Category Archives: How To

Finding local Emergency Alert Stations in the US

Many thanks to SWLing Post contributor, Mario Filippi (N2HUN), who shares the following guest post:


Emergency Alert Stations: A great source of local information

by Mario Filippi

During the pandemic a source of local information for residents in certain areas of the country can be found on Emergency Advisory Radio stations that dot the country and provide 24/7 information pertinent to a community.  Not all communities have these stations, which can be found from 1610 – 1710 kHz and operate at varying power outputs.

Author’s Yaesu FRG-100 tuned to EAS station

For example, a station I regularly hear is WRBX655 about 12 miles away in Franklin Township, NJ operating on 1630 kHz : https://www.franklintwpnj.org/Home/Components/News/News/6384/1130?cftype=News

At the moment it is broadcasting information on COVID-19 from the Center for Disease Control.  Every EAS  station has a call sign and wattage generally is from about 10 – 50 watts. However some stations do not necessarily announce their call signs so you can check theradiosource at: http://www.theradiosource.com/resources/stations-alert.htm

Now some of these stations are part of the HAR (Highway Advisory System) that broadcast on major roadways and usually have prominent road signs announcing where to tune your car’s AM radio for latest traffic conditions.  These stations were also termed TIS (Traveler’s Information Stations) at one time and were the precursors of HAR.  However, over the years the FCC allowed more leeway on what information could be broadcast and as a result these EAS stations appeared in communities and even state parks.

You can look up the locations of these stations to ascertain if one serves your community but the best way is to tune regularly from 1610 – 1710 kHz.  The optimal time to listen is during daylight hours as propagation changes greatly after dark and you’ll hear commercial AM radio stations coming in and overpowering most EAS.  As for range, I’ve heard HAR stations as far away as 40 miles depending on ground wave conditions which can vary greatly. QSB is common. Many of these stations will rebroadcast NWS weather information when no pertinent emergencies exist and that is another way to spot them. Some highway stations I’ve heard will begin each broadcast loop with a tone, they’re all different in their approach.

Attached [at the top of the page] is a picture of the author’s Yaesu FRG-100 tuned to WRBX655 from Franklin Township, New Jersey. For an antenna I’ve used a 31 foot vertical and a loop and success will depend on using an outdoor antenna but when away from the home QTH, I’ve heard many of these stations while traveling on the roadways of America, They’re a good break casual AM radio listening.  Give it a try.


Thank you, Mario! I must admit that when I travel, I often hunt down EAS transmitters via my car’s AM radio. Besides being a good source of local information, I do know some DXers who’ve identified and logged an impressive number of distant stations when conditions were ideal. 

If you live outside the US, do you have similar networks for local information? Please comment!

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Bruce’s passion for SWLing and single transistor regenerative receivers

Many thanks to SWLing Post contributor, Bruce (VE3EAR), who shares the following:

I live in the village of Saltford, ON, Canada, near the eastern shore of Lake Huron. It’s a quiet location signal wise, and I’m lucky that I have enough property to erect some big antennas. My two favourites are a 1200 foot long terminated Beverage, aimed at 50 degrees true, which targets Europe and the UK. The other is a 333 foot perimeter delta-loop, apex up and oriented north-south. Both antennas are fed with RG-6 coaxial cables and impedence-matching transformers.

I use the loop with a recently acquired Airspy HF+ Discovery SDR and the Gqrx SDR software, in my iMac. I like to listen to amateur activity on 160, 80, and 40 metres, along with the few shortwave broadcast station that are still on the air. I also like to listen to the trans-Atlantic air traffic control stations in Shannon, Ireland and Gander, Canada.

I once heard a U2 spy plane returning from a mission over Russia!

My other hobby is designing and building simple, one transistor regen receivers, most of which tune the AM broadcast band, although I have built a couple covering the lower portion of the HF broadcast bands as well, just for a challenge. All my receivers are built breadboard style.

