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Old 16-02-2012, 16:23   #1
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Do you want an HF antenna that performs 20~40 db better than a back stay ?

Yes, I had two HF antennas. A vertical with auto tuner right at the base. Auto tuners are pricey at 100 watt rating, and just downright expensive for higher power levels. A tuner is needed anytime your antenna is not resonant for the operating frequency and does not match the impedance of your radio's output. You would be amazed how well your radio can hear a signal and thus put out a signal when using a antenna resonant for the frequency that you are operating. All a tuner does is fool your radio into thinking the antenna load is both resonant and with a matching impedance.

So this is what I construct for that signal that the away stations report "are you sure your maritime mobile? Your signal is stronger than land based stations in your area". First, commit this to memory 468 / frequency / 2 = 1/4 wave length. The lowest frequency you will use is 75 meter phone @ 3.9 mhz. 438/3.9/2= 60' antenna length. OK, now to antenna design, an inverted vee antenna with downward legs at 90* to each other will have an impedance of 50 ohms, just what your radio wants to see. The center is where you feed the two legs with coax and hoist up your mast with a halyard. Without traps, this would be a single band (75 meter) antenna, but this is where you can have more resonant frequencies by adding traps along the length of those (2) 60' legs. A trap is a coil and capacitor that you design to pass all frequencies except the ones you will be using. You will make (2) traps for each band, 10 meters, 15, 20, and 40 meters. You don't need a trap for 75 meters because your entire antenna was cut for that band. The first trap towards the top, closest to you feed point is for 10 meters which would be for the voice part of the band at 28.6 mhz, so again 468/28.6/2X12= 98.1", and so forth for all the bands you want to operate. How this works is a frequency of 28 mhz sees the first trap as an open circuit, while a frequency of 3.9 mhz will see all the traps you installed as closed circuits, thus using the entire wire length. To get the correct angle between these two legs that you hoisted up your mast, I use a company that makes 40' fiberglass telescoping poles that when nested are only 12' long. These I attached on my old Cal 40 on the bow and stern and just adjusted the angle they stuck out at to dial in my impedance. That is all it takes to have a resonant and impedance matched, multi band antenna that requires no tuner at all, and from my tests are 20~40 db better than a back stay. Back then, nobody made a solid state, high power HF amp, so I built my own. You sure don't need an amp, 100 watts from your radio will do a fine job, but when it comes to my signal, I go all out.

The guy that bought my boat in Mexico really wanted the antenna and telescoping fiberglass poles after we used the radio together. Back then all the parts for the antenna were less than $20, the fiberglass poles were $85 each. Now those poles are $250 each, and parts for the antenna around $75. I'll will be building another this winter, and will document with pictures the build and I will start a new thread and share with all.
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Old 16-02-2012, 17:53   #2
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Bob,

Congratulations for your (re)invented use for the trap dipole, rigged as an inverted-Vee on your boat. The telescoping fiberglass poles must have been quite a sight to see!

Yes, there's no question you could build a trap dipole (inverted V) which if properly set up would be multi-band and would not require a tuner. If the traps were robust enough, it could also handle some power...more than the usual 100 watts.

And, it would be a respectable performer.

However, I'd have to take issue with you on your claim of a "20 to 40db" advantage over a traditional backstay. No way. Trap dipoles, at best, perform about the same as non-trap resonant dipoles. Furthermore, inverted V antennas have a high angle of radiation which do not favor DX (long distance) propagation.

I'll agree with you that the traditional backstay antenna isn't a great performer, being nothing more than an end-fed random-length sloper. But, if set up properly, it's a respectable performer on all bands, with some advantage on the high- or low- bands depending on overall length (longer favors the lower bands; shorter favors the higher bands).

Alas, the sailing world is still looking for a multiband antenna which is both practical and robust as well as having excellent performance compared to the traditional backstay with an automatic tuner at its base. I just don't believe the inverted-V....traps or not...is the answer.

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Old 16-02-2012, 18:11   #3
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Bill,

I know 20~40db was stretching it a bit, but from experience on 40 and 75 meters, I would receive a signal report of 10 to 20 over S9, while others in the same anchorage received reports of in the noise level of S4 to S5. I'll admit about 8db was just in power over the 100 watts of the standard radio, as I was running a home built solid state amp. The traps I potted, so they weren't bothered by the marine environment.

