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2.4 GHz contact over mountains

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by VK7HH, Aug 4, 2019.

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  1. VK7HH

    VK7HH Ham Member QRZ Page

    An on air contact with my 2.4 gigahertz transverter and FT817. Earlier in the day we had confirmed that Richard VK7ZBX's system was also working. The path is not line of sight and is over 1200m (4000 feet) mountains. Amazing signal considering the path and the location of my grid pack.

    K8KPO, AI3V, KD8TUT and 1 other person like this.
  2. WA4ILH

    WA4ILH Subscriber QRZ Page

    Could be Tropo ducting. I used to see that occasionally on the NOAA 10 cm weather radar (~2800 MHz)
    Tom WA4ILH
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Bent signals over a mountain range yielding beyond line of site coverage? It's called "Knife Edge Diffraction". Long documented phenomenon can be found in the textbooks.
  4. K8ERV

    K8ERV Ham Member QRZ Page

    Probably went thru, not over.

    TOM K8ERV Montrose Colo
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    Not possible at 2.4 Ghz as radio cannot penetrate rock and earth much more than 1 wavelength. It is just too dense. From that you might conclude using lower frequency has a batter chance of penetrating earth because lower frequency means longer wavelengths. In fact lower frequencies do penetrate further, and thus why there are radios made for mining and tunneling. Operating frequency is low kilohertz range of 500 Hz to 7000 Hz with a limited range of 200 to 300 meters.

    I agree with KAOHCP, it is Knife Edge Effect.

  6. K8ERV

    K8ERV Ham Member QRZ Page


    TOM K8ERV Montrose Colo
    KE7CIU, N7UJU and N5RFX like this.
  7. VK7HH

    VK7HH Ham Member QRZ Page

    I agree now that it's knife edge diffraction. Our next test will be hopefully a big further in distance and try to use the same mountain range. I also had houses/trees in the way so with a clear path it may be even stronger.
    KA0HCP likes this.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yeah, this is not uncommon on UHF-SHF.

    Here in CA we use this effect a lot, as it's pretty reliable; but we probably more commonly use a "bounce" off mountains to reflect the signal back in the opposite direction for DX that way.

    I remember in the August 2010 ARRL UHF contest I was operating from Orange County, about 35 miles SE of L.A. and on all bands up to 10.3 GHz, working "rovers" in the contest who were similarly equipped. To work them up north of me, the rover pack parked in Pasadena in some store parking lot and aimed towards me, about 60 miles to their south -- signals were very weak on the SHF bands and tough to copy; then they all aimed due north, 180 degrees away from me, so they were aiming right into Mt. Wilson, a 6200' hill north of them, and signals peaked right up to literally "59" and very easy copy, to work them all. This was with maybe 2W on 10.3 GHz, and similar power on 5.7 GHz.

    But at the same time I was able to work stations up in the San Joaquin Valley, much farther north and on the other side of that large obstacle, via knife-edge that just scattered the signals over the mountain and completed 4 QSOs with stations about 120 miles away over a very, very obstructed path.

    Fun screwing around on those bands.:)
    VK7HH likes this.
  9. K8ERV

    K8ERV Ham Member QRZ Page

    Remember you can only use Ginzu knives.

    TOM K8ERV Montrose Colo
  10. AI3V

    AI3V Ham Member QRZ Page

    Its difficult to tell "knife edge diffraction" from "troposcatter"

    Try one station as a rover, at the same distance but a different direction.

    I used to run a nightly sked wit wa3tts in Pittsburgh, when I lived in Kingwood WVa, a distance of 100 miles, and more or less rolling hills in between.

    I was running about 100watts eirp and Mike could copy me 24/7 at s5 signals

    Go here:

    And download a copy of the "microflect passive repeater engineering handbook"

    VK7HH likes this.

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