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Army Signaleer needing Antenna assistance

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by ARMYSIGNALGUY, May 10, 2020.

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  1. ARMYSIGNALGUY

    ARMYSIGNALGUY QRZ Member

    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 can’t specify for obvious reasons). The area I’m at doesn’t have much of a tactical radio infrastructure, and instead, we utilize cell-phones (which aren’t very secure at all). Because of that, I am determined to figure out how to implement radio communications in my region. 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 a 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.


    Equipment:
    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/Sigurnost/pdfs/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/..._antenna_serv_user_TM11-5985-379-14P_1986.pdf

    Attempted test:
    Distance between stations:
    roughly 50 miles
    Terrain: Station 1 – In a flat plane found up in semi-mountainous terrain, no obstructions from foliage, trees, or buildings. Station 2 – 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 it’s very popular online, and a lot of people seem to have success with it. It’s 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 “take-off” 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. Here’s my logic:
    • The antenna mast is 15’ ft tall. The Technical manual specifies to place stakes 42 ½’ ft from the base. The antenna wire (and attached rope to tie to the stake) is 45’ 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 that’s 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 I’ve read suggests heights ranging from 1/10 wavelength all the way to 1/2 wavelengths. This seems like a pretty wide gap, so I’m curious if there’s 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 naïve, 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, it’s 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.
     
    K4DMZ likes this.
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Hi Eric.

    I just happened to send out an email to some ham buddies about NVIS antennas this morning. It might shed some light on your requirements, so I attach it here:

    It sort of debunks the NVIS antenna myth...
    -------------------------------------------------------------------------------------------------------------------------
    On 5/10/2020 9:12 AM, Michael C... wrote:
    Hi, Mike,
    Reading the mail this morning on the N-Utah Web SDR.... enjoyed your comments about "NVIS."

    When you have time on your hands, would you shoot me just a bullet point outline of the points you made about NVIS? Especially your empirical experiences with respect to wire distance above ground vs.radiation angle?

    CAP is all wrapped around the axle regarding "NVIS antennas."

    I have to laugh about playing with crazy antennas on the Friendship Cruise. On one trip, at Mineral Bottom, Dave Martin and I laid out an Eyring Research "Special Forces NVIS" loop antenna that was designed to be spread out on the ground. Was fed at one corner with a balun of some kind (potted in a box--not sure.) That antenna was indeed absolutely stealthy--- it worked as a fabulous dummy load.

    ------------------------------------- my reply ----------------------------------------------------------------------
    Here is my simple analysis:

    Dirt-simple center-fed horizontal 1/2wl bare #14awg Cu wire dipole deployed above average dirt (0.005,13), zero transmission line loss. Test frequency is 3.8MHz. Two independent parameters; L=length of the dipole in feet and H=height of the dipole above ground level. If I vary H, a slight adjustment has to be made in L to bring the antenna back to resonance, which I define as happening when jX=0. Height effects the feed resistance (R), the ground loss (Average Gain, factor or dB), the maximum Gain direction, and Max Gain itself:

    upload_2020-5-10_14-57-28.png

    The L column shows the computed length of the dipole to make the jX part of feed impedance ~ zero.

    The H column is the independent variable, which I vary from 5ft to 146ft.

    The R column shows how the feed resistance changes vs height:

    upload_2020-5-10_14-57-28.png

    It is interesting that Swr50 gets close to 1 at two heights agl:

    upload_2020-5-10_14-57-28.png

    The nail in the NVIS coffin is the 3D max Gain vs height:

    upload_2020-5-10_14-57-28.png

    Notice that the gain increases rapidly as the dipole is moved from 5ft agl to about 40ft agl. This is explained by the Average Gain Factor, which accounts for transmitter power lost by heating the dirt below the antenna. It is a measure of how much of the applied transmitter power actually gets radiated as sky-wave. Transmitter power that heats the wire, heats the dirt, or is radiated as "ground wave" does not contribute to the dBi radiation pattern, especially the part of the pattern that shows how much is radiated overhead:

    upload_2020-5-10_14-57-28.png

    Again, look at how much of the transmitter power is lost for dipole heights from 5 ft to 40ft.