The difference was a lot of fun and good for the ego, as nobody ever had a stronger signal in the many anchorages I've been in. I had an antenna switch between the vertical with auto tuner at it's base and the inverted vee, always a big difference, but couldn't run the amp on the vertical because the tuner was only rated for 100 watts.
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Old 16-02-2012, 18:31   #4
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Ok, I haven't done my homework on other posts, but I'll be getting into the SSB after I finish some carpentry work in the galley. I'm not a ham, but I'm a retired broadcast engineer and there seems to be so much anecdotal information and wild claims out there. One thing I've done is purchase the KISS antenna ground, and I have an Icom with antenna tuner. I also have some SGC radiotelephones and passive antenna tuners, and they are from my heyday. Beautiful equipment, very well made, but crystal controlled, limited in frequencies. In those days it was linking up with a shore station duplex and there weren't that many shore stations.
The inverted vee is very applicable to a boat with a mast, but the limitation isn't the mast height, it's the length of the deck space. If you hoist it higher, and the angle between the legs goes acute, then your impedance changes. But at these power levels, it seems that almost anything will work well, unless there are gross deficiencies in the rig. What about trolling a copper foil and flying a kite with a great big random wire?
Good to have this thread goin' and maybe someone will claim something and someone else will reply about what was really going out over the air.
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Old 16-02-2012, 19:23   #5
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

I used (2) 40' telescoping fiberglass push up masts, mounted one to the bow, the other to the stern and flattened out SWR's but adjusting the angle of the mast mount.

You will find the SGC auto tuner for HAM is of the quality that you are accustomed to.
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Old 16-02-2012, 19:52   #6
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

You'll find as many opinions as operators and boats!

Here's a summary I did a few years back on some of the most popular options for marine antennas:

MarineAntennaChoices2

After more than 40 years of experimenting with HF antennas on boats, and countless thousands of contacts with literally hundreds of boats, there's only one antenna I know of that really stands out in performance for long-distance contacts: the single-band vertical dipole, especially for 20 meters and higher. Here's an antenna which works like gangbusters and which has been "discovered" by very well financed "DX-peditions" which can afford any antenna. They've estimated up to 18-20db gain because of the very low angle of radiation and consequent reduction in number of hops to the receiving station. I've written extensively about this antenna, beginning in QST some 30 years ago.

One proviso: to my mind, a seagoing antenna has to be very robust and practical, and should be able to stand up to the harsh marine environment...salt air, bouncing around, and winds up to and including hurricane strength. That rules out several good performers which are fine at the dock or at anchor, but can't pass the "fully marinized" test.

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Old 16-02-2012, 20:09   #7
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Bill,

Took two posts from you, but I know who you are now! I'm honored and have read your QST articles over the years. Needless to say, you have forgotten more about antenna design than I'll ever know, and I respect that.

You are correct, my trapped inverted vee is only hoisted on the hook, and that takes all of 5 minutes. Once up, I'm having a blast switching between the vertical with tuner and counterpoise to the inverted vee. The vertical sometimes comes close on 10,15, and 20 for long haul stations where the lower angle of radiation comes into play, but for the 500 mile contact at night on 75 and the same 500 mile contact during the day on 40, it is a HUGE improvement between the the vertical and vee
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Old 16-02-2012, 20:35   #8
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Bill, +1 on the vertical. From memory I think I have already posted in another thread on our bamboo pole vertical. If not- happy to expand on request. Recently discovered the J pole vertical. Advantage is the' active' is grounded so static is less of a problem.
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Old 16-02-2012, 22:26   #9
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

I've talked about antennas 'til I'm blue in the face so I'm not going to go into TOO much detail here, but I am going to say that after using every single type of sailboat antenna EVER (except for gigantic vertical poles on the ends of the boat! Ha! " the best antenna I have ever used on a sailboat is actually a very old design, quite unique, but also quite simple to set up. It is the top fed backstay antenna, otherwise known as the "sloper" in the ham radio world. It meets similar attributes of the the vertical dipoles...and the ones it doesn't meet are more than made up for by the fact that it is physically practical for a sailboat and is STRONG! AND...you can use it while underway! (the sloper is not omnidirectional, and though it has a very low angle of radiation, in theory it may not be quite as low as a vertical dipole...but, unlike the vertical dipole it is very practical for use on a sailboat and it sure is a LOT stronger! In fact it's holding up your mast.)

What does a sloper look like on a sailboat? Well, you can picture it as an upside-down backstay. (a previous post incorrectly stated a backstay was nothing more than a sloper...not true. A sloper is connected at the top) In other words you connect your radio to the sloper at the top of your backstay, NOT the bottom. You put your top backstay insulator right at the masthead on a toggle, (see the photo attached for one of my installations) and connect the center of your coax to the top of the backstay, and the braid of your coax (using an SO-239 connector) to a stainless strap that goes over the masthead and is connected to ALL the other rigging, headstays, shrouds, and mast. There you go, simple, strong, and has stood the test of time in a 7 year circumnavigation---with no failures---and fantastic worldwide communications. And the best part is that it simply beats out all the other HF antennas that you can use while underway...all that can be physically mounted on a sailboat "underway" that is.

