Many thanks to SWLing Post contributor, Bill Hemphill (WD9EQD), who shares a PDF copy of the Panasonic RD-9820 Antenna Coupler we recently mentioned in a post. He notes that he can’t remember how he found this manual, but thought he’d share it.
Click here to download the RD-9820 manual as a PDF.
Thanks, Bill!
Wellbrook Mag Loop antenna at Mark Fahey’s QTH near Sydney, Australia.
Many thanks to SWLing Post contributor, David Goren, who writes:
I need a new power supply for one of my Wellbrook loop antennas.
Do you know of good source for reliable ones? I forgot where I obtained the last replacement which worked fine until the wire attaching to the plug worked loose.
Here are the specs:
Plug in Class 2 Transformer
Model: DC1200300R
Input: 120VAC 60 Hz 9W
Output: 12V DC 300mA
manufacturer: Sandin Ltd.Searching online delivers a mixed bag of somebody’s old power supply.
Post Readers: Any suggestions for David? I’m sure he’s particularly interested in a good quality power supply–one that’s quiet and would last a few years. Please comment and include links when possible!
Many thanks to SWLing Post contributor, Mario Filippi (N2HUN), who recently discovered a model RD-9820 antenna coupler for the Panasonic RF-2200. Mario states, “[The] price is reasonable and they take offers.”
Please, someone purchase this before I do in a moment of weakness. I’ve two RF-2200s, but do not have the matching coupler. It is incredibly temping even though I know I’d rarely use it!
Click here to view on eBay (this partner link can support the SWLing Post)
My wife has an amazing ability: when she’s deep into research, writing, editing, or creating something, she has a laser-focus like none other: she can tune out the world around her to the point that it’s honestly hard to get her attention. She can work in almost any environment, and tune out (nearly!) all distractions. It’s quite impressive. She credits this ability to focus in distracting surroundings to our children, who at a young age developed the less-rare ability to generate noise, both wide in variety and sometimes quite intense in volume.
Me? Completely the opposite.
When I’m writing or working on a project––indeed, whenever I need to concentrate––I either have to work in a controlled environment where I have few interruptions, or I have to artificially create that controlled environment. I usually do this through the use of an ambient noise or instrumental (non-vocal) music. It’s rare that I’m working in an environment with no interruptions, so being able to manufacture my own audio space is important for my productivity.
When I’m here at SWLing Post HQ, I’ll often tune to an HF frequency that has no signal occupying the space. In other words, I’ll listen to shortwave radio static that might include the odd ionosonde sweep and occasional static crash….it creates a white noise that, in essence, nulls out everything else around me. Plus, as a radio geek, I confess to feeling quite at home in that static.
To help me catch some zzzs when I travel, I’ll often do the same: simply tuning to an unoccupied HF frequency and letting it play through the night. I find that it nulls out hotel hallway traffic, like doors banging and loud talking, allowing me to get some needed rest.
Photo by Jp Valery
I also turn to noise generators and numerous YouTube channels that specialize in long ambient field recordings, because finding a reliable (unoccupied) radio frequency doesn’t always work due to garrulous local radio interference or simply a lack of free space on the FM band.
This year at the Winter SWL Fest my friend, David Goren, recommended a website––and accompanying application––called MyNoise.net. As an audio engineer and radio producer, David has a finely-tuned ear and can notice looped sounds, audio irregularities, and poorly-made recordings. So I knew if David Goren was impressed with this collection of ambient noises, they would be first-class.
MyNoise.net is the product of Dr. Stephane Pigeon, a man with an impressive CV that includes consultant work for Roland Corporation and numerous audio websites and applications.
What makes his site so unique is: 1) the sheer number and variety of ambient soundscapes, and 2) the ability to finely-tune and customize each sound in a remarkable number of ways.
Want to travel to a pebble beach, a primeval forest, a Japanese garden, or fall asleep on the bridge of a starship? Yeah, you’re covered––really. And not with, as is typical, short hiccuping loops with background muck imbedded: the MyNoise collection (at time of this post) contains over 200 customizable sound generators, with lengthy live field recordings, and they’re clean. The real deal…high fidelity at its best.
If you like ambient audio, his site provides an incredibly rich deep-dive…
But don’t take my word for it. Listen for yourself!
myNoise slider controls allow you to change the level of audio tracks and loops.
When David first introduced me to myNoise, he pointed out two soundscapes in particular: one was called “Shortwaves,” the other, “Numbers Stations.” (Now that’s what I’m talking about!) Every night of the SWL Fest, I listened to these two noise machines as I slept. It was wonderful.
