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Old 24-01-2020, 14:50   #61
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Re: Backstay antenna length decision

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Originally Posted by derfy View Post
My rigger is coming tomorrow to put in the new backstay! Opinions needed now, thanks in advance.


I am a newbee to marine and ham SSB, but have a ham General License, Marine FCC License, and I am a used-to-be electrical engineer. I am preparing my vessel for offshore and need voice and data SSB. US East Coast, Atlantic, and Caribbean destinations. I am replacing my backstay tomorrow, and have the option to make the insulated part up to ~56 ft (17 m), or arbitrarily shorter. This includes to GTO wire length from the tuner in the aft lazerette.


The quarter wave resonant freq should be 4.4 MHz w 56 ft, slightly above the 80 meter ham and 4 MHz Marine bands. My tuner docs warn not to transmit on the half wavelength frequency (8.8 Mz) to avoid output stage damage to the rig - makes sense.


At 56 ft, I should be able to tune and Tx on Marine SSB 4, 12, and 22 MHz, and Ham 80, 30, 20, 15, and maybe 10 meters.


I will not be able to Tx on Marine SSB bands 8, 16, 18, or 25 Mhz or Ham 40, 17, or 12 meter. I hope I can Rx these to some degree.


Iffy for Tx are are Marine band 6 MHz and 60 and 10 meter Ham.


WHERE THE TRAFFIC IS: I note that the Marine 8 MHz has the most nets, followed by Marine 6 MHz, and Ham 40 meters. The most Winlink gateways are on 40 meters. I will not be able to Tx to any of these.


DECISON: I am screwing up with such a long antenna? I could shorten it to, for example, 34 ft, centered in the 40 meter Ham band, and be able to Tx on Marine 6 MHz and 8 MHz.


I would lose Tx-ing on the 80, 20, and 10 meter Ham bands, and lose Marine bands 4, 6, 12, and 25 MHz. These have a lot of nets and Winlink gateways also.


Voice of Experience would be very welcome. Thx in advance.
Well, for something different to consider:
1. Change your metal backstay for Dynex (12mm).
2. Run insulated 5mm ^2 tinned copper wire up the core of the Dynex and out below both splice tails. The length is not that important if you are using an ATU.
3. Cost benefit is not have to buy two insulators and necessary swages. Top eye splice can be linked to the clevis pin with a Dynex loop. Lower eye splice is fitted with a "friction" ring and lashed to the back stay deck fitting.

The cost of the Dynex was about 5% more than Duo-form wire, but the savings were made on the fittings and insulators.

Now to answer your question: Rx on any frequency with a long wire antenna is not the problem if you are using approx 17m of wire.
On Tx, couple the output through an antenna tuning unit and you will be able to load the antenna to the desired frequency with minimal increase in VSWR from the nominal length/frequency.

My rig is ICOM M802 with an AT-142 (ICOM). Definitely no problems communicating globally, especially into the Pacific.
Current LOCSTA is approx S1600.00 E15000.00.

Jeffrey
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Old 24-01-2020, 14:53   #62
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Re: Backstay antenna length decision

Well we are not installing a marine HF antenna in a controlled science lab.

1. Picking a magic length or arguing about some minimum length is really a nonsense in the real world. Sure its a target length or figure to use but rarely does reality coincide with theory.


The variables are just generally too great to be able to come up with a canned formula. Its rare for any antenna model on a yacht to coincide with reality. All the variables of all the various yacht sizes and rigging structures make it impossible to predict or model.



When someone can show me any antenna model that actually matches their VNA or antenna impedance data from a yacht I might be a believer. Then if we throw in the other variables of how the rigging is grounded and what ground is used then you in the blackhole of universe territory in terms of getting a known or predicted outcome that you can recommend to someone else on the same model yacht..



So really its wishful thinking that even the supposed bad length half wave antenna length can be accurately calculated and applied across all rigs and yacht models. Our antenna installation environment is not controlled. Repeating urban myths about this antenna length or that antenna length is just not the practical reality when doing any HF installation. The only relevance of this particular length over that particular length on your particular yacht is to you and your installation and will rarely apply to some other installation.



2. Thats why we have auto antenna tuners that if designed correctly you will rarely have to worry about this issue. For the majority it works well enough across all bands because you cant control the antenna length versus the rigging and grounding interaction. Rarely have I enocuntered the "half wave" impedance syndrome since the rigging interference throws off this bad antenna length so much that it does not affect the majority most of the time. But there is alwas a handful of installations that have a badly designed antenna tuner that cant cope. The problem of antenna tuners not being able to tune this half wave antenna is a design/cost issue not an technical impossibility. A aircraft antenna tuner can tune any antenna from 0.5 ohms or less to more than 10,000 ohms because it was designed to do so. We just have not had any communications company take up this challenge up for marine antenna tuners. It would take 100 dollar worth of parts upgrade to make any Icom tuner cope with even a half wavelength antenna on any band.