    So I show how the elevation patterns vary vs H. These "slices" are at an azimuth broadside to the dipole (max radiation):
    upload_2020-5-10_15-0-1.png

    Given a choice for communications over short paths, the best pattern is the H=41ft. Lower than that just loses energy by dissipation in earth. Remember that the NVIS propagation mode rarely appears on 80m, is even more rare on 60m, and almost never shows up on 40m, so why would you think about mounting a dipole close to earth on any band??? Note that it really, really hard to get an 80m dipole high enough to be able to work DX.
     
    N0TZU, NQ1B, WB5YUZ and 5 others like this.
  3. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hi!

    A collateral on your quest for better antennas, look up ‘Kurt speaks out’.

    You’ll be directed to Palomar Enginnering website. Fill the form and you’ll receive the download link.

    Though there are no word around NVIS propagation, that material is great debunking a lot of fallacies snake oil and urban legends in Antenna making.
     
    K0UO, N8AFT, WA9UAA and 1 other person like this.
  4. ARMYSIGNALGUY

    ARMYSIGNALGUY QRZ Member

    Mike,

    Really appreciate your reply, that's a lot of great verifiable information. I'm curious what software are you using for that? Looks like it could be great for future use. I will admit I had to google a lot of those terms so I could understand the significance of those readings, but I appreciate any opportunity to expand my knowledge. Thank you again!
     
  5. WA9UAA

    WA9UAA Ham Member QRZ Page

    Hi Eric,
    I'll take a stab at this; though, I'm not an expert by any means. In a realistic sense, the answers to your questions are all tied together.

    #1 Given the point at which we are in the sunspot cycle, NVIS is the closest option to what you need. There are alternatives but not necessarily at HF frequencies, I'll mention those later. The question will be, at what maximum frequency is NVIS propagation available? Since NVIS is aka Near Vertical Incidence Signal IIRC, then you want to shoot the signal straight up in which case it will scatter somewhat on the way down covering a wide area. The antennas needed may vary, in height some-what according to your frequency allocation, but will be relatively close to the ground and have a reflector wire on the ground underneath the antenna to improve the signal strength in a vertical direction. I would suggest a training exercise where both stations have the same style antenna since these tend to work the same way in both directions. However, and this is a big however, the ionosphere does not always cooperate. Once you have a working setup, periodic testing of communications is important.

    #2 Take off angle is calculated with reference to the horizon and the zenith. On a plane (surface) or the plains :cool: the horizon will be 0 deg. elevation and the zenith 90 deg. straight up, for your situation it sounds like NVIS is the way to go. Again, the problem is the ionosphere, The type of propagation will vary according to how high the sun is in the sky, what other effects the sun may have, and in what ever the effects of the solar flux might have. Solar effects are lessened at the amateur frequency of 160M ie. 1.8MHz to 2.0 MHz. Then, static crashes from lightning are a problem during the summer in your hemisphere at those frequencies. Here is where, again, testing and drills over various frequencies will be important. If you have, time changing antenna height may show some changes in the signal. The usable NVIS frequencies will always be low in frequency relative to the larger notion of HF frequency range, probably 5 MHz and below for the foreseeable future. Testing will again be of importance as generally as the Maximum Usable NVIS frequency will vary by the seasons, the state of the solar flux and the part of the solar cycle in which you are trying to get messages across.The time of day may be very important, what works at 0800 may not work at all by noon. Ideally, there will be a log book of weekly/ hourly tests all year long for the various allocations you have available. In your situation, I don't see anything but NVIS because of the mountains unless you put in a repeater at some VHF frequency high up on a mountain top. NOTE: There may be things I have not heard about in propagation, equipment etal. Others will probably have more thorough information on this subject.