There are however a few limitations, so let's take a look at them. Here goes; You must use a manual tuner with the sloper because most of the automatic antenna tuners are set up for single wire outputs and not coax cable. (You can't run a single wire up to your masthead). With a manual tuner you can tune coax fed antennas. You must feed the sloper antenna with coax cable (RG-213x is pretty good) because the sloper is an unbalanced antenna and you are going to use your rigging and mast for your sloper's unbalanced side and counterpoise (not foil or screen or a Dynaplate down inside your boat). Next, you must also not have the coax feed-line cut to a length that is a resonant length for any of the bands you want to use. You do not want the coax to radiate RF energy. You only want your backstay to radiate. So to help minimize this for the ham bands it simply means cutting your coax feed line to a length that falls between the ham bands so it won't be resonant or "in tune"---and there is a simple rule called the "rule of sevens" for this. You can use 27', 37', 47', 57', (not 67'), or 77' feet, etc... As far as the actual length of the physical backstay goes, I've usually cut mine to around 32 and a half feet which is close to a quarter wavelength for the 7 MHz (40 meter) ham band. The (formula for a quarter wavelength is 234/7.2 MHz = 32.5' feet) This length works well with the manual tuner and lets me cover all frequencies from there on up through the higher bands. (You can actually work lower frequencies too...depending on your tuner's capabilities).

Now for some positives; You don't need to put a counterpoise in the boat. No more foil, screen, dynaplates, etc...because now your antenna is using the entire mast, shrouds and all the rigging as it's counterpoise and working with that. So NOW your rigging is no longer a detriment to your signal...it is actually helping it. And lastly and this is a BIGGIE; experts know that current loops on resonant and non-resonant antennas, are located on the part of the antenna that shoots your signal off into space. (this is where your antenna's feed point is), and an automatic tuner with a bottom fed backstay has it's "current loop" located in the lazarette, or where ever you have your auto tuner located. But the sloper has it's current loop located at the top your your mast!! Think about that for a minute. Which has a better radio horizon? The pit of your lazarette? Or the top of your mast? ...nuff said. By the way, even the aforementioned vertical dipole couldn't have it's current loop located at your masthead----well, not without some pretty clever mounting and engineering, and then you would have huge vertical antenna sticking way up above your mast. This is not good for anyone with concerns about weight aloft.

Attached here is a photo of the masthead connection off one of my sloper installations. I hope this helps visualize the physical setup at the masthead with the coax connected to the backstay and grounding strap. Whatever antenna you choose...Good luck... It's a lot of fun playing around with this stuff!

73!

Marty
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Old 16-02-2012, 22:37   #10
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Marty,

What you said sounds really good to me and on my next boat I'll ditch the auto tune vertical and go your route. It sounds like it will play and being able to use underway has my vote. How do you think it will stack up for short haul 40 meters day, 75 meters night? That is where my trapped inverted vee really sings.
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Old 17-02-2012, 00:28   #11
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Quote:
Originally Posted by deckofficer View Post
Marty,

What you said sounds really good to me and on my next boat I'll ditch the auto tune vertical and go your route. It sounds like it will play and being able to use underway has my vote. How do you think it will stack up for short haul 40 meters day, 75 meters night? That is where my trapped inverted vee really sings.
Hi Bob,
Well, for 40 meters in the day time you can forget your worries. The sloper absolutely kills on 40. In fact I cut my last backstay to resonance using an analyzer so I didn't need a tuner for 40. For years I was a regular on the Baja Maritime Mobile Net and regularly worked stations way down in Mexico, Sea of Cortez, PV, Nuevo Vallarta, Zijuat, etc... and all the way up through Northern CA in the daytime. As for 75; I was never a fan of 80 or 75, but I was able to chat with those "Good ol' Boys" back in the deep south at night on 75. Not my thing...but they could hear me just fine. 3.820 MHz and 3.995 I believe??? My memory fails me. Ha!

