Many thanks to SWLing Post contributor, TomL, who shares the following guest post:
Loop on Ground Part 2
by TomL
My previous Loop on Ground (LoG) experiment was useful which entailed connecting my Wellbrook loop amplifier to a 100 foot loop of speaker wire in the field at my favorite local Forest Preserve. It really brought in stations I had never heard before or strong stations in a more powerful way that made the audio really pleasant to listen to. This report will describe more experiments with smaller wire loops to see what the limitations are. 100 feet of wire is quite a lot of wire to mess around with especially in the cold weather or public places that do not have as much private space.
I don’t understand all the electrical interrelationships but a long posting at RadioReference.com had a great discussion about creating a 160-20 meters LoG receive-only antenna. It is 11 pages long but is worth reading how “nanZor” experimented with various parameters for general use. Kudos to him for documenting the findings as the design changed over time. You can find it here:
https://forums.radioreference.com/threads/160-20m-log-loop-on-ground.370110/
nanZor basically boils it down to a few guidelines.
- Keep it on the ground. Lifting the wire more than an inch or two decreased the lower angle signal reception greatly.
- Calculate the optimal length for one full wavelength of wire at the highest target frequency, say for example, the top of the 20 meter band (14350 kHz). 936/14.350 MHz * 0.9 velocity factor of simple insulated wire = 58.7 feet. You can round up to 60 feet, no big deal since this is broadband. The antenna should have a predictable reception pattern from 1/10th wavelength up to 1 full wavelength. Outside that range, the pattern gets “squirrely”.
- Using a 9:1 balun seemed to be a little better than a 4:1 balun at the antenna feedpoint. This gets into things I cannot measure and has to do with rising impedance as a loop gets closer to ground level. I am not sure but I think my Wellbrook amp has a built in 4:1 balun and it seems to work just fine.
- Make sure to use an RF Choke at BOTH sides of the feedline coax cable. He was adamant that the loop can get easily unbalanced and allow noise into the antenna and/or feedline and so it must be isolated and the ground allowed to “float” in his words.
Personally, I also wanted to use less wire and happened to have a length of 42 feet of landscape wire which should work well below 5 MHz with the Wellbrook amp engaged. Results were not bad even though on hard frozen ground. Signal levels were down a little compared to the 100 foot of wire. Here are a couple of examples, first one in a fast food parking lot with a grass field next to it and second at the usual Forest Preserve parking lot on a grass field. I made sure that my car blocked the view of the wire so people would not get nervous!
La Voz Missionaria, Brazil:
Voice of Welt from Issoudun France in Kurdish:
These are not necessarily “DX” but definitely good for SWLing. I like the signal strength with the amplifier inline at the antenna feedpoint and I did not have to use an RF Choke at the receiver side as was suggested.
I had a 75 foot long insulated wire and used that at the Forest Preserve parking lot on a couple of different days. Lower frequency signal strength and signal/noise ratio improved a little bit to be noticeable.
US Air Force HFGCS “numbers” station. Remote controlled from Andrews or Grand Forks bases (https://en.wikipedia.org/wiki/High_Frequency_Global_Communications_System), there was no way for me to know which of the 6 transmitters it was coming from:
BBC from Tinang Philippines in Korean:
Then, as nanZor suggested in his postings, I purchased a 9:1 balun/RF choke (it has both a balun and an RF choke built-in) from Ham Radio Outlet and put that in place of the Wellbrook amplifier.
I have not worked with it, but it is reported that the Nooelec.com v2 model is cheaper and works just as well – https://swling.com/blog/2019/10/the-nooelec-balun-19-v2/
Examples below with the 42 foot loop and 9:1 balun/choke, no amplifier:
KSDA, Agat Guam in English
WB8U doing a POTA activation of Leavenworth State Fishing Lake
VOLMET weather, Shannon Ireland
HCJB Quito Ecuador, probably in Quechua
As a side note, there is a posting that mentions low-angle DX is better with regions that have better “ground conductivity”, salt water being the best. I have no way of verifying this. See post# 126 by KK5JY Matt.
So, bottom line is that a Loop on Ground can be useful for pleasant SWLing and portable. Best to use it on grass, not asphalt. The loop amplifier is useful to get signal levels up if you have to use a smaller loop size but the signal/noise ratio will suffer due to its smaller aperture. And, warning, the public will find a way to trip over the wire no matter where you set it up (I may try putting the wire around my car if I can park on a grass surface and/or use the gaudiest, brightest neon green or orange wire I can find – they can’t trip over THAT, can they?).
TomL
Thanks, Tom, for sharing your update. Obviously, the LoG is working brilliantly. It’s amazing that you got such clear reception from the parking lot of a fast food restaurant. If you were using a vertical instead, I bet signals would have been buried in the noise.
I can also relate to people tripping over antenna wires. I remember one POTA activation recently (the first activation in this three park run) where I intentionally laid my counterpoise on the ground, off a foot path, in the brush and where I couldn’t imagine anyone ever stepping. Ten minutes into the activation and for no reason, someone walked off the path, into the brush, and it snagged them. Maybe I’m just a Ninja level trapper and never realized it!?
Thanks again for sharing the results of your LoG, Tom. Inspiring!
