i would like to see this big hair antenna with 50 ft of element. this is all very interestig and I hope to learn much from this.
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Full wave antennas for CB
- Thread starter linearone
- Start date
i would like to see this big hair antenna with 50 ft of element. this is all very interestig and I hope to learn much from this.
What are the characteristics of a 'good' antenna?
1. Puts a signal where you want it to go, or at least where you can expect it to go.
2. Can be easily 'integrated'/matched to the rest of the antenna system.
3. Is reasonably efficient.
Putting a signal where you want it to go, or where you can at least expect it to go is a function of the radiation pattern of the antenna. That radiation pattern can be affected by a number of things, the physical 'shape' of the antenna, the number of element that antenna consists of, and how those elements are arranged.
Particular fractional parts of a wave length exhibit certain characteristic patterns which are length dependent. All fractional wave lengths have some usability, some greater than others depending on the desired abilities. A very general trend is that shorter lengths have lesser abilities than longer lengths, to some undetermined point of practicality. The shape or positioning of those single element antennas also plays a part in that.
'Integrating' an antenna with the rest of the antenna system, the feeding methods, or matching an antenna to the characteristic impedance of the rest of the antenna system is a consideration. How easy is that going to be to do? There are some particular feeding methods, or placement of feed points that are going to be much more practical/easy to deal with than others. Anything can be 'matched' to almost anything if you are willing to work at it hard enough. The most typical 'catch' to that is that it's just not very practical in practice.
Efficiency. Huge range to pick from, none -ever- 100% efficient. Higher efficiency is always nice to 'aim' for, but not necessary for all situations. Efficiencies as low as 1 - 4% are not uncommon and work just dandy for particular circumstances.
So select from those three groups, mix well, bake for the proper length of time, and you can end up with an antenna that suits your purposes very well. It will not be suitable for all occasions.
- 'Doc
(Don't forget that "eye of newt"...)
1. Puts a signal where you want it to go, or at least where you can expect it to go.
2. Can be easily 'integrated'/matched to the rest of the antenna system.
3. Is reasonably efficient.
Putting a signal where you want it to go, or where you can at least expect it to go is a function of the radiation pattern of the antenna. That radiation pattern can be affected by a number of things, the physical 'shape' of the antenna, the number of element that antenna consists of, and how those elements are arranged.
Particular fractional parts of a wave length exhibit certain characteristic patterns which are length dependent. All fractional wave lengths have some usability, some greater than others depending on the desired abilities. A very general trend is that shorter lengths have lesser abilities than longer lengths, to some undetermined point of practicality. The shape or positioning of those single element antennas also plays a part in that.
'Integrating' an antenna with the rest of the antenna system, the feeding methods, or matching an antenna to the characteristic impedance of the rest of the antenna system is a consideration. How easy is that going to be to do? There are some particular feeding methods, or placement of feed points that are going to be much more practical/easy to deal with than others. Anything can be 'matched' to almost anything if you are willing to work at it hard enough. The most typical 'catch' to that is that it's just not very practical in practice.
Efficiency. Huge range to pick from, none -ever- 100% efficient. Higher efficiency is always nice to 'aim' for, but not necessary for all situations. Efficiencies as low as 1 - 4% are not uncommon and work just dandy for particular circumstances.
So select from those three groups, mix well, bake for the proper length of time, and you can end up with an antenna that suits your purposes very well. It will not be suitable for all occasions.
- 'Doc
(Don't forget that "eye of newt"...)
This was mentioned on another thread, but Big Hair Antennas are the only antennas I have seen that has made a "true" collinear. Meaning, a 5/8th wave over a 1/4wave isn't what I would call a collinear at all, but more for marketing. Even Antron claims it's a 1/2 wave over a quarter wave.. This quarter wave often is just a matching section, or they are adding the ground plane kit to that formula. Even if it was stacked over a true quarter wave element, it doesn't make a noticable difference in gain, unless you're stacking half wave elements or above. The currents reverse every half wavelength as another has said, not every quarter wave, plus physical seperation and length plays factors in increasing the gain. A 5/8 wave element stacking are the best, but a half wave over a half wave could work, if you seperate the distance between elements by 10 feet or so. A 5/8th wave over a 5/8 wave is by far the best, becuase it also increases the spacing of elments, for true doubling of gain. This is why a 5/8th wave over a quarter wave isn't really a worthwhile solution if you're trying to stack vertical elements, to double gain.
If anyone knows someone else that has made true collinear antennas (half wave over a half wave or 5/8th wave over a 5/8th), let me know, as I would buy one!
