Wednesday, May 4, 2022

The Loop-on-Ground Antenna For The Noise Challenged

In this article, we'll discuss the Loop-on-Ground antenna and how I've used it to advantage for mediumwave and shortwave DXing in an extremely RFI-ridden environment. We'll also discuss sources of RFI and how they might be minimized.

Those of us who have been in this hobby of DXing for many years are lucky to remember the days of no problematic electrical interference. My DXing days go back to about 1959 or 1960. It was about then that the modern-day light dimmer was conceived, using newly-developed thyristors and triacs to vary the "duty cycle" (on/off time) of the full AC voltage. It was the birth of the RFI avalanche.

Electronic hash proceeded quickly. Radio frequency interference (RFI) - the crescendo of noise on the bands - is becoming virtually impossible to identify and corral. Back in the 1980s when it started getting worse, it was still possible to identify sources and eliminate them using time-worn line-choke-suppression methods. Now, not so much. The genie is out of the bottle and it ain't going back in.

One of the best tools I have found to identify RFI is a spectrum analyzer. No, a $2000 unit isn't necessary. You already have one if you own an SDR receiver. I have an SDRPlay RSP1a, purchased at $119 U.S. and it's quite easy to take a look at any frequency from 10 KHz on up to see where the problem areas are. Spread a short wire across the floor in the house, connect it up, and you will see all kinds of mysterious RF. A pocket or portable sniffer receiver can work for this too but it's much easier to see the RFI's extent on an SDR receiver's spectrum display. The sniffer receiver is better used to locate the RFI.

I currently use my RadiWow R-108 as a sniffer receiver when walking around the house or property. This is used once the RFI "problem" frequencies are identified on the analyzer. Your Tecsun PL-380, PL-310, or other portable receiver can do the same.

The next two sections of this article, BIG OFFENDERS and ANTENNA SOLUTIONS FOR NOISY ENVIRONMENTS, are reproduced here for clarity, and as a re-introduction to low noise antennas. They originally appeared in my article The RFI Menace And Reduced Noise Antennas.


Let's go over the big RFI offenders to our DXing. The big offenders at my DXing home are:

My Hewlett-Packard 24 inch computer monitor. Huge, wideband, low frequency buzzing in a range across the VLF, longwave and lower mediumwave bands, particularly in the 300-900 KHz segment. The switching power supply creates some of this but the majority comes right off the screen's surface when the display is lit. Efforts to reduce this RFI have only been mildly successful, but luckily its range is only about 15 feet. The downside is the radios need to be within 15 feet of the monitor, particularly the SDR.

My laptop's switching power supply. I have a recent (2020) Acer Nitro 5, 15.6 inch, with AMD Ryzen 5 4600H mobile CPU. Huge, wideband, low frequency hash between 0 and 600 KHz. Virtually all of this disappears when running on battery only. You can't run on battery forever, however.

Old style fluorescent lighting, particularly the old 4 ft. shop lights. Best is to just keep them turned off.

Light dimmers. Don't use them. Keep them off or remove them.

LED light bulbs for house lighting. The bad ones create a high frequency hiss. Luckily the range is only a few feet, but the house is full of them now due to power saving measures. Use good quality LED bulbs. Philips has been highly recommended.

Low voltage lighting used in the kitchen. Lots of wiring through the walls go to a transformer box in the cellar. When the lights are on they inject an additional huge buzz at the lower end of the mediumwave band, peaking at about 550 KHz. The emissions from these range throughout the house. The condition is virtually eliminated by keeping the lights off.

A myriad of switching "chopper" style wall transformers. Some are much worse than others. Try to identify the worst offenders. I try to put all of these on power strips so I can switch them off when not in use.

Unknown sources of frequency spikes. Strong 10 KHz spaced spikes from 9 MHz to 16 MHz, peaking in the 9.5-9.9 MHz and 10.7-12.5 MHz area. This one is intermittent. It can last ten minutes or an hour or more, then disappears. I have not ruled out that this signal may be coming from the mains feed to the house.

**Note: this RFI source just above has been identified. It comes from a $2000 Fisher & Paykel kitchen refrigerator. Fisher & Paykel is a major appliance manufacturer which is a subsidiary of Chinese home appliance manufacturer Haier. It is a multinational corporation based in East Tamaki, New Zealand. In 2012, Haier, a major Chinese appliance manufacturer, purchased over 90% of Fisher & Paykel Appliance shares. Partial solution: wrapping the power line cord through two Workman RFC-1 snap ferrite cores has reduced the problem 50%. More cores have been ordered.

A new 43 inch Toshiba smart TV and DISH satellite box combo. Tremendously strong RFI, a high-pitched squeal in the LW and MW bands coming out of these boxes out to a 6-8 ft. radius, which then couples to lines. It might be possible to put these on a switchable power strip, but then you have the device reboot problem every time you want to use them. Satellite box boot time is often 5 minutes. That's a no-go.

