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Loop On Ground Antenna

Discussion in 'Amateur Radio News' started by KD5W, Jul 18, 2021.

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  1. UT7UX

    UT7UX Platinum Subscriber Platinum Subscriber QRZ Page

    Modeling software takes the ground into account unless option 'free space' is chosen for particular simulation. So I believe in antenna simulations (and physics overall) more than in ham tales: real antennas perform as close to simulation as carefully they've been simulated. :)
     
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  2. UT7UX

    UT7UX Platinum Subscriber Platinum Subscriber QRZ Page

    Take them with a fork and put them into the mouth. For better conductivity it is mandatory to add more chile sauce. That's all!
     
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  3. MW1CFN

    MW1CFN Ham Member QRZ Page

    The point I was trying to make is that models don't take the topography into account (i.e. the enhancing, or degrading effects). That's what HFTA does. This is where the importance of an antenna's environment becomes very, very clear.

    Example: two 3-ele Yagis in different locations within Wales. Much the same antenna, but very big differences, notably at those all-important low angles. Note: this is taking intrinsic and ground gain into account. If unreasonable critics want to complain, I can't help you if your environment is more akin to the red line.

    [​IMG]
     
    Last edited: Jul 24, 2021
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  4. W1YW

    W1YW Ham Member QRZ Page

    Not true.

    What we can't do is try to ignore the facts on how antennas work, when that information is provided us.

    Put very simply, here is how such loop antennas work as you start from the ground (and increase in height as a function of wavelength):

    1) ON THE GROUND/ VERY LOW HEIGHTS-- the transmission line effect produces an out of phase excitation that phase-cancels, thereby lowering the radiative efficiency to poor performance (irrespective of other losses which also occur);
    2) AT LOW HEIGHT-- the transmission line effect diminishes and the radiation is launched towards the zenith and HIGH angles, providing localized NVIS communication;
    3) AT MODERATE HEIGHTS-- the launch angle is in the 20-40 degree range providing short skip advantages;
    4) AT HIGH HEIGHTS ('high and clear' as you said)--the launch angle decreases and approaches the horizon, providing longer skip and fewer ionospheric bounces--which means less propagation attenuation. You lose roughly 10 dB per hop. Hence best DX is fewer hopes.

    73
    Chip W1YW
     
    Last edited: Jul 24, 2021
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  5. W1YW

    W1YW Ham Member QRZ Page

    [/QUOTE]

    British citizens are referred to as 'Brits'. No ethnicity nor disparagement there, nor intended. Purely descriptive.

    All the antenna modeling programs I use include topographical effects.

    These statements do not obviate the physics inherent to LOG antennas--which includes cancellation from out of phase transmission line effect. You can't arbitrarily invoke other factors to shore up the dominant attenuation caused by the transmission line effect--it still dominates the performance in a highly negative way.

    Antennas placed on the ground are poor choices for performance--in all circumstances. Physics defines that fact.

    It is important that our fellow radio amateurs are not misled to believe that laying a loop antenna on the ground will ever be useful as an antenna with something beyond poor performance.
     
    Last edited: Jul 24, 2021
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  6. W1YW

    W1YW Ham Member QRZ Page

    On topic--

    ANY implication that the topography of an environment will make a LOG antenna--on the ground--work beyond poor performance is unsubstantiated and does not see support from the physics.

    Yagi-Uda (raised)antennas can benefit from topograohy because the launch angle is not pushed up by the 'mirror image effect' of ground--because the ground is no longer perpendicular to the antenna, over many wavelengths. The topography changes the mirror. Hence the launch angle is not driven to higher angles.

    That does not have any bearing in diminishing or making up for other physics effects--in the LOG case, the phase cancellation caused by the transmission line effect.

    It is unscientific and without basis to imply that the transmission line effect is overcome by other physics effects. If that is the case, show us. Use as much math as you like: I will be happy to look it over.

    73
    Chip W1YW
     
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  7. VE3VXO

    VE3VXO Guest

    And here, I thought field strength measurement was the last word in describing how an antenna performs. Good to know we don't need that anymore.

