Phased dipole model

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K7URX, May 17, 2019.

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  1. K4SAV

    K4SAV Ham Member QRZ Page

    That won't work with MMANA because it has no current sources, only voltage sources. You can't use more than one voltage source in a phased array and get the right answer. You need current sources. Try it in EZNEC and see what you get.

    Using voltage sources is also not practical. How would you produce a particular current value and phase at the end of a transmission line, not knowing what the load impedance is, if you drive the source end with a voltage source?

    Jerry, K4SAV
     
    K7TRF likes this.
  2. UA3TW

    UA3TW Ham Member QRZ Page

    MMANA is a qaint software. It does not have transmission lines but it calculates TLs made of 2 parallel wires farely well. It does calculate them even when the wires are so close that they touch each or penetrate each other.
    For example two parallel wires of diameters 20 units each and situated so that the distance between their centers is 14 units will behave as a 50 Ohm TL in a model. See the attach. The line must not be too long, But if you calculate multiband Yagi beam where the driven elements are connected with TL, about 1m long, as in Optibeam antennas, the result will be accurate enough.
    MMANA does not have current sources but people contrive to design phased arrays very well. They incert big resistance in series with the source, 1-10 kOhm, and calculate the model from many sources. They get correct radiation pattern and they get input impedances for the elements if subtruct those 1-10 kOhm values. Only Gain is not correct.
    Another way is to use Bushero bridge instead of 1/4 TL. You use voltage sources and Bushero bridges of any required characteristic impedance and get the correct model including Gain, RP and all input impedances for the ports of a Hybrid Coupler. I modeled that for the 9 el array of W0UN from the ON4UN book. See the MMANA model in the attach. I cross checked it with the EZNEC model and got perfect coincidence.
     

    Attached Files:

  3. K7URX

    K7URX Ham Member QRZ Page

    Got the antenna up yesterday. I cut the phasing lines with a swr meter, dummy load and transmitter. The 71 degree line needed to be 90 at 18 mhz so used transceiver for that one and then did the math for the 84 degree lines. It's up at 65 feet. Wow. The front to back is astonishing. S7 to s9 signals broadside to the array almost completely disappear when switching directions. The swr is at 2.4. Not sure it that is where it should land on not. More testing later today.
     
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  4. K0UO

    K0UO Subscriber QRZ Page

    20190506_103047.jpg Congratulations on getting yours working, the photo above is my old original 90-degree phasing line more information about it below, it was built back in the early 1970s


    Phased antennas are really incredible, I'm glad you got yours working. I started out years ago with two 40m dipoles at a quarter wave separation and a 90° phasing line. I just brought equal lengths of 72ohm scrap TV cable line into the shack that's all I had and all I could afford abd use double pole double throw switch in the shack. I couldn't believe how well that's simple setup worked. Back then I didn't even have an SWR meter and I just did math on the phasing lines using 72 ohm TV cable at the time. In the photograph the cool is scrap 72 ohm cable TV RG59, the two wires on the left in the photo were cut equal lengths of 72 cable coming back into the switch from the antennas. There wasn't a lot of information in reference books at that time about phasing. Total cost of my original system was Zero everything was from the junk box.
    You might want to try using a Collins power divider, that's what is used on the Comtech phasing boxes. It does dump a little power into a 50 Ohm resistor but generally it's a very small percentage, it we'll give you a flat SWR throughout the band. I've used them on my four squares for 160 and 80 running 1500 watts into the full-size verticals I might see five or 10 watts going into the 50 ohm load, and I'm able to work the complete 160 or 80 band cw to phone with 1:1 SWR in the shack.
     
    Last edited: May 20, 2019
    UA3TW likes this.
  5. K7URX

    K7URX Ham Member QRZ Page

    Thanks for sharing that information! I will look into the power divider on my day off tomorrow.
     
    Last edited: May 20, 2019
  6. K7URX

    K7URX Ham Member QRZ Page

    BTW. That's really cool that you saved that all this time.
     
  7. UA3TW

    UA3TW Ham Member QRZ Page

    IMO Hybrid Couplers are no good for 2 el antennas, and the antennas that are based on 2 element modules, like 6 in circle and so on. Hybrid Couplers are good for 4SQ antennas and the antennas that are based on 4SQ antennas as modules i.e. the complex antenna can be broken into separated 4SQ antennas. Those are 8 in circle & 9th in the center and the like. The opinion is based on my EZNEC modelling experience of various configurations.
    The reason - Hybrid Couplers divide source power by 2. The analisis shows that not all antennas require power division between the elements on two equal parts. Some elements do not require driven power at all - they suck power by coupling from other elements. Again - 4SQ is good for Hybrid Coupler because the side elements require same driven power as the front and rear elements together as a pair. Hybrid coupler deliver 50% of the power in the form
    of 0 dg phase and 50 % of the power in the form of 90 dg phase. Good for 4SQ. But no good for 2 el antenna where one element requires about 80% of the power and the other - only 20%. Certainly i could make a mistake about the whole matter. But everyone can make one's own analisis if one has EZNEC handy.
    In looking for ways of feeding the configurations, that can not be broken into two equal power element groops, i found out that 2 Hybrid Couplers can be cascaded and rounded up into a loop. Such system can delivere power into two ports with any percentage of the power division between the ports. Excuse my English.
    KF7ESM - so i would not recommend using HPs for your 2 el antenna. Yours TL way is best, though not nesessarily coaxil lines - open lines more convenient for some cases.
     
    Last edited: May 21, 2019
  8. K7URX

    K7URX Ham Member QRZ Page

    20PHASED_DIPOLE1.jpg 20PHASED_DIPOLE2.jpg .

    Took a little slack out of it and now SWR is 2:1 I think its good enough. Now to hang with heavier rope and aim for Europe. Thanks to everyone for their input. I really appreciate the help. 73
     
    Last edited: May 21, 2019
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  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    Indeed....my favorite incarnation of the phased array is the ZL special....if you have enough patience, you can achieve nearly infinite F/B ratio....at one frequency..HI!
     
    K0UO likes this.
  10. W8LLW

    W8LLW Platinum Subscriber Platinum Subscriber QRZ Page

    Holy mackerel Dave. Is that the antenna you were using during our QSO Wednesday evening? That thing looks bad to the bone, and we know it worked very well getting out to Michigan. Congrats on the results of what appears to be a lot of effort on your part. Very nice.
     

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