3. I wont go on and on about this KISS ground but you are not dealing with ground loss over seawater hence your ground system does not have to be very effective if you somehow you achieve a connection directly or indirectly with this ground via a counterpoise or independent groundplane. I can achieve the same result with a 50 cent piece of copper wire as a I can with KISS ground in a hose pipe wire. I have measured this numerous times by switching between a KISS and the 50 cent piece of random wire. This was done at midday on a ground wave signal using using a POTOMAC FIM41 and a ETS LINDGREN 3301 with a measuring receiver.



An effective ground is one that mitigates loss and therefore increases fieldstrength, if you cant measure the change you are imagining the worth of your purchase. If a piece of wire in the hosepipe works it tells you that whateverer you are using has a sufficient counterpoise and thats all, it will never tell you that you have improved or made things better or reduced losses. Only a field strength meter will give you that answer. But lets leave it at that.



Just get your radio working effectively and leave it at that, leave the ground debates to the trolls and peddlers of products. Untill someone gets the FCC or some other independent lab to make these measurements these debates will go on for another 20 years in cruising forums! Quite frankly I am tired of these voodoo arguments when the reality is that groundplanes, counterpoises and field strength is a science that can be measured and I dont have to rely on heresay, folklore, voodoo and yachtclub urban myths for the answer. I have measured field strengths in my professional career for 30 years with 0.5db accuracy so I know what reality is.



4. The only reality that we have to concern ourselves with as sailors is getting a working professional HF installation. If that means a standard Icom radio and antenna tuner with a working backstay that is effective thats good enough. The basic minimum is a minimum length counterpoise for a voltage or a current fed antenna over a saltwater that has no ground loss. Why waste effort combatting something that does not exist? A piece of wire with a 50 cent or 1 dollar coin soldered to it will achieve a saltwater connected ground. So will a dynaplate and in the absence of a direct connection so will a counterpoise or mnimum set of short radial wires, take your pick.


5. Even if your deck was a solid copper sheet, you wont notice any difference over a similar length of copper wires emulating this copper sheet. Ground loss is not THE issue, the only issue is achieving a counterpoise. There is certianly no need to pay an excessive amount of money for copper window screen or pieces of wires stuffed down a hosepipe or expensive copper flashing.



6. Hams in the sailing world have become dellusional about this ground and counterpoise issue, because on a yearly basis theres hams operating from saltwater islands working 50,000 plus QSO's with limited antennas and counterpoises consisting of 2 radial wires and nothing else on all bands. I wonder why some supposedly educated hams come onto sailing forums proposing the exact opposite of what is being done in the real ham radio and commercial world of putting out a big signal? There is certainly no messh, copper wires in a hose pipe and all the other esoteric grounding voodoo thats preached in sailing forums, so you really have to wonder about the motives and worth of this advice when its largely nonsense.


7. The final point about antenna modelling is that they can model a single antenna very well in a clear controlled space. Antenna modelling especially of the amateur kind while accurate with simple antennas cannot in reality model the true complexities of the interaction and the influence of a yacht rigs rig and all the other interfering objects. Yes, it can be done but the model might take 1 or 2 weeks of processing time the calculations are that intensive. Simplistic models in NEC/NEC4 and even programs like FEKO rarely represent the reality on a yacht. The backstay antenna and the way it is fed represents a realiable model that works, models well and its performance is excellent. And because it works so well its the antenna the majority of sailors should use. Unless someone comes up with a antenna that you can buy from Amazon in a packet that offers you something you will never get in reality, the Snake Oil Antenna. Thats all me need now is KISS Antenna like the infamous Maxon Antenna that was a dummy load in a box with wires attached that people said worked!



Good luck with the experimentation but for most its largely a time wasting exercise that achieves very little in comparison to a plain vanilla backstay installation. Trick antennas are not needed for emergency and basic communication needs. For most yachts, a backstay antenna or vertical whip like the shakespeare will serve the majority well enough and offers an reliable and repeatable solution. We need to move away from the quakery in sailing radio HF installations and get back to the basics. Those basics are a Backstay antenna, automatic antenna tuner, and good counterpoise or ground system. The jury is in and you cant do any better than this on most yachts so bending wires left or right and up or down is not going achieve much above the minimum basics above, so why confuse sailors who want go go sailing not become radio hobbyists and endless tinkerers?
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Old 24-01-2020, 15:59   #63
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Re: Backstay antenna length decision

my first boat was a steel ketch...I ran a plastic covered 1/8" dia. mild steel cable to the top of the mizzen from the transom pulpit, fed by a tuner mounted on the transom. Cable was maybe 30' long. The tuner was part of the SSB setup. I had to use the SSB to tune the wire and then flipped a switch to hook the Ham radio into the system.

The 23' length is typically for a fiberglass whip antenna,but these are seldom seen.

Additionally I ran an extension cable from the top of the mizzen to the top of the main, but later took it down, as that cable was at a very low angle, so the 30' cable to the mizzen did the trick for me and was all I needed.
Being a steel ketch, I had ample ground. This setup was used for both a SSB and Ham radio I had on board.
I could communicate pretty much anywhere in the world, depending on night or day and frequency used without any problem.