Those are just the biggest offenders. Not mentioned is the RFI coming off the computerized de-humidifier in the cellar, the computerized water conditioning system, and the two computerized heat pumps hanging off the back of the garage.

So you can see the frustration. It's not practical to try to eliminate all of this RFI unless you'd like a lifetime career in RFI removal. I suspect this is the case almost everywhere.


Being a ham as well, I've experimented with just about every wire antenna you can imagine over the last 60 years. My days of winding power line chokes are over. Common-mode chokes, current isolators, et al, are the rage these days - these to reduce RF pickup on the feedline and to lessen the possibility of the feedline from becoming part of the antenna system. They can help, but they are a Band-Aid to the real problem. Why not lessen the noise in a different way? My solution is to build inherently quiet antennas which are resistant to noise, and feed them correctly

Three things are important.

1. Get the antenna well away and out of your house.

An end-fed longwire attached to your shack window fed with 15 ft. of coax across the floor isn't going to do it. If possible, on your lot, put the feed point as far away as you can. This, for starters, is one of the most important things you can do. Don't worry about cable feed length. Coax feed at mediumwave or even shortwave frequencies has minimal loss. 100 feet of the old 50 ohm RG-58 on mediumwave presents only about 0.37 dB signal loss, virtually unnoticeable. RG-6A TV coax, 75 ohm, is even less at about 0.28 dB per 100 ft. I use RG-6A here almost exclusively, as it is cheap and readily available through many suppliers.

So, get that feed point as far away from your house as possible.

2. If you can, choose an antenna that is basically a short circuit. What did you just say?

Loop antennas are essentially short circuits to high frequency impulse noise. Long wires, verticals, and dipoles are not. They are RFI magnets, and particularly so if they are not balanced antennas (the dipole is at least balanced). Much of the high frequency noise component of RFI is short circuited in the loop. Small loops are even better for noise suppression, but their drawback is they often need active amplification due to lower signal delivery. Loops work well when placed close to the ground and you don't need high supports for wires.

They can also be laid flat on the ground itself which reduces RFI even more. This is where our Loop-on-Ground antenna will come in.

3. Use an isolating transformer at the antenna feedpoint. Very important. Feed any antenna with a transformer-balun isolating device, even if it is naturally a 1:1 match. There must be no common ground connection between the coax feedline and the antenna, i.e., between the primary and secondary of the transformer-balun. The antenna should remain floating and the coax remain floating. This isolating-matching device does three things which help abate noise:

     1) Matching the antenna greatly increases received signal strength. Increasing signal strength often will raise the signal above the noise floor. Remember when receivers had preselectors to peak the antenna, which made the difference of hearing a signal or not? This is what a broadband matching transformer is actually doing - matching the antenna to the receiver across a wide range of frequencies.

     2) The transformer, at least the one we will use, totally isolates the antenna from the receiver, eliminating the direct wire connection and lessening RFI picked up by the antenna from transferring to the coax. Much of the RFI will be consumed in what I call the secondary, or load side (antenna side) of the balun, as it appears as a direct short to the high frequency component of noise.

     3) The transformer/balun reduces antenna loading because it presents a proper load impedance to the antenna. Loading down the antenna destroys bandwidth and lowers signal strength. Take a longwire for example. A longwire antenna has an inherently high feed impedance, generally 450 ohms, nothing near the usual 50 ohms of a receiver. With no matching device, the input signal delivered to the receiver is a simple resistance ratio. The signal is delivered through a 450 + 50 ohm series divider. The receiver gets 50/500ths of the available signal without the proper transformation. That's 1/10 of the signal being picked up by the antenna! No wonder my receiver can't hear!


Now we get to the Loop-on-Ground antenna, or LoG. The LoG antenna is another variation of the close-circuited loop, only it lays flat on the ground. It is also best fed with a balun. KK5JY has the preeminent article on the Loop On Ground antenna, with illustrations. Be sure to check it out. It is the inspiration for my Loop-on-Ground which I use for mediumwave and shortwave.

KK5JY's LoG antenna performs best from about 2-8 MHz, at about 60 ft. total wire length. Wanting to try a LoG for mediumwave, I decided to buy a 100 ft. spool of insulated, 18 gauge wire. These are readily available from Amazon for about $9. I ordered one and experimented.

KK5JY, being a ham, based his design on covering the 160, 80, and 40 meter ham bands. We will increase the loop size to cover the mediumwave band. It will be effective all the way up to the 31 meter band and beyond.

The Nooelec 9:1 balun connection

The LoG is generally arranged in a square and fed at one corner. It is somewhat directional, having an extremely flattened hourglass pattern, with slight nulls at the feed corner and the corner opposite the feed. In practice I have found its directionality hardly noticable. Both high and low angle reception are good, within its range, with high angle being predominant. Studies have shown that the pattern is similar to a big ball set on the ground.

Don't have concerns about low angle reception. As I write, I am tuned to 530 KHz at 3 AM in the morning here on the east coast of the U.S. On the channel fighting it out are CHLO-530, Brampton, Ontario (193 km @ 250 watts), and 530-Radio Encyclopaedia in Cuba (2300 km).

