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FM-AM DX - TOWERS - ANTENAS - RECEIVERS

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    DPM144-5LVA ARRAYS

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    DX-er

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    DPM144-5LVA ARRAYS

    Post by DX-er on Sat 21 Jun 2008, 10:05

    DPM144-5LVA ARRAYSThe basic antenna is the DPM144-5LVA,
    a six ft long rear mounted yagi, originally computer optimized by N1DPM. It is
    a nicely performing yagi with over 9 dBd forward gain, and a good pattern. It
    is equally well suited singly for roving applications on 144, or for combination
    with other similar antennas in a large broad beamwidth array for serious VHF contesting.
    The PDF formatted manual is here.
    The
    project began with Fred Stefanik, N1DPM, trying to improve the contest score of
    NC1I, a limited multi-operator station that achieved top honors nationwide from
    Western Massachusetts over the last few years. Their original 144 MHz antenna
    consisted of one long 50 ft M2 antenna. While the antenna had great gain, the
    narrow beamwidth was not good for contesting. Long yagis tend to eat up rotators
    with gusto, and also require large amounts of time to be spent simply rotating
    to find stations in the first place. Fred dropped the long yagi idea quick, and
    eventually ended up with an array of two stacked 9 element yagis that improved
    the number of QSOS and grids. Fred thought this combination was too sharp as well,
    although their score went up markedly. He eventually ended up with a 5 element
    design that looked to be an optimum choice for contesting. It had a very wide
    horizontal main lobe and could cover large swaths of the country with no twiddling
    of the rotor control box! They never installed an LVA of these 5 element yagis
    at NC1I, but we did adopt the idea for use at K1WHS in Maine. See the picture
    below:

    DX-er

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    Re: DPM144-5LVA ARRAYS

    Post by DX-er on Sat 21 Jun 2008, 10:05

    LVA at K1WHS Fall, 2003This is the 144 MHz LVA as it appeared in
    2003 at K1WHS. LVA is an acronym for Large Vertical Array. It started out as eight
    antennas with the ultimate goal of an increase to sixteen yagis: The top 5 element
    yagi is at 115 ft, while the bottom one is at 76 ft. With a 52 degree horizontal
    beamwidth, it covers much of the United States from this location in Maine. Imagine,
    useable beamwidth is around 90 degrees or more. Really, the real "hearing"
    problems occur when you get to the nulls in the pattern. The operating beamwidth
    is much wider than the listed -3 dB points of this array. With long yagi antennas,
    those nulls occur very close to the main lobe, a real disadvantage when compared
    to short boom yagis. As antennas are added vertically, the vertical lobe gets
    more and more flattened. 8 Yagis have a 6.5 degree vertical lobe. The main lobe
    remains at 52 degrees horizontal no matter how many yagis are added vertically.
    So we merely need to vertically stack a few LVA beams to produce more gain and
    over a wider beamwidth than a conventional long yagi.A few things to consider
    in the LVA design seem counter-intuitive. In the past, gain was king. If brand
    X had 13.791 dBd forward gain, and Brand Y came out with a new model that had
    13.992 dBd gain, the DXers would flock to the store and buy all of Brand Y's new
    offering. For contesting, the priority is to actually hear the station in the
    first place. Rather than thinking about how much gain you could muster in a particular
    direction, you should be thinking about how much area can I cover with my main
    lobe. If you can put all of your RF in a wide area, more people will hear you.
    It is that simple. You will not hear weak stations calling you in your beam nulls!
    The LVA has purposely been designed with a wide main lobe. It will never win a
    gain contest at your local VHF Conference. (Well maybe it might if there are few
    entries!) BUT, it will spew RF across a wide main lobe and have a great H plane
    pattern that is so necessary for proper stacking. The -10 dB beamwidth is 89.6
    degrees. This is a good number to watch, as it covers the working part of the
    main lobe between the first nulls

    DX-er

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    Re: DPM144-5LVA ARRAYS

    Post by DX-er on Sat 21 Jun 2008, 10:05

    At our Contest station in 2004, an
    extra 8 yagis were added to the original eight LVA. Shown here is K1DY bolting
    on one of the last yagis in the array.Seen from a distance, this antenna system
    is starting to look rather large! The bottom antenna is at 32 ft, making the whole
    array occupy 83 ft vertically. This makes the vertical beamwidth about 3.25 degrees
    wide at the 1/2 powerpoints! Gain of the 16 yagi array is well over 20 dBd and
    compares favorably with the four 30 ft yagis on top of the tower. The best part
    is that no rotator is needed for the LVA to cover a wide range of azimuths. At
    K1WHS, we can work stations from Toronto (270 degrees) to Albany, NY to New York
    City, to Providence, RI. (185 degrees) without touching a rotator button. Even
    at the 90 degree -10 dB points of the main lobe, there is still almost 11 dBd
    of forward gain: the equivalent of a single 12 ft long yagi. This is more than
    enough to be heard.


    Other interesting positive points when installing a large
    number of these short yagis includes the very sharp vertical pattern that will
    allow a large reduction of power line noise if your station is located on a hilltop,
    and the power lines are at the bottom of the hill. This was demonstrated at K1WHS,
    with the middle of the array at about 925 ft asl. The local power lines are at
    about 425 ft asl, and are about 2.5 to 4 miles away. A few calculations showed
    that each offending power pole was well outside of the main lobe and caused the
    power line noise to actually drop in level. Remember that the incoming signals
    are -3 dB at -1.6 degrees elevation!! This noise reduction only showed up when
    the array was enlarged to 16 antennas. Eight or four yagis will not have a sharp
    enough main lobe to reduce close in noise. Another positive feature of side mounted
    antennas involves rain static. The side mounted array is located below the rotatable
    4- yagi array on the tower top. Interestingly, the LVA does not suffer from rain
    or snow static even while the top mounted four yagi array is experiencing 59 +30
    dB noise levels. The higher metal will bleed off the static charges. This is a
    big improvement, and adds tremendous flexibility in contest situations.
    An
    actual bandwidth plot of DPM144-5LVA is shown here: DPM144-5LVA
    Bandpass

    Return Loss plot of the DPM144-5LVA is available
    here: DPM144-5 VSWR
    Patterns?
    You want patterns? I'll show you patterns!!!

    DX-er

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    Re: DPM144-5LVA ARRAYS

    Post by DX-er on Sat 21 Jun 2008, 10:06


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    Re: DPM144-5LVA ARRAYS

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