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Full wave antennas for CB
- Thread starter linearone
- Start date
I disagree, if you have only 48' of aluminum, you're not going to make an antenna with more gain (or talk farther) than a .64 stacked over a .64 collinear 48' antenna. A full sized 3 element beam may be slightly better, but that would take more than 48 feet of aluminum, (more like 70' when including the boom), and even that wouldn't outperform a collinear by much, if any. I've tested this closely on the VHF/UHF bands, and a .64 wavelength collinear is comparable to a 3 element beam. Hidef, I still don't don't think you understand the mechanics of the end fed collinear. On 27 mhz you need 45' or so for the antenna, than another 3 feet at the bottom (or more), for the matching coil/capacitor, and a good two feet of "decoupled" tubing to use for tower/mast mounting of the antenna.
But even so, if the antenna had a 5' middle phasing section, it would be equal to better in performance anyways. This is because optimum stacking of vertical elements, is 18' of seperation. .64 is better than .625 (although the difference is small), not just because it's a better element length for low angle gain maxima, but it also increases the distance between the 1/2 wave in phase currents/sections. With .64 electrical length, you gain .38 (.14 x 2) extra seperation distance between the inphase currents. Increasing this seperation in the middle even further, up to a 1/2 wavelength (or 18 feet) at 27mhz would add even more gain, not less.
By randomly making antenna out of 48'-50' of aluminum, there is no way it would be better than a carefully and properly designed collinear.
But even so, if the antenna had a 5' middle phasing section, it would be equal to better in performance anyways. This is because optimum stacking of vertical elements, is 18' of seperation. .64 is better than .625 (although the difference is small), not just because it's a better element length for low angle gain maxima, but it also increases the distance between the 1/2 wave in phase currents/sections. With .64 electrical length, you gain .38 (.14 x 2) extra seperation distance between the inphase currents. Increasing this seperation in the middle even further, up to a 1/2 wavelength (or 18 feet) at 27mhz would add even more gain, not less.
By randomly making antenna out of 48'-50' of aluminum, there is no way it would be better than a carefully and properly designed collinear.
I think that 'distance' between elements in a vertical array is being sort of optimistic as far as being beneficial is concerned. I think 'saving' that separation distance, and putting it in the supporting mast to make the whole mess higher is more likely to be beneficial. The only thing required is enough separation to prevent arcing and for mechanical strength. I honestly can't see 5 feet when 5 inches would probably do just as well if not better. Guess that just depends on how you do that phasing, there's more than just one way.
Oh well, different strokes for different folks...
- 'Doc
Oh well, different strokes for different folks...
- 'Doc
Sorry but the aluminum needed to make your 50 plus foot bottom mounted antenna stay up in any wind would have to be quite large diameter. It would easily weigh in at what is needed to make a 3 element yagi. It would have a higher wind load too. There is more than linear footage involved here. Not only that but there are portions which need to be insulated. You can build a yagi without any element insulation. Mechanically a 50 plus foot bottom fed vertical is a very poor and expensive choice. My centerfed vertically polarized antenna had no problems with wind storms and was made with lightweight scrap parts. It didn't need a counterpoise at the bottom either. Those "decoupler" sections are OK at 146 MHZ where they are 19" long. Here we would be using 2" aluminum pipe with what looks like a sailboat mast above.
Having actually built and used both a vertical 10/8 colinear and then replacing it with a yagi I think the performance difference is well worth using the directional antenna. It's also easier to stay out of neighbor's electronics when all of the radiation is as high in the air as possible.
VHF experience is great but H.F. is not exactly as simple scaling things up.
Oh I agree with you on that point, making a 48' freestanding vertical antenna isn't easy or cheap, and it is a more difficult to make for the best performance. It can be made, as long as it is built well (I believe Zero Five actually sells 66' freestanding quarterwave verticals for the ham bands). But if collinear antennas are made correctly, it would be your best option for performance if you wanted to talk as far as possible, and in all directions at once (which is why they are used with Ham Repeaters, and stacked omni elements and bays are used for broadcast antennas), the collinear is the best choice by far. However if you also want rejection (and higher SNR) from other directions, than a 3 element beam would be a better choice. If you have a "quality" and properly made collinear antenna, you should see a noticeable difference on the S-meter. On 2 meters I've seen 2 S units of gain versus the best I could find 5/8th wave vertical made for that frequency. Pretty much same results on the S-meter as the 3 element beam comparison at 25+ miles away. One thing I noticed, is that the further the distance, the more prominent/difference in gain the collinear becomes. Meaning for stations that are local, the difference in gain from the collinear and 5/8 wave verticals may only be 1 full su unit, and stations 25 miles are more, I start to see 2 full S units.