Best results are when the overall loop length is about 15% of a full wave for the frequency of interest. As stated, a 60 ft. total length works well for the 2-8 MHz range. It is usable to about 15 MHz, though sensitivity drops off above the 25 meter band (11.500 - 12.200 MHz).

Initial testing for KK5JY's 60 feet of wire on the ground were not encouraging in the mediumwave band. Signal strengths were down except at the very high end. 100 feet total wire length works out to an optimal 1480 KHz, and greatly increases the signal strengths throughout mediumwave. 120-140 feet should be even better. Ballpark ranges are thus: 530 KHz - 278 ft., 1700 KHz - 86 ft.

Lay your 100 ft. of wire out in a square, 25 ft. to each side, and feed it at a corner. Exact square shape is not paramount, but try to keep it as close to square as possible. Remember, loop area is important - we want as large an open area as possible. The loop can be layed right on the surface of the ground or pinned down with U-nails. Some have even dug it in an inch or two. This winter, mine has even been buried under 12 inches of snow for the last month, and the LoG has still performed admirably.

The loop must be fed with a balun and remain ungrounded. KK5JY's 2-8 MHz loop exhibited a feed impedance orbiting the 400 ohm range. That's about 8:1 for a 50 ohm coax feedline. I'm using a commercial Nooelec 9:1 receiver balun, available from Amazon for under $20. It has proven to be close enough, though I'm planning on experimenting with different homebrew toroid cores and turns ratios. My loop is fed with 100 ft. of RG-6A coax (75 ohm), though I've experimented out to 175 ft. I've found the 100 ft. minimum distance from the house to be adequate in relieving 95% of the noise problem. It is important not to ground any leg of this antenna as that will upset its balance. Also do not earth-ground the coax shield. Early models of the Nooelec 9:1 balun (v1) joined the primary and secondary windings electrically through a center-tapped secondary. Be sure to get the new version of the Nooelec balun. They have eliminated this connection.

The Nooelec Balun One Nine (v2)

The LoG is an excellent low noise performer. My 100 ft. length lying on the ground shows close to 15 db less noise than a 6x12 ft. flag antenna, with about equal signal strengths. Similar results were found with tests in the tropical band (60 meters). The difference gained is in the substantially better signal-to-noise (SNR) ratio. A 15 dB reduction in noise while holding the same signal strength as the small flag antenna is a 15 dB SNR improvement!

The antenna is fairly non-directional, so no competition is claimed with the directional beverage-on-ground (BoG) or traditional above ground beverages. Internet reports have made the claim it works well in some localities but maybe not so well in others. Discussion of ground conductivity under the LoG then ensued, with pros and cons. I suspect many dismiss it outright without really doing a little deeper experimentation. Initial reaction is always "how can this work if it is lying on the ground?"

Signals need only to break the atmospheric noise level by a few dB to be received. But first you must lessen the electrical hash so it is below that level. With the LoG, general atmospheric noise levels here are well under a microvolt from MW through 30 MHz, somewhere in the -110 to -120 dBm area, depending on the band. Remember, -107 dBm is one microvolt signal level, a very small signal. Check out KK5JY's page where he has produced some signal graphs.


The best way to show off the LoG antenna is to show its reception advantages on an SDR's spectrum and waterfall displays. Using an SDRPlay RSP1a and SDR-Console gives a dramatic result.

BEFORE - SDR using a 100 ft. longwire, run from shack window out to a tree. Longwire fed at the window through an RF Systems Magnetic Longwire Balun to a short length of coax to the receiver. The electrical hash is deafening, as seen in the waterfall.


AFTER - SDR using the Loop-on-Ground antenna and fed with 100 ft. of coax. No hash.

We are tuned to 530 KHz in both examples. It's 3:14 AM in the morning in western New York (display time is in UTC, 08:14). 

In the first example, on the 100 ft. longwire, look at the broadband electrical hash saturating the band. It is running S5 on the scale at left. There are signals there at the S8 level, but they are not intelligible due to poor signal-to-noise ratio.

Now, look at the second example, using the LoG antenna. No electrical hash. What you see on the spectrum display is the atmospheric noise level, just above S1, about 0.3 microvolts. The signals at 530 KHz are at S8, and we have multiple signals. In the headphones are two stations: On the channel fighting it out are CHLO-530, Brampton, Ontario (193 km @ 250 watts), and 530-Radio Encyclopaedia in Cuba (2300 km).

The difference is in bettering the signal-to-noise ratio. In the LoG example, signals are a full seven S-units out of the noise, proof-positive that an antenna lying on the ground can work. Again, don't worry about low angle reception problems. 530-Radio Encyclopaedia in Cuba at 2300 km has a calculated arrival angle of about 7 degrees.

