Interesting Read About Blaw-Knox Towers

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W9XMT, Sep 17, 2021.

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  1. W9XMT

    W9XMT Ham Member QRZ Page

    Below for those with the time/interest are scans describing an issue and remedy relating to Blaw-Knox towers, going back to the early days of commercial AM broadcasting.

    It isn't too applicable to the amateur radio community, except maybe for the text underlined in blue on page 46 thereof.

    [​IMG]
    [​IMG]
     
    W2VW, N3RYB and N4CVX like this.
  2. W9XMT

    W9XMT Ham Member QRZ Page

    Below is a performance comparison of the 1930-era Blaw-Knox tower of WCAU vs. a uniform cross-section radiator, showing what Dr. Brown was describing in his autobiography about his/RCA's solution for the nighttime self-interference WCAU was having back then.

    [​IMG]
     
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  3. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    Those were always fascinating Towers to me, like the old 650 WSM in Nashville Tennessee.
    And WLW, all using the Diamond cantilever design.
     
    Last edited: Sep 19, 2021
  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

    Charlotte's WBT had a 3-tower array built in 1934. Two of them went down in Hurricane Hugo in 1989 and were rebuilt according to the original plans.
    800px-WBT-Towers.jpg
     
    W4HWD, N0TZU, KX4O and 1 other person like this.
  5. AK5B

    AK5B Ham Member QRZ Page

    That's what I call the ULTIMATE YARD ART! Three thumbs up!
     
    M0AGP, KP4SX and W7UUU like this.
  6. KJ4YEV

    KJ4YEV Premium Subscriber QRZ Page

    I was told by a local tower climber that only nine of those still exist. Can't verify that.
     
  7. WD4ELG

    WD4ELG Ham Member QRZ Page

    Ah yes, the most dangerous ones are those who don't know they don't know.

    Will Rogers: It's not what you know, but what you THINK you know that ain't so.

    Donald Rumsfeld: we must be particularly careful with unknown-unknowns.

    Anonymous: ignorance is bliss.

    Characterizing unknown unknowns (pmi.org)

    Black swan theory - Wikipedia

    The KEY is for the individual to NOT assume he/she knows everything...instead, relentlessly seek out the experiences of others and seek to eliminate those unknown-unknowns (also called 'blind spots'). It's not enough to look for a "subject matter expert" but instead speak to a large sampling of individuals with extensive experience on the subject.

    Also, it is VERY important to remember this: just because someone has been doing something for a long time, doesn't mean that he/she is an expert or that he/she is doing it correctly. Often, I see posters on QRZ referring to their extensive work history in field XX. That MAY be relevant, it MAY make them able to provide sound advice, but it is NOT a certainty. The automatic assumption that such a person IS an authority is faulty logic.
     
    N3RYB likes this.
  8. AK5B

    AK5B Ham Member QRZ Page

    OK; Perhaps changing QRZ.com to QRBS.com might be a more accurate url, n'est ce-pas? ;)
     
    M0AGP likes this.
  9. WD4ELG

    WD4ELG Ham Member QRZ Page

    @AK5B well-played, Sir. :)
     
    AK5B likes this.
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    The high angle radiation of the Blaw-Knox tower described by Brown is due to its excessive vertical length (223 deg, 503ft) compared to a 195 deg, 440 ft tower. The varying cross section of the tower has almost nothing to do with it.

    First, comparing apples to apples, here is the elevation pattern of a 503ft tall Blaw-Knox tower compared to a 503ft tall Uniform cross-section tower:
    upload_2021-9-20_7-11-1.png
    If the goal is to minimize the high angle radiation from a 503ft tower, then the Blaw-Knox tower is better than the Uniform cross-section one!

    Second, comparing apples to apples, here is the elevation pattern of a 440ft tall Blaw-Knox tower compared to a 440ft tall Uniform cross-section tower:
    upload_2021-9-20_6-58-36.png


    If the goal is to simply minimize high angle radiation, then for either type of radiator, make the length ~180degrees or 406ft.
    upload_2021-9-20_7-37-13.png
    In that final analysis, the net difference at high angles is ~1dB.

    Conclusion: In the article from Dr. Brown, his claims bad-mouthing the Blaw-Knox antenna demonstrates that he is one of "The most dangerous persons and groups in our society are those who do not know that they do not know." His arrogance is startling!
     
    KC4YDY and N0TZU like this.

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