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Non-Friendly / Non-Permissive Environment: HF Operation

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI5QMP, Sep 14, 2021.

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  1. M0AGP

    M0AGP Ham Member QRZ Page

    I agree with Jeff - you should consider a vertical. Here's a 6BTV I (partly) camouflaged earlier:
    upload_2021-9-14_23-29-18.png
     
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  2. AI5DH

    AI5DH Ham Member QRZ Page

    Your ground losses will turn your antenna into a dumb load at those heights. Your antenna is looking for ground 60-feet below grade before it can launch. You have a good earthworm spa and sauna. All you are doing is heating up dirt. Very little energy is radiating, nor being received.
     
    Last edited: Sep 15, 2021
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  3. AK5B

    AK5B Ham Member QRZ Page

    True enough---exactly why he needs to turn his thinking from horizontal to vertical---at least in this "dire" antenna situation of his.

    Horizontal 80 meter wire 5 feet agl==maybe five or ten dx contacts/year (roughly speaking):eek::(:(:(:mad:

    Trap vertical or 1/4-wave ground plane 5 feet agl w/ 2-4 elevated radials==5,000 or 10,000 dx contacts/year (roughly speaking, all other parameters being the same):D:p;):):rolleyes::cool::D:):):):););):D:D:D:D

    If the antenna must be stealthy thin wire and paint and other disguises can be well utilized here, too. It simply takes a bit of doing and the determination to succeed.

    73,

    Jeff
     
  4. KA4WJA

    KA4WJA Ham Member QRZ Page

    Tyler,
    1) No worries on getting on 80m from an "unfriendly" locale....I've just done this myself, this year! :)
    {and, btw....don't obsess over the SWR....on 80m, with fairly short runs of coax, we can tolerate fairly high VSWR's...}

    Up front, an important FYI....successful HF operation is all about receive signal-to-noise-ratio (s/n), the better the s/n, the more successful you are....so, controlling your receive noise (both man-made RFI and natural/band noise) is very important to your success....remember, "if you can't hear 'em, you can't work 'em"!

    I'm spending quite a bit of my time 200 miles from my home, caring for elderly family, and desired to keep-in-touch with ham friends and connect with the world of my fellow hams. So, I made some effort and have been on 80m now for most of this year, with great success, with a very low dipole / stealthy dipole, in my temporary location.

    My dipole is a bit of "v" shape, with the center-feed about 12' high, and the ends about 18' - 20' high....(would be better if I had the feed-point higher, as that is the "high-current" point....and I'm working on a few ideas to do just this in the coming weeks), and I have an excellent signal on 80m SSB all across Florida (300+ miles), and a "decent" signal (5 - 10db lower than guys with dipoles at 50' - 55') along the US East Coast, up to NJ, PA, NY (~ 1000 miles)....and my signal into central Europe (4500 - 5000 miles) is about 10db below others, but still making contacts, with a dipole at 12' - 18' high (which is probably about the same if you had your dipole at ~ 8' high?)

    This is all 80m SSB, using 40+ year old equipment...but mostly with 1500 watts output....although running barefoot, with only 65 watts, I still make many 80m SSB contacts throughout Florida (NVIS ranges), all with a "low-dipole"....

    And, although this comparison here is anecdotal, this is consistent now for many months....my barefoot/65 watts signal is consistently 6db to 10db stronger than a guy a few miles away from me, running an end-fed-half-wave 30' high, running 100 watts...

    And remember, this is summertime in south and central Florida, where 80m noise levels (from lightning static crashes) can be S-9 to 10-20db over, at times!

    Just rid your house of RFI-producing devices (or unplug them, when on-the-air), and you'll be able to make this work for you....although, if you could just get your dipole a bit higher, things would be a whole lot better! (heck, even 15' - 20' high would be great!)



    2) Before I give you some ideas....here is some darn good news for you:
    a) Waco, Texas (and much of the surrounding central/east Texas has some of the best RF Ground Conductivity Soil in the US....certainly urban / suburban areas are not as great as rural, but still a whole lot better than we have it in Florida!