    #3 Take off angle. I don't see anything but NVIS at the HF frequencies you mention.

    #4 Antenna height You are going to have look that one up, it will probably vary according to frequency.

    #5 TPO aka Transmitter Power Out. If you are getting reflection at all more power may help, it would be prudent to use the least amount necessary and work to improve the antenna system, which seems to be the reason you are here.
    73,
    Rob
    Yep, lots of others with more and better answers. 73 again, Rob.
     
    PY2RAF likes this.
  6. KM4DYX

    KM4DYX Ham Member QRZ Page

    #1: Absent SATCOM you are going to use NVIS.
    #2: Don't sweat the small stuff; NVIS is 65 degrees to 90 degrees, i.e. high-angle.
    #3: See #2; you are not going to achieve a specific NVIS angle, you're just going to achieve high angle radiation.
    #4: .15-.20 wavelength above ground level, depending on soil conductivity.
    #5: NVIS, like all radio, can work at low power if conditions merit. I routinely do 5 watt CW NVIS.

    Here is what you need to know: NVIS comms is dictated by the f0F2, i.e., Critical Frequency. It changes over time:
    [​IMG]
    Get with your S-6 and find out the ionosonde data for your A.O. or look here for the closest one:
    https://www.ngdc.noaa.gov/stp/IONO/rt-iono/realtime/RealTime_foF2.html

    P.M. me of you are really interested in this stuff.

    73,
    Al
     
    K0UO and KX4O like this.
  7. N3KE

    N3KE Ham Member QRZ Page

    Hi Eric,

    Question 1:

    SATCOM or NVIS are your options with mobile/temporary antennas in the mountains and no repeater infrastructure.

    Question 2:

    Since I'm not sure anyone specifically answered it but did show you much more detail on the whole concept of "take-off angle" the shape of the antenna and any angles in the antenna have nothing to do with it when the antenna wire is close to the ground. As another post showed the radiation pattern is primarily dominated by the height of the antenna. So you can skip measuring angles on the antenna itself. As the radiation patterns shown in previous post illustrate what primarily matters is the height of the antenna. For NVIS you want it relatively low to get high angle radiation but not so low that you just end up warming up the ground instead of radiating. I know that's not very specific but important to understand that concept in general!

    Question 3:

    As the various plots already shown illustrate there isn't any one "take-off angle" rather an NVIS antenna tends to radiate in a giant blob pointed at the sky. Certain angles do get a few more dB of gain than others but there really aren't any major lobes or nulls to worry about. You shouldn't need to fuss with the antenna much. Also it is very difficult to get any meaningful measurement of a radiation pattern in the field and both the noise environment and the ionosphere change so frequently it is very difficult to do any sort of consistent testing between stations.

    Question 4:

    1/2 wavelength too high. As others have said 1/10 to 1/4 wavelength is reasonable. It looks like you've wisely selected a NVIS antenna combined with a receiver that can tune it. I don't think you need to alter the antennas further.

    Question 5:

    More power always helps improve the reliability of any communications link and no you can't "punch through" the ionosphere. That said your mode of communications can have a lot to do with how well you can "get through".

    It looks like the radio you are using has a lot of modes to choose from. Operationally you might be constrained in what you are allowed to use but for reference if you are working at lower powers you want to use modes that are more efficient at closing the link at lower powers.

    For instance definitely use the SSB mode (J3E) in preference to AM mode (H3E) as SSB is vastly more efficient than AM.

    The radio appears to support some very low data rate modes and if those can get the job done the definitely use them! You can roughly equate baud rate to the inverse of power. So using STANAG 4415 at 75 bps is going to get through on 20W about as well as SATNAG 4539 at 9600 bps at 2000W. Now 9600 bps can support voice while 75 bps of course is more like typing. So if you are trying to push digital voice right now perhaps the link just isn't good enough for that at 20W and you need to go to a lower data rate mode that won't support voice.