My favourite of them is one based upon the Vackar oscillator, with the addition of a diode detector and “Benny”, as is used in crystal radios.

Here is the schematic of the Vackar circuit:

The diode and “Benny” connect to the collector of the transistor, then to a pair of home made headphones using two telephone earpiece elements installed in a pair of hearing protectors. The receiver is both very selective and very sensitive. Here is a pic:

Most of the electronics are on a proto-board, which allowed easy component substitutions during the build. When I had it optimized, I decided to leave it that way! The controls, left to right, are on-off switch, regen, fine tuning, main tuning, and range selector switch, hidden behind the reduction drive. Audio is taken from the DET OUT jack, to either the headphones described above, or to an audio amplifier for listening with a speaker.

Bruce, it sounds like you certainly have an excellent spot and excellent antennas for DXing! I love regen receivers as well and radio design can hardly be more simple.

Thank you for sharing!

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More about hacking VGA cables to make binocular ferrite cores

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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DIY: How to build a Passive Resonant Transformer-Coupled Loop Antenna for HF reception

We recently posted a tutorial on building a simple Noise-Cancelling Passive Loop (NCPL) antenna. This prompted SWLing Post contributor, Bob Colegrove, to share his excellent article on building a Passive, Resonant, Transformer-Coupled Loop (PRTCL) Antenna:


A Passive, Resonant, Transformer-Coupled Loop Antenna for Shortwave

By Bob Colegrove

Over the years I have resisted the level-of-effort necessary to construct and maintain outdoor antennas.  Rather, I have focused on squeezing out all of the microvolts I could get inside the house. Many years ago I had access to a well-stocked engineering library, and used my advantage to gather information about the theory and development of loop antennas – a daunting undertaking for an English major.  Ultimately, by adhering to a few basic rules, some of them dating back 100 years, I found quite acceptable performance can be had with an indoor passive antenna intersecting just a few square feet of electromagnetic energy.

Theory

There are a couple of advantages of resonant loops as opposed to non-resonant ones.  The first is the fact that the signal dramatically increases when you reach the point of resonance.  The second follows from the first in that resonance provides a natural bandpass which suppresses higher and lower frequencies.  This gives the receiver a head start reducing intermodulation or other spurious responses. The downside of all this is that the resonant loop is, by design, a narrow-band antenna, which must be retuned every time the receiver frequency is changed by a few kHz.  On the other hand, there is nothing quite as rewarding as the sight (S-meter) and sound you get when you peak up one of these antennas – you know when you are tuned in.

There is nothing new about the loop antenna described here.  It’s just the distillation of the information I was able to collect and apply.  There are a number of recurring points throughout the literature, one of which is the equation for “effective height” of a loop antenna.  It basically comes down to the “NA product,” where N is the number of turns in the loop and A is the area they bound. In other words, provide the coil with as much inductance as possible.  Unfortunately, for resonant loops, the maximum coil size diminishes with frequency.

With this limitation on inductance, the challenge becomes minimizing unusable capacitance in the resonant frequency formula in order to get the highest inductance-to-capacitance (L/C) ratio possible.  Some of the unusable capacitance is built into the coil itself in the form of distributed capacitance, or self-capacitance between the coil turns. This cannot be totally eliminated, but can be minimized by winding the coil as a flat spiral rather than a solenoid, and keeping the turns well separated.

The second trick is with the variable capacitor.  Even with the plates fully open, there is residual capacitance on the order of 10 to 20 picofarads which can’t be used for tuning purposes.  A simple solution is to insert a capacitor in series, about ¼ the maximum value of the variable capacitor. This effectively decreases the minimum capacity and extends the upper frequency range.  In order to restore the full operating range of the variable capacitor, the fixed capacitor can be bypassed with a ‘band switch.’ With the series capacitor shorted, the variable capacitor operates at its normal range and extends coverage to the lower frequencies.

