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Review: 6m, 2m & 70cm Horizontal Loop Antennas by eBay Seller Freqtester

Discussion in 'Amateur Radio Equipment Reviews' started by W2WDX, May 19, 2018.

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  1. W2WDX

    W2WDX Subscriber QRZ Page

    I'll have to search out the Par analysis I saw. I found it when I was preparing this review. I was going to do a comparative study, but I found so many contradictory papers, pro and con, it seemed pointless and opted to just have my observations drive the review.
     
  2. K1ZJH

    K1ZJH Ham Member QRZ Page

    from his claims:
    Typical results are 2 to 5 DB.

    He clearly claims dB gain, not dBi, where is that alleged gain coming from? Ground reflection? dBd is a gain over a dipole. Even so, a 5 dB gain claim over dBi would be hard to swallow. Gain ofโˆ’1 dBi to โˆ’1.7 dBi depending on directivity is more realistic.

    Regardless, this nothing new. The old Hi Par Saturn six halo was in use eons ago. And the CC Squalos are still production. Gain can be negative when measured against a standard. That is how attenuators work.
     
    Last edited: Jun 22, 2018
  3. W2WDX

    W2WDX Subscriber QRZ Page

    @K1ZJH I'm sorry ... I think you don't understand the fundamental reference figures. dBi references an isotropic. dBd is referenced to a dipole which is 2.15dB above dBi. So you cannot have negative dBi. It is the base reference, no gain, perfectly spherical pattern. On these loops 2dBi for one, 5dBi for a stacked pair. Seems about right to me. They are afterall halfwave dipoles folded in on themselves, so a little loss below dBd is expected.

    However, the convention has always been "db" is always referenced to isotropic, where dBd is always discriminated by the "d". The nomenclature dB and dBi are interchangeable since they both refer to the theoretical base reference. dBd is used for a more real world reference since it relates to a actual antenna type and not a theoretical one, like the isotropic. That's why understanding the fundamentals is important. When manufacturers use "db" the gain figures seems higher (by 2.15dB) than one designated dBd, however the figures may be accurate if you understand the reference, be it base or dipole.

    In reference to antenna gain, it any positive figure over isotropic which is a theoretical zero gain antenna. A dipole has gain, 2.15db above isotropic. Yagi's much more. Gain comes from directivity. You cannot have negative directivity. You cannot have negative gain below nothing. No gain is no gain. Zero. 0dBi antenna gain is an absolute minimum. It is not the same as other dB references, especially electrical figures, which is what attenuators are. You can have losses which can be summed to a gain figure, but the gain figure itself cannot be lower than 0dBi.
     
    Last edited: Jun 23, 2018
  4. K1ZJH

    K1ZJH Ham Member QRZ Page

    I have never seen dB and dBi used interchangeably. dBi is indeed isotropic gain. Both are relative numbers. If it is dB gain compared to isotrophic, then it best be stated as gain in dBi.

    F/B is hopefully a negative value in dB compared to forward gain and is usually a negative number. Since dB is relative, it certainly can have a negative value.

    Gain of a halo has been shown with negative value relative to dBi:

    https://en.wikipedia.org/wiki/Halo_antenna

    A "folded dipole" type of halo. Gain along Y axis 1.2 dBi, Gain along Z axis โˆ’1 dBi, Gain along X axis โˆ’1.7 dBi. Fed at the center of the bottom conductor (feed-line not shown), supported at the center of the top conductor which is at ground potential for RF. This is similar to the halo as originally patented.
     
    Last edited: Jun 24, 2018

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