Loop-On-Ground Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AI5DH, Aug 1, 2018.

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  1. KK9W

    KK9W Ham Member QRZ Page

    I like my LoG antenna. We call it the Poop Loop because it's the " " and my dogs can poop on it.

    Anyhow, for those with a transceiver without a dedicated receive antenna jack, here is what I am using.

    Ebay
    https://www.ebay.com/itm/Transmit-R...718616?hash=item23b394a518:g:En4AAOSwJclcOQZz


    Direct website
    https://www.sv1afn.com/en/products/trs-450-transmit-receive-switch-rx-interface.html

    He also sells in Amazon.

    I have mine powered by 3A power supply. You can leave it inline and without power it's bypassed and it will operate as normal with a single antenna. Power it on to switch to the loop for receive and the relays handle the rest when transmitting.
     
    PU2OZT and WZ7U like this.
  2. W1VT

    W1VT Ham Member QRZ Page

    https://www.dl1glh.de/gc.html
    Ground (Soil) conductivity and relative permittivity calculator
    for measurements with an open wire line

    Since this calculator and pages on how to use it were posted the cost of the test gear has dropped from $500 to $50.
    The NanoVNA is relatively affordable. The big cost these days is learning how to use it.
     
    Last edited: Jan 24, 2021
    WB5YUZ likes this.
  3. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    One way to infer ground conductivity is to construct a low dipole at the frequency of interest, measure feed point impedance, then model the situation and adjust the ground constants in the model to match the computed impedance to the measurements.

    N6LF describes this technique in his paper at https://rudys.typepad.com/files/soil-characteristics-qex.pdf , and it is briefly described in the 24th edition ARRL Antenna Book on page 3.33 - 3.35.

    I've used this method myself and showed results at https://forums.qrz.com/index.php?th...ent-of-ground-constants-with-a-dipole.696955/
     
    NQ8J likes this.
  4. K4SAV

    K4SAV Ham Member QRZ Page

    Like most antennas, everything"works". The real question is how good does it work compared to other antennas. You will find that the LOG antenna works very well for close stations but poorly for DX stations (confirmed by calculations and by testing). That antenna has high angle lobes. The table below compares the RDF number of several receiving antennas. The RDF numbers are for 160 meters. The numbera are different on other bands for the same size antenna.

    Antenna Type ______________RDF (dB) _____gain (dBi) ____Average Gain (dBi)
    LOG 15 x 15 .02/10 gnd __________2.8__________ -36.8________ -39.6
    LOG 15 x 15 average gnd _________ 3.1 __________-40.0 ________ -44
    LOG 15 x 15 .03/20 gnd _________ 3.4 __________ -50.1_________ -53.2
    1/2λ Beverage ________________ 4.52_________ -20.2 ________ -24.8
    Vertical Omni, 60 1/4λ radials _____ 5.05__________ 1.9 _________ -3.15
    Flag 11x22 __________________ 7.37 _________ -34.88 _______ -42.25
    EWE 10x25 __________________ 7.7__________ -28.1 ________ -35.9
    K9AY ______________________ 7.7 _________ -26.23 _______ -33.93
    1/2λ end-fire Beverage __________ 7.94 _________ -20.5 ________ -28.44
    1λ Beverage __________________ 8.64 ________ -14.31 ________ -22.95
    two phased vert's 1/8 λ spacing_____ 9.14 ________ -22.46 ________ -31.6
    BOG 366 ft __________________ 9.5*_________ -18* _________ 27.5*
    Small 4-square 1/4 λ per side ______10.70 ________ -15.79 ________ -26.49
    1-1/2 λ Beverage _______________10.84 ________ -10.88 _______ -21.72
    Small 4-square 1/8λ per side ______10.97 ________ -30.28 _______ -41.52
    Phased EWEs 15x40 ____________11.1 __________ -42.0 ________ -30.9
    Single 1.75λ Beverage ___________ 11.16 ________ -6.50 ________ -17.66
    2 Broadside 1.75λ Bev .2λ spacing ___ 11.36 ________ -3.51 ________ -14.87

    * BOG numbers were estimated by antenna comparisons. NEC calculated RDF of 12 dB is wrong.

    There are two methods of evaluating the performance of receiving antennas using NEC. One is the RDF number and the other is the DMF number. The RDF method, originated by W8JI, is the difference between the average gain and the forward gain at 20 degrees elevation. This is easily obtained from a single NEC calculation. The DMF number, originated by ON4UN, is more complicated to calculate and gives more weight to the rear half of the pattern. See ON4UN's Low Band DXing book.