    As others have pointed out what frequency to use is going to change with time. Roughly speaking in the daytime you will tend towards higher frequencies because the F layer can support NVIS at higher frequencies while the daytime presences of the D layer is attenuating lower frequencies more. At nighttime the F layer can only support NVIS on lower frequencies and the D layer disappears at night so attenuation is no longer an issue at lower frequencies. Lower frequencies do also typically have the disadvantage of more natural background noise.

    I see that your radio also supports ALE which is an automatic mode in which stations attempt to find the best frequency (and potentially data rate as well) in order to establish a link. I have no familiarity with this particular radio or the particular ALE modes it uses but when ALE works it sort is like magic removing a large burden from the user in finding a working frequency. I expect it involves a fair bit a configuration but presumably you have a manual for the radio. Basically the radio attempts to call the other station by stepping through multiple different frequencies and once both stations find a frequency they can hear on the link is established. Operationally I might imagine this is the mode you want to use. But for experimenting having control over the frequency in use is useful as well.

    Likely it is unwise for you to give us much in the way of details here so I'm trying to cover a lot of options without any awareness of what exactly you've already been using. But a key point is if you can lower the data rate the link will work better for sure and the range of data rates you can set are even larger than the effect of an amplifier. So make sure you are at SSB and the lowest workable data rate as you explore what links you can establish.

    And the correct frequency for the conditions (mostly dominated by the time of day) is of course critical as well.

    Right now with the one station receiving nothing it is hard for you to tell what exactly is wrong (e.g. does that station have a fault in it somewhere such that it will never RX anything, or does it have a TX problem and you are already using ALE such that it needs to successfully transmit for the link to be established). Getting the link to work at all at a low data rate would be my next step in debugging.

    Also I'm not sure if you are able to physically visit these sites yourself or have anyone at the remote stations that you can rely on but another good debugging step is to see if each station can hear the same things in the HF environment. Do a little more Googling and you should be able to find shortwave broadcasts or ham radio beacons close enough to be able to be received. Can all three stations here roughly the same stations at the same SNRs? Or is one of them relatively "deaf"? If "deaf" is that because there is something wrong with the antenna and its connection as indicated by a low S-meter reading or power measurement? Or is it "deaf" because the local noise environment is really bad (e.g. there is some powered device at that site that is defective and is radiating on the low bands - don't underestimate the potential for just one GI's laptop power adapter to take out the entire HF band at a site).

    I cannot emphasize enough that more than antenna theory here what you really need is a plan to debug why that one station isn't hearing the transmission. The fact that one station heard you means the antenna at the TX site is likely just fine and 20W is probably enough (or close enough). If you haven't already make sure you are SSB and try the lowest data rate modes to see if you can get that one station to hear at all. If you can then you can get an idea of how much worse it is than the other station. If it is totally deaf even at the lowest rates while the other station is fine at higher rates it likely means something wrong at the RX station. Most likely cases are the antenna isn't hearing anything well or that there is some horrible local interference. Again just listening to shortwave broadcasts or ham CW beacons can help you out a lot here.

    Best of luck and let us know how else we might help!
     
  8. AJ6O

    AJ6O Ham Member QRZ Page

    One thing is for certain is that the antenna you transmit with is not always the best antenna to receive with. I have many vertical and horizontal antennas, my "NVIS" which is only 10 feet off the ground is by far the best for receiving (even though the signal strength is less) because it has the lowest noise floor, even better than my four-element vertical array which has gain. What you can not hear on one antenna most likely you can on another if they are two different polarizations or heights above ground.
     
    N8AFT likes this.
  9. EA1DDO

    EA1DDO Ham Member QRZ Page

    Satellite ?

    Or, place a "repeater" on the top of the hill, to give coverage to all that area.

    73, Maximo
     
  10. KK4OBI

    KK4OBI Ham Member QRZ Page

    KD9PQB and KX4O like this.

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