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Old 22-02-2012, 04:53   #31
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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 Goudurix View Post
Yes Bill...the never-ending quest for the optimal all-band antenna on a sailing boat...

I would expect even a vertical 'random length' end-fed antenna will have directionality because of the effect or the nearby backstay, mast, stays, etc.

I would very much like to try and model my own sloping "alternate backstay" antenna "Copyright B.Trayfors " to really find out about the expected radiation patterns... but I'm novice at Eznec.
Modeling the mast, stays and my 1/4 wave radials etc. is feasable, but what about the pushpit, lifelines, toerail who are in fact grounded since they are linked to the copper tape to an underwater bronze....

I wish our good old friend Greg was around to help me there....

Jan
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Yeah....wonder what he's up to these days?

Just about anything you can put on a sailboat will have some "directionality" or, more properly, some "dead zones" because of absorption into the standing rigging, mast, etc. But, since there's little you can do about that and since the boat generally swings at anchor it might not be such a big issue.

I've found the "alternate backstay" antenna to work very well...as well as the traditional backstay. And, it's generally a bit "cleaner" in the feedline because the run is often much shorter and there are no rigging screws or chainplates or whatever in the path from the tuner to the antenna.

But, we're quibbling at the edges of what matters here. Backstay antennas work fine on most boats and on most bands, and I believe all sailboats should have them as the robust multipurpose good-but-not-great antenna.

73,

Bill
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Old 22-02-2012, 07:03   #32
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

yes I will keep my alternate backstay antenna, it will go into its 3rd season. I find it works very well on 17m but I have to admit 17m is also my favourite DX band. I have always had my best long distance contacts there both at home as on the boat. Maybe it is also because I hate those weekends with all decametric bands blocked by contests....

I will certainly "revamp" my vertical dipoles. I might even be tempted to try out hairpin matches on them to get the SWR down - since they are not intended for permanent use, they don't need to be that rugged.

And now waiting for the spring & the first navigation....

Jan
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Old 24-02-2013, 22:33   #33
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Do you have a updated link to Marine Antennas (http://wdsg.com/gallery/main.php?g2_itemId=125)? I get an error with this page? Could someone send me the link to the Alternative Backstay antenna instructions?
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Old 26-02-2013, 03:29   #34
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

A good demonstration of having gain at the right takeoff angle rather than a inverted V having X Db more gain than a vertical. Its a shame more people dont ask this simple question more often. The question should be. How much gain does my antenna have at takeoff angle X. Then the second question should be, what takeoff angle is optimum for the path that I am communicating on. Differences between vertical and horizontal antennas is real gain differences at certain takeoff angles rather than real gain advantage. I am sure if you did the same check on a long distance path the vertical will beat the low horizontal dipole by a substantial amount especially over seawater. Anyway a very interesting anecdotal test which can be of huge benefit if you lose your mast or backstay. A low dipole even laying on the deck tuned by an antenna tuner will enable you to communicate effectively with nearby coastal or short skip ham stations. If I was stuck in the Southern Ocean I would take the backstay vertical any day. The fact that you can obtain ultra low angles of radiation from vertical antennas over seawater is something that should never be underestimated in the search for the ultimate signal. Anyone who ignores this point has a poor understanding of the importance of takeoff angle of radiation. Another forgotten point of fact is that the typically a signal received from the ionosphere can have 2 points of arrival. The first point is the signal reflected directly from the ionosphere, The second path is that reflected directly from some distant point off land or water. You antennas radiation pattern can exaggerate either one of these reflected points giving the impression that one antenna has more gain than the other. I suppose thats why we have antenna ranges for truthful answers rather than relying on anecdotal reports with instruments that are not calibrated and not factoring all other factors. Sailors make lousy RF Engineers!
Quote:
Originally Posted by deckofficer View Post
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 26-02-2013, 06:38   #35
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

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Originally Posted by mctdog View Post
Do you have a updated link to Marine Antennas (http://wdsg.com/gallery/main.php?g2_itemId=125)? I get an error with this page? Could someone send me the link to the Alternative Backstay antenna instructions?
I'm sorry my website is down.

If you'll send me an email direct, I can email you pix and anything else you might need.