My next boat had the insulated backstay setup, with twin bronze grounding dyna plates on the bottom of the hull. As before, I had both SSB and Ham, both fed by the same SSB tuner. As before, this system worked just fine and worked as well as my previous boat.

I have many friends with home based Ham rigs and every type of antenna you could imagine, but my simple setup beats them all.

As the above poster stated, you can get too carried away with this stuff. A simple end fed long wire will take care of your needs.

Take the time to learn which frequency works best at what time. Also get to know the myriad of " nets" out there. There are many, many of them. Many offer " phone patches". It takes some time to gather all this info, but if you go online and peruse around you can find them.

Keep it simple !!!
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Old 24-01-2020, 19:23   #64
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Re: Backstay antenna length decision

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While any random length of wire works, if you are a long distance sailor you need to consider the efficiency of the overall antenna system.

If you are mainly a coastal cruiser and hugging the coast of your own country then the backstay length and how much radiated power you are wasting is hardly an issue if you are using frequencies blow 12mhz.





If you are migrating into the deep Pacific and Indian ocean I would think more carefully about backstay length. especially considering how poor propagation is at the moment.





In general on the high frequencies best efficiency for long distance communications comes from keeping your radiatiating angle and lobe below 15 degress. In general once you go over 5/8 ths wavelength in length you start to split the lobe and get a lot of high angle of radiation from your antenna which wastes power sending it to where it is doing no good for your signal strength.



In general its 5/8X984/ frequency. So if the highest frequency you are planning to operate is 15mhz then the backstay should be optimised for the length of no more than 41 feet. The difficulty comes when trying to avoid the 1/2 wavelength on 8mhz and 12mhz so the magic length will be a combination of trying not to go above 5/8th wavelength and avoiding the half wavelength on the lower coastal frequencies.



If you are a ham generally this means you want the maximum efficiency on 20 meters and hence that would mandate a backstay length of no more than 40 feet to meet the maximum 5/8 length.





I have never found that a high angle radiator that wastes power on high angle lobes to be an efficient antenna even in coastal communications. If you want long distance reach go for a low angle radiator not a high angle radiator and that means no longer than 5/8ths. I am a ham so my backstay is no longer than 41 feet on 14mhz. This is long enough for high efficiency on the lower frequencies with an antenna tuner and where signal levels are strong enough where you dont have to worry about 3db loss since you will be so strong. I want the ability to send an email and communicate with realiability hence my choice.



A piece of wet string laying on the deck is good enough for coastal communications including feeding your lifeline as an antenna. This might seem like overthinking but really there is no such thing as overthinking when it comes to the efficiency of an antenna system and when it comes to designing a communications system for reliability.



I am in the over thinking camp because the laws of physics mandates maximum effiecieny not lazyness and poor aptitude. But hey if this is too much information overload, throw it up and suck it and see. Everything sorta works when it comes to radio, even the worst antenna and ground. Being on top of a saltwater is what saves most sailors from their misinformed decision making.



I did a signal survey over many Sydney to Hobart yacht races. I used a very accurate communications receiver with a S-meter that had a less than 1db accuracy.(dbuv) There was anywhere from 20 to 30 yachts all within 20 nautical miles all with professional HF communications installations. There was an incredible 40db variation from this fleet sample from the weakest to the strongest. And this variation came mainly from poor installation, poor antennas, poor grounds and not propagation variation since they were all in the same zone.. I was using a calibrated EMC antenna. So there you go, if you overthink you can get 40db over the yacht that takes a lazy and casual non technical approach to a technical subject! You can find all this information in the ARRL antenna handbook, buy a copy its a good learning aid for those who are interested.
Gain = directivity. The reason a 5/8ths wave end fed vertical antenna has superior performance is due to the compression of radiation in the vertical plane (along the antenna axis).

But a backstay isn't vertical - the antenna itself is inclined from the vertical. Then, that 5/8ths wave directivity becomes detrimental and reduces performance. A 5/8 wave antenna will only improve performance when the mast is the radiator - not an angled stay. Using a stay, you are "talking mostly to satellites and submarines." The dominant radiation isn't horizontal, it's perpendicular to the axis of the stay.

The goal on a movable platform, like a sailboat, where the direction of the other station is random, is a non-directional spherical radiation pattern. Directivity with a non-steerable antenna is a hindrance.
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Old 24-01-2020, 19:50   #65
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Re: Backstay antenna length decision

Hmmm...whether to step into the fray or not?

We are discussing verticals over a near idealic ground plane.

Here is scan of my 65 ft #10 vertical over a decent radial field.


And here is the same with a 33ft and 16ft vertical added.


Yes, your tuner can probably fix the 65 for 40 and 20.

But you should bring a 1/4 wave for the bands you intend to use and design into your rigging a means of hoisting them if you intend to be optimal.