    I wonder how many actually read KK5JY's page? So busy pontificating (especially one...you know who you are) about efficiency. Matt says very clearly on his website that this is an inefficient antenna! You can compensate for that lossiness with receiver gain of which modern rigs have more than plenty at the low end of HF for which this antenna was intended. Connect and disconnect the antenna and see if the noise level increases with it connected. Yes? You have enough gain. You have also missed another jewel too. This antenna has a response which holds down to very low angles and therefore hears local as well as DX signals. How else are you going to get a low angle response in a restricted HOA situation? Having a combination of this antenna (and now a phased pair of them) along with a vertical loop I can attest that there are many days where I prefer to be listening on the LoG array and some few occasions where I get better copy on the conventional antenna. When the neighbor fires up the plasma TV though, it is no contest, and I would be turning the rig off in frustration if it weren't for the LoG where the noise practically vanishes and the AGC restores the signal level. Same goes for switchmode hash and other local noise. You really should try one before disparaging this idea with no actual experience to speak of. Would I prefer a horizontal Waller flag at 120ft? Yes of course but that will never happen for me. I am hearing DX on 160m now though which I never could before with the local noise. I suspect I could even get some efficiency back by resonating it, but that is another subject.

    Someone made the comment that 75 ohm cable is better. Just use what you have, you can simply adjust the turns ratio on the isolation transformer for 50 ohm cable whish is what I did. LMR-100 is very suitable, affordable, easy to work with, easy to hide, and is double shielded, and I suggest a CM choke with decent isolation at low HF. I put 14 turns of the LMR-100 on a FT-240-31 torroid for this purpose in the same box as the isolation transformer. A hollow fake garden rock gives it stealth.

    upload_2021-7-24_11-20-19.jpeg
     
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  8. NN4RH

    NN4RH Premium Subscriber QRZ Page

    I don't know about "loop on ground" antenna ... but I once made a 1000 mile contact with a "disconnected-coax-feedline-laying-on-concrete-patio" "antenna".

    It was not an "experiment", and I did not make a youtube about it. It just happened. By accident.

    So does that mean I would make that a permanent installation for my station and rave about it being a "good antenna"?

    Not hardly. Among other things, it was a b**ch to tune.;)

    I eventually I did an "experiment" and discovered that reconnecting the disconnected feedline into the actual antenna proved to be a much better performer.
     
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  9. KC2G

    KC2G XML Subscriber QRZ Page

    My 120' circumference loop-on-ground works quite nice with a 6:1 transformer and a DXE-RPA-2 preamp. Hears quite well from 160 up to 30, and gets less noise — probably because it sits as far from my house as I can make it, while my big skywire loop passes right over the house. It's simple and effective and that's really about all there is to it.

    Lawnmower has never been a problem — if you keep slack out of the wire and tack it down good, it will sit lower than the blades and not tend to get disturbed by the wheels, and after it's been installed a while the grass roots will start to pull it even further down.
     
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  10. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Modeling is the last word in describing an antenna compared to the debating and arguing which is occurring here. The great news is we have not had to 'Argue" about antenna performance for nearly 30 years. We have excellent computer models.

    A FSM gives only a single measurement at single point in space.

    If you spent days taking hundreds of measurements from, say this loop, you would still poorly describe the antenna compared to what we can derive and and understand from a numerical model. Few, if any hams have the equipment, interest or time to take hundreds of measurements of antennas to derive a model.
     
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  11. K9WW

    K9WW Ham Member QRZ Page

    quote
    K9WW said:
    "Please note that the author is comparing the LOG outside to a dipole in his attic. Apples and oranges."

    Kirk K9WW

    KD5W said:
    "Absolutely true. My dipole 20ft in the air, outside would smoke the LOG. And the beverage I had at my last house would beat the dipole some of the times. But on a deed restricted lot I cannot put my trusty dipole in the air so I am experimenting with various antennas that can be hidden to the HOA prying eyes.

