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Mobile End Fired Phased Array Antenna

Discussion in 'CB Antennas' started by LeapFrog, Mar 24, 2017.

  1. LeapFrog

    LeapFrog Sr. Member

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    CB Mobile Beam Antenna - End Fired Phased Array Antenna (Amazon)
    Is this application snake-oil, or can I really learn how to build a "key-down" style van for $3.99 and have more gain than an Antron 99?:whistle:

    This must work, why else would the "key-down" competition guys build these antenna setups?
    Please share some thoughts, ideas, & an opinion on the topic.
    I have not looked into the theory behind this setup, but this link tells me I might be onto something here!?:)



    The description on Amazon goes on to describe how the idea was taken from the "radio handbook"? (ARRL?)

    My real question is how is this not just a co-phased antenna setup if "both elements are driven" as the description reads?

    And more importantly how can I learn to build something like this:
    [​IMG]
    Where do I find the formula(s) for the spacing... And yes you can just tell me to go read an ARRL antenna book if you like.
    [​IMG]

    Maybe i'm waisting my time trying understand and recreate these style of rigs, but it is part of CB radio that I want to learn more about.
    Thank You
    73
     
    #1 LeapFrog, Mar 24, 2017
    Last edited: Mar 24, 2017

  2. 543_Dallas

    543_Dallas Sr. Member

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    A couple of local guys have used this with good results. Feeding the antennas out of phase gives some forward gain, or gain off the back side depending on how you install the coax. I don't remember the spacing and coax lengths anymore. It's been too long.
     
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  3. LeapFrog

    LeapFrog Sr. Member

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    Thank you 543, I figure it had to be a real design that people built for years!
    Somebody would have noticed if they performed too poorly to run at a competition.

    It may take some digging to find the special "sauce" that makes this setup possible.
    I'm sure somebody spent time reading the ARRL antenna handbook and had to do some math, before the "idea/design" was released into the wild.
    Maybe the exact numbers are kept out of reach from the CB public, kinda like "let 'em figure it out on his own" & that is cool too; if that is even the case at all.

    Well for $3.99 I may just buy the kindle edition and see what information is contained within!
    Thanks 543 Dallas, have a great day brother.
    73
     
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Go read an ARRL antenna book. ;) This type of phased array is valid but not practical for a mobile station except in stationary applications. Every AM broadcast station in the country (world) uses this or a similar method with the same results if they run more than a single tower on site. The description above is a little off where it says: "Install is simple just 2 standard ball mounts a set distance apart! It is this distance that does the PHASING and this distance is set by the VELOCITY FACTOR of the coax." It is not just the distance that sets the phasing and that distance is not set by the Vf of the coax cable. The spacing can be varied depending on the results you want and the length of coax cable between the two elements. Here is a chart of what can happen with two elements. The elements are aligned along the horizontal axis in these image plots. Sorry for the poor image quality but it is the best I could do at the moment. The phase angles are down the left and are 0, 45, 90, 135, and 180 degrees and the spacings are along the top and are 1/8, 1/4, 3/8, and 1/2 wavelength. The plots show the resulting pattern IF everything is done correctly. While not hard to do if you know what you are doing it is not quite as simple as the description you quoted would indicate and you must be precise with measuring and cutting.


    Clipboard01.jpg
     
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  5. PA629

    PA629 Active Member

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    Personally, I'd save the $3.99 and put it towards the ARRL antenna handbook. It covers all you need to know about phasing antennas plus a helluva lot more......;)
     
  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I cannot recommend a better book for someone wanting to learn about antennas. There are better books but they are written at a higher level than beginner.
     
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  7. PA629

    PA629 Active Member

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    But just off the top of my head, isn't the set-up for that mobile array something along the lines of 1/4 wavelength spacing and being fed 180* out of phase? Not motivated enough to look it up.....
     
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  8. LeapFrog

    LeapFrog Sr. Member

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    Thank you for the image Captain Kilowatt that'll work!

    Okay so I will be getting an ARRL antenna handbook, thank you for explaining how this is used worldwide for AM if they run more than a single tower on site.
    Measure, be precise and know what I am doing with v.f. coax & spacing; ok I will have a long road ahead of me, but if it is worth doing.. It's worth doing it right.

    I want that "ERP" increase, and so I have a driving force of passion for more gain out of an antenna system. Thanks again Captain Kilowatt :)

    Edit: Photo won't enlarge lol, I need to buy the book. The text is indiscernible but I appreciate your typing out of the phase angles.


