Category Archives: Antennas

A Compact RSPdx & Wellbrook Loop Kit for the Beach — My Approach

I have enjoyed three to four medium wave and shortwave DXpeditions per year since 1988, to sites on the Washington and Oregon coasts. I love the chance they give to experiment with antennas in a (hopefully!) noise-free location, and concentrate on catching stations that might not be heard from home.

All of my DX trips have been via car–until now! I’ve just returned from nine vacation days in Hawaii (Waikoloa Beach, on the Big Island), and I thought others might like to see the radio related items I chose to take along for air travel. I’m pleased to report that everything worked as planned, and I have five days of SDR IQ WAV files of the MW band for review, all recorded in the time frame surrounding local dawn.

My goal was not the smallest, most compact portable setup, but one with high performance and modest size. Fitting everything into a day pack was another requirement. A simple wire antenna and an even smaller Windows tablet or laptop than the one I’ve used (and a smaller SDR like the HF+ Discovery, for that matter) would make a much smaller package. However, the items I’ve assembled worked excellently for me during my enjoyable Hawaii vacation. The directional loop antenna provided nulls on medium wave of 30 dB during preliminary tests indoors, a less-than-ideal test situation.

Waikoloa Beach–just one of a zillion picturesque scenes in Hawaii.

Here is a list of what I’ve put together for my DXing “kit”:

- SDRPlay RSPdx receiver
- Short USB cable for receiver<>PC connection, with two RFI chokes installed
- Lenovo X1 tablet— a Windows 10 device with magnetically attached keyboard; this model is a competitor to Microsoft’s Surface Pro tablet
- Wellbrook Communications’ ALA1530 head amp module, modified for female SO239 connectors enabling use of large diameter LMR-600 coaxial cable as a 2-turn loop element. My antenna setup is similar to Wellbrook’s commercial flexible loop
- Wooden base for the antenna (ALA1530 is bolted to the base)
- 20 feet of lightweight RG-174 coax
- Wellbrook DC interface module for the ALA1530
- 3.0 Ah LiFePO4 rechargeable battery for the Wellbrook antenna
- 15 foot long section of high grade “Times Mfg.” LMR-600 coax cable with PL259 connectors (bought from Ebay already assembled/soldered)
- Fold-up beach mat
- Small day pack to hold everything

All the contents of this DXing setup fit a standard size day pack.

You’ll note the absence of headphones in the list. This is because my intent from the start was to record all the DX (MW band) as SDR WAV files for DXing post-vacation. That said, I did have headphones in my travel luggage for later spot checks of a few frequencies. That’s how I found 576 kHz Yangon, Myanmar lurking at their 1700 sign-off with national anthem and English announcement. The remainder of the DX to be uncovered will have to wait until I’m back home near Seattle!

The LMR-600 is a very thick and stiff coax cable, whose diameter approaches that used in the standard aluminum tubing ALA1530 series from Wellbrook. It has the benefit of being self-supporting in a 2-turn configuration and will also coil up into an approx. 12-inch package for transport. It just barely fits within the day pack I’m using. As I understand it, magnetic loops with tubing or large coax as the active element, versus simple wire, are more efficient in operation. Whether or not this holds true in practice remains to be seen.

I fashioned a wooden disc 3/4″ thick to attach the ALA1530 head amplifier, as I didn’t want to bring along a tripod or other support stand. The Wellbrook antennas all work well near or at ground level, so I was able to get great reception with the antenna right on the beach. The diameter at two turns of the coax is only a few inches smaller diameter than Wellbrook’s aluminum tubing loops. Three strips of strategically placed Velcro straps help keep the turns together when deployed as well as during storage.

In theory a two-turn loop should give 5 dB less gain than a single turn version; however, my older ALA1530 module has 5 dB more gain than the newer “LN” type, according to Andrew Ikin of Wellbrook Communications. The net result is that my two-turn antenna should have equal gain to the larger one-turn variety. Future experimentation with this DIY coax loop antenna is in order!

The Wellbrook loop antenna, RSPdx receiver, and Windows 10 tablet on the beach in Waikoloa, Hawaii.

Another view of the DXing position. Being this close to the water with my radio gear was unnerving at first, but the wave action on a calm Hawaii beach is totally different from the Oregon/Washington beaches with waves that can move in and out by a hundred feet or more.

The Wellbrook “DIY FlexLoop” works fine at beach level, and is less conspicuous this way, too.