You wouldn't settle for a flopping sail...why settle for a non-resonant antenna?
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Old 24-01-2020, 20:40   #66
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Re: Backstay antenna length decision

I have a slip neighbor who uses his steel topping lift as a radiator. He has an inexpensive utility pole guy insulator (which is intended to support much more weight than the sailboom) at the top. The coax feedline runs down the boom, and the coax shield is connected to the aft boom end.


He avoids having the topping lift couple to the backstay simply by booming out the sail.


Running an antenna parallel and near to a stay will cause it to form a couple with that stay. That may be suboptimal.
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Old 25-01-2020, 07:34   #67
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Re: Backstay antenna length decision

..I can't speak for other boaters, but my ketch did not have backstays for the mizzen mast. The wire antenna I had rigged, was attached to the top of a stiff sch. 40 pvc pipe I had attached to the transom pulpit. This pipe was about 7' long. This was done so nobody would run into the antenna while at the back of the boat, the end result was that the antenna wire was not anywhere near another stay. The wire antenna was insulated at the top and bottom attachments.

..I can't say for sure, as I had nothing to measure this with, but the direction of which way the boat was pointed seemed to have a marginal affect on signal propagation, but I never had any problem getting a signal out.

..some sloop or cutter rigged boats have split backstays or split lowers with a Y-connector leading to the main back stay. This complicates installation of the insulators somewhat.

..I have also seen sailboaters that hoist a wire antenna to the top of the mast when needed and lower it again when done.

..at the end of the day, options for an antenna installation on a sailboat are somewhat limited, but an end fed long wire seems more than adequate for good signal propagation.

..sadly, in my humble opinion, ham radio is not the same as in bygone years, the morse code requirement is gone with the dodo bird and modern day satphones, and signal boosters for cell phones, etc, are/have been replacing ham radio.

..learning code at 20 wpm was the ultimate challenge back in my day. I read, that now with the code requirement gone, there are more hams than ever, but in looking at moored sailboats it seems that few boats are rigged for HF radio these days.
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Old 25-01-2020, 09:29   #68
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Re: Backstay antenna length decision

Too bad a scaled down sailboat with rigging and antenna could not be built and tested in an anechoic chamber. That would answer a lot of questions.
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Old 25-01-2020, 09:51   #69
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Re: Backstay antenna length decision

Back when I did this for a living, the vast majority of shops either used the entire backstay however long it was or saw "23 feet" in the manual for the tuner and used than number, not realizing it was a minimum spec. For my own boat I just said put it a couple feet down from the top and 6 feet up from the bottom. To this day I don't know how long it is. Works fine too
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Old 25-01-2020, 12:58   #70
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Re: Backstay antenna length decision

Always fun looking and learnng about all the difference antenna setups on sailboats. Back in the 1970's I began using a simple antenna that everyone can research on their own in the ARRL Antenna Handbook. It's called an unbalanced sloper. The sloper antenna came about as a simple antenna hams could use who already had a radio tower for their other antennas and lots of guy wires holding up the tower. Someone came up with the idea of insulting one of the tower's guy wires and connecting a coax cable at the top of the insulated guy wire and the shield or ground side of the coax cable directly to the tower and all the rest of the guy wires. This radio tower sloper antenna worked very well. Because this antenna is fed by coax cable one must use a manual antenna tuner or the antenna tuner built into their radio, which by the way may not be able to tune a sloper without using a balancing device such as an Unun.

When I first saw the diagram of the ham radio sloper in the antenna handbook, what spoke to me was that it looked like it compared very closely to a sailboat insulated backstay (tower guy wire) and the sailboat mast (the tower) and all the standing rigging (the tower guy wires). So my first experiment and attempt at a "sloper" was installed on my old 1968 Rawson 30 sloop. I was amazed how incredible it worked on the the ham bands; 40, 20, 15 and 10 meters.

I sold that old Rawson 30 to a couple that sailed it around the world. They had similar results with that sloper antenna. In fact, I also installed a sloper backstay on my next boat, a Morgan 41 center cockpit "Classic" that I bought after selling the Rawson. I was located on the West coast of the U.S. at the time and we actually had great "sloper to "sloper" communications between the Rawson and my Morgan as they continued their voyage around the world; eventually losing contact after Australia as they entered the Indian ocean. (HF propagation was admittedly very good in those days).

I have since learned of better techniques. With my latest (dual backstay) sloper I am installing on my Beneteau 473, I am using a switchable 4:1 and 9:1 Unun which will match the feedline much better to the antennas. I am also using a toroid decoupling RF choke to eliminate the coax feedline from radiating any stray RF back down the cable and into the boat. This will help prevent all your panel lights and cabin lights blinking as you speak into your mic while transmitting; not an all to uncommon experience with SSB aboard a boat!