My email is bill at wdsg dot com

Bill
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Old 26-02-2013, 08:51   #36
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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 plebian99 View Post
A good demonstration of having gain at the right takeoff angle rather than a inverted V having X Db more gain than a vertical. Its a shame more people dont ask this simple question more often. The question should be. How much gain does my antenna have at takeoff angle X. Then the second question should be, what takeoff angle is optimum for the path that I am communicating on. Differences between vertical and horizontal antennas is real gain differences at certain takeoff angles rather than real gain advantage. I am sure if you did the same check on a long distance path the vertical will beat the low horizontal dipole by a substantial amount especially over seawater. Anyway a very interesting anecdotal test which can be of huge benefit if you lose your mast or backstay. A low dipole even laying on the deck tuned by an antenna tuner will enable you to communicate effectively with nearby coastal or short skip ham stations. If I was stuck in the Southern Ocean I would take the backstay vertical any day. The fact that you can obtain ultra low angles of radiation from vertical antennas over seawater is something that should never be underestimated in the search for the ultimate signal. Anyone who ignores this point has a poor understanding of the importance of takeoff angle of radiation. Another forgotten point of fact is that the typically a signal received from the ionosphere can have 2 points of arrival. The first point is the signal reflected directly from the ionosphere, The second path is that reflected directly from some distant point off land or water. You antennas radiation pattern can exaggerate either one of these reflected points giving the impression that one antenna has more gain than the other. I suppose thats why we have antenna ranges for truthful answers rather than relying on anecdotal reports with instruments that are not calibrated and not factoring all other factors. Sailors make lousy RF Engineers!

I wish I would have explained it like that. Sea of Cortez, 20 and 40 meters during the day, 75 meters at night for the short distance to the States, the high angle inverted Vee was loud. Had I been 1/2 way around the world from the States, I'm certain the low angle of the vertical would have been the better choice. I should have named this thread "good performing short distance HF antenna".
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Old 27-02-2013, 14:40   #37
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

Bob, et al,
If you all don't mind some actual real numbers, regarding the actual real wave angles / radiation angles, that the ionosphere reflects our signals at, I have a GREAT deal of info for you....
Quote:
Originally Posted by deckofficer View Post
I'm certain the low angle of the vertical would have been the better choice. I should have named this thread "good performing short distance HF antenna".

1) Taking advantage of the extremely low pseudo-Brewster angle of a vertical over sea water (</= 1 degree), is almost like running a KW into a yagi at 1/2 wave above ground, on an inland station!! (and is nothing new, as many have been doing it for many years, and Bill T. has been doing it / writing about it for many years as well...)


2) Taking advantage of the high radiation angles from low (~ 1/4 wave height) horiz antennas, for Near Vertical Incidence Skywave (NVIS).... depending on time of year and sunspot activity, up to 10mhz daytime (typically 3mhz-8mhz) and 1mhz - 5mhz nighttime....is also nothing new (hams, military, and commercial operations have been doing so since the 1930's)
See below...


3) What is relatively new (within the past 10 - 15 years), is that we have real-world data from ionospheric soundings/studies and from real measured wave angles along many skywave paths and many different frequencies...
(I'm an educated and informed guy, who has been working on radio comms for about 40 years.....and even I was surprised by the concentration on such low angles, when I first saw some of these numbers about 15 years ago...)

First, is some info that I posted last summer, specifically dealing with long range (2500 - 12,000 mile) comms in the mid-HF range (12mhz - 18mhz), and then some info regarding the lower HF freqs (3mhz - 8mhz) and both long range and shorter range comms....

Here is just some of the information I posted last summer, from the SSCA discussion on the KISS-ground....
http://www.ssca.org/forum/viewtopic.php?f=5&t=13490
http://www.ssca.org/forum/viewtopic....bf442&start=75

Quote:
A) Let's start with the ionosphere....(F-layer)
What reflection angles / radiation angles it supports for a particular path (at a particular freq and time), is just that...what IT supports.....and has nothing to do with your antenna....
Mother Nature makes this decision and there is NOTHING that we can do about it....no matter what antenna, no matter how much salt water we have around us, the ionosphere controls what angle waves are reflected at......

Meaning that when the ionosphere supports a path, from say the US to EU (a common HF path to work, whether ham or maritime freqs are used), it is supporting that path at a specific reflection/radiation angle, of say 5* or so, at 12 or 14mhz, for a double hop connection......and at differnt times (differnt layer heights) may support a triple hop for this path as well....(and sometimes at the same time of the double-hop, it may support a triple hop path at a higher angle, but usually not...)

The only part the ionosphere plays regarding antennas, is how much gain your antenna has at this specific angle....

