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Interesting NVIS use anywhere HF antenna

Discussion in 'Amateur Radio Antennas' started by Moleculo, May 4, 2012.

  1. Moleculo

    Moleculo Administrator Staff Member

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    One of the guys that just joined our MARS unit sells radio equipment and systems to military customers. They have unique requirements and applications that are different than most hams' use cases. One such use case is the ability to put up an NVIS HF antenna that operates from 1.8-30 Mhz, be stealthy, and have reliable comms out to 200-500 miles. Here is an example of just such an antenna that he's working on and testing on our MARS net. It lays on the ground in an H configuration, about 300 feet long and uses some specialty baluns (I haven't seen them myself). Remember, the guys that would use this in the field aren't antenna experts and just need it to work. Yesterday he was able to successfully communicate with other stations about 200 miles out and he was running less than 20 watts on 7 Mhz.

    Neat stuff!


     

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  2. IMD262

    IMD262 Well-Known Member

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    I always thought NVIS occurred mostly at 40M and below and very rarely occurring above 40M??
     
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  3. depark

    depark W9WDX Amateur Radio Club Member

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    There is a small company in California that makes antennas and he is a big proponent of NVIS as well. The company is Chameleon Antenna. Here is the link: Chameleon Antenna. I am not affilated with the company but I do have a few of their antennas. I have to say that the build quality is very good. I have the V22L, Hybrid and MIL Whip. I get some nice results with these antennas considering that they are a compromise. Where they really shine is portable. The Hybrid is the best starting point IMO. You can use it alone with a supplied 30' end fed wire that you can configure in any shape. You can also add length to the wire if you choose. Some people have lengthened it to 99' with great results. You can use the Hybrid as the base and them mount different pieces on top for different setups as wel (eg. Hybrid, V1L bottom section and MIL Whip top section). It might be worth a look anyway.(y)
     
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  4. RatsoW8

    RatsoW8 Supporting Member

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    I thought NVIS antennas were generally dipoles erected below 1/4 wave in height and useful below 20 meters.
     
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  5. Moleculo

    Moleculo Administrator Staff Member

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    Generally you would do NVIS around 7 mhz and below. However, if the antenna also works up to 30 Mhz, you could make a longer range contact if necessary. I think the idea on this antenna is to get something that works well for NVIS and can be pointed in a specific direction (this antenna is apparently somewhat directional) and can be used on higher frequencies if desired.

    Generally you see NVIS antennas constructed as dipoles and mounted low. However, if you're deployed as a military unit as a scout team in some back country packing everything you need, would you rather carry some wire that you can lay on the ground, or tripods, masts and stuff to erect a dipole?
     
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  6. KC9Q

    KC9Q Supporting Member

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    I think NVIS applies to any antenna less than 0.1 wavelengths above the ground. One of the net operators on Midcars uses a 40 Meter dipole 7 feet above the ground for exceptional close in coverage.
     
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  7. Moleculo

    Moleculo Administrator Staff Member

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    More accurately, Near Vertical Incidence Skywave propagation is basically sending a signal almost straight up so it can be refracted back down. The idea is to get a signal footprint in a localized, 500 mile or so radius. Wikipedia has a good short article on it: Near Vertical Incidence Skywave - Wikipedia, the free encyclopedia
     
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  8. Mudfoot

    Mudfoot Supporting Member

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    It also helps avoid direction finding by the enemy.
     
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  9. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    This was successfully done for comms during Desert Storm, the vertical antennas were basically useless due to all the static, they laid them down horizontal using the vehicle as a reflector/ground plane and NVIS props allowed reliable comms to other field ops.

    Read that on the military.com site article was interesting.
     
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  10. W5LZ

    W5LZ Crotchety Old Bastard

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    There is no benefit with NVIS antennas as far as direction finding is concerned, they can be DF'ed like any other antenna.

    Mole', I think you might mention CCD antennas to your friend. They aren't all that directional, but can certainly be "ground mounted" if assembled correctly.
    - 'Doc
     
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  11. Mudfoot

    Mudfoot Supporting Member

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    Which is why I said, help avoid.

    NVIS energy is received from very sharp angles, which makes location finding very difficult, It is also more immune to local ground wave jamming. NVIS, a known and proven part of military communications.

    This is one reason we used NVIS, plus it's easier to shoot and scoot.
     
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    Last edited: May 5, 2012
  12. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Wake up DOC:whistle: no one said anything about direction finding using an NVIS antenna.
     
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  13. KD8MBP

    KD8MBP Member

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    Just saw your post about the NVIS antenna that lays on the ground. Very interesting. Do you have anymore info about it or if it is avaiable?

    Greg
     
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  14. W5LZ

    W5LZ Crotchety Old Bastard

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    wavrider,
    See post #8. And I didn't say anything about using them for DF'ing either.
    - 'Doc
     
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  15. Moleculo

    Moleculo Administrator Staff Member

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    I could find out what they did with it.
     
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: nvis

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