I need your help!

Discussion in 'Wireless & RF Design' started by KL7AJ, Mar 22, 2015.

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  1. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
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    Greetings all experimentally minded hams! I am writing a QST article, or perhaps a series. I need to collect a lot of data from across the country.

    What I need you to do is build a 40 meter wire dipole, precisely 67 feet long, including center insulator or balun.

    I need you to lay it on the ground in a straight line. With an antenna analyzer, Noise bridge, RX bridge or other instrument you're competent with.....

    I need to know the precise frequency of resonance (0 reactance) and the resistance value, preferably within 0.1 ohms.

    I need two measurements, one at high noon local time, and one at midnight local time.

    I need your coordinates (as closely as possible) and a description of your terrain. I don't care if it's in a swamp or over a concrete sidewalk. I just need to know the radiation resistance and resonant frequency at ground level.

    This will be a REALLY cool experiment. I'll be putting a simple spreadsheet together that you can fill out.

    Thanks immensely!

    More exciting information to follow.


    Eric
     
  2. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
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    Well, that was a thunderous round of indifference!
     
  3. BR-549

    Well-Known Member

    Sep 22, 2013
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    Alright let's see now.....

    all you need is for me to purchase and construct a 40 meter dipole with an insulator at exactly 67 ft. long.

    and install at ground level.

    then at noon and midnight, you want me to measure the precise resonant frequency and the radiation resistance.

    I'm excited.
     
  4. PRFGADGET

    Active Member

    Aug 8, 2011
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    A few point's for consideration !
    1. The U.S.G.S. did rather extensive Ground Conductivity Testing (EARTHING) some years ago , their Map's are available online, this seems to be where you are headed (whether you realize it or not).
    2. All commercial Radio Stations" (and many Amateur Operators , especially contest stations using the "light bulb test") and Power Productions facility's do "EARTHING" study's before building their installations, why not just pick out some in your area's of interest and send them an e-mail and ask for their data (you might be surprised).
    3. The actual point of your request seems to be lost (to me at least) except for your interest in 40 meters. perhaps a bit more detailed explanation of what you think you wish to accomplish is in order, we may be able to help "smooth" the path a bit.

    While the price of Commercial Ground Testing (earthing) equipment has come down considerably over the past years and "MFJ" has done a good job of making the "259" series antenna analyzer affordable, not every ham has these toy's available or has the knowledge to use them correctly.

    I have to agree with "BR-549" , you seem to be asking people to spend what will amount to a good deal (for some) of money, time, and effort , FOR WHAT ?
    Not to mention that a properly constructed Dipole will be at resonance (R0) and will change very little at it's proper elevation , laid out on the ground it will change and go out of "tune" , add moisture content , rain , snow , ambient temperature ect. , these factories will all have an effect on the point of resonance.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there is a mode of propagation called NVIS near vertical incidense skywave that uses low mounted antennas for better close in (up to 300 miles) comunications. that might be what you are trying to do, but those would be mounted about 1 to 12 feet high for best results. the reflective layer in the ionosphere changes hcight from noon to midnight, but I dont see how it could affect the antenna, only the distance you could talk.
     
  6. BR-549

    Well-Known Member

    Sep 22, 2013
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    Maybe there is a difference in the earth's charge, between the facing side and the dark side to the sun.

    Or maybe the earth's dielectric properties change daily due to environmental cycles.

    It is curious.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Hi Eric,

    I am not a ham, but I support such experimentation. I live in the country and suspect there are many hams in my area. The only big antenna within several miles that I see is approximately here:

    upload_2015-3-24_12-27-8.png

    The address is at the intersection of Quarry Road and Ohio State Route 20 in Oberlin, OH 44074. Several times a year, I see his antenna taken down on the field -- I suppose for some modification or adjustment. If getting his call sign would be helpful to you, I would be happy to stop on my net trip into Cleveland.

    John
     
  8. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
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    As well you should be! :)
     
  9. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
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    This is not a ground conductivity test.
     
  10. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
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    To answer a previous question...I'm not expecting anyone to buy anything....just enlisting the participation of anyone who already has the equipment. (And anyone can use an extra 40 meter dipole, right? :)
     
  11. DickCappels

    Moderator

    Aug 21, 2008
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