And, if we look at the range of angles we typically have supported over common paths, we see surprisingly low angles, which is why using an antenna which has as much gain as possible at very low angles, provides for better signal strengths....
Statistical analyses have been done over long periods of time, so we do have factual data that we can use to determine what angles are supported over many different paths....
As an example, for the US East Coast to EU on 14mhz (over the entire 11-yr solar cycle), although the range of possible angles is broad (from 1* to 20*), typical angles are 3* - 12* (making up 75% of all paths, whether double or triple hop), with the statistically most prevalent angles being 5* and 4* (making up about 25% of all paths)

So, here you can see why vertical antennas over sea water can really play well!!!
Quote:
1) When the ionosphere can support a skywave communications path between two specific points on earth, on a specific freq (meaning that this freq is between the LUF and MUF) at any given time, it IS the ionosphere that sets the angle that these signals are reflected at, and travel at to/from each station, NOT the antennas.....(although some laypersons tend to think opposite, this is a scientific fact...)

When I (or others) comment on-the-air, "propagation is changing" or "signals have really changed", many times this means that the ionosphere is reflecting at a different angle than before and/or the layer height has changed, and the difference in our antenna patterns (the amount of signal they send/receive at any specific angle) at the "new" reflecting angle makes up most of the difference in signal levels.....


2) Further, as you operate closer to the minimum or maximum freqs (LUF or MUF), the changes of the actual ionization (and changes in layer heights) of the various layers of the ionosphere has a significant effect on signal levels / fading....
And, as you operate closer to the critical freq, and are using Near Vertical Incidence Skywave (such as daytime comms on 6 - 8mhz and/or nighttime comms in the 3 - 4mhz range), the changes in ionization can have significant effect on both the critical freq and on the absorption levels....

a) As solar-flux and the MUF go up, the absorption of the D-layer (and even the E-layer) also goes up....and this can make a significant difference in signal strengths on daytime mid-HF region comms (8-16mhz)......
And, this one of the largest contributors in determining the LUF.....
This can mean that long-dist comms on say 12mhz are good early in the day and late afternoon, but not near midday....
This is one reason why fading can be so deep on what the "computer generated propagation charts" might show as "good propagation"

b) And, the opposite can happen just as easily, if you're operating near/at the MUF, any change in ionization (lower) can plunge your signals quite rapidly, giving you deep fades....



3) And, lest we forget that there are times that the ionosphere can support multiple modes of skywave comms, from these two points, at the same freq, at the same time....meaning that one "mode" may allow a single-hop, and another "mode" may allow a double-hop, etc...and, while comms using less "hops" almost always have much stronger signals, in some instances (usually short skip distances) this is an area that the antenna patterns at each end may effect the relative signal differences between skywave comms of different "modes" (sometimes allowing a double-hop signal to be stronger than the single-hop....although not common, it can actually happen more often than many think when the paths are all over sea water, as the ocean makes a very good reflector for a second, or third, hop to take off from....)


PLEASE understand that ALL of the above can change over very short periods of time.....while minor fading can have effects over short periods, such as 30 - 60 seconds, significant changes usually take 15 - 30 minutes, and there are some times that significant effects can be noticed in just a few minutes! And there are rarer times when significant fades/effects can take just seconds!!! (I've seen 20db - 30db fades happen in 10 seconds...)


4) Now you need to add into the mix the various antenna lengths (for our backstays, whips, etc.) and their various elevation patterns.....PLUS the variables of the slope of these antennas.....PLUS all the rigging which can effect both the vertical radiation angle and the azimuthal pattern.....PLUS the difference in the direction that each boat is "pointing" as well as their exact location (a few miles apart can make a difference).....


5) And, then add into the mix that ALL of the above CHANGES when you CHANGE FREQUENCY!!!
Meaning what works well, at one specific time, to/from one specific location to another specific location, at one specific freq, will change when you change frequency.....(not much change when making small freq changes....but making changes of a few mhz and/or a half-octave or more, means that you can now have a completely different set-up and completely different results!!!!
So, it is VERY difficult (if not impossible) to compare/contrast systems operating on different freqs, even just minutes apart....and when at different times as well, all bets are off!!!


6) Now, please understand that I realize that I cannot type enough here to give a complete explanation of HF Radio Wave Propagation (I don't even hit more than the "highlights" when teaching this in seminars), but what I was trying to hit on here was that while there are MANY variables that we have little control over, it makes common sense (and good seamanship) to make the best of what we DO have control over, at least that which is within our budget ($$) and within our area of understanding (hence the reason I was posting about the improved performance gained from using a better ground plane / counterpoise, than the KISS-Ground!!!)


