Tag Archives: Homebrew Mag Loop Antenna

Bruce compares two homebrew NCPL antennas to the Airspy Youloop

The Airspy Youloop

Many thanks to SWLing Post contributor, Bruce (VE3EAR), who writes:

I decided that more testing of the Noise-Cancelling Passive Loop (YouLoop) antenna was needed, but I wanted to start with a clean page.

I built two identical loops using some 3/8 inch heliax scraps I had on hand. Both are one metre in diameter and employ the same feed arrangement, with a balun wound on a half inch square binocular core of type 75 mix. There are four turns on the antenna side and eight on the feed line side, of #24 gauge plastic insulated wire. The feed line shield connects to the antenna shields. The only difference between the two antennas is at the top of the loop, opposite to the feed point. One has a simple one inch gap in the shield, with the centre conductor passing across the gap, while the second one uses the crossover connection of the YouLoop design.

I’ve been running some A-B comparison listening sessions, both mid-day and in the evenings after local sunset. The testing is done outside, with the antennas hanging on a low limb of a maple tree in front of the house. The feed line is about twenty feet of coax which connects to my Realistic DX-440 receiver on the front porch. Testing is done listening to the AM broadcast band and the 160, 80, and 40 metre ham bands, with the loop aligned both E-W and N-S and about one loop diameter off the ground.

Both loops work well, but I do have to give the nod to the YouLoop (by Airspy), which produces a stronger signal of two S-units higher than the conventional loop. It also has deeper and sharper nulls, which can sometimes produce total nulling of the station!

73, Bruce, VE3EAR

Thank you so much, Bruce, for sharing your findings with us! I, too, have found that the Youloop generally outperforms my homebrew NCPL antenna. I believe one of the reasons for this as Youssef at Airspy once told me is because the Youloop has a lower loss transformer than anything that can be wound by humans (0.28 dB)–this improves gain.

Click here to read our review of the Youloop and click here for step-by-step instructions on building your own Noise-Cancelling Passive Loop antenna.

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Giuseppe’s cross-loop experiments

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Many thanks to SWLing Post contributor, Giuseppe Morlè (IZ0GZW), who shares the following:

I’m Giuseppe Morlè from Formia, central Italy, on the Tyrrhenian Sea.

I wanted to share with you and friends of the SWLing Post community this antenna project of mine dedicated to those who do not have enough space on the roof or in the garden to install antennas.

These are two separate loops, with two different diameters, one 60 cm, the other 90 cm, each with two variables for tuning … the system is able to receive from 3 to 30 MHz.

I joined these two loops in an opposing way, better to say crossed that can communicate with each other due to the induction effect that is created between the two small coupling loops that are placed one under the other at the top.

In the videos you will be able to see how the antenna system receives. I can use one loop at a time, to detect the direction of the signal or I can use them together for a more robust signal and in an omnidirectional way.

I really like experimenting with the induction effect and you can see that even when closed at home the two loops do a great job.

From my YouTube channel:

I’m not a technician but I really want to experiment to try to listen as well as possible.

Thanks to you and CIAO to all the listeners of the SWLing Post community.

Giuseppe Morlè iz0gzw.

Very cool, Giuseppe! I must say I’ve never tried dual loop experiments like this where one can experiment with the induction interplay. I imagine this could give you some interesting nulling capabilities if you have an unwanted station interfering with a target low-band signal. Thank you again for sharing!

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Bill’s first DX contest using a Panasonic RF-2200 and a hombrew diode/loop radio

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Many thanks to SWLing Post contributor, Bill Hemphill (WD9EQD), who shares the following guest post:

My First DX Contest

by Bill Hemphill, WD9EQD

Being a recent new member of NJARC, this is my first time competing in this contest. I have always been a big fan of BCB DXing and have recently got back into it – especially with the amateur radio bands being in such poor conditions. The acquisition of a couple of Loop antennas plus two Panasonic RF-2200 radios have just enhanced my enjoyment.