If you know someone else on the net that makes 50' collinear base antennas other than Big Hair Antennas, I would like to see, as I would probably order one. Needs to be free standing, so I can mount it on my tower.
If anyone knows someone else that has made true collinear antennas (half wave over a half wave or 5/8th wave over a 5/8th), let me know, as I would buy one!
If you know someone else on the net that makes 50' collinear base antennas other than Big Hair Antennas, I would like to see, as I would probably order one. Needs to be free standing, so I can mount it on my tower.
the big-mac is a true conventional 5/8 over 1/4wave colinear with 6 x 9ft radials,
it does outperform any 5/8wave groundplane i ever owned but it clearly wont mach a correctly built and phased 50ft tall 5/8 over 5/8,
the big-mac is only about 32.5 feet long.
we dont get something for nothing, colinears also have a narrow vertical beamwidth,
when they are very long they tend to move in the wind which brings with it some strange characteristics compared to single element antennas.
it does outperform any 5/8wave groundplane i ever owned but it clearly wont mach a correctly built and phased 50ft tall 5/8 over 5/8,
the big-mac is only about 32.5 feet long.
we dont get something for nothing, colinears also have a narrow vertical beamwidth,
when they are very long they tend to move in the wind which brings with it some strange characteristics compared to single element antennas.
44' is the magic maximum 5/8 over 5/8 colinear if one is considering a vertical for 11 meters.
Any longer and the pattern goes from low angle of radiation to high.
The QRZ discussion is quite informative if you throw out the posts from the usual dummys who post on every subject and have not a clue.
Full wave dipoles are useful and CAN be matched with stuff found in any good junkbox.
Full wave antennas have broadside gain over a simple 468/F dipole when installed horizontally. The gain will be somewhat reduced if the antenna is not mounted high enough. Broadside gain continues to increase until length exceeds 10/8 wavelength total. It then breaks into a cloverleaf pattern.
Antenna gain should not be viewed as magic. The only thing happening is energy gets focused in certain directions and away from others. Ever see a modern automotive headlight bulb lit but out of it's fixture? It's not all that bright. Install it into the reflector and the brilliance will give you an instant headache if you look right into it. That little bulb makes a giant light in one direction. Gain antennas work the same way only not quite as simple.
Any longer and the pattern goes from low angle of radiation to high.
The QRZ discussion is quite informative if you throw out the posts from the usual dummys who post on every subject and have not a clue.
Full wave dipoles are useful and CAN be matched with stuff found in any good junkbox.
Full wave antennas have broadside gain over a simple 468/F dipole when installed horizontally. The gain will be somewhat reduced if the antenna is not mounted high enough. Broadside gain continues to increase until length exceeds 10/8 wavelength total. It then breaks into a cloverleaf pattern.
Antenna gain should not be viewed as magic. The only thing happening is energy gets focused in certain directions and away from others. Ever see a modern automotive headlight bulb lit but out of it's fixture? It's not all that bright. Install it into the reflector and the brilliance will give you an instant headache if you look right into it. That little bulb makes a giant light in one direction. Gain antennas work the same way only not quite as simple.
Hidef, you're actually short on your measurements, as you need to add a few feet back in, if making a finished product or anything practical. .64 at 27mhz is actually 22.6", with normal sized conductors, so for both .64 wavelength elements together, is 45' right there alone. The Big Hair Antennas were 48', because you also have to add a phasing section in the middle, and you need to add an additional 2-3 feet for the matching coil and mast mounting section (to mount on towers or a mast..), but I would make them 50' as a safety measure. You have to also add room for the matching coil, and a foot or two for the mounting.. 45' of antenna elements creates a lot of torque at the bottom, so you probably should use a good 24"-36" for the mounting section below the coil.
For example, an IMAX 2000 is 24' tall, but only 22'6" is the antenna and radiates, the bottom is for matching, and 12" is dedicated to a aluminum tube/plate for mounting to a mast. Each element should be .64 (which is better than a 5/8th wave, esp for a collinear) which is 22'6" (45' for both elements), but you need room for the middle phasing section, between the elements, the bottom matching inductor, and the mounting section. 22' for each element alone would have less gain, the big hair antennas website has them at 22'6" per .64 wavelength element. You would lose gain is using anything less than 22' 6", unless you're using a very wide conductor that would be impractical.
Your formula applies to only the "electrical" length of a dipole, and is way off for determing finished physical sizes, and spacing of elements and middle phasing section. Also, you want a .64 wavelength, not a 5/8th wave. Even if you made them 24' each, it would still be better than 22' or less.. You can verify this with antenna modeling software.