The ALA1530 module is bolted to the 11-inch wooden disc for support. I’ve modified the module’s sockets to securely hold SO239 female connectors.

The commercial Wellbrook FLX1530LN is a fine product, and worthy of your consideration as a compact and high performance travel antenna. Full details can be found at this link.

SDR WAV Files for Download

One of my goals from the start for my Hawaii trip was to bring back SDR “IQ” WAV files for sharing with others. These approx. 900 Mb files cover the entire medium wave band as heard from my beach location in Waikoloa.

The overall page is: https://archive.org/details/@4nradio Clicking on any of the entries will bring you to a details page. From there just right click on the “WAVE” link, and choose “Save as…” to download. For a few of the recordings I also posted the file that precedes the one that goes across the top-of-the-hour, because things seemed a bit more lively prior to 1700 (which was at local sunrise, give or take a couple of minutes).

The IQ WAV files are only playable with suitable SDR radio software: SDRuno is first choice (but you need a RSP receiver connected). The files are also is compatible with HDSDR and SDR-Console V3. It may also play on Studio 1 software.

I hope other DXers enjoy the chance to tune through the MW band, as heard from the Big Island of Hawaii.

Guy Atkins is a Sr. Graphic Designer for T-Mobile and lives near Seattle, Washington. He’s a regular contributor to the SWLing Post.

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

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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 ([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).

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Tecsun AN-48X Loop Antenna: One simple suggestion to improve performance

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Many thanks to SWLing Post contributor, Robert Richmond, who writes:

I recently received the new Tecsun AN-48X loop antenna. I have not had much time to thoroughly test it, but I can make one immediate recommendation IMO. Replace the bundled “feedline” between the loop and controller with an actual *shielded* 1/8″ male-to-male stereo audio cable.

The bundled cable causes near-hand capacitance at the controller, potential RFI issues, etc.; at least for my received unit. The noted concerns largely corrected when replacing the bundled cable with a 6′ shielded audio cable. Tuning now works as expected, and SNR seems much improved.

I have longer 12′ shielded cables and some 1/8″ female-to-female couplers on order to eventually try longer feedlines should the need arise. I will try to drop you a line if/when I get around to testing them.

That’s a sound suggestion, Robert! Thanks for sharing!

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

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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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Coastal DXing with the AirSpy HF+ Discovery and a homebrew passive loop antenna

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Last week, we packed the car and headed to coast of South Carolina.

The trip was a bit impromptu but through the creative use of hotel points, we scored a two bedroom ocean front unit with a fantastic little balcony.

The vacation gave me an excuse to test the new passive loop antenna my buddy Vlado (N3CZ) helped me build recently.

The loop design came from AirSpy’s engineer and president, Youssef Touil.

This passive mag loop takes advantage of the new AirSpy HF+ Discovery‘s exceptionally high dynamic range. Youssef had reported impressive results, so I had to build one.

Vlado had a length of Wireman Flexi 4XL that was ideal for this project. The only tricky part was penetrating the shielding and dielectric core at the bottom of the loop, then tapping into both sides of the center conductor for the balun connections. Being Vlado, he used several lengths of heat shrink tubing to make a nice, clean and snag-free design.

The results were truly exceptional. I spent most of my time on mediumwave from the hotel balcony because I was determined to catch a transatlantic signal.

Check out the spectrum display from my Microsoft Surface Go tablet:

Our ocean front hotel was inundated with noise, but I still managed to null out most of it and maximize reception using the passive loop. I simply suspended the loop on the balcony rocking chair–not ideal, but effective and low-profile.

Want to take a test drive?

If you’d like to experience this portable SDR setup, why not tune through one of the spectrum recordings I made?

Click here to download the spectrum file [1.7GB .wav].

The recording was made on November 17, 2019 starting around 01:55 UTC–I chose it at random and have yet to listen to it myself. You’ll need to open this file in AirSpy’s application SDR# or a third party SDR app that can read AirSpy .wav files.

Stay tuned…

I’m writing an in-depth report of the HF+ Discovery, my experiments with this setup and AirSpy’s soon-to-be-released passive loop antenna for the January 2020 issue The Spectrum Monitor magazine. Spoiler alert: I am truly impressed with the wee little AirSpy HF+ Discovery. It’s a powerhouse!

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Guest Post: ZIPWALL10 poles as antenna supports

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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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