Construction

I have constructed similar loops covering long wave, medium wave, and shortwave all the way up to about 23 MHz.  I wanted to optimize this loop for the most active portion of the shortwave spectrum. Consequently, it covers approximately 2.6 to 12.3 MHz.  See Figure 1.

Figure 1.  A Passive, Resonant, Transformer-Coupled Loop Antenna for Shortwave

Figure 2 is a schematic diagram of the antenna.  Cd (in red) is the distributed capacitance of the primary coil, L1.  This is not tunable capacitance, but it still contributes to the resonance; likewise, the 15 pf minimum capacitance of C1.  By adding C2, the minimum total capacitance can be lowered to greatly increase the upper range of the antenna. S1 is the ‘band switch.’  It shorts out the series capacitor, restoring the maximum low frequency.

Figure 2.  Schematic Diagram

Frame – The frame is made from 3/8”-square basswood or poplar dowel (see Specialized Parts).  Two pieces, each 36” long, have been predrilled at ½” intervals to accommodate the primary and secondary coil wire (think of a tennis racket).  It is a good idea to drill holes along the length of each dowel – more than you will need. You may decide to change things later on, and drilling holes in an assembled antenna is not easy.  Also the two dowels are notched in their centers to fit together. See Figure 3 and Figure 4. The clear plastic disk in Figure 4 is a packing disk from a spindle of CDs; it is cemented to the square dowels, and used to hold them at right angles.  Any rigid, light-weight material will do.

Figure 3. Square Dowel Showing 1?2” Hole Spacing and Lacing of Secondary Coil


Figure 4. Cross Members Notched and Square Dowel Reinforcement

Primary Coil – With a coil size 36” in diameter, you likely won’t be able to get more than two turns of wire to resonate at frequencies up to 12 MHz.  This takes into account the precautions described above to minimize unusable capacitance.  AWG 22 stranded, insulated wire was used to lace this coil; ensure the dowels remain at right angles with one another.  Note that one set of holes in the dowel is skipped between the first and second turn.

Tuning Capacitor – Almost any salvaged variable capacitor can be made to work.  For a typical 2-gang unit, the gangs can be connected in series through the common rotor sections and metal frame with the stator terminals of each gang used as the outer terminals.  This will create a lower minimum capacitance as described above.

For the antenna described here, a single-gang, 365-pf capacitor (see Specialized Parts) was used with a fixed mica capacitor in series.  The minimum capacitance of the variable capacitor is nominally 15 pf. Figure 5 shows the capacitor assembly for the primary circuit. Components are mounted on a perforated circuit board, which, in turn, is mounted to the bottom of the vertical square dowel.  A portion of the base can be seen at the rear. A large diameter tuning knob is suggested, as the peak tuning for a properly constructed loop will be very sharp and require a delicate touch. As an option, I have used a planetary reduction mechanism on other antennas to give an 8:1 ratio with the capacitor shaft.

You may notice at high frequencies that the antenna is somewhat unstable with body contact of the knob or around the tuning capacitor.  This is because the resonant circuit is operating at a very high L/C ratio with capacitance at just a few picofarads. Body capacitance will tend to detune the antenna.  It may be useful to extend the knob 2 or 3 inches from the tuning capacitor with an insulated shaft.

Figure 5.  Capacitor Assembly

Secondary Coil – The secondary coil operates at low impedance to feed the lead-in.  There are two extremes governing the size of the secondary coil. A coil which is too small will not pick up much of the magnetic field generated by the primary circuit at resonance.  On the other hand, a secondary coil which is too large will overcouple or load the primary circuit. This will reduce the Q, or sharpness of the tuning.

The secondary coil is 16” diagonal at the largest turn and consists of 7 turns of AWG 20 buss wire.  Buss wire was used so the coil can easily be tapped after the 1st, 2nd, 3rd, 4th, and 6th turn.  The 7th turn is not currently used.  A tapped coil will provide better impedance matches to the lead-in when the antenna is used through a wide frequency range.  The taps are selected with a rotary switch. The taps are connected so that the outer turns are used first, and inner turns connected as needed.  It is important that unused turns remain unconnected (free) rather than shorted. See Figure 6.

