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Modified Vector 4000

Discussion in 'CB Antennas' started by bob85, Oct 3, 2009.

  1. Shockwave

    Shockwave Sr. Member

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    I'm sorry Eddie, I'm not aware of any online references directly dealing with this and the Sigma4 online. To understand more about this characteristic, Google "Electrical beam tilt". That will explain how when two co-linear radiators are fed slightly out of phase, you can tilt the TOA to hit the target area. With a conventional co-linear array that incorporates beam tilt, the phase offset takes place in the transmission line feeding one of the antennas. In the case of the Sigma, the basket length serves as the transmission line to the top section.



    All tuning was done on the FM broadcast band so there was no skip and a stable carrier to tune against. I picked a station in the center of the band, about 50 miles away and at about the same elevation as me. This was so that I could duplicate a TOA that was as close to the horizon as possible. This angle fits most customers best unless they are dealing with large changes in elevation between the site and target area.



    What I see is 2 or 3 db above a center fed vertical dipole in the FM band, not over the new stock Vector. I doubt my measurements have nearly as much gain over a new Vector. Although I can tell you when I scaled the design back to the other bands mentioned, my radiator length is longer than the current Vector in terms of wavelength and the basket is nearly identical. I also believe the original Sigma used a basket that was too short to maximize the beam tilt effect and the new Vector has corrected that by adding length to the basket arms.
     
    #436 Shockwave, May 22, 2019
    Last edited: May 22, 2019

  2. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Donald, thanks for your post.

    I'm trying to rehash some of these old ideas to see if I missed something.

    I remember Bob posting an image of a Vector antenna that you built with a much larger loop and shorter radials. He also told us, at the time, you had not yet got it tuned for distance. I don't recall what you found after getting it tuned.

    Do you recall any of this?

    Back at that time I posed a question on my copy of the patent in the area for column #3 line 66 saying, "SW proved this wrong ?"

    If so, what did you discover making that mod and getting it tuned at a distance?

    Did you ever consider why Avanti came to their conclusions that making the loop bigger...required one to make the radials shorter...rather than making the loop larger and keeping the radials near a 1/4 wavelength as noted for both the S4/V4K?


     
    #437 Marconi, May 29, 2019
    Last edited: May 29, 2019
  3. Shockwave

    Shockwave Sr. Member

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    Hi Marconi. I do recall that test model that was constructed after reading the Avanti patent. The patent suggested increasing the angle could increase gain and is why I built it to test their idea.


    Back at that time I posed a question on my copy of the patent in the area for column #3 line 66 saying, "SW proved this wrong ?"

    Tuning at a distance of 50 miles on HF proved very difficult. My partner and I used a 27.120 RF generator with a very stable 100 watt carrier into an Interceptor 25K for the test. At this distance, the atmospheric conditions do effect signal strength regardless of how stable the test equipment is.

    Those fluctuations could easily be a few db within moments and at other times, remain stable for many minuets. That mislead me into thinking there was some improvement when continued testing revealed that the variables on HF at 50 miles were larger than the gains I was measuring with antenna changes.

    It was only after more testing on VHF that I found the gain dropped when the antenna was tuned with a larger loop. The larger loop with more angle means the radials must be shorter to maintain 1/4 wavelength resonance. This is the opposite direction than what appears to focus the TOA on the horizon.

    When you lengthen the cone, you delay the signal to the top section by a few degrees with respect to that which appears on the outside of the cone. This provides a few degrees of "Electrical Beam Tilt" which places the maximum signal much closer to the horizon than is possible with single section, vertical antennas.

    Also. don't forget that both the original Sigma IV, LW-150 and old Vector 4000 used radials that were many inches shorter than 1/4 wavelength and were not taking advantage of phase delay between sections. The FM version of the antenna had been using near 1/4 wavelength radials that are resonant with the loop around the top for many years before the new V4K followed.

    In summary, there are 3 main thing to consider with the dimensions of the cone.

    1) Its outside surface and ring must be fairly close to a 1/4 wavelength resonance regardless of the size of the ring or length of the radials. Changing one means you must change the other to keep this resonance.

    2) Changing the length of the cone also changes the phase angle of the signal driving the top section, useful for beam steering.

    3) Changing the length of the cone also changes how much of the out of phase radiation coming from the central element inside the cone, is shielded from contributing to the rest of the pattern. Too short a cone and lots of the out of phase radiation escapes into the far field, lifting the pattern above the horizon. Too long a cone and the delay to the top section becomes too much as you begin to cover over more than the just the first 1/4 wavelength of the inner radiator.

    Keep in mind, the velocity factor to the vertical element inside of the cone is different than the exposed, outside surface of the cone. So you can see there are at least 3 or 4 different things going on as we make changes in the cone. Finding the best balance between them all, that puts the most signal on your target areas is what the goal is whenever you're working with beam tilt. Unfortunately with the mounting heights used on HF, what works best for one person is not always the same in the next installation.