It's a fun experiment and still a work in progress. Here are some basic details. Both backstays are using Hayne radio insulators mounted right at the masthead. One backstay is cut for 53' and the other 35' with inline Hayne radio insulators on the bottom ends. I will have the choice of using either backstay with the 4:1 or the 9:1 Unun which is switched by a small relay box at the masthead. The backstay not in use will be "floating". I will also be running grounding strap from the ham rig (TS-480S) to the keel bolts on our 8,700 lb cast iron keel.

Can't wait to start experimenting with this setup but... We are still in the downside of HF propagation so I'm not expecting any miracles yet. :-).
Just some fun food for thought...

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Old 25-01-2020, 13:21   #71
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Re: Backstay antenna length decision

my now gone father-in-law was an old time ham...an avid ham at that...but his forte was CW...never see that anymore..but lordy....he could send and receive at blistering speed......he tought me that rather than count dots and dashes, learn the " sound" of a letter in CW, so this I did....never could get to his speed, but got pretty proficient at it...like learning a new " language".....fun days, but I don't do it anymore :-(

He wanted to stay in touch with his daughter while we were plying the high seas and he motivated me into getting into ham. Back then, the general license bands were pretty crowded, so he wasn't satisfied until I got my extra license, so we had room to chat without stepping on someone else.
He was very motivating !!

He advised to go the simple route on my boat, which I did, and I never had a problem hooking up with him.

But CW died out with the old school. Sad :-(
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Old 25-01-2020, 16:39   #72
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Re: Backstay antenna length decision

CW is still alive and well.

I am a 'no code ham' but I still do the best I can. Unfortunately, I learned visually and so I am topped out on audible decode at about 10-12 wpm.

BUT, there are actually enough decent programs to overcome my inadequate training, so I run CW from my home like this:
-run CWskimmer and monitor the radios signal via the USB sound driver it enumerates on my PC. CWskimmer shows CW signals playing from right to left over the 3kHz bandwidth of my radio. Here's a pic of a comparison test between my TS-590SG and IC-7300 (bottom). I am running 300Hz filters on both radios for this pic.

CWskimmer attempts to decode the CW, but I don't pay a lot of attention to it's decode and I just watch the dots and dashes. This is also a common thing for deaf hams.
-I then run FLDIGI and tie the output from it to a USB soundcard that is then tied to a converter in the FLDIGI help that converts the audio signal to a 'contact closure' and that output is tied across my straight keys wires.

So, I can opt to try to send using the straight key, or send using fldigi. This lets me play with getting better with the SKCC guys or anyone else my speed. But also operate in contests or chasing DX at higher speeds.

Some will call this cheating. I think CW is just another digital mode.
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Old 25-01-2020, 19:20   #73
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Re: Backstay antenna length decision

...ironically, in my opinion, it is easier to learn CW at high speed rather than the slower speeds. At the slower speeds, the dots and dashes are far enough apart that one needs to pay attention and count the dots and dashes and write them down as you hear them, then you have to decipher what you've written.

..at higher speeds, "counting" the dots and dashes becomes more difficult as they run so close together.

..this is where listening to the "sounds" of each particular letter is much easier.
..after a while it is like learning another language and you get to recognize not only individual letters, but also entire words...
...but that is just my opinion..it's how I learned...

..I used to listen to CW tapes while traveling somewhere in my car, and after a while, playing them over and over again, you start to recognize the sounds to letters and words you had previously deciphered.

..it is really no different from a young child learning to speak a given language.

..repetition...repetition....repetition...

..folks that are really proficient at CW, don't even write what they hear, they just " chat" using CW as a language. I never got to that stage, but..........close enuff :-). Listening to CW at high speed was easy enuff, but sending at high speed was a different matter.

...back in the day, newcomers to Ham were petrified about CW....almost all stopping at a General license, but with a little effort, CW is easier to learn at high speed....but like I said...just my opinion.

..having lived on boats most of my adult life, I never had the opportunity to build a land based ham operation, so it was " keep it simple Sam" for me, though in later years I did add a computer to my radio's, but this was mostly to download weather charts, etc...

...to get back to the OP's dilemma, a simple setup as I've (and others) discussed will do the trick just fine. A good tuner and end fed wire is really all you need, ok, a good ground also :-)
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Old 26-01-2020, 16:16   #74
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Re: Backstay antenna length decision

Wow, this is still going???

Up front, let me say that I love the fun discussion....just don't want defry (the original poster here) to get so much info that his head explodes....
So, with that in mind...



Richard, et al,

When you all get done reading this post, you're probably going to say "damn, couldn't he have just reminded us that a 40' - 45' backstay antenna length is good and typical....with a longer one good for the lower bands?"
Well, just for redundancy....I did remind you all of that!

So...



1) I do understand the necessity to stay within your budget....and, I'm not saying to throw money down the drain...and if not cutting your backstay allows you to cut costs, as long as you're not sacrificing communications effectiveness, then of course that is just fine.



2) But, when I see some of these words....it appears to me that you haven't read what has been written here and most probably not in the stickies either, and certainly not those links (here and in the stickies)?