Figure 6.  Secondary Coil Switch

Lead-in – A twisted pair of AWG 22 stranded wire is used as the lead-in.  This will be more flexible than coax. The lead-in should be kept as short as possible and twisted tightly so it will not pick up any signal by itself.  This is important at shortwave frequencies. A twisted pair can be fabricated from two lengths of wire with one set of ends anchored in a vise, while the remaining ends are twisted in the chuck of a hand drill.  Most portable radios are equipped with a standard 1/8” phone jack at the external antenna connection point.  So, this antenna is terminated with a 1/8” phone plug.

Base – There is nothing special about the base.  Your only guidance should be to make it as stable as possible.  Since the frame is light, most of the weight will be at the bottom with the capacitor assembly and other parts.  That helps stability. This antenna uses a 5” plastic jar lid for the bottom. Keep the base small, as the antenna will likely be operated on a desk or table.

Operation

The antenna is intended to operate in close proximity to the radio, such as on a desk or table.  There must be sufficient space to rotate the loop laterally. As described, this antenna has a range of 2.6 MHz through 12.3 MHz with a band overlap around 8 MHz.  Depending on your selection of capacitors, your range and overlap may be slightly different.

  1. Tune the receiver to a desired frequency.
  2. Set the band switch on the antenna to the corresponding band.
  3. Tune the antenna capacitor to resonance (peak signal).
  4. Rotate the secondary switch to the position of maximum signal strength.  Begin with the fewest turns (generally one) in the secondary.
  5. It may be necessary to repeak the primary circuit.

Repeat the procedure to test operation of the upper or lower band.

Unlike similar loops for long and medium wave reception, this antenna is not especially responsive to direction for peak or null signal reception.  However, you will find it very useful to reduce or possibly eliminate locally produced noise. Simply rotate the antenna on its base.

Modification

The basic concept for this antenna can easily be extended to higher or lower frequencies.  Removal of the inner turn of the primary will significantly raise the upper frequency; whereas, adding turns will increase the lower range.  Note that the lacing of the primary coil skips one set of holes in the square dowels between the first and second turn. This minimizes distributed capacitance between turns.  This separation should be maintained if additional turns are added to lower the operational frequency.

Specialized Parts

Some sources for square wood dowel and single-gang 365 pf variable capacitors are listed below.  The author does not endorse any of them. Prices for similar capacitors vary widely.

Square wood dowel:

Variable capacitor (365 pf):


Bob, thank you so much for sharing this excellent, detailed tutorial. Although I don’t have the exact same variable capacitor, I have all of the other components to make this antenna. I will have to put this on my Social DX bucket list! Thank you again!


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

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!

Readers, you can follow Oscar on Twitter by clicking here.

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Beating the Quarantine Blues: Readers build homebrew NCPL antennas

My homebrew version of the NCPL antenna.

Recently, I published a step-by-step guide on building a Noise-Cancelling Passive Loop (NCPL) antenna. Evidently, this antenna project really resonated with readers! [See what I did there? If so, my apologies!]

I think this passive loop antenna project has been so appealing because (1.) most of us around the world are sheltering at home due to the Covid-19 pandemic and (2.) this project is simple and you likely have all of the components in your tool shed or junk box at this very moment.

A number you have written to tell me about your antenna builds and some of you have agreed to allow me to share your projects with the SWLing Post community.

Below, you’ll find three fine homebrew examples of the NCPL antenna–all of which were made with what these fine radio enthusiasts had on-hand:

Jerome van der Linden

Jerome’s NCPL antenna

Jerome writes:

Hello Thomas,

Well, I took up the challenge and built a NCPL antenna pretty close to your instructions.