Even longer would still may have higher gain, as physical seperation (up to a halfwave length or more) increases gain as well with collinears.
For example, an IMAX 2000 is 24' tall, but only 22'6" is the antenna and radiates, the bottom is for matching, and 12" is dedicated to a aluminum tube/plate for mounting to a mast. Each element should be .64 (which is better than a 5/8th wave, esp for a collinear) which is 22'6" (45' for both elements), but you need room for the middle phasing section, between the elements, the bottom matching inductor, and the mounting section. 22' for each element alone would have less gain, the big hair antennas website has them at 22'6" per .64 wavelength element. You would lose gain is using anything less than 22' 6", unless you're using a very wide conductor that would be impractical.
Your formula applies to only the "electrical" length of a dipole, and is way off for determing finished physical sizes, and spacing of elements and middle phasing section. Also, you want a .64 wavelength, not a 5/8th wave. Even if you made them 24' each, it would still be better than 22' or less.. You can verify this with antenna modeling software.
Even longer would still may have higher gain, as physical seperation (up to a halfwave length or more) increases gain as well with collinears.
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Yes, a full wave element can be better only if you stack two half wave antennas on top (.64 elements is best though) on top of each other, or if you shorten its vertical/horizontal size, by forming a quad or loop shaped design. A full wave vertical antenna, would have less gain than a 5/8th wave (unless stacking/a collinear) A .64 is the best (just a smudge larger than a 5/8th wave).
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Doctor master is correct. The 468/F formula you quoted is always going to be 5-10% too short, because it's a formula for making a halfwave dipole with a 50 ohm impedance.
The true half wave resonance is more like 473/F, and a full sized dipole would have closer to a 70 ohm impedance. The dipole and formula are shortened about 5% intentionally which is where the 468/F dipole formula comes from, so the dipole will be smaller than full size by about 5%, which would lower the impedance to 50 ohms. 50 ohms creates a better SWR match without adding additional matching, and so the radio operator would have an ideal match standard 50 ohm unbalanced feedline. The formulas are not exact however, but get you in the ballpark.
A full wavelength at 27mhz is actually about 35.5 feet (some round up to 36'). If you take the .64 multiplier times the full wave length of 35.5 feet, you have 22.7'. This is about 45.4' for both collinear .64 elements, perhaps another .5' of space/room in the middle for a phasing line/coil between them, and then a good 2 feet or more for the bottom coil (for matching to 50 ohms), and a mast mounting coupler or plate of some sorts so you can mount the antenna on a mast.
So you also need to consider that the 468/f dipole formula itself is too short as well.
The true half wave resonance is more like 473/F, and a full sized dipole would have closer to a 70 ohm impedance. The dipole and formula are shortened about 5% intentionally which is where the 468/F dipole formula comes from, so the dipole will be smaller than full size by about 5%, which would lower the impedance to 50 ohms. 50 ohms creates a better SWR match without adding additional matching, and so the radio operator would have an ideal match standard 50 ohm unbalanced feedline. The formulas are not exact however, but get you in the ballpark.
A full wavelength at 27mhz is actually about 35.5 feet (some round up to 36'). If you take the .64 multiplier times the full wave length of 35.5 feet, you have 22.7'. This is about 45.4' for both collinear .64 elements, perhaps another .5' of space/room in the middle for a phasing line/coil between them, and then a good 2 feet or more for the bottom coil (for matching to 50 ohms), and a mast mounting coupler or plate of some sorts so you can mount the antenna on a mast.
So you also need to consider that the 468/f dipole formula itself is too short as well.
Well, if we're gonna be 'picky', why not do it right. Forget 468/473, do it the long way. That's (492 x R)/Mhz = feet. That 'R' is the diameter of the conductor used. For typical diameters of wire, it amounts to about 95%, so about 468. That 'magic' number will result in a 1/2 wave length that's just slightly too long, not too short for resonance. Then again, it's better to be too long cuz it's easier to cut it off than to glue it back.
Wanna do it the long way? Then find yourself an ARRL Handbook, that 'R' is not a direct relation to conductor diameter, it's a ratio, and usually found by a chart in that handbook. None of this stuff is cut and dried, engraved in stone. There is always some 'fudge' in those electrical lengths because everything around them affects them.
As far as the .625 versus .640 wave length thingy goes, there's just not enough difference to make any difference. If it makes you feel better, call it whatever you want to, it still ain't gonna make that dog spit up hairballs like a cat.