    This means two things right off the bat:

    --- your actual gain of a low dipole will be as much as 3db higher than if you had just "average" or "good" ground conductivity....and, hence use of a low dipole for local contacts (out to 200 - 300 miles) will actually work. {this is typically the "range" of NVIS = Near Vertical Incidence Skywave.}

    --- for longer range contacts, past 750 - 1000 miles and out to many 1000's of miles, a vertical antenna with a decent amount of radials / decent antenna ground system (25 - 40, buried radials, of 30' - 40' long....or 4 elevated / tuned radials and a ground screen), will work well for you.


    b) Working stations in Central/East Texas should be easy (assuming you control your received RFI), as other stations there-abouts also have an advantage of excellent ground conductivity....fyi, signals from stations from Houston, Abilene, San Antonio, etc. should all arrive at angles of 60 degrees or higher (signals closer to you, such as Dallas, will be 75 degrees or higher....and those out further than San Angelo, etc. will be lower than 60 degrees...)

    Once you move out past the ~ 200 mile range / 60 degree angle range, you're starting to press the definition of "near" in NVIS, and by the time you're out past Lubbock, TX (300 - 350 miles?), with angles of 45 - 50 degrees, you're really not in "NVIS" territory any more....(although, it's all semantics....doesn't really make any difference to how you operate...but, it's good info to know, yes?)



    c) Using a full-size half-wave dipole (center-fed, with a decent balun), is a great start! You do not have the losses of those guys running end-fed-half-waves! And, yes, you'll find with the antenna that low to the ground, that the formula will only get you in the ballpark, and you will need to fold some wire back to get the antenna resonance where you want it....and, remember, even if you find you cannot get as good of VSWR as you desire, at these low frequencies and short runs of coax, the extra losses are very minor (certain almost insignificant compared to the ground losses from having the antenna so low!), so if you only get 1.5:1 or 2:1, etc. as the best you can get, that is perfectly fine!



    3) Even though you're in an area with excellent ground conductivity, and your low dipole will have "gains" 3 - 4db higher than predicted for a low dipole over "average soil", every foot or two you can raise the antenna WILL help....and even at say 18' high, you'd have a dipole with the same gain as a guy with average soil has with his dipole at 30' high...

    Higher is better!! Optimal height for NVIS paths, for your ground conductivity is about 41' high, but going down to 30' high only looses you about 0.3db (yep, 3 tenths of a db!), the "break-point" is about 25' - 30'...so, getting the antenna up to there (~ 30') should be an ultimate goal...but, any height that is higher than you have it now will be better!!! {Just take note that you do NOT need it to be 60', for it to work well!!}

    Now, for longer range comms on 80m, certainly the higher, the better....but, here again, your excellent ground conductivity will be an advantage, as a vertical antenna can really play very well! :)

    So....get your dipole a bit higher, and you'll find tuning it will be easier, AND you'll be talking all over central and east Texas, and will even find good comms out across the US.....and then if desiring DX, etc., look into a vertical.



    4) Finally, and probably most important here....please remember what I wrote above:

    Successful HF operation is all about receive signal-to-noise-ratio (s/n), the better the s/n, the more successful you are....so, controlling your receive noise (both man-made RFI and natural/band noise) is very important to your success....remember, "if you can't hear 'em, you can't work 'em"!

    Your receive noise, particularly your local RFI (from your own house or close neighbor's) is going to be the determining factor in your 80m success....AND
    And, getting your dipole up and away from those sources of noise will be of great help here....

    Yes, we've all been talking about optimizing for best transmit performance, but the fact is getting your dipole up higher (25' - 30' high, or higher) and as far away from RFI noise sources as possible will go a LONG way to having much success on 80m! :)


    I hope this helps.

    73,
    John, KA4WJA

    P.S. I'm not a big QRZ reader, but a friend sent me a link to your query, as he thought my recent success in using a low-dipole on 80m, from an "unfriendly location", might just be what you needed to hear! :)
     
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  5. M0AGP

    M0AGP Ham Member QRZ Page

    A question for anyone out there for my education please: I understand why a more conductive ground is better for verticals - the “image current” flows in the same direction as the “real” current in the vertical.

    But is the opposite not true for horizontal antennas? Here the image current runs the opposite direction to the real current and acts to mainly cancel it out no?

    So would that not mean that a highly conductive ground is worse for lower horizontal antennas?

