ad: ARR

Loop-On-Ground Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Aug 1, 2018.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: FBNews-1
ad: Left-3
ad: L-MFJ
ad: Subscribe
  1. WN6F

    WN6F Ham Member QRZ Page

    Jerry - I found the problem with my common-mode!

    Metric thread coax jumper AND it didn't even have any teeth inside - just flat. I guess depending on which way the wind blew, or maybe temperature expansion, that got flaky. Arrrgghhhh.

    Thanks for making me dig. I removed the commercial choke at the rig, and no problems. Although I guess I'll leave it in for engineering practice.

    It worked so well, that it cured a related antenna project issue that I'll put into it's own thread.

    tnx agn !
     
  2. WN6F

    WN6F Ham Member QRZ Page

    Underground antenna - yeah, not going there. I have that book / reference too.

    The point of the pvc just *barely* underground is to provide a gap between the soil and wire, and not to totally cover the top either. For RX ONLY.

    That other project from the old days to me is a one-off joke. Heh, just like trying to xmit into the on-ground loops, with about 30-40db ground loss, you'd have to pump a KW into it, to get what - about 100 milliwatts erp? That's too extreme. :)
     
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    OK then quit listening to them. They do not know a LoG antenna is RECEIVE ONLY.
     
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Perhaps you should read my post with the proceeding post as context.

    That's exactly what I was telling the person that posted a query about using the LOG as an indoor transmit antenna. It would make a terrible transmit antenna and only sees application as a receive antenna. I understand that fully as do most of the folks who have contributed to this thread.
     
    N0TZU and AJ5J like this.
  5. AJ5J

    AJ5J Ham Member QRZ Page

    OK, but for what it's worth, 9 out of every 10 gophers polled* swear by them---I kid you not! Until KK5JY came up with his LoG idea they were 100% in favor of their completely underground antennas. To each his own, though.

    73,

    Jeff



    *(source: 2018 ARRL** poll)


    **(American Rodent Radio League)
     
  6. WN6F

    WN6F Ham Member QRZ Page

    In regards to common mode with this antenna, I think I have been giving out some wrong information. Pretty sure of it.

    I have been re-reading some of W8JI's information about common mode not changing patterns of verticals, but perhaps skewing or filling in nulls on beverages. But what about our antenna?

    In the case of the canonical KK5JY log, I added a "5th wire" to the loop for modeling. Basically just an inline extension to one of the existing wires. Wanted to see what that would do to the pattern emulating "common mode" of a sloppy 15 foot unintended extension.

    SURPRISE: based on my limited modeling skills, I see no major change to the overall "squashed bowl" pattern, although very low down angles may have changed a bit. BUT how about an additional 2-3db increase in level!!

    Want 4-6db ? If you have the room, put another 15 footer extension symetrically to your original extension. (At this point, just put up a larger loop right?)

    Here's the problem - I've reached the point with my limited modeling skills and other than "by ear" testing, I don't want to go down the "magic antenna" path with wrong information. I need some skilled backup to truly model this kind of stuff.

    This is a slippery slope. So what if I want a simple "extension" - I already have one - my feedline. So instead of an isolator at the feedpoint, how about purposely using an autotransformer (sacrilege!) at the feedpoint, and 15 feet down my coax, I put an isolater *there*. Basically forcing common-mode of the coax for 15 feet to act as an extension.

    See what I mean - these derivatives are seemingly endless with some small tweaks here and there, so apologies to KK5JY, and I advise anyone to stick to the canonical project details first.

    I'm starting to doubt myself - I don't want "magic" antennas, which I may seem to be heading down that rabbit hole.
     
  7. K4SAV

    K4SAV Ham Member QRZ Page

    There are several types of receiving antennas. The most popular ones fall into the first category below.

    1. For DX purposes the antenna should have maximum gain in the direction of the received signal and minimum gain in all other directions. Some of these types are Beverages, BOGs, phased verticals, phased loops, or single loops like a K9AY, EWE, flag, delta, pennant, and diamond.

    2. There are antennas that have a null at very low angles which is useful for reducing the effect of low angle local noise sources. Mag loops and vertical loops are typical of this type. These have two nulls in opposite directions and can help if the noise source is not in the same direction as a low angle received signal, but may still be a help if the received signal is at high angles and in the same direction as a local noise. The response in other directions of these loop antennas is such that propagated noise will not be attenuated very much, so it is very limited at reducing atmospheric noise, which can, and does, sometimes come from all directions.

    3. There are other antennas that have good high angle response but poor low angle response. These can help the signal to noise ratio on high angle signals but response for DX signals will be very poor. The LOG and a dipole on the ground are examples.

    4. An omnidirectional antenna like a single element vertical can have good low angle response for DX. However it receives noise signals from all directions and is generally not regarded as a good receiving antenna for DX.

    For DX purposes RDF is a popular metric for rating the effectivity of antennas. DMF (reference ON4UN) is also a metric but not often used. Using 20 degrees elevation as the reference, here is a short list of RDF numbers for a few popular antennas.

    Antenna type _____________________________ RDF _____ Gain dBi at 20 deg el
    LOG 15 ft / side 160 meters 1.5 inch height _____ 2.0 ______ -42
    Single 1/4 wavelength vertical, average ground __ 4.4 _______ 0.3
    K9AY 160 meters __________________________ 7.3 ______ -27
    Dipole at 1/2 wavelenth height 80 meters _______ 7.7 ______ 6.7
    *BOG single direction, 350 ft on 160 meters ____ 9 to 9.5 ____ -16 to -18
    Beverage 1000 ft 160 meters 10 ft height _______ 12.9 ______ -7.7

    * BOG numbers are measured. BOG height was 1.5 to 2 inches. Gain is highly dependent on exact height and ground moisture content. I estimate RDF at about 9 to 9.5 by comparison to other known antennas. NEC does not compute the correct answer for a long BOG. NEC becomes more accurate for shorter wires on the ground, so it may be useful for something like a LOG. NEC calculated numbers for a 350 ft BOG is RDF 10.5 and gain -16.5 dBi.

    Minor variations in these numbers are possible depending on the antenna termination value used and the equivalent ground resistance. No feedline loss is included in the numbers above.

    Jerry, K4SAV
     
    K7TRF likes this.
  8. AC6LA

    AC6LA Ham Member QRZ Page

    This seems like a good opportunity to put in a plug for a free tool which might come in handy. Given the 3D pattern data produced by any of several different modeling programs (EZNEC, AutoEZ, 4nec2, Antenna Model, or MMANA-GAL) the tool can show different metrics such as Average Gain, RDF, and DMF.

    3DMetrics.png

    The tool can also use 3D data from one program, say EZNEC, and show a 3D pattern plot using a different program, say 4nec2. Here is EZNEC sample model NBSYAGI.ez at 60 ft above Average ground with a 1 deg step size, EZNEC 3D plot on the left and as shown with the 4nec2 3D viewer on the right.

    Compare3D.png

    Note that there is no need to open or calculate the model directly in 4nec2.

    The tool is called XLGTa and can be downloaded from here:

    https://ac6la.com/xlgta.html

    Dan, AC6LA
     
  9. KN6CSB

    KN6CSB Ham Member QRZ Page

    Been following this thread..
    interesting, but am I to believe a loop wire on or very near the ground will outperform the longest wire you can get up the highest height for RECEIVE only?
     
  10. AJ5J

    AJ5J Ham Member QRZ Page

    Not if your objective is increasing the SNR which is the usual reason for installing a separate receive antenna.
     

Share This Page

ad: hrd-2