I also enjoy SWLing. My 100 ft. LoG is effective to the 31 meter shortwave band and beyond to 25 meters. Better results for higher frequencies can be had by shortening the wire length some. One of my favorite things to DX is Asia as the sun sets there. If conditions are good, signals just pop on the 31, 41, and 60 meter bands with the 100 ft. LoG. Right now I am tuned to the BBC/English service at Kranji, Singapore on 9580 KHz (125 KW) as I write at 1115 UTC (15,100 km distant). They are arm-chair copy.

An excellent 16 page thread discussing the LoG antenna and matching techniques can be found on the QRZ forums. It is well worth a read.

Testimonial from that thread:

"Give it a try and post back here with results. I would like to hear how it works out for you. Just do not panic when you first hook up the antenna. Initially it will look like a Dumb (Dummy) Load because there is no noise, and signal levels will be down. But SNR (signal-to-noise ratio) levels will more than make up for signal loss. A signal level of -100 dBm is a HOT signal when the noise level is down at -140 dBm, that leaves you 40 dB SNR, a crystal clear signal."


For the MW broadcast band, feeding the LoG or any low noise antenna to a pocket or portable radio is easy. I find inductive coupling best.

Salvage a short ferrite rod or bar from an old pocket radio. Three inches in length is about right. Remove all the magnet wire from it. Using some solid, insulated telephone wire of about 24-26 gauge, wind about 15-20 turns close-wound around the ferrite rod. Solder or clip the two ends of wire from this coil to the coax feeder coming from the antenna, one to the center and one to the shield. Hold the ferrite close to the radio's internal ferrite which will inductively-couple the signal to the radio. The advantage over a passive loop here is you have a broadband antenna which does not have to be tuned.

Ferrite coupling


Fabricating Impedance Transformers for Receiving Antennas, by John Bryant:

Broadband Receiving Antenna Matching, by Mark Connelley, WA1ION:


I would encourage many of you with RFI problems to try the Loop-on-Ground antenna. Don't dismiss it just because it lies on the ground. Cut to the right size, the LoG can be effective anywhere from longwave to 30 MHz. Experiment!


N2ICZ said...

Great article, Bill. I really enjoy your blog.

I recently retired into one of those pesky HOAs where something BIG and visible would raise eyebrows. I could build this right after lawn mowing season and let it sit there during DX season and no one would be wiser. Also, I wonder if it could be made smaller using 60 feet or so of 300ohm twin lead with the ends twisted together into a loop, although I seem to think it might act as a linear loaded antenna.


Thank you for your kind comments.

Not sure I totally understand what you mean. The original KK5JY LoG was indeed 60 ft. total length. You could take 300 ohm twin lead and cross-twist the ends to make a two turn loop, but it would still be 60 ft around.

In any event, lessening the area of the loop will have a negative impact on signal pickup.

I like to do a little medium wave DXing, and I found the 60 ft. version to be a little insensitive on the AM broadcast band. I found a 100 ft. loop to be a better compromise. The 100 ft. loop also had a little better signal pickup in the 2-12 MHz bands than did the 60 ft. loop.


KB9NHZ said...

How about the 160 meter band ? You show results from the broadcast bands and nothing in the band. 1.7 and 2 MHz is OOB. Do you have any data before I go and build this?



My 100 ft. square loop had good response in the 160 meter band between 1.7 and 2 MHz. I don't have hard data, only what my ears told me. I built my loops to try to conquer an extreme local noise problem, and they worked for that.


Sean - G4UCJ said...

I'm definitely going to build a LOG to complement my broadband active loop(s). I have a question regarding the balun/unun/transformer. Reading elsewhere, a 3:2 ratio on a #73 core has been used, which I presume is a different core material to the Nooelec 9:1 one. My interest in this antenna is for 160 down to VLF, with an emphasis on NDBs. I don't have a large enough plot to lay out a 250-350' loop, which would be ideal but I can get 120' in a square or 160' in a rectangle of 30'x50'. LF/MF is where I suffer the most in terms of RFI, so a LOG would seem to be the obvious choice here. My active loop is good at LF but I want a lower noise antenna to phase with it. The only thing I am finding conflicting reports on is the transformer, both in turn-ratio and core material. My instinct is to go with #73 material, as it seems to be more effective at lower frequencies than #43 or #31 but I could be interpreting that wrongly. Also, common mode choke at the feed-point? Good idea or not? I'm intending to use some RG6 (or similar) direct burial coax as I have a reel of the stuff (nice green jacket too). I'm wondering if I can wind a common mode choke with the same enameled wire, (or whatever I end up choosing for the transformer) using the bifilar winding method, on a #73 toroid and put it in the same box as the transformer, thus saving the expense of buying an FT240-73 core and wrapping coax around it. I asked some of these questions on a FB group and there was not a single reply, which was disappointing. Hoping that someone here may have done this before me and has some insight. Trying to save myself some expense by buying only what I need to complete this, but if no-one else has tried any of this I might have to have a go myself, when funds allow the purchase of the extra bits. 73, and good DXing 'up' on the MW band :) de G4UCJ IO91 (742 NDB logged since about 1999). Now using Airspy HF+ Discovery and rotatable 1m active loop, with LAA+ from Cross Country Wireless.


