Category Archives: Accessories

Airspy Youloop and Homebrew Passive Loop Antenna designs

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.

Overdue corrections…

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:

#1 Schematic of my homebrew passive loop antenna

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.

#2 The Airspy Youloop passive loop antenna

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.

More to come!

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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Guest Post: Radiofreunde NRW’s DXpedition-grade signal distribution system


Many thanks to SWLing Post contributor, Joachim von Geisau (DH4JG), for the following guest post:


Signal distribution at SWL camps: The new JK-1000 HF distributor

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:

  • Frequency range at least 100 kHz – 30 MHz, as linear as possible
  • frequencies below or above desirable
  • Running on 12 V DC or integrated noise-free power supply
  • Remote power supply for active antennas
  • Robust structure
  • Versatility
  • Hobby friendly budget

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:

  • Input with 90V arrester & 100 kOhm MOX resistor to dissipate static interference
  • Remote power supply, switchable, 10-14 V, max. 350 mA
  • Amplifier stage with 14-14.5 dB
  • Resistor network for distribution

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 (dh4jg@darc.de) 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).

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Troy finds Tenergy Centura low self-discharge batteries a great value

Many thanks to SWLing Post contributor, Troy Riedel, who recently shared his observations about low self-discharge batteries with me. He has kindly allowed me to post his message here on the SWLing Post. Troy notes:

I’ve lauded Tenergy rechargeable NiMH batteries and I wanted to share something with you.

Mighty Bright Navigation Light

I have a box of Mighty Bright combination Red & White LEDs that I use for astronomy (they’re a clip-on light used by pilots and also marketed for use in the automobile – they hold three AAAs).

Approx. 18-months ago I put fully charged Rayovac, Energizer, Eneloop & Tenergy Centura Low Self-Discharge batteries in them.

Last night I pulled them out.

Rayovac: 0% charge.
Energizer: 0% charge
Tenergy Centura LSD & Eneloop: both averaged ~ 70% of a charge … (6 batteries in two lights) … though some of the Eneloops had a slightly higher charge (maybe 2 – 5% higher), most of the batteries were virtually indistinguishable.

You can buy 8 Tenergy for $9.99 while 8 Eneloop cost $17.99.

If cost were not an issue I’d still go with Eneloop (a longer track record), but the Tenergy is a worthy – no, very worthy – value vs. performance choice.

Panasonic Eneloop batteries

Thanks for sharing your real-world feedback, Troy.

I’m a big believer in low self-discharge rechargeable batteries. Indeed, I’ve almost replaced all of our “legacy” (meaning not low self-discarge) NiMH AA and AAA batteries with Eneloop cells.

Eneloops are pretty pricey, though, and the costs add up if you have a lot of devices that require batteries. As you might imagine, portable radios demand a steady supply of AA batteries at SWLing Post HQ.

I’ve been very pleased with my Eneloop batteries and, frankly, haven’t switched brands because of the terrible luck I’ve had with “legacy” rechargeables in the past. I’ve purchased so many that worked wonderfully for a few months then began to lose their capacity even though I employ an intelligent charger that properly breaks-in and cycles them.

I do believe I’ll add some Tenergy AA and AAA batteries in the mix now–especially for non-radio applications like lighting, remotes, clocks, and other consumer electronics.

Click here to check out Tenergy batteries and click here to check out Eneloop batteries at Amazon.com (affiliate links support the SWLing Post).

What are your observations?

Have you used Tenergy and Eneloop batteries? What about other brands?  Please share your thoughts by leaving a comment on this post.

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Commercial circuit simulator, Micro-Cap 12, now a free download

Many thanks to SWLing Post contributor, Grayhat, who writes:

Maybe it’s old news for you, I just discovered it and thought you may
be interested, the commercial circuit simulator “Micro-Cap 12” which
was sold at around $4,500 for each license is now *free*, I found the
information here along with some further details:

https://hackaday.com/2020/01/08/commercial-circuit-simulator-goes-free/

The decision of releasing it as freeware seems to be related to the
fact that the company selling it (Spectrum Software) closed (not sure
for the reasons); anyhow, since the site or the download link may
disappear in some time, I think it would be a good idea to pick a copy
of the software, the full CD image including the program, libraries and
everything else can be downloaded from this page

http://www.spectrum-soft.com/download/download.shtm

Thank you for the tip! I agree with you about grabbing a full install of the application while you can!