Statistical analyses have been done over long periods of time, so we do have factual data that we can use to determine what angles are supported over many different paths....I don't have Mex to US path data handy, but it IS very similar to the data for other single-hop (1000mi - 2500mi paths) and surprisingly close (within a degree or two) of the double-hop (2000 - 5000mi paths).....

In addition to the data above:

For 14 mhz....
For the US East Coast to EU on 14mhz, over the entire 11-yr solar cycle {the range of all possible angles is from 1* to 20*, with typical angles of 3* - 12* (making up 75% of all paths, whether double or triple hop), and the statistically most prevalent angles being 5* and 4* (making up about 25% of all paths).....here is the same data for 3.5 - 4mhz and 7 - 7.5mhz...


For 7 - 7.5mhz....
For the US East Coast to EU on 7 - 7.5mhz, over the entire 11-yr solar cycle {the range of all possible angles is from 1* to 24*, with typical angles of 4* - 15* (making up >63% of all paths, whether double or triple hop) and 1* to 17* making up >86% of all paths, and the statistically most prevalent angles being 1* and 6* (making up about 19% of all paths...)
{approx. 31% from 1* - 6*, approx. 24% from 7* - 10*, and approx. 23% from 11* - 15*, and approx. 21% from 16* - 24*...}


For 3.5 - 4mhz....
For the US East Coast to EU on 3.5 - 4mhz, over the entire 11-yr solar cycle {the range of all possible angles is from 1* to 23*, with typical angles of 6* - 15* (making up 60% of all paths, whether double or triple hop) and 6* to 20* making up >85% of all paths, and the statistically most prevalent angles being 13* and 14* (making up about 20% of all paths...)
{approx. 35% from 1* - 10*, approx. 32% from 11* - 15*, and approx. 32% from 16* - 23*...}



It is easy to see that for normal skywave comms (single, double, or multi-hop) over most paths, having an antenna with some gain BELOW 15* - 20* makes a difference, and in the mid-HF range (12mhz - 18mhz) having one with a decent amount of gain below 10*- 12*, makes a significant difference!!!





4) For "close-range" low-freq HF comms, beyond the typical 20 - 50 mile "groundwave" range, out to 200 to 500 miles.....this is the realm of Near Vertical Incidence Skywave (NVIS).....
Depending on time of year and sunspot activity, NVIS is "do-able" up thru 10mhz daytime....but typically only practical on 3mhz-8mhz daytime and 2mhz - 5mhz nighttime....

{Although the Near Vertical Critical Frequency can be from 1mhz to as much as 12 MHz, at the far extremes, it is typically from 2mhz - 9mhz....this is the frequency above which the ionosphere can no longer reflect a near vertical incidence signal, and therefore skip zones appear at these higher freqs as the ionosphere cannot support comms on these specific paths on these freqs.....

A nice happenstance is the direct correlation between the "critical freq" and MUF.....the "MUF" (for F-layer) is 3.5 times the "critical freq".....
Meaning that when 10m is wide open, the critical freq is above 8mhz....and as the MUF rises past 35-40mhz, the critical freq is above 10mhz and approaching 12mhz.....
And on the other end, when I'm getting echos / multi-pathing on close-in 75m comms (effects from operating close-in paths <50 - 100miles, at/near the critical freq), you can be assured that 20m is dead and the MUF is close to 30m (10mhz).....}


For excellent results and reliability, low-HF freq NVIS usually requires antennas with high radiation angles, as opposed to what is typically required for long-range skywave comms (also usually done on higher freqs w/ lower absorption)...
These high radiation angles are exactly what a low (~ 1/4 wave height or lower) horizontal antenna produces.....and exactly what vertical antennas do NOT produce (as verticals have a "null" overhead)....

Antennas with low radiation angles (such as verticals over sea water and yagis on tall towers) have significant nulls overhead (typically down 20db - 30db, from 60* to 90*).....and a dipole at 1/4 wave height has its main radiation at 90* above the horizon (a quite broad lobe, being only a couple db down at 60* above the horizon), and being 20db - 30db down at ~ 10* radiation angle.....
So, yes, choosing the correct antenna, for the path/time-of-day/time-of-year/etc. CAN make a 20db to 30db difference!!!

