mast, stay,counterpoise or conterpoise, stay1, stay 2). What kind of bandwidth would you expect? I am using the CG 3000 tuner.

Another question about corrosion: If you connect your mast to a copper line, is there not a severe risk of corrosion due to the highly different potential of the two metals?

Many thanks
Klaus

Hello Klaus,

My advice would be to keep the installation as simple as possible consistent with placing the tuner as near to the feedpoint as possible. Any conductor between the tuner and the feedpoint is a radiator (even if you use coax). This is a point that's missed by most proponents of insulated backstays: they believe the small physical separation they have between the bottom insulator on the backstay and the boat somehow improves RF isolation to the rest of the boat. They don't understand that the entire feedline from the tuner to the backstay is radiating RF and is in fact part of the antenna. Even by using coax (which I have never seen properly terminated to ground at the outer shield where it connects to the backstay), the only condition underwhich that coax is not radiating is the extremely rare circumstance where the backstay at the feedpoint has a characteristic impedance of 50 ohms (if that were always the case - they wouldn't need an antenna tuner at all).

Since you already have one insulated backstay, unless you want to remove the insulators, I would keep it and rig a switch to select either antenna to feed from your tuner. A simple knife switch will do. It would require re-tuning when switching, but you will probably find that the insulated backstay is more efficient at some frequencies. I'd use the un-insulated backstay as my "default" that I'd keep selected most of the time because it provides some protection from lightning, whereas the insulated backstay has no DC path to ground (except through the tuner) and will be much more vulnerable to lightning damage to the tuner/radio.

Regarding bandwidth, the real advantage of a delta loop becomes apparent: whereas the user of an insulated backstay has to carefully avoid having its length be any multiple of one-half wave (which results in infinite - and untunable - impedance at the feedpoint) over all intended frequencies, a delta loop has much more gentle excursions in its impedance characteristics. I am able to tune my antenna to a VSWR of less than 1.5 to 1 over the entire range of 1.7 to 30 MHz, with no points excluded. Since I use my radio on both the ham and marine bands, there are few bands of frequencies that I do not use.

There will be some galvanic corrosion from any dissimilar metals in contact with each other. But in the case of a comparatively very small piece of copper attached to a very large piece of aluminium, the corrosion shouldn't significantly erode the aluminum. You should occasionally clean and re-seat the connection. For strapping, bonding, and counterpoise conductors, I use 1 inch wide braided stainless steel strap that I buy from American Grounding Systems (Ground straps and braids, ropes & wires by AGS. Online Catalog and Custom Design- SAMPLE REQUEST -tinned and bare copper, nickel plated copper, stainless steel, braided ground straps). It's a bear to cut the stuff. I use a sharp chisel and hammer.

Here is an example of the efficiency of my antenna. I transmit APRS position beacons on 30 meters (10 MHz) with 25 watts of power as an occasional radio check. My daytime range is over 600 miles, and my nighttime range is over 2,000 miles, with occasional reception to 7,000 miles. You can see the data here: Station info for N8QH-9 – Google Maps APRS. Look under the section: "Stations which heard N8QH-9 directly on radio." I only run this test on occasions, so if you view this in the future, look for March 2015 (2015-03). Even though I am competing with land-based stations, some of which have highly optimized antennas, my station is usually the furthest or nearly the furthest station heard by the receiving stations.

[dannyjoh]

Dear Pat
Thanks for the very useful and practical info about the delta loop antenna. I have a "dumb" question. Would the delta loop configuration work on a fractional sloop in which the forestay doesn't go all the way to the top of the mast? My boat (a Marieholm 26) is a 7/8th fractional sloop.

[Snowpetrel]

Very interesting. How would it work on a metal boat. Would the hull work as the bottom loop part, and does it all need to be isolated from the water? Also on RF burns. Would plastic hose over the antenna protect crew? Cheers

Sent from my HTC_0PCV2 using Cruisers Sailing Forum mobile app

[deckofficer]

Originally Posted by Snowpetrel

Very interesting. How would it work on a metal boat. Would the hull work as the bottom loop part, and does it all need to be isolated from the water? Also on RF burns. Would plastic hose over the antenna protect crew? Cheers

Sent from my HTC_0PCV2 using Cruisers Sailing Forum mobile app

From my experience (but my metal boats were on the large side, 500'+) a vertical with tuner and counterpoise is the hull can't be beat. Folks spend a lot of coin on a Dynaplate just to get a fraction of the sea surface area for their FG boat than what you get with a metal hull. Delta loops are nice when you don't have the luxury of a metal hull IMHO.