- 'Doc
Wanna do it the long way? Then find yourself an ARRL Handbook, that 'R' is not a direct relation to conductor diameter, it's a ratio, and usually found by a chart in that handbook. None of this stuff is cut and dried, engraved in stone. There is always some 'fudge' in those electrical lengths because everything around them affects them.
As far as the .625 versus .640 wave length thingy goes, there's just not enough difference to make any difference. If it makes you feel better, call it whatever you want to, it still ain't gonna make that dog spit up hairballs like a cat.
- 'Doc
If you have the length for a 1/2 wave, multiply by 2. For a 1/4 wave, by 4. A 5/8 wave? Divide by 5 then multiply by 8. Will any of them be -exactly- correct? Nope, but neither will any other formula you use. That -exact- length is also determined by where the thing will be 'mounted', it's environment. You'll have to "check-n-chop" to get the 'exact' length for your installation. Add a couple of feet to start with and you won't be too short to start with. Also gives some length to play with when making connections, etc. There just ain't no -exact- numbers with antennas. There are some real close numbers though...
- 'Doc
- 'Doc
While on the subject -...- here is a description of 2 longer than full wave verticals I had on the air a few years back. Scroll down to my post
http://www.worldwidedx.com/amateur-radio-antennas/31653-ladder-line-fed-vertical-2.html
The difference between .625 and .64 is a few inches. I'd love to see exactly what eznec shows in increased gain. I already know what that increased length does to the elevation pattern when one ventures 500 khz upward from the design frequency.
A bottom fed colinear with a coil and center phase delay section taking 5 feet would be a poor form factor for the gain involved. There are better ways to use a given amount of aluminum. If I had a 190' tower a bottom fed colinear would be fun to try.
http://www.worldwidedx.com/amateur-radio-antennas/31653-ladder-line-fed-vertical-2.html
The difference between .625 and .64 is a few inches. I'd love to see exactly what eznec shows in increased gain. I already know what that increased length does to the elevation pattern when one ventures 500 khz upward from the design frequency.
A bottom fed colinear with a coil and center phase delay section taking 5 feet would be a poor form factor for the gain involved. There are better ways to use a given amount of aluminum. If I had a 190' tower a bottom fed colinear would be fun to try.
Can't resist!
Them Dentron 'Stupid' Tuners and me fit together real good! I'm working on trying to destroy a second one. Only took something like 5 years to kill the first one. This one has lasted a lot longer than that.
If the 'Stupid' Tuner I have won't tune it, a little fiddling with whatever it is I'm trying to tune usually 'cures' that. A few of those 'whatever' antennas have really been odd, to say the least. It's amazing what you can think of when you get bored enough, ain't it? R.R tracks, chain-link fence, metal flashing around a fire station (you DON'T wanna know about that! Statute of limitations has run out, I can talk about it now.
), how about a hose filled with salty water? They all work? Sort of, kind'a. Doesn't say how well, or the complications thereof, but it was entertaining, for me anyway, mostly.
Longer than normal typically works 'better' than shorter than normal, or is easier to get to sort of work. Oh well. Nuff'a that.
- 'Doc (<-- 'Stupid Tuner', all puns intended.)
(The Post Office next door where the Post Master boot legged liquid cattle feed, had a large tank for that liquid behind it. You have no idea what that smelled like in warmer weather. If you could get around the nausea, the fumes could get you higher than any antenna!)
Them Dentron 'Stupid' Tuners and me fit together real good! I'm working on trying to destroy a second one. Only took something like 5 years to kill the first one. This one has lasted a lot longer than that.
If the 'Stupid' Tuner I have won't tune it, a little fiddling with whatever it is I'm trying to tune usually 'cures' that. A few of those 'whatever' antennas have really been odd, to say the least. It's amazing what you can think of when you get bored enough, ain't it? R.R tracks, chain-link fence, metal flashing around a fire station (you DON'T wanna know about that! Statute of limitations has run out, I can talk about it now.
), how about a hose filled with salty water? They all work? Sort of, kind'a. Doesn't say how well, or the complications thereof, but it was entertaining, for me anyway, mostly.Longer than normal typically works 'better' than shorter than normal, or is easier to get to sort of work. Oh well. Nuff'a that.
- 'Doc (<-- 'Stupid Tuner', all puns intended.)
(The Post Office next door where the Post Master boot legged liquid cattle feed, had a large tank for that liquid behind it. You have no idea what that smelled like in warmer weather. If you could get around the nausea, the fumes could get you higher than any antenna!)