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Rebuilding a 6 element quad

Discussion in 'CB Antennas' started by 6.0 Liter, Feb 9, 2012.

  1. 6.0 Liter

    6.0 Liter Coax abuse???

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    I recently came across an old Lightning 6 antenna. The wire and the matching system was beyond repair. The boom and the fiberglass spreaders cleaned up good as new. Got all new hardware to put the boom together, sanded and painted the spreaders, and now need to make a decision. I was in touch with George at the new Lightning antennas location, and I can still get the element kit and matching network. All the wires are premeasured and labled for each element. Just wondering if anyone has run this antenna in its stock form, how does it perform? Wonderingif it could be maximized a bit? Basicly I have a 30 ft boom with 6 hubs, even tho they pass through the boom, I suppose they could be moved to newly drilled holes for differant element spacing if there was somthing to be gained by it. Then new wires could be made up to center it on the frequency of my choosing. Thoughts anyone? Maybe Henry HPSD wants to chime in? All ideas are welcome.


     
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  2. Marconi

    Marconi Supporting Member

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    6.0, drilling more holes in the boom just don't sound like a good idea to me. How are you ever going to know if it does better or not, modifying it that way?

    Did you order the parts?
     
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  3. Robb

    Robb Yup

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    Gee, think I would just rebuild it to the same standards that it was built in the first place. The element spacing are the same as a 6 element Yagi would be. The loops diameters of your Quad should be all standard for any 6 element Quad would be too. Perhaps Henry can say if it can be improved upon, since the day that antenna was first designed wasn't with the benefit of computer modeling. Might be some improvement in the element spacing and boom length. Henry should know.
     
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  4. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    here ya go,....... Quad Antenna JavaScript Calculator just plug in the vitals
     
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  5. 6.0 Liter

    6.0 Liter Coax abuse???

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    Thanks hookedon6...........Marconi, I havnt ordered anything,just thinking, if there is merit in optimizing a bit, now is the time to do it. Maybethe feed system could be improved on a bit, direct fed maybe? This is my first big antenna, having fun with this stuff................
     
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  6. Needle Bender

    Needle Bender Well-Known Member

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    If you use different wire like stranded insulated 12 gauge you will have shorter wires because of the lower velocity factor of the insulation coated wire. Problem is, once the UV has it's way with the insulation and it falls off it won't be tuned right because the velocity factor will increase and it will go down in frequency, plus since it has been up a while in the wind it is already stretched and will have lowered in frequency.

    I believe it will stretch less and last longer if you use stranded copper wire instead of the solid 14ga they sell for it. If you use stranded without insulation then you won't have that changing velocity factor and tuning problem but it's hard to find stranded copper wire without insulation for as cheap a price as home depot has it insulated, so you might want to sharpen your Buck knife or put a new blade in your Stanley drywall knife and strip it off.
    Then the tuning process begins.:unsure:
     
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  7. Marconi

    Marconi Supporting Member

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    Quad Antenna JavaScript Calculator


    Above is the link that hookedon6 posted for us. Just enter 27.205mhz so we can compare the results to some SE L4+ dimensions I’ve posted below.
    Here are the dimensions I have for the L4+ model. As I understand it, add on kits come in units for additional elements, and they are probably all the same dimensions. So each element past director #1 will be equal or close to 72.25” spacing and 422" in wire length. This is just my assumption however based on studying the L4+ instructions, and asking questions about this antenna for some years.

    Boom = 17’ 10”

    Spacing
    R to Dr=84.25”
    Dr to D1=56”
    D1 to D2= 72.25”

    Wire lengths as best I know,
    Reflector=453”
    Driver=438” Driver wire per side=109.5”
    Director1=425”
    Director2=422”
    based on the above information any following directors will also be 422”.


    6.0 Liter, I can’t be sure what frequency the SE L4 was designed for, but understanding it’s for CB I assume these measurements are close to the lower end of 27 mhz up to about 27.205.

    So, compare these measurements with hookedon6’s link for a Quad calculator above, and you will see that Robb’s claim that all Quads are the same dimensions…might not be as truthful as he would have us believe. I don’t believe the Quad generator that HO6 gave us is accurate for this antenna either, because there is no adjustment for the wire diameter, whatever it is. That might make some difference too.

    I’m also not sure whether the unique feeder device, itself, used by SE makes a difference in overall dimensions it has, but I wouldn’t be surprised if it did.

    SE made these antennas at least as far back as 1978. That was before antenna modeling was available to the average Joe, just like Robb has noted. We didn’t have the personal computer at the time either. However, NEC was developed in the late 70’s and it was based in large part on math and science developed years earlier. I wouldn’t be surprised if the guys at Signal Engineering were smart enough to use such math and engineering to come up with their matching idea for this dual polarity Quad, even without the use of a computer. The dual polarity feature was what was very unique as Quads go, but I think the feeding idea itself…might be quite a bit older in other applications.

    6.0Liter, you might be able to set this antenna up with a vast variety of dimensional difference and it still work, but I would first try to get it working as close to specks as possible. If you keep some good notes during construction and testing, you might even be able to detect some differences in performance using your radio.

    From my personal experience with a friend who has a L8 that is over 60 miles away, we can talk just about any time using less than 5 watts on SSB after we get each other’s attention that we’re on the air.

    6.0Liter, it you measure any of your kit, let me know how your numbers jive with mine, OK? I think your measurements for the fist 4 elements should be about the same as my L4+ measurements above.
     