    Or is the picture not so simple?
     
  6. W9IQ

    W9IQ Ham Member QRZ Page

    The picture isn't quite that simple as the ground isn't only resistive. But for a horizontal antenna, the ground often improves the gain of the antenna when its height above ground is optimized. This is due to reflections from the ground re-enforcing the direct radiation of the antenna. If the ground was less lossy, the reflections would be even more beneficial.

    A good example of this is the simple, 1/2 wave horizontal dipole. In free space, away from all reflecting or impeding mediums, the gain of an ideal dipole is 2.15 dBi. This gain is defined as 0 dBd gain. Now take that same dipole and mount it about 1/2 wavelength above the earth and its gain can easily exceed 7 dBi or 4.85 dBd due to the re-enforcing reflections from the ground.

    - Glenn W9IQ
     
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  7. KA4WJA

    KA4WJA Ham Member QRZ Page

    Michael, et al,
    Just a brief clarification (and a big thank you to Glenn, for not hounding me on db vs. dB), the theoretical differences in zenith gain of a half-wave 80m dipole (used for local / NVIS comms) between excellent/very-good soil and poor soil conductivity is about 2.3db...(if I remember correctly, from my talks with the late L B Cebik), but these are of course at different optimal heights, etc...

    At very low heights, I've been interpolating data from my old textbooks and using my own anecdotal info....so, I am not making absolute value comments here, just approximations. :)

    In any case, the ground losses with a dipole that low are quite high, but with better ground conductivity it is better mitigated.

    Hope this helps.

    73,
    John, KA4WJA
     
  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Many people have been recommending vertical antennas for the OP, and if he wants to work DX without spending a lot of $ that's the way to go. It's what most of us who want to work DX on (80 or 40) do.

    However, OP may be dismayed by the idea of building a vertical antenna 60 feet high. If so, he should look into the inverted "L" (the solution I decided on for my own station) or a loaded vertical. You can work DX on 80m with a vertical only 30 ft. high!
     
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  9. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Unfortunately, that FCC map is very inaccurate for many (most?) parts of Central Texas. There was insufficient understanding on the part of those who drew it up how many different types of soil are included in the area they grouped together, and how the conductivity of the soil in much of that area (the Blackland Prairie, where I live) varies by extreme amounts with moisture content. They measured in someplace where the soil is very conductive, apparently while it was damp, and put a very good number on the map across an area where that number actually varies greatly.

    I suspect (but cannot know) that the map is similarly inaccurate in describing the conductivity of other areas, and I strongly urge anyone who needs to know what their soil conductivity is to measure it themselves, once when it is very wet and once when it is very dry.
     
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  10. KA4WJA

    KA4WJA Ham Member QRZ Page

    Yes, of course a vertical over a good antenna ground system would be good for DX....and his dipole, raised up at least a bit, would be good for local / regional work...
    But...

    But, since we don't know what his desires are....well, as I always answer the question of "what antenna is best?", the answer is: "it depends....on where, when, etc., you wish to communicate to".

    And, while nothing wrong with an inverted-L (of course over a good ground system as well), even a simple butternut vertical or other multiband vertical may be easy-peasy for him...
    But, again....we don't know what his desired use / application is....so, it's all just fun speculation. :)

    As for ground conductivity.....I probably shouldn't have even mentioned it here....as it can cause the discussion to veer off on tangents that probably won't be too helpful to Tyler.
    And, btw...Thank You to Dan, WB5YUZ, for informing us of the errors/inconsistencies in the old FCC Ground Conductivity Maps.
    But, as I wrote....it's probably a rather minor issue to concentrate on, 'cuz he really should just start by getting the dipole up a bit higher... :)

    73,
    John, KA4WJA


    P.S. to Glenn....thanks....I guess you got the message about my dyslexia, stigmatisms, eyesight issues, neuro issues, etc....so, now you grasp if I could actually see / read CAPITAL letters better and/or see and read certain letter combinations (and certain number combinations) better I'd use dB and mHz/kHz, instead of db, mhz, khz....not sure who actually sent you the info on me, but thanks to them as well....kinda embarrassing to just post it for the world, but oh well....that's life, huh?
     
    Last edited: Sep 17, 2021
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