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Mobile antennas for NVIS at 80 meters

Discussion in 'Mobile Radio Systems' started by N0IOP, Oct 9, 2019.

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  1. N0IOP

    N0IOP Ham Member QRZ Page

    ::shrug:: There are many things that few amateurs understand. Few amateurs understand process gain. Few amateurs understand Fourier transforms. Nonetheless, many amateurs utilize FT8, which is based on these things.

    With mobile HF, the goal is usually to have an antenna, that is "less bad." It wonders me how much gain and directivity are indeed necessary to achieve practical communications. It is easy to build an antenna for 80m that is mobile and has -15 dBi gain. It is possible to build a "less bad" antenna that has, say, -8 dBi gain and a main lobe that is vertical. How much is good enough?

    http://kv5r.com/ham-radio/nvis-army-fm-24-18/

    The army seems to think it is practical enough to be useful, or at least thought that at one time. Or perhaps they were just experiencing groundwave propagation and, as you suggest, mischaracterized it as NVIS. But if you can get reliable ~300 mile comms, maybe it doesn't matter much.
     
  2. KI7SYG

    KI7SYG Ham Member QRZ Page

    I stumbled upon this thread and it reminded me of an idea I had but never tried.
    Being a trucker with my own trailer, I had the idea that I could epoxy an insulated horizontal wire loop to the aluminum roof of my trailer. This would give me a bit over 36 meters in perimeter. Since height is an issue, it wouldn't be an ideal height above the ground plane, but I thought it might work. I abandoned the idea because tree branches would probably destroy it eventually.
    K0BG, given the 53' trailer do you think my idea might have some merit, or is it just another of my dumb ideas?
     
    Last edited: Oct 10, 2019
  3. WG8Z

    WG8Z Ham Member QRZ Page

    Forget all the NVIS gobbly gook. The military's goals are pretty much opposite then a typical hams.
    Hams term is cloudburner. Same mechanism at play. To get the RF up instead of out.
    90% percent of 80m ragchewers are using this and don't even know it.
     
    K8AI and WA8FOZ like this.
  4. WG8Z

    WG8Z Ham Member QRZ Page

    KL7AJ Eric has valid insight.
    Love his X O stuff.
     
    WA8FOZ likes this.
  5. N0IOP

    N0IOP Ham Member QRZ Page

    I am a ham of very small mind. Upthread it was stated that most people trying to use NVIS are actually using ground wave and don't know it. But now I see that 90% of people using ground wave are using NVIS and don't know it. I am confused.
     
  6. WG8Z

    WG8Z Ham Member QRZ Page

    Ground wave is Vertically polarized and is not affected by ionosphere.
    Directwave can be Horizontal , Vertically, Diagonally or Circularly polarized and is not
    affected by ionosphere.
    Except that cancellation can occur if the ionosphere comes into play (fading)

    A lot of people confuze these.

    Military's NVIS is about minimal power, minimal readable signal to avoid interception outside targeted area.
    Hams look toward max signal, max coverage.

    Your idea is valid. Operating mobile is about minimizing losses.
    I ran a screwdriver mounted 45deg on my minivan for many years on 75M.
    It worked well.
    I assure you no ground wave or directwave was involved at distances > 50miles.
     
    NH7RO, KX4O and N0IOP like this.
  7. WG8Z

    WG8Z Ham Member QRZ Page

    What ur wanting to do is eliminated the overhead null.
    Tilting the donut so to speak.
     
    NH7RO and N0IOP like this.
  8. WG8Z

    WG8Z Ham Member QRZ Page

    Remember this is going to be affected by seasonal ionospheric changes.
    If 0 to 300Miles is your goal at your latitude this time of the year the sweet spot
    will likely be a 2 hour period in the AM and 2hr period in the late afternoon early evening.
     
  9. N0IOP

    N0IOP Ham Member QRZ Page

    Thanks. Sounds like this isn't an area where very many people have tinkered.

    I'm interested in low-band VHF and NVIS because of their application to regional comms in areas where repeaters are unavailable. Makes my propeller go around I guess. I can do some experimenting at my house, too, and use that as a starting point. I'm curious about your screwdriver antenna but I'll start another thread for that.
     
  10. WG8Z

    WG8Z Ham Member QRZ Page

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