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