The fact that many cruising boats can operate / maintain 3.5 -4mhz, 6mhz, and 7 - 8mhz, daytime comms over distances of hundreds of miles, using VERTICAL antennas, for these NVIS paths is a testament to the fact that you CAN communicate quite well with fairly low power (20db below 150 watts is 1.5 watts)....
And, although "groundwave" comms over seawater using vertical antennas is SIGNIFICANTLY better than that of land-based stations and horizontal antennas (where 15-20 miles is typical), you are still very hard pressed to get decent groundwave past 50 - 60 miles (100 miles is usually the max), but since the skywave signal (NVIS) is usually MUCH stronger (30db+ at 20-50 miles), HF groundwave comms for cruisers is only really used/applicable at < 20-25 miles....



Gosh, there's much more, but I gotta' go....


Fair winds..

John
s/v Annie Laurie
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Old 27-02-2013, 15:01   #38
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

John,

Great write up, you are into propagation. So in a nutshell, as I was hanging on the hook near Mulege, Mexico, and Baja net control was in San Diego at around 400 miles distance, then on 40 meters daytime, 75 meters at night my inverted vee and 500 watt solid state amp gave me the so called 20~30 db advantage over the verticals in the same anchorage. Had net control been 10,000 miles away, the verticals would have the advantage. Right?
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Old 28-02-2013, 03:48   #39
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

For cruisers that dont want to be propagation study experts. The higher the sun and the closer you are to the equator use the highest available frequency. The lower the sun the lower the frequency. Theres always propagation so just keep changing frequency following the above rules and you wont need to read a HF propagation manual. Since most people cant control their angle of radiation within the limits of your chosen antenna, it will always be suck, try and see. If you have internet access use the following simple propagation prediction link and all will be revealed. If this software link says theres no propagation theres no propagation possible. End of story. VOACAP Online - professional-grade high-frequency (3-30 MHz) point-to-point propagation predictions Use verticals for the path calculation and set the power limit to something like 50 watts to account for antenna and ground efficiency loss. You can also do general wide area propagation models without all the technical mumbo jumbo. Most ham texts on propagation have simplistic models and notions about propagation. Most ham texts on propagation rely on out of date 40 year old theories that current day HF propagation specialists would not use. Use the above link because the VOACAP software incorporates current day modern thinking on HF propagation area coverage models.
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Old 28-02-2013, 10:35   #40
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

Bob,
Yes....but..
Quote:
Originally Posted by deckofficer View Post
Great write up, you are into propagation. So in a nutshell, as I was hanging on the hook near Mulege, Mexico, and Baja net control was in San Diego at around 400 miles distance, then on 40 meters daytime, 75 meters at night my inverted vee and 500 watt solid state amp gave me the so called 20~30 db advantage over the verticals in the same anchorage. Had net control been 10,000 miles away, the verticals would have the advantage. Right?
The short answer is a qualified Yes....(I'm removing the transmit power differences from the calculations, in all of this...)

The long answer is:
1)
a) An inverted-v does NOT have the same exact pattern as a flat-top dipole, so there are variables here that effect the exact numbers...
b) Your inverted-v is NOT a 1/4-wave high (~ 65' on 75m), so its "gain" is less than it would be at 1/4-wave height, so you lose a couple db here as well...
c) I believe you have traps (or loading coils) in you inverted-v, and these will also add some loss, of typically 1.5 - 2db PER trap (3-4db for the pair)....

So, your trapped/loaded-inverted-v is probably (my "guesstimate") down 4 - 5 db, from a flat horiz dipole at 1/4-wave high....


2) I have no direct info on the verticals in the anchorage, so they are of unknown height/length, slope, azimuthal pattern/direction.....(nor their ground system losses, nor tuner losses, etc.)
Therefore it's difficult to know, exactly what their patterns and ERP's are...