You know the irony of me knowing all this stuff? Last month I purchased another sailboat after being away from sailing for five years. Now I own a Freedom 32 with a free standing carbon fiber mast. I HAVE NO RIGGING!!! LMAO! Now what the heck do I do?????? I'm stumped for a good antenna while underway. Right now at the dock I've hung up a trap dipole for 40 thru 10, but it won't tune on 40 so I've got to drag out my analyzer and see what's going on with that. I did manage my first contact on it today with KB5HA, Kermit, the net control in NM on the Manana Net....boy do I miss my sloper!!!!!!!! I'm going to have to give this some serious thought.
Anyone tried loading into carbon fiber???? heh heh....
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Old 17-02-2012, 10:26   #12
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Marty,

You might have to go with a store bought vertical and auto tuner at the base. That was my "under way" antenna and wasn't too bad.
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Old 17-02-2012, 11:14   #13
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Yes, using a vertical is the plan so far. I already have a Hustler mobile antenna and ALL the individual band coils for the top. I'm thinking of adding that capacitive "top hat" that DX Engineering sells called "hot rods" to broaden the bandwidth a bit. Then I can manually tweak it for low SWR so my tuner that is built into my Kenwood TS-480SAT ham radio can tune it further. Additionally; for a counterpoise I am going to tie in my stainless davits, stern pulpit, and lifelines. My stanchions are all bolted to the huge aluminum toe rail and not the deck, so that toe rail is also getting tied in. That will give me the full circle of pulpits/lifelines/toe rail/stanchions as an 'attempt' to get a decent counterpoise under the antenna. It probably won't work great, but hopefully good enough to be heard by good land-based stations. But....now that I think about it, my Freedom 32 is a quarter wavelength long on 40 meters! ha! Maybe that Mickey Mouse counterpoise I'm creating will work great! Who knows? Antennas on boats is kind of a mystical art...

Then when I'm at anchor I'll just hoist up an inverted V to the masthead. At least the inverted V won't have any rigging in it's way! ha! Still, I'm going to seriously miss the convenience and performance of the sloper---especially the performance.
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Old 17-02-2012, 11:30   #14
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Marty has described an antenna system which worked well for him. You're right, Marty, a "sloper" antenna is generally fed at the top or in the center in the case of a sloping dipole. A backstay fed at its base is more properly called a "sloping wire antenna". End fed, random length. What you have described is generally called a "half sloper".

Half slopers are very well known and documented in the ham antenna literature, mainly because they're very easy to construct if you have a tower supporting, e.g., a beam antenna. Just rig a sloping wire, feed it with coax at the top (tying the shield of the coax to the tower) and, bingo: you've got a half sloper. Most of the experience with these is on the low bands...40, 80, and 160.

Results with the half sloper have been mixed, and very much depend on the tower setup. Some hams report very good performance...as you have. Others report lousy performance. Extrapolating from that, one would expect that the half sloper antenna on a sailboat would be very good in some installations and not so good in others.

In terms of DX performance...say, over 1,000 miles on 40 meters and above....the vertical angle of propagation is extremely important. For example, from the U.S. East Coast to Europe or to South America the optimum vertical takeoff angle is less than 15 degrees, with 10 degrees or less being preferred. Not many antennas found on sailboats can claim to have such low angle takeoff.

The center-fed single-band vertical dipole rigged with the lower end near the deck and the center insulator about 1/4 wavelength above deck, fed with coax and trimmed for resonance, indeed can claim such performance. It typically has a HUGE lobe...all round the horizon...with most power radiating at less than 10-15 degrees vertically. Terrific for DX. Almost no other antenna can match it. Anyone interested in vertical takeoff angles of common antennas can find details in the ARRL Handbook or some of their antenna compendiums. See, e.g., the graphs in Chapter 20, Antennas and Projects of the Handbook.

Anyone interested in building a "marinized" vertical dipole antenna can find construction details here: Marine Antennas

These antennas, by the way, are very robust. Mine survived several major hurricanes with winds in the marina over 100 knots in Tortola. The vertical dipole can be used easily at anchor, at dockside, and underway on long tacks. To get it out of the way for tacking, just undo the lower end and move it back into the shrouds and tie it there, where it will still work but with some detuning.

Vertical antennas rigged at the stern of a sailboat can exhibit pretty good low angle performance as well. Not as good as the vertical dipole, but very respectable. So, too, can the traditional backstay antennas on certain bands, though not on others. Performance of these antennas depends very much on the configuration of the individual boat and, of course, on the care taken with the installation.

Marty, I'm not sure of this but I believe I read somewhere that in tests it turned out that carbon fiber isn't a very good conductor, so it's use as an antenna might be compromised. I think your best options would be either a vertical whip at the stern as already suggested, or an "alternate backstay" antenna made of s/s lifeline and hauled up on a spare or dedicated halyard and tied off on the pushpit. These both work very well.

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Old 17-02-2012, 11:33   #15
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Marty,

Our posts passed in the ether.

The pushpit/pulpit/lifelines/toerail complex will work very well. I've installed a bunch of them. There's no need for the counterpoise to be either resonant or tied directly to seawater.

I think the "alternate backstay" would work well for you.

No need for the inverted V at anchor....you'll do just fine with the vertical or backstay.

Bill
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