For the contest, I used two completely different radios. First was the RF-2200 and second was a spur of the moment creation.

The RF-2200 was its usual good performer. While the RF-2200 has a beautiful built-in rotating bar antenna, I enhanced it with the 27” Torus-Tuner Loop Antenna as made by K3FDY, Edmund Wawzinski. I think I had picked this antenna up at one of NJARC’s swap meets. So I wish to thank whoever it was that was nice enough to bring it and sell it at the meet. I have really enjoyed using it. With this setup, I was hoping that I might be able to pull in Denver, Salt Lake City and maybe even a Mexican station, but it was a complete bust on them. But I did have a nice surprise in receiving the Cuban station Radio Enciclopedia on 530 in addition to the usual Radio Reloj time signal station. Following is photo of it in operation:

Originally, I had thought that my second contest entry would be done with a 1962 Sony TR-910T three-band transistor radio. This radio has a fairly wide dial along with a second fine-tuning knob which would be a big help. I would have again used the 27” hula-hoop antenna.

But I made the nice mistake of running across Dave Schmarder’s Makearadio website:

http://makearadio.com/

Dave’s site is a wonderful resource for creating your own Crystal, Tube, and Solid State radios as well as Audio Amplifiers and Loop Antennas. While going down the rabbit hole of his site, I ran across his Loop Crystal Set, #19 Crystal Radio:

http://makearadio.com/crystal/19.php

What grabbed my attention was the wood frame loop antenna which is similar to one I had acquired a couple of years ago at a ham fest:

It was a really nicely constructed, nice swivel base.

I replaced the tuning capacitor with one that has a 6:1 ratio.

At this point I started thinking that I could create something similar with my loop.

I randomly grabbed a diode from my parts box. Not sure what the exact model is. (I later found out that it was an IN-34 which is what I was hoping it was.) Then quickly soldered the diode, a resistor and capacitor to a RCA plug:

I then proceeded to use some jumper cables and just clip it to the tuning capacitor on the antenna base:

The RCA plug was then the audio out (I hope) from the radio.

I quickly realized that I did not have a crystal headset or any headset that would reproduce any audio. So I used an old Marantz cassette recorder to act as an amplifier. Fed it into the mic jack and then tried to listen to the monitor out. Bingo – I could pick up or local station on 1340 really weak.

So I then fed the audio from the Marantz into a Edirol digital recorder. Now I was getting enough audio for the headphones plus could make a recording of the audio.

At last I was receiving some signals. To boost the audio some more I removed the resistor from the circuit.

I found out the I could only tune from about 530 to 1350. I probably needed to clip the lead on one of the loop turns, but I really wanted to see how it would do at night. I spent several hours and was just totally amazed at how well it performed and how good the audio was. The hardest part was when there were very strong signals on the adjacent frequency. What I found really interesting was that it was not linear in its tuning. At the low end of the band the stations were more spread out than at the higher end. This made tuning fairy easy at the low end and very touchy at the high end. I was able to hear a couple of Chicago stations along with Atlanta and St. Louis.

Here’s photo of it in action:

I have created an audio file of the station ID’s heard with the diode/loop radio. The audio file is on the Internet Archive at:

https://archive.org/details/bcbstationidsondioderadio

I had a lot of fun in the contest and especially enjoyed trying something really different with the diode/loop radio. Now I have a whole year to try to think up something really creative for next year’s contest.

Absolutely brilliant, Bill! I’m so happy to see that your ham fest homebrew loop has served you so very well in a contest. I love how you pulled audio from your homebrew, make-shift diode radio as well–using your audio gear in a chain for amplification obviously worked very well.

Thanks so much for sharing your experience, Bill!

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Guest Post: KK5JY’s Porch Loop Receiving Antenna

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Can you spot the antenna in this photo?

Many thanks to Matt Roberts (KK5JY) who has kindly given me permission to re-post the following article he recently published on his website KK5JY.net. Many thanks to SWLing Post contributor, Grayhat, for the tip!