Hi Sean. I've used both 73 and 43 type cores. To me, it's hard to tell the difference. The Nooelec 9:1's always gave me pretty good results without a lot of effort. On the hand wound cores, go for the higher turns count, keeping the ratio you want. Many guys wind only 5-9 turns on the primary and 2-4 turns on the secondary (receiver side). This may work fine for shortwave but fails miserably at MW. In my opinion, the primary impedance is too low (the antenna side), and loads the loop down, reducing the signal transfer. Something more like 18 turns primary and whatever needed on the secondary gives a better signal transfer at MW, if you can afford the extra wire on the core.

I wouldn't worry too much about turns ratio. Try a few ratios and see if you see a difference. The impedance of the loop across LW and MW will vary greatly. Stick to something in the 300-1500 ohm to 50 ohm (or 75 ohm) ratio. I believe 900-1500 is better.

120 ft. will do fairly well at MW, and much better than the original KK5JY 60 ft. loop. Your 250 ft. loop will certainly improve the signal output, but it may raise the background noise floor a little more than wanted. Please do experiment with lengths.

Be careful with common mode chokes. Try it, but if it introduces a severe elevation of background noise then remove it. The choke in the same box as the feed balun should be fine. Don't introduce anything that upsets the balance of the feed system. Use pure galvanic (voltage) transformers in the feedline, that is, baluns with a primary isolated from the secondary, with no common ground connection. Common mode chokes sometimes have common grounds. Ferrite snap on chokes which can be found on eBay, can be a benefit. Install several at the feed point and several at the shack terminus.

Be cautious when connecting multiple antennas on antenna switches. This can sometimes introduce unwanted ground currents and EMI. Keep your SDR as far away from your computer (and especially the monitor) as possible. Monitors produce a tremendous amount of hash. I've bought extra long USB cables and keep my HF+ Discovery (the unit itself) in an adjoining room.

The LoG is somewhat directional, in my experience showing about 6 dB difference between max and min. Feed at a corner. The directionality will be on a line 90 degrees to the feed. The LoG has good high angle results and also good low angle as well above 10 degrees. The pattern is more of an elongated ball.

I split this up into two parts...



Part #2

While you are laying wire out on the garden, be sure to experiment with the DoG, or dipole on ground too. Take that same wire you use on the loop and make a straight run as long as you can get, feed in the middle. Feed with the same balun arrangement. Directionality and gain are about the same, about 6 dB. Gain is off the ends of the dipole. Orient both the LoG and Dog for minimum electrical noise. I've found a 120 ft. (total) DoG to be even a little better than a 120 ft. Log. It gives a little more signal, but at the expense of a slightly raised noise floor.

Your HF+ Discovery is an excellent SDR. I have one as well. I also have the SDRPlay RSPdx. The sensitivity of the RSPdx is not comparable but is more bullet-proof re:overload. If you live near any MW transmitters, be careful of overload. On either of these antennas, try to keep the noise floor at below -110 dBm. Keep strong, nearby MW stations below -45 dBm by using attenuation. My noise floor on MW runs about -120 dBm, about 20 dB above the base noise floor (-140 dBm) of the HF+ Discovery. I can often copy signals with audio intelligibility in the -110 to -105 dBm range. -107 dBm is = to 1 microvolt.

Longwave here for me is unusable. Too much electrical and computer hash. I've tried everything.

If you don't have one, try a passive YouLoop on your HF+ Discovery. They are an excellent, matched combination. I added an extra 1 meter to the loop's circumference by purchasing a couple of 50cm RG402 coax pigtails and female-female couplers. The normal YouLoop circumference is 2 meters (two 1 meter sections).

From studying loop mechanics, loop voltage output is directly proportionate to its area. So, instead of an area of approx .317 meters, the new version has an area of .716 meters, 2x + a little more. This should result in about a 6 db voltage gain, or about one S-unit, and that gain has been reflected in what I have experienced on the MW band.

It adds a little juice to the YouLoop. I've found the YouLoop to be an excellent antenna in its own right, and especially coupled with the Airspy HF+ Discovery. I don't get nearly as good results with my SDRPlay RSPdx. It handles the house's electrical hash pretty well, and I can always turn it to null the crazy stuff a bit.

Hope this helps Sean.

Best DX,


dbnut said...

Just a quick thank you for great food for thought.

Sean - G4UCJ said...

