Loop-On-Ground Antenna

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

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  1. WN6F

    WN6F Ham Member QRZ Page

    Alternate setup using 9:1 UNUN

    Although not the same as described at KK5JY's site, I get similar results using a different setup with an open-loop:

    1) 9:1 UNUN - typically used for non-resonant wires antennas.

    2) Use the normal wire attachment at the UNUN to form 3 sides of a square.

    3) At the ground terminal of the UnUn, make the 4th side of the square, but don't connect the loop together. Just an inch or two separation. Not critical.

    4) Be sure to use a common-mode choke on the feedline. Preferably somewhere close to the loop with a jumper, but the jumper length does not appear to be super-critical - at least on the low bands.

    You just don't want to fool yourself with a complicated mess of a common-mode random wire, so choke it!

    Handy for those who want to just get a taste of what's possible with perhaps a 9:1 unun sitting on the shelf, OR for those who simply can't move their log to a new location, and have tried changing corner feeds and there is still that nasty little squeal. Try this option.
     
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  2. K2AR

    K2AR XML Subscriber QRZ Page

    I temporarily set up as an experiment two 132 foot circumference loops on ground spaced 80 feet apart and phasing them with a DXE NCC-2. The results were quite surprising. I was able to take a station on 160M that was 10 over S9 and knock it down to S3. I was able to hear clearly a Greek station on 80M on the LOG pair and barely able to hear him on the invert-v. I found that this LOG pair was good up to 30M and drops off rapidly on 20M and above. Preliminary results seem to indicate that the phased LOGs provide better front to back and better S/N than my dual reversible 265 foot beverage on ground antennas. One other interesting note is that there appears to be minimal to no interaction with my tower and 160M transmit antenna 60 feet away from the edge of the closest loop. Still have more testing to perform but I am thrilled with the results so far.
     
    Last edited: Aug 1, 2021
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  3. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    Deleted.
     
  4. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    I have serious noise that the source(s) has yet to be found. The NCC-2 and 2 W6LVP loops spaced 20 ft each on rotors is my best receive antenna with my 15 X 15 ft LoG coming in close behind except I haven't phased it yet with another antenna. They are what get me on the air now 80 - 17 meters. Just wondering how did you come to the 80 ft spacing? Any thoughts on minimum spacing for a 15 X 15 ft loop? I have about a 45 X 40 front yard area the rest is concrete or gravel.
     
  5. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    I seem to have struck out on the noise problem being common mode. I bought a My Antennas CMC 330 -5K tried it inline with my vertical, yagi and the LoG no noticeable difference on the S-meter. Then put the CMC inline in series with a Balun Designs 1116di that has been in use outside shack window for a couple of year, no improvement noted there. I guess it is safe to say I don't have common mode noise?

    My LoG seems to do well with minimal noise 160 - 10 mtrs except for 30 meters where there is an S-2 or 3 noise level. The magnetic loops with NCC-2 phasing unit does give me a lower noise floor when checking on the SDRPlay 6 dB less occasionally more depending time of day. So I'm thinking of moving the feed point some, to a side (not a corner) to rotate the lobe more towards north than SE - NW. I need a good RX antenna on 20 & 40, 30 mtrs is fun but 20 & 40 are DX bread and butter :D. 15 - 10 meters are noisy but doable with the Yagi when conditions are good. Any thoughts on moving the feed point to get a quieter receive signal ... or other suggestion?
     
  6. K2AR

    K2AR XML Subscriber QRZ Page

    I was originally trying for one loop diameter spacing recommended by KK5JY but since this was a crude and temporary implementation, it ended up being 1.7x the loop diameter spacing. The current loops are 33 feet per side and when I decide on a more permanent installation, I will reduce the size to 25 feet per side and the spacing between loops will be at a minimum of one loop diameter (35 foot spacing). For your loop, 21 feet should be the minimum spacing.

    I'm in the middle of doing an experiment this evening with using one loop and phasing it with my bidirectional beverage on ground antennas and the results so far are very promising. I am also going to try adding a third loop to phase between NW/SE and NE/SW quadrants and if successful will add it to receive antenna farm, just another tool in the tool box.
     
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  7. K2AR

    K2AR XML Subscriber QRZ Page

    When I was playing with a single loop LOG last year before I installed my dual reversible BOGs, I found that in my application, feed point location didn't make any difference since it seemed like the single LOG was omni-directional, at least on 160M and 80M.

    A couple of suggestions I would make if you decide to run with two LOGs and phase them is feed them both the same way. An example would be if loop one is fed on the SW corner, the loop two should be fed the same way. Also try to make both feedlines to the LOGs the same length to make phasing easier.
     
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  8. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    Thanks!
     
  9. WN6F

    WN6F Ham Member QRZ Page

    Glad to hear the common-mode doesn't seem to be part of the issue. I still recommend a cmc even if it seems over the top, because common-mode doesn't *always* show up as noise - but can be detrimental with pattern skew.

    The larger 133-foot circumference we can ballpark as to it's highest frequency before the pattern goes totally cloud-burn or bizarre lobes by not exceeding a full wavelength. (934 / f Mhz). At 20 meters that would be funky with the 133 footer. 934 / 14 = 66.7 ft. Yup, too large for 20 meters unless you like cloud-burn. :) 30 meters might be just a lark, but at 133 foot circumference, 40m would be the highest I'd go.

    By ear, the skywave seems mostly omni. For me the biggest thing noticeable by moving feedpoints is down low, where you may be able to put a neighbors noisy battery-charger in a null. That might be more of a concern than trying to point the major skywave lobe towards a desired direction.

    I moved mine around using chopsticks in the ground to keep the shape, and once the best orientation was found, used ground stakes for something a little more permanent.
     
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  10. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    Thanks for the tip on the CM choke, will leave it in. I hope to experiment with the feed point point some in hopes of getting rid of a little more noise.
     

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