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Thread: Army Signal Soldier in need of some assistance

  1. #1

    Default Army Signal Soldier in need of some assistance

    Hello everyone!

    My names Eric, and I am an enlisted servicemember in the U.S. Army. I'm a proud member of the Army's Signal Corps, but my military training hasn't gone very in-depth regarding HF theory and operation. I am currently deployed overseas to a region in Europe (which I canít specify for obvious reasons). The area Iím at doesnít have much of a tactical radio infrastructure, and instead we utilize cell-phones (which arenít very secure at all). Because of that, I am determined to figure out how to implement radio communications in my region. I I've attempted to research this on my own, but a lot of resources out there require a broad foundational understanding of radio theory (which I lack). I know some of these questions may seem very elementary, but I really hope you all can offer some valuable information to help me out.

    Here's an overview of what I'm attempting to do:
    1. Establish reliable communication in a very mountainous area.
    2. The area I want coverage is roughly 9,000 sq Miles (a square with a base of 100mi, and height of 90mi).
    3. The terrain is very mountainous, with mild-to-medium vegetation cover; similar to forests you would find in the pacific northwest.

    Equpiment:
    R/T: Harris PRC-150; RT-1694D
    Frequency range: 1.6-59.999 MHz
    Power: 1, 5, 20 watts
    RF Iput/Output Impedence: 50 ohm nominal, unbalanced
    Data-sheet: https://www.zsis.hr/UserDocsImages/S...AN_PRC-150.pdf

    Antenna: As-2259/GR NVIS antenna
    Frequency range (from Technical manual): 2-30 MHz
    Azimuth: Omnidirectional
    Elevation: Near vertical incidence
    Technical Manual: http://www.radiomanual.info/schemi/S...9-14P_1986.pdf

    Attempted test:
    Distance between stations: roughly 50 miles
    Terrain: Station 1 Ė In a flat plane found up in semi-mountainous terrain, no obstructions from foliage, trees, or buildings. Station 2 Ė In a large field, in middle of a large bowl-shaped valley roughly 20 miles wide.
    Frequencies attempted: 3-10 MHz
    Antennas: AS-2259/GR
    VSWR: 1.1:1
    Results: Station 1 received strong TX from Station 2 on frequencies 3-4.5 MHz; Station 2 did not receive any TX from Station 1.

    General notes:
    - Traditionally in the military we primarily use FM communication (30-89 MHz), but this is limited by terrain due to line-of-sight issues. After researching, it seemed like HF frequency using NVIS propagation would allow omni-directional coverage for the entire area regardless by the terrain.
    - I chose the AS-2259/GR because itís very popular online, and a lot of people seem to have success with it. Itís also orderable through the military because it has a National Stock Number (NSN).

    Question #1: Given the terrain and short distance, is HF using NVIS the best option to provide consistent reliable radio communication? If not, what are some recommendations on different techniques, or different antenna styles?

    Question #2: How do you calculate a ďtake-offĒ angle?
    - It may sound very simple, but I cannot find any cut-and-dry answer to this, but I have tried to figure this out for myself using geometry. Hereís my logic:
    - The antenna mast is 15í ft tall. The Technical manual specifies to place stakes 42 Ĺí ft from the base. The antenna wire (and attached rope to tie to the stake) is 45í ft long.
    - This essentially makes a Right triangle. Therefore:
    - The Angle between the Mast and the ground is 90 degrees .
    - The Angle between the stake and the antenna wire is 19.44 degrees.
    - The Angle between the antenna feed cone and the antenna wire is 70.56 degrees.
    - I know that NVIS only is possible with a take-off angle of 70-90 degrees; so logically, I assume the take-off angle for the AS-2259/GR is 70.56o because thatís the only measurement close enough to the NVIS range.

    Question #3: In your experience, what would you suggest as the right take-off angle if you were to want to communicate within 100 miles and could not rely on ground-wave transmission?
    - If I was correct about the take-off angle being 70 degrees, I have a theory that this caused a small skip-zone and if I adjusted the take-off angle to a more aggressive one (80-89 degrees), I may be able to eliminate any coverage gaps.

    Question #4: What antenna height is optimal for NVIS?
    - A lot of what Iíve read suggests heights ranging from 1/10 wavelength all the way to 1/2 wavelengths. This seems like a pretty wide gap, so Iím curious if thereís a preferred general height people go by.

    Question #5: What effect does TX power have on NVIS?
    - In my current configuration I only use 20 watts. However, the radios manufacturer makes power amplifiers in: 150 & 400 watts.
    - If I were to use more TX power, would NVIS still work? I know it sounds naÔve, but in my limited knowledge of HF theory I thought that if a signal was transmitted with too much power it runs the risk of punching through a layer (in this case the ionosphere) and not being refracted. Is that correct? If not feel free to laugh and call me dumb.

    I just wanted to say thank you to all of you on here, because you all are such an invaluable resource for the military community. I am truly impressed by the dedication you all show to harnessing and refining this craft. Additionally, itís mind blowing seeing some of the genius ideas you all come up with. I know I asked a ton of questions, so I truly, truly, truly appreciate any information you all can provide.

    Thank you all, and God bless,

    -Eric D.

  2. #2

    Default

    [QUOTE=EricDoregon;40941]Hello everyone!


    Here's an overview of what I'm attempting to do:
    1. Establish reliable communication in a very mountainous area.
    2. The area I want coverage is roughly 9,000 sq Miles (a square with a base of 100mi, and height of 90mi).
    3. The terrain is very mountainous, with mild-to-medium vegetation cover; similar to forests you would find in the pacific northwest.

    Equpiment:
    R/T: Harris PRC-150; RT-1694D
    Frequency range: 1.6-59.999 MHz
    Power: 1, 5, 20 watts
    RF Iput/Output Impedence: 50 ohm nominal, unbalanced
    Data-sheet: https://www.zsis.hr/UserDocsImages/S...AN_PRC-150.pdf

    Antenna: As-2259/GR NVIS antenna
    Frequency range (from Technical manual): 2-30 MHz
    Azimuth: Omnidirectional
    Elevation: Near vertical incidence
    Technical Manual: http://www.radiomanual.info/schemi/S...9-14P_1986.pdf


    Question #1: Given the terrain and short distance, is HF using NVIS the best option to provide consistent reliable radio communication? If not, what are some recommendations on different techniques, or different antenna styles?


    Question #5: What effect does TX power have on NVIS?


    Eric - going to give you short answers.

    NVIS: Remember hearing the military using it in terrain you describe. On vehicles, they folded the antenna over horizontally.
    Lots of antenna info on the web. Seen dipoles just above the ground work. Play with ideas like this and experiment.

    Troposcatter. May not be possible with the equipment you have. Good book by G. Roda on this, although it's old.

    Your on the right track with NVIS, imo.

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