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Phasing a couple of verticals

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by G0VQY, Aug 8, 2020.

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  1. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Yes. AFAIK OP will have to pick a band and optimize the set-up for that band. Then, he can select a single vertical for the other bands. I know of at least one op who does this.

    Here's a phasing scheme I've always wanted to try:

    [​IMG]
     
    Last edited: Aug 9, 2020
    AK5B and PU2OZT like this.
  2. W9XMT

    W9XMT Ham Member QRZ Page

    Interesting that the peak directional gain you posted for your array when (presumably) using a perfect ground plane is less than the 8 dBi value published for a single 'Himalaya' type vertical by an OEM of such.

    Out of curiosity I modeled the performance of a single such vertical radiator when driven against a single, 2.44m (8-ft) ground rod buried in average dirt. Its peak gain is about 0.67 dBi (not 8 dBi).

    The graphic below shows that and some additional results for it, along with using a 2nd identical radiator spaced λ/4 away from it as a parasitic radiator. The gain improvement for that two-radiator setup isn't great, but it doesn't require a corporate feed system, either.

    [​IMG]
     
  3. AI3V

    AI3V Ham Member QRZ Page

    Yes, you can get a tiny bit of gain.

    How much gain is 3 db?

    [​IMG]

    If we assume 6 db per "s unit" adding a second antenna would move the meter to about a needle width on the other side of 8


    What may be more noticable is the deep null , perhaps 4 or so s units.

    If you have a noise source in that direction.

    Rege
     
  4. KK4MIJ

    KK4MIJ Ham Member QRZ Page

    I posted this utility elsewhere, but I think it will show
    how your vertical will respond. Feedback Welcome.
    ses.
    It is a stand alone program and requires no install.
    I have checked for any kind of malware, but encourage you to check for yourself.

    1. The Propagation radio button enables an interactive graphic plot of two radiating elements.
    The phasing of the elements, along with the separation can be changed. The view is looking down the radiating elements.

    2. The Dipole radio button enables an interactive graphic showing the impedance in free space of a dipole antenna at fundamental frequency, second and third harmonics. Shows why a center fed dipole is not recommended on the second harmonic.

    3. The Feedline radio button is a work in progress, but is intended to show how reflected power in feed lines can cause feed lines to radiate due to incomplete cancelation.

    I would welcome your thoughts if you care to comment.
    This program is offered "AS IS", but would consider suggestions.

    Regards,
    Steven

    Attached Files:
     

    Attached Files:

  5. KK4MIJ

    KK4MIJ Ham Member QRZ Page

    Here are some screen shots showing
    what radiation patterns are possible by varying the phase, and antenna spacing.
    Just play with the sliders.

    Enjoy
    Steven
     

    Attached Files:

  6. KL7AJ

    KL7AJ Ham Member QRZ Page

    When you're down near the noise floor, half an S-unit can make a real difference....when you're above S9....not so much.
     
    M0TTQ, PU2OZT, AK5B and 3 others like this.
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    The Cardioid pattern I show in post #10 is the basis of the follow-the-needle "homing" type radio direction finding equipment such as is used to track emergency radio beacons used to locate crashed aircraft. Back in my CAP days I used both commercial systems as well as home-brewing them... I built the one that I had installed in my personal Cessna 182, and actually found several crash sites using it.

    Typically, two 1/4 wl whips are mounted at right angles to the center line of the aircraft about 1/4 wl apart. The coax "delay" line that produces the phase shift to produce the Cardioid pattern I showed is switched back and forth between the whips at about 100Hz, effectively reversing the Cardioid pattern.

    If the signal arrives from directly in front of the search airplane, then the signal is received with equal strengthregardless which way the two Cardioids are switched. If the signal arrives from the right or left of the flight path, the two Cardioids Amplitude modulate the received signal.

    A synchronous detector is used to drive a zero-center meter which shows which direction to turn the aircraft so that it is flying directly toward the signal source. The technique goes all the way back to pre-WW2 and is attributed to Watson-Watt, the British inventor of Radar.
     
    Last edited: Aug 9, 2020
  8. KK4MIJ

    KK4MIJ Ham Member QRZ Page

    Please help my understanding regarding gain in a phased array such as described above.

    If a given amount of power is sent from the transceiver, for sake of discussion lets say 50 watts.
    If phased together with same lengths of coax, equal power should go to each antenna. In this case 25 watts each.

    Here is where I need guidance...
    Both antennae radiate a full pattern at 25 watts. When the wave have maximum constructive interference, the effective power is 50 watts.
    Where the waves have maximum destructive interference, the effective power is 0.
    It seems to me that some of the power radiated from each antenna is used to either reduce or add to the power transmitted in any given
    direction. that said, the sum of the two antennae could not be larger in any direction than the original transmitted power. Therefore, no gain.
    But the advantage that I see is that the shape of the radiated pattern can be altered as to create directions of higher sensitivity (main lobe) as compared to other directions (nulls). These directions can be altered by phase changes.

    Please pass along any help you can,
    Regards,
    Steven
     
  9. KK4MIJ

    KK4MIJ Ham Member QRZ Page

    I forgot to add that the sum of the two phased antenna could
    be 3db gain over either one in the array. I think the sum of the two would be equal
    in effective radiated power to a single vertical. Again , the difference is directionality.
    Steven
     
  10. W9XMT

    W9XMT Ham Member QRZ Page

    Maybe the graphic below showing the fields of a directional array for a licensed AM broadcast station will help.

    The circular, ~205 mV/m field shown would be produced by a single tower of that array driven with the licensed output power of their transmitter.

    Applying that same power to the common point of the power dividing/phasing network feeding each tower of the array produces the directional fields shown.

    The difference between the peak field of the directional pattern and the "omni" field determines the maximum power gain of that array.

    In this case it would be about 20log10(340/205) = 4.4 dB.

    NOTE: The areas within the directional and the omni patterns are equal.

    [​IMG]
     
    Last edited: Aug 10, 2020
    K9MRD likes this.

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