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USB Charging Cubes and Cables: Bill’s tests prove that not all are created equal

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


Power Cubes and USB Cables Multiply Like Rabbits

by Bill Hemphill (WD9EQD)

If your house is like mine, you have a box or drawer somewhere that has a tangle of 5V power cubes and cables.  This is what one of my drawers looks like:

And yes I do have two full drawers.

Every new toy I receive comes with another cable and a power cube.  With Christmas coming, we can all look forward to even more of them.

But I have learned  that not all power cubes or cables are created equally.  Earlier this year I realized that sometimes my tablets would take forever to charge and other times they seemed to re-charge a lot faster.  That got me wondering what was causing the difference. I found that switching power cubes or switching cables could make a difference.

I decided to try some experiments.  First I acquired a couple of Drok USB testers.  These are small, inline, digital USB voltage and amp testers.  They clearly show the amp draw and the voltage being furnished to the device being charged.

Second step was to gather up my power cubes and test them against a device that would load the cube close to it rated capacity.  I quickly found that ANY power cube I owned that was rated at less than 1 amp at 5 volt was not capable of providing anywhere near their rated capacity.  Some would drop all the way down to 4.11V at 0.47A. So I made the decision to throw away ANY power cube that was rated at less than 1 amp at 5 volts. That trimmed down the total number.

I proceeded to label each of the remaining power cubes from 1 to 10.  Following is list of the cubes with their power rating:

Note:  Power cubes 8, 9 & 10 have two USB ports.  I had purchased these so that I could charge two devices at once.  I had also thought of using them to power two Raspberry PI computers.

The following tablets were discharged down to less than 15% capacity:

  • Amazon Fire 10” HD Android Tablet
  • Amazon Fire 8” HD Android Tablet
  • Winbook 8” Windows 10 Tablet

Typically the Fire 10” and the Winbook will draw about 1.8 amps when charging.  The Fire 8” draws slightly less than one amp. So they would make great test subjects to exercise the capability of the power cubes and cables.

I tested several of my cables with the Winbook to make sure that the cable used for testing would provide the amps and voltage.  I then tested each of the power cubes using that cable with each of the tablets and got the following results:

Notes:

  1. All the cubes performed very well within their rated capacity.
  2. It’s interesting to see how the 1 amp rated cubes did with a higher draw.
  3. It’s clear that the cubes do NOT have limiting to their rated capacity.  I would have thought that the 1 amp cubes would have been limited to providing up to but not over that amount.
  4. Likewise, I would have thought that the tablets would limit amp draw when the voltage drops below 5 volts.

Next test was to see if the selection of cable makes a difference.  I randomly selected some cables and labeled them. I used one of the Anker power cubes since they perform the best.  The results were very interesting:

Notes:

  1. The cables were of various lengths from 12” to 36”.  Some of the short cables performed poorly and some of the long cables performed very well.  So cable length is not necessary an indication of how it will perform. You have to test it.
  2. All the cables performed well at 0.95 amps.  But some of them could not adequately handle higher loads.
  3. I had accidentally left the Winbook charging, so it was not at maximum charge during the cable tests.
  4. The cables in Red have been thrown away.

I have two special cables that I had purchased.  These were power splitter cables, single USB to two mini USB.  I had used these for a while running two Raspberry PI’s off of one power cube.  But they would reset every so often, so I thought that the splitter cable might not be providing power evenly between the two PI’s.  Time to test my theory.

Notes:

  1. The a & b denotes each of the legs of the spitters.
  2. It’s pretty obvious that the two legs do NOT provide the same capacity at the higher loads.
  3. These cables will also be tossed away.

Now for some fun testing.  I thought I would try to load the Anker Dual Port power cubes to see if they will provide their rated power on each port.

Very impressive.

And last, I have two Anker large capacity 5V battery packs:

Battery one – Anker Astro E7, Model A1210.  Capacity: 26800mAh. Rated: 4A@5V – 2A max per port.

Battery two – Anker Powercore Model A1277.  Capacity: 26800 mAh. Rated: 4A@5V – 2A max per port.

Update [18 Dec 2019]:  I had received a comment that I didn’t show the Anker Dual Port with both ports fully loaded.

I did another test – this time adding in my Pixel cell phone which draws about 1 amp when not fast charging.

Attached is photo showing the Anker power supply fully loaded:

(Fire 10 & Pixel on one port & Fire 8 and Winbook on the second port)

Port 1: 2.59A @ 5.03V

Port 2: 2.75A @ 5.01V

Pretty good for a cube only rated at 2.4A per port.