3) So, my "guesstimate" is that your horizontal antenna is probably about 15 - 20 db better than those verticals over a 400mi NVIS path on 75m and 40m.....
And, that those verticals are the same 15 - 20 db better than your horizontal antenna on long-distance/low-angle F2 comms, such as 2000 - 2500mile paths....and possibly 20db+ over the longer multihop paths of 4000 - 12,000 miles.....


~~~~~~~~~~~



I agree with Plebian, that you do NOT need to be a "propagation expert"....and VOCAP is good software....(I've used it some, in some classes, but just like humans, it ain't perfect....quite frankly, there are many times when there IS propagation, when "the computer says there is not"....)
Quote:
Originally Posted by plebian99 View Post
For cruisers that dont want to be propagation study experts....
If this software link says theres no propagation theres no propagation possible. End of story
...But, having a working knowledge of radiowave propagation IS a large part of being a good radio operator...and simply deciding to be ignorant of the facts that will make someone a better operator is, in my opinion, foolish....
Relegating the task of "knowing" something to a website / or a piece of software is becoming acceptable these days.....and in some cases this is fine...but in other cases, I think it is also a bit foolish....
(Just my opinion here....others might be different....but everyone's is valid!!)


And, understanding these basic concepts is really not that hard....
a) the "low angles of radiation from verticals (of .64-wave or shorter), is good for long range comms"...
b) the "high angles of radiation from horizontal antennas (1/4-wave high or less), is good for 'local' (50-400 mile) comms"...
c) how to choose the correct freq, for the path and time-of-day (and time-of-year)....

A quick read through of an ARRL Handbook, will easily teach these basic concepts....and no internet connection, nor computer, is necessary to tell the operator how/where to use his radio or what antenna to select....


Again, I FULLY and COMPLETELY agree and understand that VERY few sailors/cruisers/radio operators will decide to study radiowave propagation, antenna design and construction, nor advanced radio communications in general, etc....
But, since not only are these my forte's, I actually teach these classes/seminars, I thought some here might be interested, at least in the basics....



Fair winds....

John
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Old 28-02-2013, 13:40   #41
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

Thank you again John. Now your answer to my next question will be of importance to many others, so here it is...

Since my plans for cruising the next time is going to take me much further than the Sea of Cortez, and I want a good signal over a 5000~10000 mile path, from what I have gleaned for you excellent post is a vertical as long as commercially available with an automatic antenna tuner at its base with as much counterpoise as I can create for it through out the hulls (cat) and I'm good to go. The only thing that makes me flinch is the cost of the automatic tuners capable of 500 watt operation. On the ships I served on, that is what the company used, something like a 32' fiberglass vertical and high wattage tuner at its base. With 32,000 tons of steel, counterpoise wasn't a problem as it is on a fiberglass boat. That setup on the ships worked good.
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Old 28-02-2013, 16:10   #42
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

Bob,
1) First off, everyone should understand the significant compromise designing/building an effective antenna system for the typical cruising boat is...and the fiberglass hull is actually the least of the worry....

For maritime MF/HF comms, there are freqs between 1.6mhz and 26.2mhz...
For amateur radio MF/HF comms, there re freqs between 1.8mhz and 29.7mhz....
While these are extremes and you're most likely to be using 2mhz thru 21/22mhz, this still represents a quite wide range of freqs (3.5 octaves), and a very broad range of operating conditions....

Then you add in the various locations/ranges that you may require communications with....
At anytime day or night....24/7...

And, then it HAS TO work perfectly every time, with no operator "tweaking"....especially in emergency situations when some anxiety / stress enters into the picture...

And, then it needs to "survive" in both the salt water environment and with heavy winds/seas....lots of UV radiation, etc...

And, then we need to input the BIGGEST design/construction criteria of all:
The antenna(s) needs to fit into the design/plan of the vessel, without effecting the vessels safe operation nor impacting on the vessel's ability to "sail", etc....

Oh and lest we forget that everyone wants it to CHEAP, as well....


So, designing and building antenna(s) for our cruising boats IS a big compromise!!!





2) I think you're on the right path with most of what you write here....
Quote:
Originally Posted by deckofficer View Post
Since my plans for cruising the next time is going to take me much further than the Sea of Cortez, and I want a good signal over a 5000~10000 mile path, from what I have gleaned for you excellent post is a vertical as long as commercially available with an automatic antenna tuner at its base with as much counterpoise as I can create for it through out the hulls (cat) and I'm good to go. The only thing that makes me flinch is the cost of the automatic tuners capable of 500 watt operation. On the ships I served on, that is what the company used, something like a 32' fiberglass vertical and high wattage tuner at its base. With 32,000 tons of steel, counterpoise wasn't a problem as it is on a fiberglass boat. That setup on the ships worked good.