With permission, I have made a couple one-minute audio recordings of the two radio-specific soundscapes from myNoise.net. Keep in mind that these recordings were set at a preset level and left alone; in other words, I did not move the control sliders during the recording. In reality, the sounds can be tailored to your listening pleasure via the sliders and generous array of controls. By the way, I suggest wearing headphones.
While I love these two radio sound generators, I have to say, I’ve truly enjoyed exploring the more than 200 sound generators also available on myNoise.
MyNoise.net is a free website supported by user donations. (Donations, by the way, can unlock an array of extra features and sounds.) Even though I have the app (see below), I still sent a bit of extra support though their website; after all, this is just the sort of project I love supporting.
MyNoise is also available as an iOS or Android app. If you have a mobile device or tablet, I highly recommend downloading the app and purchasing the full set of recordings for a mere $10.
A screenshot of the myNoise app running on my iPad
Stephane also has a YouTube Channel with a number of soundscapes.
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.
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:
*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.
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.
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.
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.
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.
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.
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!
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. 
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, however…if, 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.
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.
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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Almost two weeks ago, at the 2020 Winter SWL Fest, I gave a presentation called “A New Era in Portable SDR DXing.”
The presentation was essentially an in-depth version of an article I published in the January 2020 issue of The Spectrum Monitor magazine (see cover above).
I devoted a good portion of the presentation describing how to build a passive loop antenna design by Airspy’s engineer and president, Youssef Touil. This passive mag loop takes advantage of the Airspy HF+ Discovery‘s exceptionally high dynamic range and is an impressive performer.
The homebrew loop on the balcony of a hotel.
You may recall, I posted a short article about this loop in November after enjoying a little coastal DXing.
In short? This passive loop antenna pairs beautifully with the Airspy HF+ Discovery. I’ve also been very pleased with results using the new SDRplay RSPdx on the mediumwave band where the receiver now sports a high dynamic range mode.
After returning from the Winter SWL Fest last week, I was hit with an upper respiratory bug. No doubt, a souvenir of my travels! It wasn’t the flu (I was tested), nor COVID-19, but it did knock me off my feet for a few days with fever, coughing, and headaches. You might have noticed a lot less posts last week and almost no replies from me via email. I’m only now feeling totally human again and trying to catch up with my backlog.
Shortly after my SWL Fest presentation, I realized I made (at least!) two mistakes. I had planned to post corrections here on the SWLing Post last week, but the bug delayed all of that, so here you go:
When Youssef started experimenting with passive loop antenna designs, he posted a few schematics of at least three build options.
Although I described how to build my passive loop antenna, I grabbed the wrong schematic for my presentation slides. Many thanks to those attendees who noticed this.
Here is the schematic I should have shared:
Note that the transformer has four turns on both sides (the one in the presentation had 4:2).
Again, apologies for any confusion.
If you’re not inclined to build your own passive loop antenna per the diagram above, Airspy is planning to manufacture and sell a lightweight, high-performance loop of a similar design.
Prototype of the Airspy Youloop in the field (note bright blue cable jacket)
During the presentation, I called the future AirSpy antenna, the “Spytenna.” I was incorrect. (Turns out, I got this name from an early antenna schematic and somehow it stuck in my head!)
Airspy is calling their passive loop antenna the Youloop. Youssef posted the following note in the Airspy email discussion group:
We are currently arranging the shipping of the affordable passive version to Airspy.us and RTLSDR Blog.
Btw, It’s called “Youloop”
Many thanks to Richard Langley and a number of other readers who pointed this out last week.
I’ve had a prototype of the Youloop since November and brought it to the SWL Fest and presentation. It’s a quality antenna and incredibly compact when disassembled and rolled up.
When the Youloop is available to order, we’ll post links here on the SWLing Post.
Once I catch up here at SWLing Post HQ, I plan to publish detailed construction photos of the homebrew loop antenna.
Many of you have questions about how to tap into the center conductor at the mid-point of the loop. These photos should help guide you.
Stay tuned!
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Many thanks to SWLing Post contributor, Joachim von Geisau (DH4JG), for the following guest post:
by Joachim von Geisau (DH4JG)
The Friends of Radio NRW – an independent group of shortwave listeners and radio amateurs in Germany – have been organizing 2-3 SWL camps per year for a number of years, where they meet as far away as possible from electrical noise in order to listen to shortwave together.
To distribute antenna signals, we have previously used an RFT AVV01 antenna distributor.