Conclusions:

  1. Don’t just select a random power cube from that drawer.  Be sure to select one that will provide both the required amp draw at a minimum of 5 volts.
  2. Likewise, don’t just select a random usb cable from that drawer.  Make sure the cable will carry the required current and voltage.
  3. The Anker products that I have (power cubes and batteries) produce the rated current and voltage.  I would highly recommend them.
  4. Where before  I had two drawers full of power cubes and cables; after throwing away about half of them, it has been consolidated into a single drawer.
  5. I may buy some more of the Anker power cubes.

Wow…thank you, Bill!

Your timing is impeccable. I’ve also been weeding out a number of USB power cubes from my own “drawer-o-plenty!” I had been simply looking at the rated amount on each cube and deciding which ones to keep–tossing all of the lower amperage ones. I think I may actually save a little time and simply invest in a few Anker Elite Dual-Port chargers (note this Amazon affiliate link supports the SWLing Post). At present, the white ones are $8.99 each. I especially like the fact that the plug folds and that it automatically switches between voltage standards (100-240 VAC) while travelling between countries.

Side note: I have also been very pleased with Anker’s customer support. I purchased some Soundcore Anker bluetooth earbuds in January–by November they started having issues maintaining a Bluetooth connection. I contacted Anker customer service and after a little troubleshooting, they dispatched a new replacement pair.

Although I know well that not all USB cables are created equally, I would have never guessed there would be much difference in terms of charging ability. Your tests certainly prove otherwise. I suppose I should not be surprised because most “free” USB cables that accompany consumer electronics are of the cheapest quality. I imagine many of the conductors/wires inside those cables are as thin as a hair, hence can’t handle the demands of devices like tablets and larger smart phones.

Again, Bill, thanks so much for sharing this excellent guest post!


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New Product: Tecsun AN-48x (now available)

Anon-Co just announced that Tecsun has released their new portable, active loop antenna – the AN-48x (27.99 plus shipping) – and it is available for purchase.  Copied below is their announcement:

Tecsun has launched its latest antenna which is now available at Anon-Co! This active loop antenna has a portable design and aims to enhance AM (LW, MW, SW) frequencies. The antenna comes with three types of connector cable and a ferrite coupler for connecting to different types of radios.

Personally, I like my TG34 (DE31MS equivalent).  Though I have *no* experience with this model – as it is new – this is the type of antenna users either love or hate.  My TG34 and the equivalents will amplify everything, including noise, but it has helped me make inaudible or barely audible signals audible.  It’s inexpensive, portable, easy to deploy and store (great for travel) – but it’s really geared towards the SWL hobbyist who can’t invest in, or erect, something bigger and/or more expensive.

The biggest advantage that I can see with this new model: the antenna has three types of connections including BNC & RCA sockets.

Click here for more information: Tecsun AN-48x

Guest post by Troy Riedel

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Guest Post: ZIPWALL10 poles as antenna supports

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


ZIPWALL10 poles

Recently we had a remodeling job performed at the home QTH and the workers used telescoping poles to form a dust barrier.  When the job ended, they said I could have the telescoping poles, a product called ZIPWALL10, which when collapsed are four feet long but extend to ten feet.  This got me pondering about how handy these could be in the radio shack, especially for indoor impromptu antennas.

Close up of the ZIPWALL telescopic pole.

Indoor antennas, especially wire antennas usually have to be secured to a wall somehow, and should be as high as possible in the room.  That requires using adhesive tape to attach the wire and a ladder (most ceilings are eight feet), but using the ZIPWALL10 poles it’s easier and safer.  Below is a temporary random wire antenna in my shack using 26 gauge insulated wire strung between the two poles.

Random wire in shack room is a bit hard to see but it is strung between the two poles.

What’s nice about these poles is they have rubber feet to grip the floor and plastic pads on top to avoid damage to the ceiling. The top section is spring loaded to assure a tight fit.  The ZIPWALL10 model extends to ten feet in three telescopic sections. No tools are needed to set these up, and they conveniently collapse for storage.

ZIPWALL10 pair along with roll of 26 gauge wire for temporary indoor antenna installation.

These poles just happened my way due to a remodeling job, but surely other types are available on the market for those wanting to experiment with indoor antennas.  The price for a ZIPWALL10 pair on Amazon is around eighty dollars. Thanks for reading.


What a great use for ZipWall poles, Mario! I’ve spent the past few days at an ocean front condo and could have used two of those supports to suspend a small, lightweight passive loop antenna safely on the balcony. That’s fantastic your contractors simply gave you those poles! 

Thanks for the tip!

As you mention, Amazon sells a full line of ZipWall options (links below support the SWLing Post) but these can also be found at most home improvement stores. 

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