    When the antenna is less than 1 or 2 wavelengths above ground (as is the typical case on HF) small changes is height make larger changes in the TOA. Once the antenna is many wavelengths above ground (easy to do on VHF), the effects of height on TOA become less. The typical goal here is to maintain a signal parallel to the horizon and is easier to repeat from one installation to the next.

    For as simple as the antenna looks, there is certainly more going on than meets the eye at first glance.
     
    HomerBB and Shadetree Mechanic like this.
  4. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    Not to get too far off subject I did Google " electrical beam tilt" and it is a very interesting subject.
    I need to read much more but there is reference to using this with outstanding results in the new 5 G networks used by Cell companys!
    I agree with Shockwave that The Vector is interesting in many ways, some that I thought I had a grasp on.....
    Only to have to change my mind again.
    Thanks to everyone that has and continues to contribute to these threads about this antenna.

    73
    Jeff
     
  5. Dr_DX

    Dr_DX Active Member

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    OK, need some advice from you guys that have been working on this antenna far longer than I have. I have read all 30 pages here and Henry's 40+ page article on the antenna as well. I understand 95+% of what is said. As a back story over the last 30 years, I have had 3 of the LW150's and 3 Maco 5/8 antennas center radiator's all bite the dust due to ice loading and/or high winds (I live on a 1700' hill in S. Texas Hill Country). But the LW150's were the original 7/8th wave design with the shorter GP. I am willing to try the new design with the theoretical changes if it can get me a 1-2 DB improvement.

    I have what is left of my 3rd Maco (just the GP) for the extra GP, a 24"x 1.25" Delrin rod to isolate the mast from the antenna, and a homemade ferrite CMC with >5K Resistive Impedance to isolate the feedline from the antenna at the antenna feed. I have decided to do the direct feed (Gamma Match delete) after I have done the other mods so I can create a baseline first.

    I am skeptical that the "new" design will fair any better than the old design as it relates to the weather. It still uses .049 wall aluminum, probably 6063, and even though it is shorter, it isn't as short as the Maco's which couldn't handle the weather either.

    SO, any build tips to make the center radiator stronger, more durable, etc. will be greatly appreciated. I generally change all the hardware out to SS, also I use closed ended steel shanked aircraft rivets, not screws to join the Aluminum tubing together - usually 3 per 4" overlap and NoAlux - ala Force 12.

    The top section where it goes into the 2nd section with the collar and set screw look pretty gimpy to me - any improvement on that would be appreciated.

    Thanks,
    Dr_DX
     
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  6. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Bob, I recently asked Donald if he ever got the antenna above tuned and working. I also asked if it showed more signal at a distance than a stock optimized Vector.

    He gave me an answer basically saying: that when he tried to make the adjustments, he found it very hard to do. He also said the conditions were very bad at the time. I don't want to have to read this whole thread to try and find out.

    Do you know if Donald ever got this antenna tuned, and if so, what were his results?

    Is the stock optimized Vector different than a stock Vector, and if so, can you describe the difference?

    With your help, I would like to model these ideas.
     
  7. Shockwave

    Shockwave Sr. Member

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    While it was not easy to measure on HF, it was not so difficult on the FM band. Whenever you make the loop bigger, you have to shorten the radials to maintain resonance. That causes more of the out of phase radiation from the bottom 1/4 wave of the inside element, to radiate into the far field and drops the gain on the horizon.

    I also have to add that the comment I made 10 years ago about the loop not having much radiation was based on a test done with a field strength meter. Since then I've learned that these meters respond mostly to the voltage node on the antenna. Typically showing the highest reading towards the top of the antenna were the least radiation comes from but, where the RF voltage is highest.
     
    #442 Shockwave, Jun 5, 2019
    Last edited: Jun 5, 2019
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  8. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Donald here are my models of a Stock Sigma 4 with a 30" diameter loop and regular length radials according to Antenna Specialists Manual. It has a physical gamma match included in the model. I added my antenna notes for my stock S4 too.

    The other two models are end fed for my convenience in modeling and I did not try and improve the matches nor did i make antenna notes. In fact by surprise doing this project I noticed this might be the way to end feed the S4/NV4K.

    One has a loop = 60" diameter with standard length radials.

    The other has a loop 100" diameter with standard length radials.

    Both the models with the wider loops and standard length radials (not shortened) show to become inductive just as you've noted. I did not see this as a big deal. I left these two just like they came out on changing the loop diameters. You can easily see the difference in the loop diameters in the models on their Antenna View images.

    The radial lengths in inches are posted on each Antenna View at the bottom left.

    In part I used a gamma fed Sigma 4 model to show how the presence of the gamma effects the pattern and gain. We may argue this, but IMO we see here a positive effect on adding the matcher. Adding the matching device produces lots of RF and this can change things.

    Notice all 3 models maximum gain angles are at 8* degrees. No sign of tilting here yet. I don't see any increase in gain either like predicted by Avanti on making the loop wider. If you can give me the radial length that you used as you went wider with the loop, I would be happy to try and model the shorter radials idea too. That might produce the maximum gain you're looking for.

