Feedback on building a BOG antenna.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF4ITA, Aug 11, 2019.

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  1. KF4ITA

    KF4ITA Ham Member QRZ Page

    Hi all,
    I'm about to build my second BOG antenna. My first one was tore up after Hurricane Michael blew down all the trees, and the land owner brought in bulldozers to clear the lot. My main interest is AM BCB but also enjoy 160M and 80 M.
    I have a little over 260ft to run the BOG antenna. I plan on loading it to bring the VF down to make it seem longer, but not down to 50% where I understand the directionality starts to falter. I plan on using Military Field phone wire, like here, Unless
    someone convinces me otherwise, and I will just use both wires and solder the the two wires together at each end.
    (Is it better to have 1/2 the wire resistance or worse to have more capacitance to ground by a the double wire?)
    I have noted ingress problems using coax feed lines which degrades the pattern. I found an improvement using twisted speaker wire as my feed line. This build, I think I will use outdoor rated Cat 6 cable. I will use a termination resistor of the proper value, to be determined using my RigExperts antenna analyzer. I may make this variable in the future. I had a variable previously, but lightning took it out. Since I have extra wires in the CAT 6 cable for power, I may even try comparing a transformer to Dallas Lankfords, FET follower amp on the BOG. about 330k input and 150 ohm output. If requested I'll send more info about that.
    I will be putting the antenna on the edge of a drainage ditch, I have a question about putting it on the ground or 1" of the ground, is there a best way? I'm in Fl, no snow but plenty of rain.
    Anyway, Those are my thoughts, I'm looking for as much info as I can get before I start to build, so I can get it right the first time.
    Thanks for your feedback, Mikek

    btw, I have a video comparing my first 250ft BOG to a 150ft longwire . I think the BOG shows off well.
    W6KCS likes this.
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    I am curious about the long wire used in the comparisons in the video and why it picks up so much more noise.

    How is it deployed?

    Is it in the form of a self-contained Hertz antenna (floating wire with respect to earth ground), or is it more like a Marconi antenna (mostly vertical or inverted-L where current is returned to earth ground).

    How do you couple the long wire to the receiver input?
    K0UO likes this.
  3. KF4ITA

    KF4ITA Ham Member QRZ Page

    My long wire was a vertical up 20ft then went east 150 ft sloping up to height of 50 ft. It's been a while, but I think I have an isolation/impedance transformer outside a foot from the grass where it enters the house.
    In my research a long wire (inverted L) has a mostly omni pattern, maybe 1db gain in the direction it points. But it is mostly a vertical with a long (wire) capacitance hat. (that's a whole nuther discussion)
    I don't recall turns ratio. One side of primary to the antenna, other side to a ground, secondary to radio. Actually, each antenna went to a coax switch then to radio.
    I think that answers all the questions except why so much noise.
    In my description I write that I'm in Fl. and at the time of those tests we had a lightning storm off the coast.
    That is what I found so great about the BOG, it is a quiet antenna and is known for that! It especially useful here
    on the coast because so often we have a storm out in the gulf. I'm in Panama City Fl.
    I don't feel my Long wire is noisy, it was just a storm going on, but even so, the BOG is a quieter antenna on quiet nights.
    My BOG runs N/S and hears best to the N. I can confirm it has a decent null off the sides, I have a local to my East that was weak
    with the BOG and fine on the long wire and 1200kHz out of Texas to the West which is good on my long wire is not heard of very weak on my BOG.
    That is one thing that makes it quiet, the pattern of reduced sensitivity to signals off the sides and rear.
    I have one more short video where I compare these two antennas to a mini whip antenna, like this one,

    I only test it on one frequency, and this is the same day and time.

    WA7ARK and W6KCS like this.
  4. W6KCS

    W6KCS Ham Member QRZ Page

    A friend talked me into trying one of these, I'll be doing that as soon as I get time. Very interested in your results.
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    Thanks for the description of the antenna.

    I recognized the 1160kHz freq in the video. I lived within 20mi of that transmitter most of my adult life...

    A couple of my ham friends work for the media corp that owns that transmitter.
    K0UO likes this.
  6. NH7RO

    NH7RO Ham Member QRZ Page

    Hope you succeed in doing so---but be aware---it's often all too easy to get bogged down in the details with some types of Beverages.
    W6KCS likes this.
  7. KF4ITA

    KF4ITA Ham Member QRZ Page

    One of those details is coax or twisted wire feed line? I did some tests a couple years ago with a maybe 200ft feed line
    laying on the ground. Two comparisons of coax vs twisted speaker wire, I shorted the end or resistor terminated the end, then checked signal strength of stations I could receive on just the feed line.
    It was clear to me the coax was a receive antenna, where the twisted speaker wire was almost dead. So if you want a clean antenna pattern, go with twisted wire instead of coax.
    BTW, I tried everything to quiet the coax, transformers, common mode chokes, sleeve ferrites, and many winding through ferrite toroids. Couldn't fix it. Twisted wire is the way to go.
    This is info that Dallas Lankford used with his phased antennas to keep from spoiling the good patterns he got. I just verified it for my own edification.
  8. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    If you can't get coax feedline to operate without Common Mode then something is wrong. Coax doesn't change properties just because it is connected to a Beverage.

    My guess is that you tied the feed shield/ground and antenna grounds across the transformer.
  9. KF4ITA

    KF4ITA Ham Member QRZ Page

    This was just the feed line, I connected a 50 ohm resistor at the far end and the other end to my radio. Then did a band scan and recorded signal strength.
    I did this with the end shorted and open also. The coax picks up signals, the twisted wire does not, or at least much less signal.
    You can believe me or not, I just know if you want to preserve the pattern of a receiving antenna, and not contaminate it with another signal, use twisted wire.
    As far as "My guess is that you tied the feed shield/ground and antenna grounds across the transformer." I tried every combination of connections to get rid of signal, and I'm sure at one time I grounded it.
    I welcome anyone to do the experiment and prove me wrong.
    There could be a way to quiet the coax, (I couldn't find it) but if you lay out 200 ft of coax and connect it to your radio, it will pick up AM radio signal, terminated, open or shorted.
    Twisted wire not so much!

  10. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    No, sorry I don't believe that. I and tens of thousands of of hams use long runs of coax on low bands without Common Mode pickup.

    Something is wrong with your coax, like a short, low quality, or incorrect connection.

    Yes, with no termination you can pick up strong signals, if the length is great enough. However, that is not how coax is used as a feedline.

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