Hi Andrew,
I don’t know if you have tried some bigger LOG’s, but they are offering a better SNR compared to the one you have tested in this review. As you, I have made a number of test setups during the past year. The one that offered good results is a 40 meter (131 Ft) model lying flat on the ground without any elevation. If I elevated it with 30 cm (1 Ft) its SNR became worse due to several local interference sources coming from my neighbours. At present a big LOG of 200 meter ( 650 Ft) is used wich is 50 meter further from the houses. This one is also lying flat on the ground between the trees. The SNR was raised by 7 dB on average over the 100 kHz to 30 mHz spectrum. A quad shielded RG6 coax is used and two common mode chokes and a 3:1 balun. All is home brew stuff. I tried 2:1, 3:1, 4:1, 6:1 and 9:1 baluns but the 3:1 is measured to be the best performer. The common mode chokes are made with FT240-75 material and the balun uses a FT140-77 core.
A ratio’d balun probably is fine at HF, but I tossed mine years ago on my coaxial LoG. The reason is because even at 148′ the loop will be low impedance at MW and especially LW. Impedances aside, I did not find much signal transfer difference with or without a balun even at HF frequencies anyway.
A 1:1 choke can help with common mode and possible balance, if needed. Again as with the balun, I did not even need that, though I do have a few snap ferrites on the feedline just in case. YMMV.
I am not too concerned about balance due to using a shielded coaxial loop, as it should help balance the antenna by design. See “ideal coupling method” at W8JI’s page on magnetic receiving loops:
https://www.w8ji.com/magnetic_receiving_loops.htm
Admittedly, at HF my LoG is not a small receiving loop, but it does become one at MW and lower.
Could you please offer some more details about the “coaxial LoG”, I’m really curious to understand how it’s built and connected
As for the BalUn for the “standard” LoG, I’ve tried 1:1 and 4:1, but I found that the 9:1 “as for the book” is the one which offers better overall performance, as for the choke, about 18 turns of thin coax around a #43 material core placed right after the 9:1 transformer and hosted inside the same box will take care of most sins :), then one may decide to place some chokes along the coax, but that’s usually optional
A way to avoid people stepping over your LoG when you go mobile may be using some red/white (or the like) taping like the one used in buildings and road works, just lay it along with the wire so that it will show where the wire is laying … and in case someone asks, just tell the truth (avoiding someone to step over my antenna)
Thanks Robert and Andrew for your thoughts. i am also curious about a coax loop on ground but I wanted something simpler, using just wire at this point. I am concerned that a coax with a soldered phase connection at the top of the loop might be too fragile for portable use. I could be wrong but just want to keep it simple for now.
I have used speaker wire, landscape wire, and even three conductor outdoor extension cord all with similar results. 18 gauge speaker wire seems just fine and easier to carry and setup. I did not do extensive testing with different kinds of balun ratios because I guessed that it might be a waste of my time. I will let others do that and report any improvements.
I do prefer either the 75 or 100 foot circumferences but sometimes do not have the room to throw that down. The 42 foot amplified fits nicely around the car and may have to do at times. So I need to balance convenience vs. optimal performance.
Hi Tom !
Thin wire will do fine for a portable antenna setup, but for “home” setup I’d recommend using some thicker insulated wire (AWG#14 or the like), since it will “survive” better to a permanent installation, also, in such a case a nice “trick” is to slide the LoG wire through some teflon rings and then use some cable tiers to lock the rings to the holding stakes, with such a setup it will be possible to change the antenna orientation just by (gently) sliding the wire so that the feedpoint (balun box) will move from a corner to the adjacent one, this will effectively “rotate” the antenna by 90° 😀
As for feeding it, I’ve the NooElec v2 and found that it works just fine with the LoG, plus it’s really cheap, so not willing to wind your own, it could be a good pick; also, I believe that the LoG doesn’t need an additional preamp, I agree with KK5JY about the fact that the receiver built-in preamp will offer more than enough preamplification, also, if you are transmitting too, the LoG will pair well with a transmit antenna, in such a case you’ll use the transmit antenna for TX only and the LoG for RX only, the combo may offer surprising results ;-D
It is built with RG-6 coax since I have lots of it available. The inner conductor is the actual loop anteanna. The shield is broken at the far side opposite from the feedpoint, and the the shield is grounded to a ground rod near the feedpoint.
Basic idea and drawings here:
https://www.hfunderground.com/board/index.php/topic,29940.msg114696.html#msg114696
Thank you for the informations, never tried such a design; also and since we’re at it, did you consider the idea of modifying the loop to connect the shield and center conductors as in the “youloop” antenna ? In such a case the antenna would become totally ungrounded (no connection to ground stake), and to feed it one may use a simple transformer wound on a binocular core, the primary of the transformer (to the antenna) will have a tap in the middle so that the two ends will go to the center conductors from both sides while the braid (shield) to the tap, the secondary of the transformer won’t have any tap and will go to the feeding coax, with such an approach the loop will mantain its balance, plus it will be galvanically isolated from the feedline (which helps a lot with static) and, being insulated from ground (even if laying on ground), will greatly reduce atmospheric noise
If you have some RG6 around and want to try, I believe it may be a nice experiment
Hi Tom, sounds like you got catched by the LoG, didn’t you 😀 ?
As for the BalUn, I don’t know how the one you’re using is wired, all I can say is that the NooElec v2 is exactly wired as the original KK5JY one, that is a 9:1 transformer, such a config offers better performance since the galvanic isolation it offers allow to have less noise from statics, then adding an optional choke after the balun won’t be difficult and the choke may easily be hosted inside the same box hosting the balun