Unfortunately, the coax I had available used (had aluminium shielding, and too late into the project I discovered solder would not take to it. My solution was to cannibalize a coax cable joiner (see photos attached), where – normally – the centre conductors are joined / held by a plastic centre piece and screw fittings.

The braid / shield for the two bits of coax is clamped / squeezed by an outer metal piece. My cannibalising effort involved removing the plastic centre bit which joins the two centre cores, and keeping just the outer metal component which I used (after completely cutting through the coax) to clamp the two metal braid sections, while the two centre copper bits were far enough apart for me to solder the leads for the ferrite balun.

Of course, I could not do the same at the top of the loop where the internal and external conductors need to swap over. I soldered some quite thick copper wire (perhaps 2mm in diameter) to each center core, pushed the center core into the opposing coax and coiled the 2mm thick copper tightly around each end of the coax.

Once it was all taped up it looks no worse than yours, and it does indeed WORK! [see photo above]

Here in Oz, I could not source the identical ferrite, but I think it’s pretty close. Best performance for me is on 11MHz, where the Radio New Zealand signal on 11725 is markedly better using the loop than the internal whip on my Tecsun PL-880. Other bands not quite so significant, but the Noise level is definitely lower.

As you say, Jerome, once all packaged up, it looks great! Sure, the mixture of materials you had on hand wasn’t ideal (aluminium shielding, etc.) but you found a way to make it work from the resources you had in your home. And I love the fact it’s lowed your RFI level!  Thanks for sharing!

Giuseppe Morlè (IZ0GZW)

Dear Thomas,

I’m Giuseppe Morlè (IZ0GZW), from Formia, central Italy, on the Tyrrhenian Sea.

I wanted to build your noise canceling loop seen on SWLing Post …
seems to work well especially from 40 meters. upward…
the diameter is 50 cm.
I will do other tests soon.
You can see the initial test on my YouTube channel via this link:

Thanks for the nice idea and a greetings from Italy.
73. Giuseppe IZ0GZW

Thank you, Giuseppe! What an amazing view you have there from your balcony! I’m quite impressed your PL-660 can take advantage of this design so well. We look forward to your other tests! Grazie mille!

John Mills

Hi Thomas,

My idea was to use a fitness hoop 75cm diameter bought off eBay. I removed the flashy striping to reveal a plastic like hoop that was joined in one spot with a plastic insert.

I have wrapped the whole hoop in tin-clad copper foil tape that has a conductive adhesive backing, but to be sure I have soldered all the overlapping seams. I drilled two holes opposite each other for the upper foil connections and the lower exit to the Balun.

Hopefully the three pictures will be helpful, I did the 4 turn design on Airspys website and it works really well connected to my RSPdx.

73

John

Thank you, John. What a fantastic way to build the NCPL antenna without using a coax for the loop. Indeed, since your plastic hoop has a small insert in the middle, you’ve an ideal spot to make the shield to center conductor cross-over.  Very clever! I also like how you mounted the 1:1 Balun (or Unun) on a small board. Thanks for sharing this.

Got Loops?

Post readers: If you have your own unique NCPL antenna design, please consider sharing it with us! Contact me with details and photos. I’ll plan to publish at least one more post with examples here in the near future.


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DIY: How to build a Noise-Cancelling Passive Loop (NCPL) antenna

I’ve gotten an number of inquiries from SWLing Post readers asking for a step-by-step guide to building the passive loop antenna I’ve mentioned in a number of previous posts. This antenna is the homebrew version of the commercially-available  Airspy Youloop.

It works a treat. And, yes, folks…it’s fun to build.

There are a number of loop designs out there, and to distinguish this one, I’m going to henceforth refer to this loop as in the title above:  the Noise-Cancelling Passive Loop (NCPL) antenna.