Hi Bill, sorry for the delay in replying, it's been a bit busy here. I have a long-winded reply typed out but may need to 'trim the fat' before pasting it to the comments :) I'm in the process of sorting the core(s) and wire for the transformer, having digested your comments. Rather than a binocular/pig nose core, I think a toroid might be better for accommodating an increased number of turns. The primary on one side and the secondary on the other. The core itself will be a #75/J mix with an OD of 0.5". The wire I intend to use is around 28AWG/0.3mm. The turns ratio is yet to be decided but will likely be higher than the 2:3 that I have seen elsewhere. I need to consult the net on likely impedance ranges over the frequency range I intend to use the loop. It may end up that I need different turns ratios for different ranges. Should that be the case (likely), I might end up making two or three boxes, each with a different ratio transformer that I could swap as needed. That does complicate things slightly as I will need to have stainless steel connections on the outside of the boxes rather than bringing the wire ends into the box via waterproof glands. That would likely be the easiest way, rather than trying to set up 3 individual transformers in one box, with a switch to select each one. Waterproofing will become an issue if I introduce a switch that is accessible from the outside of the box, and the dimensions of the box will need to increase. I think I have talked myself out of the larger and more complex box idea! I did cover some of this in the other reply, which I will post after this one - just be prepared to wade through some unedited waffle! Thanks for the info, Bill it's appreciated and has been most useful. 73, Sean G4UCJ

Sean - G4UCJ said...

Hi Bill, below is my unedited original reply - it's rather long and gets a bit side-tracked at times. Pt 1 follows:

Hi Bill,
Thanks for the detailed reply, there is a lot of useful information to digest there. I may have made a typo in my original post about the largest loop I can squeeze in, as it is around 150ft, not 250 (that would be great, but I'd have to use a neighbour's garden as well). The dipole on the ground (DOG) is one I hadn't heard of but it's not something I could employ here, if I could it would only be about 60ft long which is really too small to be of much use down where I am hoping to use it.
My Setup:
The way I have things set up here is: a 3ft diameter active loop (using an ex-Wellbrook aluminium loop) that is around 2.5 ft above the ground. It is situated in the middle of my garden and has the first 20ft of feeder buried in a plastic conduit, the feeder then runs along the fence for the remainder of its length and into the shack. This goes into a passive 2-way splitter, one branch going to the 'aux' input on an MFJ-1026 phaser, with the main TX antenna (a 20m perimeter triangular loop, with a 4:1 balun) occupying the 'main' antenna socket. This feeds my Yaesu FTdx10. The other branch of the splitter goes to the 'aux' input on a second MFJ-1026, with the 'main' antenna being an active inverted delta (which uses CAT-5 cable as its feed line) with a span of about 6ft. This is around 3.5ft off the ground. The output of the second MFJ-1026 (this one is modified to work better at MW) feeds into the Discovery. The audio from both radios is available via a small mixer so that I can monitor the SDR, the dx10 or both at the same time, with the balance and audio levels being variable to take account of band conditions, etc.
My intention with the LOG is to replace the active delta as that can be used for monitoring other bands.
Noise levels:
My background noise level varies with frequency and time of day/year as I guess most of ours do. There have been occasions when the noise level has been over the s9 mark for a few hours, but luckily these are reasonably infrequent. Other noises come and go - there is one that I haven't tracked down yet which comes on with a small, wideband, burst of noise for a couple of seconds, then returns to normal levels for 5-10 seconds before coming back and staying at the same amplitude for 10-20 mins at a time. It's not a destructive noise (on all but the very weakest signals) as it only raises the noise level by around 10dB or so. I don't think it is PLT/PLA but it could be related to heating as it seems more prevalent in winter. There are a few heat pumps in this area, including ours, so it may be one of those with a noisy thermostat.
On the subject of noise, my Discovery is actually less than a foot away from my monitors. I didn't realise they could pick up the monitor emissions directly, and I know at least one of mine is a bit noisy on certain bands, despite being festooned with ferrite. I'll have to look at where the SDRs can be moved to, although sadly I doubt it will be very far away as I'm compromised for room in that respect. It has given me a few things to think about and maybe I can reduce the background noise by a further few dBm. I have made a custom insert for my loop rotator that has various places/stns marked, plus the nulls for various noise sources - and which bands are affected. That has proved to be a real-time saver.
I wonder which software you use with your Discovery and RSPdx - I usually use SDR COnsole v.3 for LF/MF/HF and SDR# for general monitoring above HF as I prefer some of its features, they seem more suited to scanning and P-P comms. Also, it works very well with the Airspy R2. There is also an Airspy HF+ Dual port in my armoury which is great for VHF comms but is trickier to use for FM broadcast band due to the limited sampling rates of the HF+ range.

Sean - G4UCJ said...