    I honestly don't think I will find anything better for my HOA situation than my trusted Terminated folded dipole(receive only) hidden in the attic so when I try another antenna I do compare it to the dipole. Is it a fair comparison of antennas? Probably not, but it is a fair comparison of which one works best for my situation. Since many hams are living in HOA restricted homes they want to know what their options are and what they should try. I hope my videos gives them a starting point or at least shows them options they might have not thought about. Real world application should always be more valuable."


    Getting back to the point of this whole thread, the author has a 40m dipole in his attic, according to his QRZ page, right above all of the RFI generating devices in his house. He compared his LOG, away from his house (unknown just how far) and posted the video of his results. The video shows quite clearly how his LOG compared to his attic dipole for receiving signals at his QTH. YMMV!
    His attic dipole might work OK for transmitting but is undoubtedly noisy on receive and he found a viable solution in the LOG.

    My suggestion is that he consider a flagpole vertical, erected as far from his house as possible, with an auto-tuner at the base and with as many radials of whatever lengths he can pin to his lawn.

    73, Kirk K9WW
     
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  12. AA4MB

    AA4MB XML Subscriber QRZ Page

    I'm sure I must have overlooked something in the conversations, because I thought that this antenna was 'receive only' as it was clearly specified in the video screen intro. I could be wrong, but it sounds as if we diverged into transmitting antenna theory complete with take off angles, etc. From my mind, the facts are inescapable. In the posted video, 4 out of 5 signals had a better SNR in receiving - plain and simple. Maybe it's psychological and my brain is convincing me of something which isn't true. I know that the power of suggestion is significant. Anything is possible, but I can tell you with certainly that on receive, the LoG as shown is not one iota worse than the attic dipole for at least 4 out of 5 of the examples. Maybe I'm just naive or plain ignorant, but the take from me watching the video is when you're in an HOA and you want to be able to transmit and receive as best as you can, I'm led into believing KD5W might be thinking about transmitting on the attic dipole and receiving on the LoG anttenna. Maybe it favors one part of the world better - on the majority of the signals shown. From the basis of the supplied real world recordings, I just may try one for the heck of it - for receive only. I don't really expect any ground breaking improvement in my receive SNR, but now I have to give it a shot - even if it doesn't last until the next time the lawn mower is started.

    Users of commercial receive only loops mounted a modest distance over the ground often tell you to ignore the receive signal strength and concentrate on the signal to noise ratio, due to loops having a lower noise floor from the get go. I know that a lot of stuff gets tossed into the blender - what type of loop, its size, where it's mounted, how it's oriented for a particular signal, etc. I thought that was pretty much a 'given,' too - but I'm not nearly as smart on the technical side of things as a lot of other hams I know. I'm always reading and love when folks step out of the comfort zone that we tend to live in and try something rather 'out there.'

    - Matt, AA4MB
     
    Last edited: Jul 25, 2021
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  13. KD5W

    KD5W XML Subscriber QRZ Page

    Sadly even flagpoles are prohibited in my HOA or I would do a flagpole vertical.

    You are correct, this is a receive only antenna.

    For transmitting, I use a 40m dipole in the attic and FT8 with 10 watts which I've been able to reach as far as Australia and New Zealand with, I am happy with that.

    For receiving, I also like playing with my SDR so I am always trying different antennas for fun. The terminated folded dipole also in my attic is all I need.

    I do like experimenting and seeing what works good for stealth in an HOA.
     
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  14. KM1H

    KM1H Ham Member QRZ Page

    It all depends upon the software and the users ability to properly apply it to a particular model....and then be able to properly interpret it.


    Modern antenna system engineers use a drone to do those measurement and ham hobbyists are often avid users of them even to lift a wire up over trees. Those results take all the guesswork out of the software and are really the last word.

    Carl
     
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  15. KM1H

    KM1H Ham Member QRZ Page

    Dont you think it would be more personally enjoyable to do that with 100W and CW?

    Ive worked over a hundred DXCC entities with 5W on 160-10M and also 19 on 160 with 100 milliwatts.... all on CW. No FT8 thankfully which I still dont consider real radio...just an opinion, take it or leave it.
     
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