Before we start building, a little antenna theory…

I’m neither an engineer nor am I an antenna expert, so I actually turned to Airspy president and engineer, Youssef Touil, to learn how, exactly, this passive loop works. Youssef was the guy who experimented with several loop designs and ultimately inspired me to build this loop to pair with his HF+ Discovery SDR and the SDRplay RSPdx. “The main characteristic of this loop,” Youssef notes,  “is its ability to cancel the electric noise much better than simpler loop designs.” Got that!  [See loop diagram below]

“The second characteristic of this loop antenna is that it is a high impedance loop, which might appear counterintuitive. This means it can work directly with many receivers that have a low noise figure, in order to mitigate the impedance mismatch loss.

Note the resonance lobe near 4MHz. The resonance frequency is controlled by the diameter of the loop, the parasitic capacitance of the cable, and the loading from the transformer. It happens to be located right where we need it the most.

The transformer is basically a 1:1 BALUN that covers the entire HF band with minimal loss. Our BALUN has typically 0.28 dB loss.

[…]By connecting the center of this outer shield to the ground of the transmission line, you effectively cancel all the electric noise. The BALUN is required for balancing the electric noise, not for adapting the impedance.

[…]If you want to boost the performance in VLF, LW and MW, you can try a different impedance ratio, but this will kill the higher bands.”

What makes this loop so appealing (to me) is that it can be built with very few and common parts–indeed, many of us have all of the items in our junk boxes already. As the name implies, it is a passive design, so it requires no power source which is incredibly handy when you’re operating portable.

When paired with a high-dynamic range SDR like the Airspy HF+ Discovery or SDRplay RSPdx, you’ll be pleased with the wide bandwidth of this antenna and noise-cancelling properties.

If you don’t care to build this antenna, Airspy sells their own version of this loop for a modest $35 USD.

But building an antenna is fun and you can tweak the design to customize performance, so let’s get started:

Parts list

  • A length* of coaxial cable for the loop (see notes below regarding length)
  • Another length of cable terminated on one end with a connector of your choice as a feed line
  • A BN-73-302 Wideband 2-hole Ferrite Core
  • Enough coated magnet wire for a total of eight turns on the BN-73-302
  • Heat-shrink tubing or some other means to enclose and secure the cable cross-over point and balun. (You may be able to enclose these connection points with PVC or small electrical box enclosures, for example)
  • Electrical tape

Tools

  • A cable stripper, knife, and/or box-cutter
  • Soldering iron and solder
  • A heat gun (if using heat shrink)
  • Some patience 

*A note about loop cable length: Vlado and I made a loop with 1.5 meters of cable. The Airspy Youloop ships with two 1 meter legs that combine to give you an overall loop diameter of about 63.6 cm.

Step-by-step guide

When I first decided to build this loop, it was only a day prior to a trip to the South Carolina coast where I planned to do a little DXing. I didn’t have all of the components, so I popped by to see my buddy Valdo (N3CZ). Vlado, fortunately, had all of the components and was eager to help build this loop. As I’ve mentioned in previous posts, Vlado is an amazing engineer and repair technician, so when I say “we” built it, what I really mean is, Vlado did!  But I could’ve done it myself.

This is actually a very simple build––something even a beginner can do, as long as they’re okay with using a soldering iron. It does take patience preparing the loop cable properly. Take your time as you start, and you’ll be on the air in an hour or two.

1. Strip the ends of the loop cable.

Although your cable type and diameter may vary, strip back the cable ends roughly like this.
To make finding the middle of the cable easier, we taped off the ends.

2. Make an opening in the middle of the cable to attach Balun leads to center conductor.

This is the trickiest part of the whole operation. The goal is to create an opening to tap into the center conductor of the cable.

You need to open a hole in the middle of the cable by

1 cutting away a portion of the outer jacket;

2 carefully separating and opening the shielding;

3 digging through the dielectric core, and finally

4 exposing the center conductor of the cable

Try to make an opening just large enough to gain access to the cable’s center conductor, but no bigger. Don’t allow any piece of the shielding to touch the center conductor.