[Snowpetrel]

Originally Posted by deckofficer

From my experience (but my metal boats were on the large side, 500'+) a vertical with tuner and counterpoise is the hull can't be beat. Folks spend a lot of coin on a Dynaplate just to get a fraction of the sea surface area for their FG boat than what you get with a metal hull. Delta loops are nice when you don't have the luxury of a metal hull IMHO.

I've always done it that way with good results, but this whole delta thing looks pretty interesting. I had a mate who just hooked it up to his backstay without insulators on a steel boat and he reckoned it worked fine, maybe he had set up a delta antenna by accident? Also I've often just clipped a SSB receiver onto the shrouds and got a big boost to reception for wx fax. Same thing?

[ka4wja]

Hello to all,
A couple years ago, Capt Pat posted of his results from using a non-standard type of maritime HF antenna....
And, kudos to him for experimenting/designing something different...

I did not wish to rain on his parade, and I continue to wish him well....BUT....
But, with all the additional comments / queries, I thought it might be good if I added a few facts to this discussion that most (all?) will find helpful??

Originally Posted by Snowpetrel

I've always done it that way with good results, but this whole delta thing looks pretty interesting. I had a mate who just hooked it up to his backstay without insulators on a steel boat and he reckoned it worked fine, maybe he had set up a delta antenna by accident? Also I've often just clipped a SSB receiver onto the shrouds and got a big boost to reception for wx fax. Same thing?

So, here are some facts to keep in mind when considering various antenna systems...

1) Anything metallic that conductors electricity, can be used as an antenna of some sort...anything!! (see below for what I've actually used!!)
And, with our modern antenna tuners/couplers (whether the typical remote auto-tuner, a simple manual tuner, or even built into some ham rigs), actually getting our transmitted energy coupled to the antenna (and received signals from it) is not too difficult....(albeit the worse the antenna, the more loss in the tuner/coupler, of course...)


2) There are 100's of antenna designs that work....many are cheap to build....but the ones that work well over a very broad range of freqs, and perform well for the various types of comms that we typically need on board, and are reliable / last a long time, etc. are fewer in number!!!
(please note, this is NOT about "able to easily match" or "it's got a good SWR"....'cause neither of those mean much to how efficient / effective the antenna actually is....remember, a dummy load is widebanded and has a good swr...


3) A horizontally polarized antenna, mounted a 1/2-wave or higher, will have a significant advantage over even a full-size vertical (such as backstay or whip) over sea water, on most long-distance / low-angle paths...(and this is typically noticed on the higher HF bands, above 12mhz/14mhz, and the advantage becomes noticeably greater as the freq increase and/or height increases)
BUT...ALSO
A horizontally polarized antenna, mounted low (1/4-wave high, or slightly lower), will have a VERY LARGE advantage over a vertical antenna (such as a backstay or whip), on the short paths / high angle paths of 100 - 400 miles, where Near Vertical Incidence Skywave predominates...(this is on the LOWER HF bands or 1.8mhz/2mhz thru 7mhz/8mhz)


4) While Pat's antenna design is not your typical "delta loop" it does work...BUT...
But, EVERY boat is different and the dimensions of the antennas will be different....and you cannot make assumptions that just because a unique antenna of specific dimensions, on a specific boat, on some bands for some communications paths, etc. works well for one, that what
you build, with your dimensions your boat your communications paths, etc. will work the same....
(this is why there are certain specific antennas that have become the "accepted standard" for specific applications....not because there aren't alternatives, but because these "accepted standard designs" are reliable/repeatable...)




I hope these facts help some of you out....
Please note that I'm not voicing any opinions here, nor am I panning Pat's antenna....just posting some facts and hoping you'll all see that there is a LOT more to this...
{BTW, I started designing/building HF antennas in the early 1970's and in addition to making my living in communications for 30+ years now, I have also taught antenna design / construction, radiowave propagation, etc...and fyi, I have not only designed/built/used delta loops, my first one was about 40 years ago...and while I can afford to use the best on-board, I use a long insulated backstay vertical against sea water ground...}

Fair winds...