Because an antenna ground (when floating in sea water) is actually NOT a big problem at all.....except on the internet of course, where it seems like most sailors try to complicate a rather simple system.

If you look at what is here for you all, and read the referenced links, etc., you'd see that most anything metallic can be used as an antenna ground (and also for an antenna, for that matter), but the performance is a matter of degree....heck, you can make contacts with no ground at all (I've done this, as have others), and make contacts using the proverbial "coat hanger" as an antenna, but this is certainly not what anyone would recommend...


[And, please please please don't use "foil"....I know, I know, that seems to be the generic name used these days in these on-line forums.....but, can we please all understand that if the copper (or whatever conductor) you're using for an antenna ground connection could be easily torn by hand, and/or cut with a scissors (as "foil" can be), then it's most probably too thin / flimsy to last long on-board / in the bilge, etc....so, please use wide copper strapping to make the short run from your remote tuner's ground lug to a direct sea-water connection (whether that be a bronze thru-hull or two; a underwater grounding plate / Dynaplate; or in a pinch, a close-by keel-bolt...)....its thickness isn't too critical (I use 0.022" and/or 0.012" thick), as long as it's thick enough to survive (and easily be painted or coated or epoxied), it is good.....but that is not "foil", rather called strapping or flashing...]



I read that some don't wish to drill holes in the boat....and if a cored-hull, I understand the reasons, 'cuz you gotta' do it right! And, then you seem to discount the idea of using what you already have available (one of your current bronze thru-hulls)....but rather seem to think that a capacitively-coupled connection to the sea water is good? (when there is ample evidence right there in those links, that show it far inferior to a direct sea water connection....and ironically also more expensive and time consuming than just making a direct sea-water connection...)


And, again, you seem to looking for some "solution" that allows you to not use an antenna ground, rather than seeking an antenna system that best suits your application?? (see below for some basics on the "how" and "why" of the historic and modern recommendations of HF antenna lengths for offshore sailboats)



And, finally, please remember that the performance here is all a matter of degree!



3) BTW, I'm truly sorry that my words have not made any impact....and I was going to simply wish you well in your endeavor without posting here again, but then I see your comments on your proposed antenna design....which isn't really much a "delta loop", and even so you're not really grasping the basic concept of choosing an antenna to meet your application.....
{but, then again you've never shared your application.....although we can assume offshore sailing in Coral Sea, Pacific and/or Indian Oceans, using AMSA coast stations and Aus BOM HF weather, as well as the GMDSS (and maybe NZ Maritime comms, etc.?) }

So, I thought I'd give it one last go....


This is where I'm again saying that a 40' - 45' long backstay antenna is good and historically recommended, with a slightly longer one (up to 65'), better for lower freq bands....(and, yes tuner losses are typically low here as well as the antenna pattern being decent...)


To be clear, I (and others) have politely commented negatively on that delta loop, and you thank us for this, saying this is exactly what you're looking for....but then say you're going to set-up some "alternative backstay" anyway ("just to have some options for experiments")?
And then go on to write "otherwise rely on a radial type counterpoise or just a wire dropped into the water...." ?

To which I'm confused and I say: Huh?


a) First off, an "alternative backstay antenna" is electrically the same as a "backstay antenna" (just that it isn't holding up the mast), and as such needs an antenna ground....


b) Secondly, I'm wondering how you think just a wire dropped in the water is adequate?



c) Then just as I was going to make my third comment here about your words (regarding using "radials" versus the sea water)....this is when I realized that we are probably not discussing the same things, nor designing for the same applications.... Opps....

Sorry about this....

It just dawned upon me that your application must be totally different than what we are assuming here.....'cuz who is going to go out on deck to throw out their "trailing wire" to make an emergency call??

So, perhaps I've misread your queries completely?

Maybe, all you want is to "play radio" when on-board?

Especially to just have fun and experiment on ham radio, when out sailing, etc...
And, if that's the case, sure go ahead and rig-up some nifty looking antennas and have fun experimenting....


But, most of my recommendations are based on using HF radio comms on-board for Distress, Safety, Weather, and basic / routine maritime comms, primarily when offshore and/or in remote locales....and needing comms from 100 miles to 2500 miles (or more)....



Much of what I've written / recommended might seem to be a bit overkill for just some fun/casual ham operations...