    Thank You PA629, I appreciate the input. (y)


    Best Regards
    -LeapFrog
     
    #8 LeapFrog, Mar 24, 2017
    Last edited: Mar 24, 2017
  9. Road Squawker

    Road Squawker Sr. Member

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    [QUOTE="LeapFrog, post: 582309, member: 46697...My real question is how is this not just a co-phased antenna...[/QUOTE]

    OK, Lets start at step #1.

    Forget that you have ever even heard the term "co-phased".;)
     
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  10. LeapFrog

    LeapFrog Sr. Member

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    Okay duly noted,
    I thought I pulled that exact phrase (co-phase) from the product description, but I now realize they just say "phasing".

    So to be clear "co-phased antennas" is not a real phrase nor an accurate description (of 2 elements that are radiating); would a more correct term be "phased array" even if only two radiating elements are used? I'm just putting pieces together here, don't shoot this wrascaly rabbit! :)

    One thing makes me wonder how they "split the feedline".. A T splitter and 75 ohm coax really?
    Maybe it's a bal-un they use, oh well I can read up on that.

    I do hear they must be spaced farther apart than usually seen on the big rigs.. but that is just more internet regurgitation.. Ok time for me to pick up an actual book, and read (ARRL).


    Thank You Road Squawker
    Best Regards
     
    #10 LeapFrog, Mar 24, 2017
    Last edited: Mar 24, 2017
  11. The DB

    The DB Sr. Member

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    They didn't read any real radio book on the subject, if they did they would have worded this very differently.

    Which book? "The radio handbook" isn't very descriptive, and can refer to any number of books. Seriously though, what they would have read, if they read anything, would be an antenna book of some sort.

    This is a warning sign. A low SWR is not necessarily a good thing, and a low SWR over a huge bandwidth is more often the sign of a problem than a good antenna.

    This isn't necessarily the case. If you get the spacing correct, the parasitic "reflector" element will generally add more forward gain, but the front to back ratio will be slightly worse. In other words, for key-downs this would be second to another very similar looking setup.

    That depends on how high the Antron 99 is. If it is mounted at ground level, sure, however if it is on a tower 30 feet off the ground and this setup outperforms it you need to figure out what is wrong with your Antron 99. It may seem like it outperforms it for a short distance, but the phrase "height is might" really does mean something when it comes to antennas, and really is far more important than anything else when it comes to performance.

    This isn't the only setup used in key downs, and is really more a sales pitch than anything.

    A "cophased" antenna array generally refers to a 0 degree phased array, which is another way of saying that both antennas get the same signal at the same time. An end fire array like this is not a 0 degree phased array, one of the antennas gets the signal a little later than the other. The two setups will have very different results, including different directions for whatever gain they may have.

    Assuming these setups were done with the same type of phasing, setting these up would simply be adding more antennas in line with the same distance between them. If you master getting the first two working, adding more in is just following the same directions again.

    Here is a more complete and more readable version of the chart Captain Kilowatt posted above. It is larger than the forum will show so if you need it to be larger right click to see the whole thing.


    [​IMG]

    The columns denote the antennas separation, so everything in the second column are two antennas 1/4 wavelength apart.

    The rows are the phase differential between antennas. The first row, for example, are what people in the CB world like to call "cophasing" and the term is limited to this row. As you can see, their really isn't much gain to be had with cophasing, at least with the distances used on vehicles, however, if you can get the antennas further apart you can get some real gain from such a setup..

    The phasing commonly used for end fire arrays are in the third and fourth rows. Actually, the setups I have seen used in the CB world are row three, 90 degree separation, and the distance apart is about halfway between the first and second columns. This is used more for the easy setup than anything, their is more gain to be had with other setups, but getting the antenna system tuned really gets to be a pain, and you can't easily direct feed it without some form of matching, which is not desirable when used in key downs, which is where this type of setup is generally used.

    If you want forward gain and rear rejection, and have enough area on the roof for this type of setup, this is one way of achieving it.

    If you really want help setting up such an antenna system, don't buy this, their is plenty of information available for free on-line.


    The DB
     
  12. LeapFrog

    LeapFrog Sr. Member

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    The DB: They didn't read any real radio book on the subject, if they did they would have worded this very differently.



    Which book? "The radio handbook" isn't very descriptive, and can refer to any number of books. Seriously though, what they would have read, if they read anything, would be an antenna book of some sort.

