We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissible in your locale.

Author Topic: LoG receive antenna, Loop on Ground!  (Read 9397 times)

Offline Antennae

  • Hero Member
  • *****
  • Posts: 652
  • CA, USA
    • View Profile
LoG receive antenna, Loop on Ground!
« on: September 12, 2016, 1628 UTC »
Its a loop flush on the ground. You can also phase the things for directionality!  Cool shtuff, mang.  Check out the website with pictures:
http://www.kk5jy.net/LoG/
California Coast
Antenna: random wire

Offline Pigmeat

  • Marconi Class DXer
  • ********
  • Posts: 6684
    • View Profile
Re: LoG receive antenna, Loop on Ground!
« Reply #1 on: September 13, 2016, 0846 UTC »
I like them. We had a particularly noisy summer about 14-15 years ago when no one was getting out well, not even KIPM which was running a buttload of power. I started screwing around with things after reading an article in ham mag about them. I was using around 145 ft. of wire, close to a full wavelength for the funny band. That thing was near dead quiet. I used a small MFJ tuner for it. I could peak the signal on the loop, then adjust the gain on the portable, a DX-398 like you have, to hit that sweet spot where the signal could be best copied. They're not really for gain, they quiet the noise down enough to allow what's out there to be heard.

If you wanted to boost the gain, you could unfasten the end of the loop going to the ground terminal of the tuner. It was still a very quiet antenna, but not a closed loop. It's something you have to experiment with. Sometimes the complete loop can be so lossy as to be near dead. I found that to be the case when using the big radios in the dead of winter with it, when I was sure it was going to kick butt. Different ground capacity and atmospheric conditions would be my guess. I'd unhook the ground side and the band would come alive, but it still wouldn't outperform a dipole cut to frequency and well elevated in the quiet season. Or a BOG for that matter.

Have fun with it. The ground doesn't freeze hard as rock out your way like it does where I live. It might prove to be a good all year antenna for you.
« Last Edit: September 13, 2016, 0848 UTC by Pigmeat »

Offline Josh

  • DXing Phenomena
  • *******
  • Posts: 4322
    • View Profile
Re: LoG receive antenna, Loop on Ground!
« Reply #2 on: September 23, 2016, 1619 UTC »
Some of the arrl antenna compendiums have on ground and in ground hf antenna articles. They make for interesting reading.
We do not encourage any radio operations contrary to regulations.

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1841
  • Tampa, FL USA
    • View Profile
Re: LoG receive antenna, Loop on Ground!
« Reply #3 on: October 24, 2016, 0020 UTC »
I have an 148' square loop on the ground. It is a "shielded" coaxial loop design. Why shielded? I have lots of RG-6 coax available, so I figured why not? Likely does not matter much, if at all, but anyway.

Interestingly enough, it is my primary LW, MW, and HF receiving antenna. I sometimes use a preamp, though it is rarely needed for frequencies under 15MHz.

I have attached my extraordinarily basic - as in Paint.NET ;) - antenna details below. I went for a loop size slightly larger than a wavelength at the 40M band, but being on the ground, the actual resonance could be (and probably is) much lower.

There used to be a dedicated balun at the feedpoint, but it offered little to no discernible difference, so it was replaced with a direct coaxial feed as depicted and several snap-on ferrites on the feedline. I do use a common mode choke (~3000-ohms rating at HF) back near the attached receiver, though it is not really needed either IMO.
« Last Edit: May 30, 2017, 0657 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
148' + 60' Loops-on-Ground | 31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline Aegir

  • Newbie
  • *
  • Posts: 1
    • View Profile
    • Email
Re: LoG receive antenna, Loop on Ground!
« Reply #4 on: February 19, 2024, 2022 UTC »
I know this is an old thread; what is the purpose of the shield break at the far end?  Your feed point is very simple to understand. I do not understand why the shield needs to be broken if it is a continuous loop, unless you're showing where the cable was spliced together. -Bryne N7BB

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1841
  • Tampa, FL USA
    • View Profile
Re: LoG receive antenna, Loop on Ground!
« Reply #5 on: February 20, 2024, 1132 UTC »
It is a magnetic loop design. Note the "Let's look at the ideal coupling method:" here:

https://www.w8ji.com/magnetic_receiving_loops.htm

An often-cited claim for a shielded loop is the design somehow blocking electrical fields to optimize reception of magnetic fields. Outside of maybe some slight near-field effects, a shielded loop does not really shield much of anything.

Instead the shielded design is more or less to help balance loop symmetry to potentially equalize differential currents and limit common-mode currents. Therein is why a "shielded" loop might improve reception if CMC is present on the feedline. If not, then there is not much, if any difference versus just a simple wire loop.

These days, I might would make some changes. I probably would use a mix 73 binocular ferrite with a 1:1 winding ratio at the feedpoint. Using 4 turns towards the loop and 4 turns towards the feedline should suffice in my experience. The result is an isolation transformer. You probably could just float the loop shield in such a config.



BTW, another often-cited LoG design consideration is software modelling might suggest a couple or so dB in directionality if feeding the loop at a corner instead of a midpoint along a side. Being realistic I kind of doubt any noticeable real-world difference.



Another popular alternative for a coaxial loop would be the NCPL design, which is basically a mobius loop. It might help a little with low-frequency performance for a typical-sized loop-on-ground antenna.

https://swling.com/blog/2020/04/diy-how-to-build-a-noise-cancelling-passive-loop-ncpl-antenna/
https://www.hamradio.me/antennas/airspy-youloop-lf-mf-hf-mobius-receive-antenna.html



All the above said, unless you have the coax available for experimenting, I would suggest first trying a simple wire loop-on-ground. 60' to 150' of whatever wire should suffice for MW to mid-HF. You might need a preamp towards upper-HF. Use an 1:1 balun or an isolation transformer at the feepoint, plus perhaps similar back near the receiver.

Case in point, my old 148' "shielded" LoG ended up buried under leaves, pine needles, and shifting soil/sand. A typical LoG is already well into negative dBs, and going underground can make the losses even worse. Mine was old enough to not bother with it anymore, so I eventually just deployed another LoG at a different spot. My current LoG is 148' of copper pet fence boundary wire with a LDG 1:1 balun at the feedpoint and a mix 73 isolation transformer near the receiver. The simple wire LoG seems to suffice for my purposes at the moment. YMMV of course.
« Last Edit: February 20, 2024, 1142 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
148' + 60' Loops-on-Ground | 31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

 

HFUnderground T-Shirt
HFUnderground T-Shirt
by MitchellTimeDesigns