Note: The Porch Loop project below is a re-configured Small Receiving Loop (SRL) antenna. For SRL construction details, check out Matt’s primer.

The Porch Loop

by Matt Roberts (KK5JY)

The small receiving loop, or SRL, is a versatile, effective, and very space-efficient receive-optimized antenna for the HF bands. They are easy to build, and can be made very inexpensively. Most typical designs use symmetric shapes, like circles, diamonds, octagons, etc., and are mounted on some kind of mast. This makes it easy(-ier) to install the antenna clear of nearby metal and electronics. It also makes the antenna rotatable, so that the nulls can be pointed at RFI sources.

These aren’t the only options for the SRL, however. These little loops can be made to fit in just about any available space. In fact:

They are effective at any reasonable installation height, including very close to the ground. The installation height doesn’t change the pattern shape, only the pattern strength.
They can be made nearly any shape. The shape does not have to be symmetric about any axis or combination of axes.
They can be fed at just about any point on the loop. A typical feed location is bottom-center, but off-center feeding has negligible effect on the pattern shape.
The wire can be bent out-of-plane; in other words, the loop doesn’t have to be “flat.”

There are a couple of requirements for obtaining predictable performance, however. First, the antenna does need to be an electrical loop. That is, it is a single wire connected between the conductors of the feedline, forming a complete circuit. Also, the circumference of the loop wire should be electrically small (i.e., significantly less than ? / 4) on the bands where it is to be used.

Figure 1. The antenna location (click to enlarge)

As a personal challenge, I recently installed such a loop on my front porch. Everything about this installation defies conventional wisdom — it was installed very close to the ground, it was an irregular shape, it was fed off-center, and the wire was wound in and around an irregular support structure, rather having all the wire in a single plane.

And the resulting antenna still performed very well.

Figure 2: Antenna Location Outlined in Red (click to enlarge)

The loop is essentially the same device as the one in the original SRL article. See that article for more construction details. This version is simply stretched and twisted to make it fit the space and supports available. The wire was woven around the boards in the porch’s deck rail, and fed off to one side, so that the transformer housing could be “hidden” behind the trash cans.

Figure 3: Feedpoint Transformer (click to enlarge)

The wire was insulated with an off-white THHN, which made it blend in with the color of the trim of the house.

Figure 4: 40m Reception 10h Overnight (click to enlarge)

Even with its suboptimal installation details, the overnight 40m DX spots were numerous and well-distributed, as seen in Figure 4. There were DX spots at nearly 10,000 miles, there were NVIS spots, and there were countless at all distances in between. So the antenna was just as effective as its more ideally shaped brethren, despite it’s unconventional installation details.

Other ideas for possible locations of such a device could include:

In an attic. The antenna could be nailed to a vertical panel, or strung like a spider’s web inside the frame of a truss or other open area.
Under a tree. Taking another idea from the spiders, the antenna could be hung and pulled into shape using light guys or tree branches.
On a wooden fence. If you have a wooden fence, the antenna could be installed against the fence panels. This option could allow a wide range of circumference lengths.
Attached to an interior wall of an apartment. The shape could be chosen to keep the loop clear of in-wall wiring, to help preserve its performance.

The original mast-mounted SRL antennas still have some advantages. Perhaps the biggest advantage is that they can be easily rotated to null out a nearby strong noise source. That said, if you are looking for an antenna with better receive performance than a large resonant vertical, the SRL can be stretched and squeezed into service just about anywhere.

Many thanks for sharing this project, Matt! So many of our readers live in situations where they are forced to use stealthy and compromised antennas. What I love about your porch loop is that even though it breaks several loop antennas “rules,” it’s still amazingly effective.

I encourage SWLing Post readers to check out Matt’s website as he has written articles covering a number of interesting radio and antenna projects.