Your findings on mix types and turns ratios were an interesting read. One thing I hadn't considered was the varying impedances that will occur over the frequency range it will be used for. Feeder length will hopefully play no real part in the impedance matching. My triangle TX loop seems to be affected by feeder length. With the 'standard' length of feeder for this QTH it resonates on 10m @ 1:1 (despite being a 2ƛ loop) - whereas it should resonate properly on 20m - it does resonate, but at a much higher SWR so the balun ratio required is something other than 4:1. When I insert a decent length of additional feeder, the SWR on 10m increases and the SWR on 20m decreases. I haven't analysed this on the nanoVNA but the feeder must be playing a part in the resonancem despite it being choked at the feed point with 12 turns FT240-43 toroid coaxial choke (i.e. 12 turns of the feeder wrapped around the toroid). Now, to the transformer/balun for the LOG: I think a larger core may be beneficial here if I am going to use a higher number of turns. If I wind this transformer on a #73 toroid core, will there be enough mutual coupling between the primary and secondary windings if they were wound on opposite sides of the core, rather than on top of each other as is usual with a binocular core? The addition of a common mode choke increasing noise level is not something I had considered, ever, really. When I make common mode chokes, they are just a good number of turns (usually between 6 and 12) of the feeder coax around a ferrite toroid. Sometimes I will cross over the windings, as was shown in the RSGB books a few years back. The jury seems to still be out on whether this makes any appreciable difference in effectiveness. The only thing I could see would be the mutual capacitance between the first and last turns would be reduced as they would be on opposite sides of the toroid. Being as these are receive-only antennas, the toroids/binocular cores can be small and hence cheap. I think it may be worth investing in a handful of smaller size #43 and #73, and maybe #31 along with some #28 gauge wire and wind a few different ratios to see which I get the best signal transfer and lowest noise with (i.e. best SNR).

Sean - G4UCJ said...

Pt 3:
The last antennas I built for MW were passive loops of varying sizes. My last one did have a switchable preamp, as well as a bank of switchable capacitance, to stretch the tuning range. I never had much success with making LW loops as I always fell foul of the number of turns required. This was back in the early 80s before all the man-made crud and a loop would work perfectly well indoors. I did attempt a 2m x 2m wooden frame loop but it was too wobbly (and big). a 1.5m loop was the biggest I made that actually worked, it definitely gave a stronger output than the 1m and below that I had previously worked on. a 12" loop with around 15-18 turns was pretty effective, but really needed the preamp, especially down the low end. I would have loved something like a Wellbrook back then, it would have made my Sony sing! I had a pair of ICF-7600s back then, an 'A' version (analogue) and a 7600D (digital tuning and SSB). Both were OK and I heard plenty of TA with them. Later I purchased an ICF-2001D. Probably enough said - it was superb and a real step up from the 7600s. I'd happily have one now, to complement my little collection of portables and SDRs, but the prices are often way too high, given that they are the best part of 40+ years old now. My 2001D died after a long, and very busy, life. The PLL put its legs up and as these were pre-internet days, there was nowhere I could find to service it, without charging the earth.
I don't often measure my background noise levels, other than a cursory glance to make sure they are roughly the same as they were for the previous session. They do vary in strength between bands and, of course, direction. The loop can remove one of the noise sources very well, but I'm still left with another, on certain bands, that comes from a different direction. This is where the LOG and the MFJ-1026 will come into their own. In theory, I should be able to null/steer the remaining noise source away from the frequency in use. Looking at the SDR waterfall, it is interesting to see the null moving up and down the band as I rotate the control(s) on the MFJ-1026. It doesn't work on all noise but if I can remove the 2 biggest offenders, the rest should be acceptable as they should be at a much lower level. I hope practice is as good as the theory!

Sean - G4UCJ said...

Below are my comparative noise levels, both with the MFJ switched in and adjusted, and without it, just running on the active loop.

These were measured on clear frequencies, at dusk (around 1700 UTC)
1543kHz: -94dBm (approx) -105dBm
947kHz: -102dBm -117dBm
597kHz: -88dBm -110dBm
445kHz: -82dBm -110dBm
210kHz: -90dBm -117dBm

This the the BBC R4 transmitter at Daventry (about 35km from here), with the loop on target. It's a pretty strong signal as you would expect. What I didn't expect was the 7dB improvement in SNR when using the correctly adjusted MFJ. Although the overall signal strength is down by 20dB, that doesn't matter as the increase in SNR means it will be easier to hear (not that was difficult in the first place).
198kHz: -26dBm; 71dB SNR -46dBm; 78dBm SNR (+7dB improvement on SNR using the modded MFJ-1026.
366kHz: -71dBm / 20dB SNR -96dBm / 34dBm SNR (+14dB improvement on this NDB signal, also the NDB was fighting in amongst some very wideband QRM that exists from about 250-450kHz).

Without the MFJ, my LF/MF DXing would be much less fruitful. There is still room for improvement, and the LOG is the logical next step as far as antennas go. Low noise and virtually invisible are both major plus points. I already have 5 antennas set up in the garden, so it's getting such that anything additional would likely cause issues due to parts of the antenna crossing over/through existing antennas. There is also the aesthetic viewpoint to consider. As much as I like seeing massive arrays, my neighbours might not be so keen - they have been very good up until this point, so no need to rock the boat unnecessarily by introducing a K9AY/Pennant/Flag/EWE type of antenna to the mix.

I started DXing when I was a young boy, around 7/8 years old when I first started to get interested in those funny squeaks, pops and odd voices I heard coming from the other side of the room. Over 45 years later I'm still just as intrigued, maybe even more than I was back then!