When you reach the center conductor, expose enough of it so that you can clip it in the middle and create an opening to solder your balun leads to both conductor ends.

Once you’ve finished with this step, your cable should look something like this…

In the photo above, note that the shielding is completely pulled away, the dielectric core has been cut through, and we’ve clipped the center conductor, leaving a gap large enough to solder.

3.  Make a 1:1 Balun

Grab your BN-73-302, and with the coated magnet wire, make four windings on one side, and four on the other. It should look like this:

Don’t have a binocular ferrite core like the one above? If you have a broken cable with ferrite cores, you can hack one! Click here to learn more.

4. Connect the Balun to a feed line.

Vlado just happened to have a BNC pigtail in his shack (he’s that kind of guy), so we cut and stripped one end, then connected the center conductor and shield to one side of the balun. We then enclosed the balun in heat shrink tubing to make it a little easier to attach to the loop later:

Of course, you could also create this junction in a small enclosure box or short cross-section of PVC. There are a number of ways you could secure this.

Youssef also added the following note about the feedline:

To use the NCPL antenna without a preamp, it is recommended to keep the length of the cable below 10 meters. The supplied Youloop 2 meter cable [for example] is sufficient to keep the antenna away from the magnetic interference of a computer or a tablet, and has very low loss and parasitic capacitance.

5. Connect Balun to the coaxial loop.

To make a solid connection, tin both sides of the center conductor. Next, attach the other end of the balun leads to each portion of the center conductor, as seen below:

Update: Note in the loop diagram near the top of the page that the ground wire on the output connector connects to the loop coax shielding on the primary side of the balun. I don’t recall that we did this in the build, but I would encourage you to do so. This should result in even lower noise, although admittedly, I’m very impressed with the performance of ours without this connection. Thanks to those of you who pointed out this discrepancy!

6. Secure the Balun/Coax junction.

Since this loop is intended to be handled quite a lot in the field, make sure the junction point of the balun and coax loop is secure. Again, we used several layers of heat shrink tubing since we had some in the shack.

7. Solder and secure the cross-over point.

Next, create the cross-over point of the loop by simply attaching the center conductor of one end of the cable to the shielding on the other end…and vice versa.

Before you grab the soldering iron, howeverif, like we did, you’re using heat shrink tubing to secure the cross-over point of the loop in the next step, you’ll first need to slide a length of tubing onto the coax before you solder the ends together. Vlado, of course, thought of this in advance…I’m not so certain I would have!

Take your time soldering this connection and making it as solid as you can. If you solder it correctly, and you’re using a high-quality cable as we did, the cross-over point will be surprisingly durable. If you’re using a thinner cable, simply make sure the connection is solid, then use something to make the junction less prone to breaking––for example, consider sealing a length of semi-rigid tubing around this point.

Vlado cleverly added heat shrink tubing around the cross-over point to protect and secure it.

You’re done!

That’s all, folks! Now you’re ready to put your loop on the air.

Depending on what type of cable you used for this loop, you might require or prefer some sort of dielectric structure to support the loop so that it maintains the ideal round shape. My loop maintains its integrity pretty well without supports. I’ve supported it a number of times with fishing line/filament from two sides (tying on at 10 and 2 o’clock on the loop). That seems to work rather well.

In this setup, I simply used the back of a rocking chair to hold the antenna. As you can see, the loop maintained its shape rather well.

If you’d like to see and hear how this antenna performed on its first outing, check out this post.

Show the Post your loop!

If you build a NCPL antenna, please consider sharing your design here on the SWLing Post! Considering that there are a number of ways this loop can be built, and likely even more optimizations to improve it or make its construction even easier, we’d love to see your designs and/or construction methods. Please comment or, if you prefer, contact me.

And many thanks to my good friend Vlado (N3CZ)  for helping me with this project and allowing me to document the process to share it here on the Post. Got a radio in need? Vlado’s the doctor!


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