    Agreed 100%

    This is a warning sign. A low SWR is not necessarily a good thing, and a low SWR over a huge bandwidth is more often the sign of a problem than a good antenna.

    Thank you


    This isn't necessarily the case. If you get the spacing correct, the parasitic "reflector" element will generally add more forward gain, but the front to back ratio will be slightly worse. In other words, for key-downs this would be second to another very similar looking setup.

    Thank you

    That depends on how high the Antron 99 is. If it is mounted at ground level, sure, however if it is on a tower 30 feet off the ground and this setup outperforms it you need to figure out what is wrong with your Antron 99. It may seem like it outperforms it for a short distance, but the phrase "height is might" really does mean something when it comes to antennas, and really is far more important than anything else when it comes to performance.

    12 feet, I am going to raise it higher before getting an antenna build going.

    This isn't the only setup used in key downs, and is really more a sales pitch than anything.


    A "cophased" antenna array generally refers to a 0 degree phased array, which is another way of saying that both antennas get the same signal at the same time. An end fire array like this is not a 0 degree phased array, one of the antennas gets the signal a little later than the other. The two setups will have very different results, including different directions for whatever gain they may have.

    Thank you for explaining the difference !


    Assuming these setups were done with the same type of phasing, setting these up would simply be adding more antennas in line with the same distance between them. If you master getting the first two working, adding more in is just following the same directions again.

    Very very cool, I was hoping this was the case!

    Here is a more complete and more readable version of the chart Captain Kilowatt posted above. It is larger than the forum will show so if you need it to be larger right click to see the whole thing.
    Awesome, thank you once again!

    [​IMG]

    The columns denote the antennas separation, so everything in the second column are two antennas 1/4 wavelength apart.

    The rows are the phase differential between antennas. The first row, for example, are what people in the CB world like to call "cophasing" and the term is limited to this row. As you can see, their really isn't much gain to be had with cophasing, at least with the distances used on vehicles, however, if you can get the antennas further apart you can get some real gain from such a setup..

    Good to know


    The phasing commonly used for end fire arrays are in the third and fourth rows. Actually, the setups I have seen used in the CB world are row three, 90 degree separation, and the distance apart is about halfway between the first and second columns. This is used more for the easy setup than anything, their is more gain to be had with other setups, but getting the antenna system tuned really gets to be a pain, and you can't easily direct feed it without some form of matching, which is not desirable when used in key downs, which is where this type of setup is generally used.


    If you want forward gain and rear rejection, and have enough area on the roof for this type of setup, this is one way of achieving it.
    Excellent

    If you really want help setting up such an antenna system, don't buy this, their is plenty of information available for free on-line.

    The DB
    I won't buy the e-book, thank you for all of your help explaining what is happening and how it is working, the image graphic is hi-resolution thank you very much!
    -LeapFrog
     
  13. M0GVZ

    M0GVZ Sr. Member

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    Looking at the maximum gain offered in those charts above, mostly 3-3.5dB, most people with mobile installs could get that improvement just by using a decent sized antenna, mounting it on the roof with a fixed mount and doing bonding.

    Unless you've a desire to get a specific azimuth radiation pattern in order to null out a source of QRM/N then to match the benefits of the gain from phasing, assuming you already have the most efficient mobile antenna system install you can do, doubling your power is easier than trying to implement phasing in a mobile installation.
     
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  14. LeapFrog

    LeapFrog Sr. Member

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    As a matter of fact, I have several 1/4 wave verticals laying around, and a source of QRM about two miles away..

    I will focus on getting my A99 higher, and one day i'd like to build a beam; A yagi one day, but I want to play with some of the spare bits I have laying around here first. So I will study all the information presented and buy the ARRL Antenna book.

    One day I can find an old suburban or van and make it happen, only I will be able to drive the whole rig on a hill! First I might play around with something on my roof, or in the backyard, to get the concept down.

    Thank you
    73
    -LeapFrog
     
    #14 LeapFrog, Mar 24, 2017
    Last edited: Mar 24, 2017
  15. 543_Dallas

    543_Dallas Sr. Member

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    The only people I've known to use this setup already had an ideal antenna install but wanted something directional for competition use.

    They were all larger vehicles with roof mounted antennas. A Suburban, sprinter van, and one a pickup truck with a custom ladder rack with a couple of 4x8 sheets of aluminum on top.

    Most of them were already running anything from an 8 to a 32 pill. Doubling the power would have been expensive and/or put them in different class at a competition.
     
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