Bob, I'm flattered that you value my opinions....but I haven't got the time today to write too much detail....so here are just some highlights...

--- If I had to lay out the things that are not always talked about (the "counterpoise" and ground system are discussed at length, many places elsewhere.... such as here...
SSCA Forum &bull; View topic - KISS-SSB Counterpoise
SSCA Forum &bull; View topic - KISS-SSB Counterpoise )
.....but are important nonetheless...here are some thoughts....

a) Learn as much as possible about radiowave propagation and advanced radio communications/operations...
Bottom line:
An excellent, experienced, and well-trained operator can make a poor/mediocre system work well....
But a poor, inexperienced op, can't be helped by even the best system!!!

There is NO substitute for knowledge/expertise on-the-air....



b) Do NOT skimp on the antenna's ruggedness/robustness....
The old saying, "make it once - make it last", applies here...
316 SS wire and quality insulators, etc. ARE what is called for...

Do NOT consider the things you use at anchor and/or gunkholing around Cortez / Bahamas / etc. as "proper" offshore long-range antenna components...
Things like copper wire (strung on its own), "temporary" antennas, traps/coils/etc., support poles, etc. are fine "radio nuts at anchor", but should never be considered part of the vessel's real antenna system (neither primary or secondary antennas...)

The old ham saying that if the antenna survives the winter (or summer storm season) without falling down, then it ain't big enough.....does NOT apply here!!!



c) Decide on what freqs you desire to optimize for....not necessary absolutes, but as "guidelines"...

If you're a low-band DX'er, or desire to use the lower HF Maritime freqs a lot...and/or desire "close-in" (50-500 mile) comms on the 2-8mhz bands....AND you can accept the slight compromise on the higher HF freqs, then using a long backstay antenna (50' - 70' overall) might be a good choice...

If your primary use is going to be in the mid-HF range (12 - 16mhz), then keeping the overall antenna length to 40' is good....

While this is NOT a critical decision, and the "advantages" one way or the other are not too dramatic, they are measurable and useful...
You may wish to read over the SSCA Disc Boards...where this has been discussed (with real world results)....

But, it is no coincidence that the common advice is to use a backstay antenna with an overall length of 40' - 45' (from the top insulator of the remote tuner, to the top backstay insulator).....
This IS good advice!!!
And, nothing I write here should be construed to say otherwise....rather I'm just giving some context to this common advise....

(BTW, my backstay antenna length is 64'.....as I decided the lower HF freqs were my priority....)

If you cannot rig a "backstay antenna" or "alternative-backstay antenna", and you are limited to using a whip....all is not lost...
A longer (32' - 35') whip is a great idea, and they work great...but they ARE pricey!!!
So, your 23' - 28' whips are more typical....
And, they DO work....although you do sacrifice some efficiency and effectiveness on the lower freqs (primary below 6mhz, and especially on 2 - 4mhz)....
Using a 23' - 28' whip will, however, give you an advantage on long-range comms on the higher HF freqs (>18mhz....)

But, again whatever antenna you can install, use my recommendations above (in "a") and don't skimp on the sturdiness/ruggedness....




d) Do NOT skim on the remote tuner....
Icom and SGC (and Sailor, Tharne&Tharne, Harris, Rockwell, ITT/MacKay, etc. etc.) all make excellent remote auto-tuners...
The tests I've seen / "tuner losses" that I have seen published have always shone that You Get What You Pay For!!!

I'm not trying to "China-bash", but the made-in-China knock-offs are, in my opinion, a "fools bargain"....and while MFJ makes some inexpensive toys, the facts are the tuner losses are much higher and these are poor choices....
They may provide a decent vswr to your transmitter, but loosing a few db (in some circumstances as much as 6 db), is something that should make you pass 'em by...but, in case you're tempted (maybe because you desire a higher-power unit, without spending the $$$), their reliability is also questionable (and MFJ has had serious QC issues for at least the pas few years, and I suspect the "made-in-China" knock-offs do as well...)

As for needing a remote auto-tuner that can handle a 500 watt output, you can pick any one you want, as long as you want an SG-235!!!

But, before you cringe at the $1200+ price, maybe you don't really need it at all....

If you have an SG-500 amp AND you have a VERY stiff and robust 12vdc source (lots of A/H's of batteries) and a very short and thick run of power wire, you may find using the SG-500 to be okay....

But, the IMD products produced by 12vdc hi-power transistors / amplifiers are quite high....and the maintaining adequate collector voltage (B+) at the transistors (not at the batteries!) is VERY important or you'll have very poor transmit IMD, and you'll be splattering up/down the band.....
And, IF all the above is good, you'll need to keep from overdriving the amp...yes, it does have the auto-attenuate that keeps you from damaging the transistors, but that is NOT quick enough to keep from overdriving on voice peaks, and then here again causing very poor transmit IMD....
Since the M-802's factory-set power levels are 20w, 60w, and 140w (that's not a typo), you'll find 60 watts to be overdriving the SG-500 by about 2.5 to 3db....and you'll need to use the 20 watt setting....