    Many of the numbers above were calculated by W8JI. Some are my calculations. There is some small variation in the numbers depending on exact size and details of how the antennas are constructed. Also some small variation due to ground quality. For antennas lying directly on the ground NEC may give incorrect data if the antennas are long. For short antennas the amount of error may be acceptable. All numbers above are with average ground, except as noted.

    More info on RDF:
    http://www.w8ji.com/receiving.htm

    All this data is for 160 meters and for DX purposes because the numbers are calculated at 20 degrees elevation. If you wish to do antenna comparisons at other elevation angles (like maybe for NVIS) then you will have to do calculations at whatever angle you like, and not use the data above.

    Much can be said about the RDF numbers and what they mean. It isn't a perfect method of determining the best antenna for all locations, but overall it is very good for the average location. There may be cases where the noise in a particular direction makes it more desirable to have an antenna with a big null in that direction, and that may not happen with all the antennas above or with the antenna with the highest RDF. If the noise comes equally from all directions, or the direction is unpredictable, the antenna with maximum RDF will be the best choice most of the time.

    A local noise source can be nulled with an antenna like a vertical loop and that can be a big benefit for some people that have that problem. A loop doesn't do well at reducing atmospheric noise. The RDF number for a loop is very low.

    Jerry, K4SAV
     
    WB5YUZ likes this.
  5. W1VT

    W1VT Ham Member QRZ Page

    The advantage of small antennas like a 11x22 ft flag is that it is more easily moved around modest back yard than a Beverage to optimize RDF. I have nine small flags hanging between trees. One every 45 degrees and one aimed at the powerlines.

    I've only run one Beverage, and while it was great for hearing stations to the North on 80M, it wasn't long enough for 160M. I've taken it down in favor of Flags that cover 160 through 40 meters. The relatively high gain of a Beverage makes them great beginner antennas as you have more signal to work with.

    The other extreme is the Waller Flag. Two small loops phased for a really good pattern. Signals are so weak that it requires a lot of expertise to get it working properly. A feedpoint mounted preamp is required. But, it can offer low angle horizontal polarization when placed on top of a 100ft tower. Great for working DX when you have vertically polarized powerline issues that can't be solved any other way.

    Zak W1VT
     
    Last edited: Jan 24, 2021
  6. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Yes. It involves using a VNA to make measurements and then using a computer to do the calculations. Below is a link to measurements made by one ham, explaining his technique and detailing his findings. He found that ground conductivity varied widely across his relatively small area of measurement, which lends credence to the idea that in America we can't simply look at that FCC map and know with certainty what the ground conductivity is at our QTH:

    (Later) The link Zak posted in #142 is better than the one below: both describe the same technique, but the one Zak linked has a calculator!

    https://dh1tw.de/how-to-measure-ground-conductivity/
     
    Last edited: Jan 24, 2021
  7. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    15 ft by 15 ft - 60 ft. Coax Rg-6U from DXE. Also bought impedance transformer from DXE.
     
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  8. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    Has anyone tried a loop smaller than 60 ft to use above 20 meters like 17 or 15 meters? FWIW I have decent signal levels up to 17 mtrs on my 60 ft LoG.
     
  9. 2E0CIT

    2E0CIT Ham Member QRZ Page

    Hi Paul, I'm just down the road from you a bit. Probably the same soil. Hard to believe but I'm getting a reading of zero ohms DC on my multimeter from two 1.5 metre long 22 mm dia copper pipes banged into the ground at a separation of 5 metres!
    I'd be interested to see what readings you get on such a simple test. Possibly far too simple a 'test' to be of any real quantative use but interesting just the same.
    Soil is soaking wet London clay and right now if I dig a hole greater than 8 inches deep it fills up with water. There must be a way to calculate resistivity from this kind of simple set up?? ...(or maybe not :rolleyes:?)
    73, Jeff
     
    Last edited: Jan 25, 2021
  10. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    I respect the modeling (wish I knew how :) ), my LoG works, it fits on our 70X120 lot without need for adding supports and the cost was great. I have severe RFI noise here, between the LoG and a couple of W6LVP magnetic loops some IMO nice DX can be worked - LoTW doesn't lie. Propagation does a whole lot of the work.
     
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