John


P.S. In addition to clipping a wire to a stay/shroud, using the entire rig, running a wire up a halyard, a whip, etc. etc...I've also used a metal window screen, a metal window frame, a vhf/uhf police scanner antenna (also indoors), a telephone drop cable, a cable TV drop cable, a SS "slinky", a metal fence, a 55 gallon drum and alum tube, as well as dozens and dozens of more traditional antenna designs....all of these WORKED and I made long-distance HF contacts with them!!!
(one that surprises some is the indoor vhf/uhf scanner antenna, that I made dozens and dozens of HF contacts with all over the Caribbean and S. Amer.....but they all worked to some extent...)
BUT...
But, understand there ARE reasons that the normal/traditional designs proliferate...it's 'cause they work, and usually work better than most anything else for the specific applications!!! (remember we have some rather demanding needs in our typical applications....

[NevisDog]

Very informative discussion here from 2015 and earlier. If anyone is still listening then thanks for the information. I've spent a year puzzling how to solve my SSB problem - combining a vertical dipole antenna left over from the PO with the (new to the boat) Icom M700pro and AT-130 tuner - apparently the two are simply incompatible, regardless of how well it is grounded, so I've been wasting my time.

This delta loop idea solves some major headaches for me at a stroke: (a) creating a decent ground on a small GRP boat that has never had a ground; (b) chopping the backstay (undesirable and expensive) then locating the tuner in the middle of the aft cabin berth (obtrusive and inconvenient).

My plan is to try it out with some old copper wire below deck to forestay, inner forestay and backstay chainplates; if this works then I'll try to find some proper braided 1" stainless strap. Can't be any worse than what i've got (surprisingly good reception but hopeless transmission).

1. I take it the ground end of the AT-130 and/or the M700 should also be connected to the common ground bus for the batteries/electronics? Is ordinary copper wire sufficient here?

2. How important is it to ensure the below-decks section of the loop is in the same plane as the mast and stays? Can they follow the contour of the side of the hull, following the cabling ducts for other wires, or should they align with the boat's centreline?

3. My multimeter tells me the rigging is not fully isolated from toerails, stanchions, lifelines and radar arch (even anchors and chain are in contact through the bow fitting); is this a problem (other than remembering never to touch anything metal while transmitting)?

4. I'm guessing loop antennas are directional - does it transmit/receive better when angled across the direction to the shore contact station or when aligned with that direction, or does it not matter?

[Cpt Pat]

1. I take it the ground end of the AT-130 and/or the M700 should also be connected to the common ground bus for the batteries/electronics? Is ordinary copper wire sufficient here?

Yes, copper is OK, but if it's exposed to salt water, it'll dissolve over time. The most important reason to make a connection to the common ground is for bonding in case of a lightning strike.

2. How important is it to ensure the below-decks section of the loop is in the same plane as the mast and stays? Can they follow the contour of the side of the hull, following the cabling ducts for other wires, or should they align with the boat's centreline?

It's ideal to have the "bottom" if the loop run directly down the centerline. I ran mine through the bilge because it was continuously accessible. The fact that there would be seawater exposure in the bilge made using stainless critical. I tried tin plated braided copper strap first, and it just crumbled into dust after exposure. Running the strap off center won't matter much, but bends are a problem. If you must put in bends, make them follow a wide radius turn. To RF, a bend is an inductor.

3. My multimeter tells me the rigging is not fully isolated from toerails, stanchions, lifelines and radar arch (even anchors and chain are in contact through the bow fitting); is this a problem (other than remembering never to touch anything metal while transmitting)?

Yes, this is a problem. If it's a low resistance path, you essentially have a short circuit in your loop. But if the multimeter shows thousands of ohms of resistance, then you are probably seeing only low conductivity paths created by salt accumulation. Trying spraying everything off with fresh water and measuring again to confirm it's salt. A very low conductivity (high resistance) path shouldn't degrade the antenna by enough to notice. I had to cut my stainless toerail away by an inch on either side of the stem fitting. The anchor chains will be a problem if the chain extends an appreciable fraction of a wavelength. It will be less of a problem if it's coiled or stacked in a small area. The higher the frequency, the bigger a problem it'll be.

My anchor and chain are stowed in my stern locker. I deploy the anchor and chain (50 feet) from the stern, and then when I get to the nylon line, I use a snatch block to haul the line to the bow. I recover the anchor using a sheet winch and reverse the process. That way I never leave the cockpit. It's an old single-hander trick. That procedure also keeps stinky bottom mud out of my cabin.

4. I'm guessing loop antennas are directional - does it transmit/receive better when angled across the direction to the shore contact station or when aligned with that direction, or does it not matter?

I haven't experienced any directional characteristics with my antenna. While doing a DX with stations, I've made 360s and they couldn't detect any signal strength changes.

You are right to set up an experimental test first. I hope it works out well for you!