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Thread: Sirio SD27 and SY27-3

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    Sirio SD27 and SY27-3

    I'm unhappy with my modified SD27 vertical dipole. Modified in that I added a homegrown reflector. I'm going to add a SY27-3 (3 element Yagi Uda) to my array of antennas.

    I'm dismantling the SD27 mod and will go with it alone, vertically mounted, below the SY27-3. There is some interesting reading, https://www.qsl.net/kk4obi/Standard%20vertical.html which speaks to the elevation of the vertical dipole in terms of elevation angle on the horizon and beam width.

    The matter of beam width raises the first question. In my mind width is equivalent to how wide the signal is on the horizontal while depictions are indicating a measurement of degrees of height. I'm illiterate when it comes to the terms of the cabal. Please clarify for me if right or wrong; the omni-directional broadcast of the signal maximum reaches to a height of 40d above the horizon when 1/2 λ height mounted and 25d if 1 λ height mounted? And peak signal strength is either 15 or 10d respectively?

    Second query is the presumption that mounting the vertical dipole at 3/4 λ the signal properties will be midway between the aforementioned 40 and 25d properties. I'm looking for affirmation?

    FYI: I assembled the SD27 according to manual with a minor adjustment to element length. I reasoned the 5420mm L was closer to some forbidden territory in 12 meter band and shortened length to guidance for 27.205mHZ. But what was surprising was the specifications for setting up the gamma matching device. Set exactly to specifications the resulting SWR was perfect, 1:1 on both ends of 11M band.

    Sadly I don't expect the same luck with the forthcoming SY23-3. 1stly, as is my understanding, the vertical dipole (SD27) SWR measured with a 9' AGL feed point doesn't change with height. Horizontally mounted the same radiating element, as SD27, will change with height and I dread the labor therein involved.
    Last edited by Alabama Buckeye; 05-15-2022 at 02:37 PM.
    All answers are opinions and may, or may not be technically correct.

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