    I just took a different route to making radials wider, and I found no trouble finding resonance. They aren't perfect, but they are close.

    These two 3/4 waves are very close to a good match and still keep a decent gain and angle for the maximum gain to the horizon. Even a 100" inches, over 3x the stock Sigma4 loop diameter, handles these cloud warmer trends in 3/4 GP antennas just fine. However, you can't go to much more or things change for the worst real fast.

    Thanks for responding, I was trying to horn-swag-gel Bob into this old thread.
     

    Attached Files:

    #443 Marconi, Jun 5, 2019
    Last edited: Jun 6, 2019
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  9. davev8

    davev8 Gold Star/Marvin Award Member

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    Well that was a long read ..i read this tread to find some figures that i think shockwave posted and i must have missed them reading this long thread again ..i give the back story
    I have only just got my head around some modeling software (MMANA) and decided to model something i can make quickly for 6M a 5/8 wave with 4 ground radials and when playing with the software i made the mistake to see what defence the angel of the ground radials make and noted the T,O,A going lower as they went up and ended up putting a ring on them twerking all the lengths and moved the T.O.A from 40 degrees to 6 degrees so its a sigma 4 .. because of time constans i will make the 5/8 1st but the info i was looking for and i must have missed i think shock wave posted on this thread (or maybe on Bobs attentive viewpoint) was his dimensions in the format of xxxx times mhz for the ring.radiator and radials .... . many thanks in advance
     
  10. El Kabong

    El Kabong Active Member

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    I never did read what the optimal changes were to a stock Vector so I left mine in the box in a closet.
     
  11. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Dave 8 and El Kabong, when Bob posted this thread he was introducing Shockwave's version of a modified Vector with shorter radials and a loop at the top of the radial cone that was much larger in circumference and diameter...than the original Vector loop at 30" inches diameter.

    As I recall they both got the idea from something written in the Sigma4 patent that suggested it was possible for this S4 design to show even more gain at a distance to the horizon if the loop was made larger. I never did understand why Shockwave decided to make the radials shorter in his process.

    Shockwave posted his dimensions in post #14. Click below
    Modified Vector 4000

    In my post above #443, I was still trying to model Shockwave's idea, but I never saw any change in the TOA or more gain at a distance on the horizon.
     
    #446 Marconi, Jan 2, 2020
    Last edited: Jan 2, 2020
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  12. Jay Mojave

    Jay Mojave Well-Known Member

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    Hello All: I am reading all the postings here on the Sigma 4 Antenna. And its all healthy hobby interest stuff. I am not a fan of this antenna for my own opinion of unmeasured reasons. But the interest in the antenna is impressive.

    I have made upgrades to the Sigma 4 type antennas, using heavier aluminum tubing and aluminum pipe for its base piece. To make it significantly stronger and bullet proof. These antennas were designed for easy production and not for the very strong 100 MPH Santa Ana Winds we have here in the Mojave Desert, or ice conditions back east.

    I know some stations run both a Interceptor 10K or other type 5/8 wave ground plane antenna and a Sigma 4 type antenna. And a high quality (with 60dB isolation or better is used ) Coax Switch allowing the operator to switch between the two antennas without them effecting each other from lack of isolation at the coax switch. This allows the operator to switch between the two antennas that may have different elevation angles or take off angles as said. And these two antennas are purposely several hundred feet apart to avoid any reaction between them.

    I didn't read any measured field strength comparisons in the thread here, so if I missed it please let me know. I might just build one and measure it.

    Jay in the Great Mojave Desert
     
  13. davev8

    davev8 Gold Star/Marvin Award Member

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    thanks Marconi but the post i was looking for has the formula to scale the antenna for different bands.....it was 3 lots like xxxx times the mhz for the ring.radials and radiator...i did take note at the time but i forgot what i named the file or which computer i saved it on ...It may not even be in this thread it may be in Bobs an alternative viewpoint thread but as it take me 2 days to go through this one i think it was worth asking ...i suppose i could use my very basic primary school math and work it out from the 11m V4K... i want to make a 6m antenna
     
  14. davev8

    davev8 Gold Star/Marvin Award Member

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    Sounds a lot of hassle and expensive coax just to change TOA ...i think i would just switch the mast in or out ...a mast normanly when connected to the bottom of the antenna makes the antenna think its longer than it is and buggers up the patten and puts the TOA upwords ...try modeling a I10K say at 10 meters high with no mast and then with a mast and see what happens.....
     
  15. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    I have no doubt that Jay has plenty of Antenna related stuff on hand to tackle this project.
    I would like to see the results if you get the time Jay.
    I have to say that your I 10K is The most rugged antenna I have ever used.
    It has survived everything that the Sierra Nevada mountains could throw at it for 20 years.
    Snow storms, wind, freezing rain, you name it.

    Not to get too far off topic, but how far did you get with your Beam project?
    73
    Jeff
     

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