At an SWL camp there are high demands on signal distribution. Both very weak and strong signals should be distributed well, un-distorted, without noise and other interference. The signal levels are approximately between 0.2 ?V (S1) to over 5 mV (S9 + 40 dB), with a frequency range of at least from 150 kHz to 30 MHz, thus broadcast bands from LW to SW are covered, also all amateur radio bands from 160 m to 10 m.
Popular among listeners are RFT AVV01 RF distributors from the former GDR, at least 30 years old. However, the use of an AVV01 has several disadvantages: high power consumption, difficulties in getting spare parts, high upkeep with corroded contacts and the like. In addition, the transmission of the LW/MW range drops, which is a disadvantage especially for MW listeners. The NV-14 system from Rohde & Schwarz from the late 1960s has the same weaknesses.
Two years ago, the desire arose to develop a concept for the replacement of the RFT system.
The following aspects were important:
The amateur radio market offers several products for RF signal distribution (e.g., ELAD, Bonito et al.), but no solution to distribute 6-8 antennas to 10-12 receivers. It was clear from the beginning that DIY development was inevitable.
The starting point of the considerations was to integrate remote power supply for active antennas, an amplifier stage and a distribution network.
Such a distributor is able to distribute an antenna signal to several receivers; several antennas require several such distributors, which led to the decision to implement the project in plug-in technology.
With OM Frank Wornast DD3ZE (www.dd3ze.de), known e.g. for his converters, filters and the like, a well-known RF developer could be won, who took over the implementation of the concept based on the detailed specifications. OM Wornast first produced a prototype without remote power supply, which already did an excellent job of RF signal distribution.
A “hardness test” at an SWL camp showed that this distribution module easily fulfilled our requirements: Frequency range 10 kHz – 50 MHz (also usable with a few dB loss above 50 MHz). Supplemented by a switchable remote power supply and a 90V gas discharger at the antenna socket, the final PCB layout was created, representing the core of the new HF distribution system of Radio Freunde NRW
The distribution block consists of the following components:
The device is characterized by a very smooth frequency response and has a very low inherent noise. It offers the possibility of using levels of -120dBm with very good SNR
to process up to strong levels of up to + 14dBm. In addition, the reception on VLF is now possible, which did not work with the previous system.
The PCB is designed in a very practical way: series resistors for LEDs are integrated as well as fixing points for coaxial cables. The remote power supply can be switched separately, but can also be used permanently by means of a jumper.
With this concept, the distribution block can be used universally: use on an active or passive antenna with distribution to several receivers, by means of a step switch in front of it also for several antennas; if you leave the remote feed path unconnected, the block can also be used as a simple distributor, so it is almost universal for hobby purposes.
For use on SWL camps, we decided to install them in 19 “rack-mount technology. A standard rack can thus accommodate 4 distributors and a power supply, allowing distribution of 4 antennas to 12 outputs each. An example of the installation is shown in the following picture: Parallel to the input is another BNC socket, which is connected via a C 100 nF where the input signal can be used DC-free for measurement purposes or the like. The distribution unit is installed in a transport case. The components themselves are mounted in slide-in housings which are provided with a corresponding front panel: Such front panels might be obtained from CNC manufacturers.
On the back + 12V DC must be supplied as operating voltage. For the power supply units, we opted for linear power supplies because we have made the best experience with these without interference. For a distribution unit with 4 slots, a power supply with 12V 1A is sufficient – each distribution block takes about 55 mA, an active antenna up to 150 mA, so even with “full load” a power supply with 1 A is sufficient. The distributor was tested with various well-known active and passive antennas, including a PA0RDT MiniWhip, active loops, long wires and T2FD.
Due to the wide input voltage range, the module can handle nearly any antenna. The cost for a distributor for 4 antennas amounts (depending on the version: housing, sockets, switches, power supply, etc.) to about 700-1000 €. That may seem a lot at first glance. However, taking into account that a simple 5-gang distributor from mass production costs already around 250 ¬, the cost of the distribution of 4 antennas to each up to 12 outputs are not that much. The Friends of Radio NRW use two of these distribution units for SWL camps.
If you are interested in building one, please contact the author ([email protected]) for further information. The development history of the distribution unit is also available at www.dx-unlimited.eu.
Wow! What a beautifully engineered antenna distribution solution, Joachim! I love how you worked together to sort out all of the requirements for your system then build it for ultimate performance and flexibility. No doubt, you and your colleagues at Radiofreunde NRW posses a lot of design and engineering skills! Simply amazing and thank you for sharing your design with the radio community!
Contact Joachim for more details and check out notes and discussion at www.dx-unlimited.eu (may require registration).