So, if we are talking about two different applications, your comments and desires become clear....and my (more strident) comments / recommendations might also be more understandable??


~~~~~~~~~~~~




4) A bit of clarification, in addition to my earlier explanations (about antenna efficiencies and lower tuner losses), regarding more "why's" of a 40' - 45' backstay antenna becoming historically recommended (has nothing to do with the modern myth surrounding "5/8-wave antennas"), and why a slightly longer one is better for the lower freqs..
(and also some tiny bit of the why a 5/8-wave antenna isn't the holy-grail!! and if you don't want to believe me here; nor believe modern antenna modeling adapted for "perfect" sea-water ground; nor believe L.B.....why not read the research and testing done decades ago by Motorola, RCA, and General Electric, it will open the eyes of most....but hey, hams worldwide are gullible...we'll buy anything that says it has "gain"...LOL )

This ain't voodoo magic....and it's all been well engineered / researched....

So, while low angles of radiation are desirable for long-range comms....these words ("low" and "long") are subjective.....and of course how much energy you have at the "low" angles....and the width of the lobes of radiation, etc., all make a big difference!!


(hence why L.B. published his "5/8wave antenna myth" paper many years ago....in brief, in general for HF sky-wave comms a 1/4-wave vertical is almost always better than a 5/8-wave, with 1/2-wave vertical about half-way between the two but closer to the 1/4-wave performance if over sea-water....)



So, yes I agree for really long-range comms, low angles are important....just not at the expense of the width of the antenna's radiation (which, with verticals on land isn't an issue....it's not until you look at verticals over sea water where you may find an issue, ironically caused by the wonderful properties of the sea water we're floating in...and here again, this is where most texts and software fail, and ironically where the older research from the 1930's thru the 1970's, really comes into its own!
Remember that until the 70's most overseas telephone calls were via radio....and it was companies like RCA, GE, Motorola, AT&T, IT&T, etc. that spent millions of $$$$ researching / testing...as well as Marconi, and these others, also working on maritime comms....please remember radio waves travel the same way they did decades ago, just 'cuz we have fancy computers doesn't mean we need to re-invent the wheel to solve a problem that doesn't exist...)



For what I quantify as very long-range comms (such as multi-thousand mile / ocean-spanning paths), there is no question that having an antenna that has sufficient energy at low angles (from 1 to 20 degrees....but primarily 10 degrees and below, on the especially long paths....heck from Florida across to Oceania / Aus / NZ, on 12mhz and 14mhz, about 45% of comms occurs at angles of 5 degrees and below!!) But, on more normal long-range paths, such US to EU or especially more usual across the continental US, the angles range all the way up past 35 degrees, with 7 to 25 degrees being most prominent....but what about on the lower freqs??

And what about on shorter paths??


Well, for comms across the US and most single-hop and double-hop paths of 1500 - 2500 miles, at 7mhz/8mhz, and at 3.6mhz/4mhz, except for an anomaly at 9 and 10 degrees, it is fairly consistent at all angles from 7 degrees thru 40 degrees....


And, except for the middle of long passages / middle of oceans, almost all of our HF maritime comms paths are less than 2000 - 2500 miles, with a majority of "long-range" HF maritime comms being 750 to 1500 miles (being on 6mhz, 8mhz and 12mhz daytime; and 8mhz, 6mhz, and 4mhz, nighttime)....and a majority of all MF/HF maritime comms being from 2mhz thru 12mhz....and also remember that most HF weather broadcasts being 4mhz thru 12mhz, and most maritime cruising nets being on 4mhz and 8mhz (and 75m & 40m ham nets), with some 6mhz...and some long-range nets on 12mhz (and 20m ham nets)....
AND...


And, what angles are used by these more normal "long-range" paths? Well, a 750 mile HF path generally uses an angle of about 45 degrees....with 35 degrees for a 1000 mile path....



And, if looking at the average comms paths of most "cruising nets", we're typically looking at 300 to 500 miles, with angles of 75 to 60 degrees.....and if more local, with paths of 100 to 300 miles, angles of 90 to 75 degrees (these angles, above approx. 70 degrees, are typically considered "Near Vertical Incidence", the N V and I in NVIS/Near-Vertical-Incidence-Skywave....and are exclusively only reflected on freqs below 11mhz, but most typically only on freqs below 8mhz, of course depending on solar flux at the time...)

So...


So, as you can see there are different angles of radiation / reflection used for different paths on different freqs....and, you can also see one reason why the attraction to a 5/8-wave antenna with its narrower primary lobe (and other lobes/nulls) is usually a false attraction (kinda like a school-boy crush, rather than true love...LOL!)
Sure, if you're looking for a single-band antenna, almost exclusively for very long-haul work, then a 5/8-wave over sea-water is great....but, for most of us here / our applications, making it no longer than 0.64-lamda at your highest primary freq is okay, but could be short-sided (depending on your application)....



Now, while some may look at all of this above and say "okay, now I know what to do"....BUT, sorry, we need to understand another issue....
(of course, you really don't need to understand all of this if you accept what was written earlier....and for decades....that a 40' - 45' backstay antenna length is good and typical....with a longer one good for the lower bands....if you accept that, you can ignore most of this post... LOL)


But, now we have another is to understand.....most of us aren't using a "vertical", but rather a "sloper"....and the more the wire "slopes" the less it operates as a "vertical" and more like a "horizontal antenna".....the fact is on our boats, it's likely a slope angle of only 15 degrees (or up to 30 degrees at most), but even 15 degrees is enough to really effect our antenna's radiation pattern! (see below)
But, no....rest assured, most of the energy isn't being sent into the water and into outer-space....it just doesn't work like that in the real world....especially when close (< 10 to 20 wavelengths) to earth...



5) Yep, our sloping verticals, while still doing very well, aren't performing like true verticals.....we loose the deep nulls overhead and the vertical pattern broadens (and rises a bit)....and BOTH of these things are actually very good for us on boats!!!
[I'm purposely not posting the models here....in addition to not being needed, I suspect it will just dissuade most from actually learning here...]



Those on land (especially those needing the overhead null to improve receive S/N) , and/or those looking for extreme long-range might find these to be detriments, but for us on offshore sailboats, these are pluses....actually allowing decent signals at very high angles for NVIS comms from 50 to 300 miles, and allowing decent signals at mid-angles of 45 to 60 degrees, useful for comms from 500 to 750 miles, and even a good advantage (versus a true vertical) on paths out thru 1000 miles...



Just to give examples....
A true vertical (such as a 1/4-wave vertical over very-good ground, w/ 32+ radials, or over sea-water....or a 1/2-wave vertical over very good ground or over sea-water...all based-fed, down low...) would have very deep nulls overhead...
It would be ~ 30db down at 75 to 90 degrees, and ~ 20db down at 60 to 75 degrees, and 10-12db down at 45 to 50 degrees....
But even a slight slope of approx 15 degrees from vertical, reduces these nulls overhead to 9-10db at 75 to 90 degrees, 8-9db at 60 to 75 degrees, and 6-8db at 45 to 50 degrees....


What does this mean for us?
Well, it means that we have a serious advantage (versus a true vertical) on very high-angle NVIS paths, and even a good advantage on the longer regional paths....


But, now you're about say "hey, you forgot about the "null" from the mast, you know the 'front-to-back-ratio'...." Well, I didn't forget that!

Discounting all the other rigging that can be reflecting and/or coupling/reradiating your signal, the actual F/B of a 1/2-wave 40m sloping vertical (at 15 degree slope angle, off of a grounded/conductive mast) is only 3db!! and the pattern is damned symmetrical....

But of course, we do have a great deal of other rigging that will effect the pattern in rather random and un-modelable ways, so the actual F/B from just the slope is a fairly moot point to worry about....




6) Also, please exercise caution by drawing too many conclusions because of what antennas are used my many/most merchant (and military) vessels, as they have significant advantages over our small fiberglass/GRP sailboats.....they have HUGE metal hulls, with antennas mounted up high...and can/do compensate for any antenna deficiencies with increased transmit power....

This is not to say that you'd be wrong to learn from them....but rather to actually understand that our small fiberglass/GRP sailboats are a rather unique situation / application....just like shore-stations take advantage of high horizontal / directional antennas (as they are on land, and don't have the sea water to better use verticals), just use caution when comparing your antenna choice to those of large merchant vessels...