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Patrizio’s simple homebrew NCPL antenna

More about hacking VGA cables to make binocular ferrite cores

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A few days ago, we posted an a short article showing how Oscar hacked a VGA cable to make a binocular ferrite core for his homebrew NCPL/Youloop antenna. Many thanks to SWLing Post contributor, Grayhat, who explored this clever hack a little further:

Hi Thomas, Having some time in my hands Sunday afternoon I decided to try pulling out the ferrite chokes from a VGA cable I had around, and while doing so, I decided to coarsely document the process with some pics.

Figure 1

The first thing to do is use a cutter to carefully cut around the “washer” shaped plastic at the connector end of the choke (fig.1, #1,#2, #3 above), then on the same side, after cutting the plastic also cut the inner conductors (fig.1, #1).

Move to the other side of the choke, gently cut around the “washer” w/o cutting the inner conductors, now pull the cable to extract it from the choke (fig.1, #3), repeat the process for the other choke.

Now look at the “cans” containing the chokes, one side of those will show a “cap” (fig.1, #4), insert a small screwdriver into the center hole and gently ply to one side to raise the cap and extract it (fig.2, #1).

Figure 2

The result will be as in fig.2, where #1 is the closing cap, #2 is the ferrite choke and #3 is the “can” containing the choke. Repeat the process and you’ll have two ferrite chokes as shown in fig.3 (the VGA connector is there to give an idea of the dimensions):

Figure 3

At this point, use some tape (duct tape will be a better idea, I used clear tape just to make an example) to tie the two ferrites together as in fig.4 and you’ll have your “binocular ferrite”:

Figure 4

Willing to use whatever you have there to wind the transformer, you may now extract the tiny insulated wires from the VGA cable (fig.1, #3, see wires) and use them for the windings.

Notice that other cables may use different choke “cans” which may need to cut a larger portion around the flat faces at the ends. But remember that in any case, those are just “snap-in” cans containing the ferrites, so with a bit of attention and patience, it shouldn’t be difficult extracting the ferrites.

Based on a little online research, it sounds like the ferrites used to choke the VGA cables (HDMI ones too) are generally type #31.

Looking at some #31 datasheets it appears that while #73 is works fine at frequencies below 50MHz, the #31 is best suited for the 1-300MHz range.

This means that #31 won’t be the best pick for mediumwave, although if one doesn’t have another choice… well, go for that! Also notice that the ferrite permeability is different:1500 for #31 and 2500 for #73. This means that we’ll need to increase the number of windings to achieve acceptable signal transfer, otherwise the transformer loss will make our antenna deaf.

One might try increasing the number of windings to say 8:8 or 16:16; as long as the winding
ratio will remain the same, there won’t be problems (although the resulting bandwidth will become narrower).

Thanks for documenting and sharing this, Grayhat! Since most of us have more time on our hands at home, I think it would be worth experimenting with the number of windings to see how it affects the antenna performance. That’s a clever thought, too, to use the VGA wires to wind the Balun. As long as the cable is long enough for the amount of turns, it’s certainly the most efficient use of resources!

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Hack a broken VGA cable to make a binocular ferrite cores for your NCPL antenna

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Many thanks to Oscar (EA3IBC) who shares this simple hack.

I’ve gotten quite a few emails from Post readers telling me that the only thing holding them back from building a NCPL antenna is the BN-73-302 binocular ferrite core needed for the 1:1 Balun. While so much of the world is sheltering at home due to Covid-19, it’s less convenient to purchase one just for this purpose.

But almost everyone has an old VGA or USB cable with ferrite cores they can cannibalize for this very purpose. Oscar shared this super-simple hack on Twitter:

1. Cut the cable and remove the ferrite cores

2. Tape the two cores together

3. And wind four turns on both sides

Admittedly, this 1:1 balun might not have the same properties as the BN-73-302 from our tutorial, but it seems to be working for Oscar. Check out this screenshot he shared from SDR# while hooked up to his NCPL antenna:

Thanks again!