Loop-On-Ground Antenna

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

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  1. KF5LJW

    KF5LJW Ham Member QRZ Page

    Yeah that is what I thought too. What good is an antenna pinned down on the grass and dirt? Answer was surprising to me come to find out. I acquired a SDR Receiver SRDPlay RSP2 FWIW to integrate and use as a Pan Adapter and play around with. Secondary reason is to listen to Commercial AM Broadcast, 160, and 80 meter bands. Even see if I can pick up NDB's.

    The RX has 3 Antenna Inputs to aid breaking up the broad spectrum of 100 KHz to 2 GHz to spread across 3 antenna systems. I started a thread asking for ideas on broadband antennas. Did not get much traffic in that thread, but I did get a couple emails about giving LoG (Loop On Ground) a try for frequencies 100KHZ to up around 15 MHz. Only requiring 60 feet of wire laid on the grass in a 15 x 15 square pattern is so simple, and I had the wire, I gave it a try.

    Mind you initially I did not measure things out or use any kind of Balun or Transformer, I just wired it in direct to the Hi-Z Antenna Input (1000 Ohm Balanced) terminals on the RX. At first I thought this LoG is not worth a flip, I lost 10 to 15 dbm of signal strength on the Spectrum Analyzer. Tuned in a distant AM Clear Channel Station about 100 miles away and it came in crystal clear with a SNR of 30 to 35 db. I could see stations I could not see using my 80/40/20/10/6 OCF Dipole. Not only could I see them, I could hear them pretty clearly with a SNR around 10 db.

    Encouraged, I went ahead and made a 9:1 transformer pill box to terminate the Loop to a 75 Ohm Coax ran inside to a 1:9 Transformer inside and terminated in the Hi-Z antenna port. Works better than my crude test model, so I am pleased.

    Yep I lost 10 to 15 dbm of signal level using my OCF Dipole up at 25 feet. However the Noise Floor fell from -100 to -95 dbm down to -140 to -135 dbm. So I traded 10 to 15 dbm of Signal loss, for a 15 to 20 db gain in SNR. Well worth the trade-off.

    There are a couple of downsides, and one of those may be a plus for DX'ers. The big downside is the LoG Antenna is restricted to the lower HF bands. Some say up to 15 MHz. Not so much IMO. I would say 10 MHZ for me at my qth. However on the lower frequencies from 400 KHz up to 40 meters is excellent. Example I could never hear WWV @ 2.5 MHz or Canadian 3.3 MHz time signal on the OCF Dipole. The other downside is it is not great at NVIS reception. It likes the ground waves coming in at low angles on the low frequencies which can be a plus for DX.
     
    N5YPJ, KU3X, KX4O and 3 others like this.
  2. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Which loop on ground design did you use? I was considering something similar to this one, which a friend of mine has had success with: http://kk5jy.net/LoG/

    The ham who created that is on QRZ a lot too.
     
    N0TZU likes this.
  3. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Thanks. Just read through that link from KK5JY. Very good work and description of the LoG antenna and what to expect from it.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You can say you're using a LOG! Or a Beverage could be a BOG.

    Now, if you buried a Yagi underground it could be a YIG. But better would be a Yagi in ground, combined with a Yagi above normal ground, which could give you a YIN-YANG.

    I use a reflector in ground, or of course, a RIG.
     
    N5YPJ and AF7XT like this.
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    Inspired by KK5JY with my own tweaks. I left the loop size alone for now at 15 x 15. Major change was Core Material selection (I used 75) and I used a Toroid core instead of a Binocular core. My interest are in 200 KHz and 2 MHZ, and 75 is a better material for the LF and MF. You give up the high end above 15 MHz using 75 material which is no problem for me. The Antenna is for 2 MHz and lower.

    Really simple stuff. A Pill Box type Antenna Match with a 9:1 isolation transformer to 75 Ohm Coax and F Connector to run to my SDR.
     
  6. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Sounds good. And, yeah type 75 better for those LF bands.

    I am hoping to set one up soon. I have about 125 ft of rand new direct burry RG-11 the cable guy left me. I was thinking of an amp out at the antenna, but may just use one in the shack.
     
  7. K0OKS

    K0OKS Premium Subscriber QRZ Page

    I am wondering what, if any, effect metal tent stakes would have on the antenna if used to hold it down. I have some plastic stakes as well. Just curious if you had tried one or the other.
     
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    If you are going to use a pre-amp, do so at the antenna and use a LP filter.
     
  9. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Good call. Do you think a broadcast band filter would be necessary as well? While I am not right next door to any transmitters we have some within 10mi.
     
  10. KF5LJW

    KF5LJW Ham Member QRZ Page

    If you live near a AM Broadcast transmitter it may be necessary, and one SDR manufacture I just received yesterday, Airspy HF+, has an optional Bandpass Filter Board that can be added to the SDR..

    Best way to tell if you need a Pre-Amp is disconnect the Antenna Circuit and note Noise Floor level. Example say it is -140 dbm with antenna disconnected with a Terminated Receiver to a resistor or dummy load. Now connect Antenna and watch Noise Floor. If the Noise level comes up in the band of frequencies of interest, You do NOT need a Pre-Amp and adding one will not gain you anything. In fact can make a Noisy location even more noisy.

    As for me my Noise Floor comes up 3 or 4 dbm when I connect my loop. But we are talking real Low Noise. With an antenna my Noise Floor is down around -145 to -150 dbm. Connect loop and it comes up to -140 to -145 dbm. On the flip side if I use my OCF Dipole the Noise Floor jumps up to -100 to -95 dbm.

    For me at my location the LoG works because I live in a high noise area. Sure signal levels are down 10 to 15 dbm from my OCF, but I lost -45 dbm of noise. So now I can pull in signals I cannot even see on the OCF. Example one Clear Channel Station I listen to comes out of Tulsa OK, (KRMG @ 740 KHz) I could only pull in at night and was noisy as could be. With the LoG I can pull it in during the day with about 10 to 15 db SNR, and at night crystal clear with 30 to 35 db SNR. One heck of a difference.
     

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