~~~~~~~~~~~~~



As others have said here....there is no voodoo magic here....it's all been done....and there are actual reasons for what works best....


Please note that I didn't throw any "math" at you....nor did I tell you to "model it", nor did I simply post some nice graphics....nope, I didn't do any of that...
(I've done this in the past, and the links are here....but tinypic.com no longer has all of my almost 100 scans/test results....and I don't have the time to find 'em all!)

Instead I actually provided you with the very basics of HF radiowave propagation, some skywave communications properties, some basic/simple details of antennas, and some minor specifics of peculiarities / idiosyncrasies of HF antennas on our sailboats...


These are not provided to you with modeling software ('cuz you're expected to know all of this and a whole lot more, before using modeling software), nor would you find this info in a radio or antenna manufacture's manual (too many variables for them to deal with), and certainly are almost never going to get some "internet expert" to take the time to write all of this ('cuz you're not going to find it on wikipedia, nor probably on Google)....
Yes, you can find some of this in older RF Engineering textbooks / manuals...and find some from RCA, GE, Motorola....and find some in ARRL Handbooks.....and find some in RF engineering classes....but, fact is, nobody out sailing really needs to know all of this, if they can just accept that there are real engineering reasons for both the historic traditions AND modern recommendations....any "expert" that cannot target their recommendations to your application might be smart/educated, but unfortunately might also be unaware of these intricacies (and probably ignorant of a whole lot more)....




I do hope all the above has helped, some??
So, can we all now please just let derfy use his HF radio, and have fun??
I mean, hasn't this gone on and on, a bit too much?

Fair winds.

John
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Old 26-01-2020, 16:33   #75
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Location: Half Moon Bay, CA, USA
Boat: 1963 Pearson Ariel, Hull 75
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Re: Backstay antenna length decision

An alternative no-holes-in-the-hull ground for those using an end-fed backstay antenna: get your desired length of stainless steel braid (I suggest at least 50 feel of 1 inch wide braid), connect/attach one end to your backstay chainplate, and trail it astern in the water when underway. At a speed of a few knots, it'll stay at the surface. There's nearly no drag from the streamlined braid.


Electrically connect the chainplate to the tuner ground. I suggest using the same braid for that connection.


Here's a source for the braid: http://www.ags.bz/


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