20 watts into the SG-500 will give you about 400 watts out....
The difference between 140/150 watts and 400 watts is about 4db....and even if you decided that transmit IMD be damned, and had plenty of 12vdc current available, the difference between 150watts and the approx. 550 watts max that you could get out of a SG-500, is about 5.5db....

So, if you DO desire to use the SG-500 amp, and you meet all of the specific requirements above, then you basically have a choice of the SG-235 (or other much more expensive tuners), or decide on only using the SG-500 amp with tuned/resonant antennas (such as Bill T's "20m vertical dipole", etc. or at anchor you could use your existing 40m/75m inverted-v..)

And, that's REALLY it....


Now, if you are using another 500 amp.....you'd probably better off without it...
The Ameritron AL-500 and Tokyo Hi-Power HL-450, will at best produce 400 450 real watts out....and neither would be too clean (both will have poor transmit IMD products, but the Ameritron will be awful)!!!
The Mentron/Transworld will do 500 or so watts with just as poor transmit IMD as the AL-500, but are VERY old amps and are getting to have reliability problems....
The TenTec Hercules, also getting old and questionable reliability, has the same issues as the others here....

Please take note that ALL of these will only meet their specs when the collector voltage is at 13.8 - 14volts.....and that's almost impossible off anything other than AC Main power supply.....and certainly unavailable from 12vdc batteries, even those being charged by solar/wind....


So, bottom line:
---If you do NOT have an SG-500, spending money on a high-power remote auto-tuner is, in my opinion, a waste....
Either use the amp only when you can use a tuned/resonant antenna, or even better, don't use the amp at all....
---If you DO have an SG-500 (and can meet all the requirements above), you either use the amp only when you can use a tuned/resonant antenna, or you spend the $$$$ on the SG-235....



e) Do NOT skimp on your "ground" / "counterpoise".....if using copper strapping (as I recommend), paint it with some clear lacquer, etc. (except of course at the connection sites) and it will last a long time....




There is more...but I gotta' go!!!

Fair winds...

John
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Old 28-02-2013, 17:25   #43
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

John, your my hero.

While in the Sea of Cortez I tried to minimize IMD by using a 25 amp power supply for the radio and a 75 amp PS for the solid state amp run off the inverter. I'll be using LiFePO4 cells for my next house bank, and are using them now, they just don't sag like lead acid under load, so no need for a PS running off the inverter. I no longer have that amp (sold with the boat) and I now have the Ameritron that you don't think too highly of. I would have chosen the SG-235 regardless, but now that you have schooled me on why I was a big dog in the S of C, I'm deciding now to make my life simple and just go with the radio's output and forget the amp. I'll still use an auto tuner by SGC, but not the really expensive one since at 100 watts, don't need it. So now that you have schooled me, I have to decide back stay or vertical. I'm leaning towards the back stay because I'd rather have a better signal on 75 and 40 meters for buddy boating.

Thanks again for all your help.
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Old 10-03-2013, 01:15   #44
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

John,

I don't want to wear you out, but would like some more input. As much as I hate having equipment that isn't being used, you pretty much convinced me not to use AL-500. I would rather have a clean signal than a 6 db gain. This choice will of course save me $$ on the auto-tuner. Which would you recommend, the 200 watt SG 230 @ $500 or the 100 watt SG 237 @ $360 which tunes 6 meters along with 160 thru 10 like the SG 230?

Now on to a base antenna. What do you think of a delta loop? In keeping with SGC's recommendation of a 9' run from the tuner to radio, I figure on mounting the tuner to my balcony railing on the upstairs bedroom/radio room and center feed the delta loop which will be supported by a telescoping 50' fiberglass mast attached to the railing. The two bottom corners will be tied via egg insulators to trees about 80' apart. Using Pythagorean theorem, total wire length will be 208'. The bottom (base) will only be about 20' off the ground. The only wire I could find that is acceptable is 12 AWG, 259 strand copper wire. Do you have any sources for dipole wire of a heavier gauge?

I figure by using your expertise I'll have a good playing base antenna at the least cost, so when you have some time tell me if I'm on the right track or how you would do it for my situation. I live on 2 1/2 tree covered acres and on the side of a ridge that has an unobstructed view to the Sierra mountains 70 miles distance to the east. The delta loop will be running north/south. The area of the back yard that is unobstructed just happens to be centered to my upstairs balcony.

This is the balcony railing and the back yard. Thanks again John, hope to get back on the air soon.
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Old 10-03-2013, 09:53   #45
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

You might be better off, with a stronger antenna, if you use Copperweld wire, which is copper clad steel. Stronger than pure copper, won't stretch as much, and behaves electrically largely the same because RF will be traveling on the copper and not in the steel because of skin effect.

Chip
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