73 de Sean - G4UCJ


Hi Sean. I read everything, thanks for your detailed reply. I'll break this up into two parts.

I'll let you know ahead, I'm headed off mid-week for a vacation holiday until about April 1st, so probably won't be online as much.

I've also used the Amidon FT-114-J core. On Amazon:
It worked well and I think is 75 permeability.

I also have a NanoVNA. I had some screenshots of SWR and impedance charts for the 120 ft. LoG (and the DoG) but unfortunately lost them when I suddenly had to reinstall Windows about a month ago. The LoG impedance from LF through MF and up to the lower part of the SW spectrum will vary wildly from almost zero to upwards of 2000 ohms. I guess you could pick a frequency and go with that impedance. Be sure you also run the NanoVNA scan by attaching the NanoVNA directly to the loop outside at the feed point. You will get drastically different readings, of course, between there and the other end of the feed in the shack. If you want the best match, be sure to do your balun matching at the LoG feed point.

OK on your MFJ-1026 phaser. I've never tried phasing. Glad it works for you. Maybe if I was younger, but that time has passed. I'm 76 years old here and in declining health. Can't really do much antenna work anymore. I've been a ham for 61 years. Not active anymore, at least transmitting. I do mostly MF and SW DXing. Back in the day it was almost all CW.

My DoG antenna is just 60 ft. in length, split in the middle. I get plenty of signal at MF. So much so at night that I have to crank in the attenuation about 6 dB at times if I am viewing the entire band. I find it best on the Discovery to run at reduced FFT bandwidth. I usually run at 128 ksps sample rate using SDR# Sharp software. It gives me a 100 kHz wide spectrum and knocks the noise floor down a lot. Better results had if you go even lower.

I've tried all the software that runs the Discovery and also the SDRPlay RSPdx units. I used SDR Console for quite a while. I liked it. Great product. SDR# is tailored for the Airspy product however and has some options I like which SDR Console doesn't have. I can run the FFT sample rate way down to 10 ksps allowing me to chase carrier offsets down to 0.1 Hz and lower. It's tough to get that fine with SDR Console as far as I remember. Or HDSDR. The RSPdx won't go anywhere close to that narrow of FFT.

Be sure your long USB cable is shielded if you run the Discovery a distance from your computer/monitors. I've found most of the monitor hash is 900 kHz and below, a lot of it centered between 500-750 kHz. You are lucky if you get a good hash-free monitor. Longwave is a disaster here. Mostly unusable for many reasons, but I'm not sure where all the EMI is coming from. After chasing noise for several years here, the surprise finds which I never suspected were the garage door opener unit (the motor unit and receiver) and a very expensive refrigerator. The garage door opener puts out terrible hash for 100 yards between 500-700 kHz. The refrigerator had low level 10 kHz spikes clear through 30 MHz, peaking between 10-20 MHz. Can't cure the garage door opener. I put a line filter on the fridge and cured 90% of that. I've since found a second garage door opener that does the same thing.

Bill, WE7W


Part #2

You can also use 1:1 galvanic (no through ground connection) baluns either at the LoG feed point and/or at the shack end too (with coax feed of course). They are cheap and readily available, or you can make them yourself. I've gotten some off of eBay straight from China for about $8 each, receiver grade. They will help to isolate the EMI even more by keeping it off the coax shield. The Chinese copies I have do attenuate the signal about 2 or 3 dB at MF, however.

Here's a link:

There is no requirement to cross over the primary and secondary windings. I've used that technique and also wound them at opposite ends of the core. I've gotten about equal results. I haven't been able to tell the difference.

Thanks for showing your dBm noise floor levels. Interesting. Try to keep the base noise floors as low as possible. Through preamps, a bigger LoG, or whatever method you use, the idea is to bring signal levels up above the base sensitivity level of your receiver. Most receivers will provide copy at much less than a microvolt, which is -107 dBm. -107 dBm is S-3. S-2 is 0.4 microvolts, or -115 dBm, and S-1 is 0.2 microvolts, or -121 dBm. For example, if you want to get intelligence out of an S-2 signal you have to reduce the base noise floor and atmospherics far enough below -115 dBm to give you enough signal-to-noise ratio.

A lot of guys will put a LoG antenna down and give up when they think they can't hear anything. The noise floor can be so low that you think you are on a dummy load. The first thing is to turn off the AGC and control things with the RF gain and the attenuators. SDR# has a great attenuator setup, 0-46 dB in 6 dB steps. And it has a preamp too if you need it. headphones are a must too.

That's an amazing signal level on 198 kHz if I read you right, at -26 dBm. That would choke my Discovery. I truly shoot for no signal to be above -45 dBm in the FFT passband. I find my Discovery tends to overload if anything is stronger than about -45 dBm. I'm in a high signal MF area, and am only 1 mile from two 5 KW MF transmitters.

Good luck and good fun with the project, Sean.

Bill, WE7W