It would be more costly to make a 48' vertical I'm sure, but if I wanted to talk far away, to as many stations at once, the collinear is the best option from a antenna length feet to feet perspective. Pound for pound comparison for your money, well that may be another thing, but I thought we were comparing 50' of antenna length versus 50' of antenna.
It would be more costly to make a 48' vertical I'm sure, but if I wanted to talk far away, to as many stations at once, the collinear is the best option from a antenna length feet to feet perspective. Pound for pound comparison for your money, well that may be another thing, but I thought we were comparing 50' of antenna length versus 50' of antenna.
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I know this is a old thread...But recently I was wondering the same thing, then ran across this article which not only explained why a full wave antenna is not a good antenna, but also had pictures to make it easier to relate to!
.64 Wavelength Secret - K3DAV - Amateur Radio Operator
Then I also seen this thread listed...Didn't see it the first time around.
I also just ordered one of Mr. Dan Coilys Enforcer antenna's, which is a .64 wave, so now I can't wait for it to get here and see if it was money well spent, or if I should have just stuck with a wire coat hanger...
.64 Wavelength Secret - K3DAV - Amateur Radio Operator
Then I also seen this thread listed...Didn't see it the first time around.
I also just ordered one of Mr. Dan Coilys Enforcer antenna's, which is a .64 wave, so now I can't wait for it to get here and see if it was money well spent, or if I should have just stuck with a wire coat hanger...
That article is one of many that make it appear that going from 5/8 (.625) wavelength to .64 wavelength makes a noticeable difference. That difference is on the order of wishful thinking. I'm sorry but that .015 difference in wavelength is virtually irrelevant.
To put it in perspective we are talking a physical difference between the two antennas of roughly six inches at CB frequencies.
Conditions between the two radio antennas will make more of a difference in received signal than that small amount of extra length.
The DB
To put it in perspective we are talking a physical difference between the two antennas of roughly six inches at CB frequencies.
Conditions between the two radio antennas will make more of a difference in received signal than that small amount of extra length.
The DB
...and take anything you read on THAT website with "a grain of reactance", I emailed him a couple corrections but only received a CB-Myth type response.
I have a question on these questions / comments ! Antenna sizes lengths, where does a person buy the light weight aluminum tubing for the 16' - 18' long elements ? Copper is fairly cheep but heavy. I am trying to build A - 4 element - 11 meter antenna.For a 16' element i do not want 3 or 4 joints in ever element. Thanks for your help.
Arkieguide
Arkieguide
Good question. Some areas seem to have aluminum tubing lots of places and others you have to REALLY look hard to find it. The preferred way however is indeed to have various sections of different diameters as it lightens the weight considerably as well as the wind load. In order to have one continuous length you would need to go with a much larger diameter for strength which increases cost as well as weight and wind load. Nothing wrong at all with shorter sections of smaller sizes telescoped inside each other in fact all commercially made antennas are this way.
I understand it's your antenna and how it is constructed is up to you, but, what is wrong with correctly sized overlapping tubing?
DX Engineering sells 12 ft 6063-T832 tubing,....................... but, you better have a big wallet.
https://www.dxengineering.com/searc...4294951163&sortby=Default&sortorder=Ascending
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And don't get caught up on a 16' length. The reflector element will be more like a bit over 18 feet while the driver will be a bit over 17 feet and the director will be about 16 feet and maybe a couple inches. I grab any old antennas I can get to salvage the aluminum tubing and stainless hardware from. I built a nice heavy duty six element 6m OWA yagi out of an old Wilson shooting Star 11m antenna including the element to boom brackets.
YES and NO.
As an antenna approaches a full wave length then there are lobes and nulls that start to appear and as you reach and go past a full wave length the nulls get deeper, sometimes -30dB or more, and the lobes get larger, sometimes 10dB of gain or more, and you get more of them but they become narrower.
Now this is where you end up with both advantages and disadvantages. With a horizontal antenna like a dipole you can use these to your advantage to give you more gain in a specific direction by altering the direction the dipole runs. The disadvantage is you may end up with a significant -30dB or higher null in a direction you want however even the nulls can be used to an advantage to massively reduce the strength of an interfering signal coming from one direction.
I used to use an inverted L, the principle is the same. I modelled my antenna using EZNEC to see where the lobes and nulls would be for each band for given lengths of the antenna. I then used an azimuth map which you can generate here to see what compass headings were for the areas I wanted to reach. I found that at a specific length on 20m it had a radiation pattern that was a X. Running the wire north/south, from here in the UK that gave me gain into Northern Europe and towards Australia, South Africa, South America and North America. It had the advantage of nulling out Europe and the Italians but the disadvantage of nulling out Mexico etc and North/South poles.
I built an end fed 44' 9.1 unun 18g wire antenna. Have tried it out yet. With all of you gentlemen's knowledge, experience do you think it will work and have a low swr on 11 meters if I use an atu. Any help would be greatly appreciated.