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    Last edited: Feb 9, 2012
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  8. Henry HPSD

    Henry HPSD Well-Known Member

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    Hello,

    Marconi has a very valid point.
    It is not wise to keep drilling holes in a boom. Though it might be “still oke” from a boom-strength point of view. It is not wise to keep on drilling holes. To be honest..I do not like the drilling holes solution from a manufacturer upfront.
    1- No matter how you see it, it does reduce strength.
    2- If the wind starts to blow, at some point there will be some much friction the holes become larger. That will give irritation regarding “extra” noises etc.

    You might start thinking about some kind of “hubs” . There are quite some different solutions. I’m sure you will be happier with that. Especially if you keep up your antenna work (and you will) it is always easy to make the antenna in such a way you can always replace the “everything”.

    It wouldn’t be wise to go for the same spacing’s as a yagi has. It is a different antenna. The diameter as well as the “length” is different. It would only be logical if the spacing is somewhat different.
    It might be that the 6el quad can be improved…I don’t know, I do not have the “original” measurements.

    What I do know…
    The 17,1dBI gain expressed is not real. You should expect a 11/12 dBI from a 30 foot boom.

    Just for fun: have you taken a look at the plots given?
    If you take a look at the attached PNG file I have enlarged the “plots”. Oke, please believe me when I say 11 dBI is about max from that boom length, heck ill make it a 12 dBI just for fun.

    Here comes the fun,
    We all know gain comes from suppressing the beam width (your aim becomes more narrower)
    This is expressed in the -3dB beam width figures. (please see http://www.worldwidedx.com/cb-antennas/130846-explination-radiation-patterns-how-see-them.html) for further explanation about beam width.

    What it comes down to: Signal engineering is showing us a -3dB beam width in the order of 20 degrees. Nobody in this world is able to do that. Bare in mind…it would take at least a 3 times multiplication of boom length to get that !
    So the antenna pattern provided is..Let’s say “less accurate”.

    Besides…the FB is fun too!, in the specs they are -44 dB. However if I take a look at the antenna plots and interoperate them right it is nowhere near 40…just above 20 dB (and that’s not done with the 9meter boom length!)
    And, no…I’m not against the this quad…I’m sure it works just fine.
    I am against all those wrong figures

    Last thing..
    That might get a brain working, the SWR beamwidth.
    The reason for that is the bandwidth expressed (SWR) it is almost 2 MHz wide! Opposite to what most people think Quads are not know for SWR bandwidth! The 2MHZ expressed means it is an OWA design. OWA designs are known for many positive things but not for maximum gain.

    Antennas are fun!

    Kind regards,
    Henry
     

    Attached Files:

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  9. 6.0 Liter

    6.0 Liter Coax abuse???

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    Marconi, I plugged in the numbers as you guys suggested, I am gonna relay them here because this is good info for everyone.
    Frequency is 27.205
    Reflector = 454.328"
    Driven = 443.301"
    D1 = 430.068"
    D2 = 417.166"
    D3 = 404.651"
    D4 = 392.511"
    The spacing they suggest is as follows.....
    Reflector to driven = 80.5"
    Driven to D1 = 66.164" and the same measurment follows through wit the other elements. I need to measure the existing spacing now and see how it compares.
     
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  10. 6.0 Liter

    6.0 Liter Coax abuse???

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    Henry, good info here, I really appreciate your response and highly value your opinion. This is really a lot of info to digest, all good stuff. Now I need to get to work. I have a 20 ft pipe rite now for support till I get it dialed in, have my eyes on a tower, just need to take it down and move it. What type of stranded wire do you guys suggest for elements? I guess I should ask what size works best 14 gauge? Shall I try direct feed or use a similar matching device that was originaly used? Fun fun fun(y)
     
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  11. Needle Bender

    Needle Bender Well-Known Member

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    Those are generic calcs (1030, 1005, 975) that should get you in the ballpark.
    If you calc for about 10-15 channels low, you can carefully trim it and dial it in for your chosen center frequency, or maybe a little higher, remember, it will slowly stretch in the wind so you might want to set the lengths for a little higher frequency than you want it to be, but tune the match as flat as possible on your chosen center frequency since the matching network shouldn't stretch much at all.
    You'll probably be able to watch it slowly lower the SWR where you really want it to center up, as it stretches into resonance a little below(maybe 10 channels?) where you trimmed it.
     
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  12. Robb

    Robb Yup

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    The Ultimate Guide to 11 Meter CB Antennas

    This Java app on that link/page allows you to just plug in the desired center freq, and it will give you all of the dimensions for up to a 7 element beam.
    Not sure this has been compiled from the latest 'n greatest EZNEC program; but I bet it will still knock 'em over on the other end . . .
     
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    Last edited: Feb 10, 2012
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  13. Needle Bender

    Needle Bender Well-Known Member

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    That size and spacing is real close to what I helped build, but any full wave loops will work that are close as a hand grenade, and about 3%-5% smaller going back to front.
    /It's only when you dial it in and carefully tune it to a gnat's butt hair for peak with your wire, boom, exact element lengths and spacings that it shines like a quad should, opening and closing the band while the Yagi beams have already gone to nothin' but noise 15-20 minutes earlier.
    Just toss some wire up there and tune the match for lowest swr and it will work well, but tune each element carefully as they interact together and watch out for gain you won't believe :eek:
     
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  14. GnG8d

    GnG8d Well-Known Member

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    I wouldn't worry about wire stretch changing the center frequency.


    Sent from my iPhone using Tapatalk
     
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  15. Needle Bender

    Needle Bender Well-Known Member

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    Really, why not, if it does?
    I guess it depends on how tight you want yours. Some people are satisfied with horseshoes, others need a .243 into the bullseye at 300 meters.
    :cool:
     
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