Tag Archives: @LondonShortwave

London Shortwave refines his tablet-based portable SDR

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One of the great things about the SWLing Post is that readers share their varied–and highly creative–methods of playing radio.  A few weeks ago, SWLing Post reader, London Shortwave, shared his portable SDR set-up with us; he uses this outdoors to mitigate London’s heavy radio interference. Dennis Walter, president of Germany-based Bonito, commented, and later posted an alternative portable SDR solution using the Bonito RadioJet IF receiver.

Below, London Shortwave shares a guest post (also viewable on his blog) which describes in detail his design for his portable SDR around the FunCube Dongle Pro+ and an 8″ Windows tablet, and explains how effectively it works for him. This post includes recordings and a video; it’s an excellent tutorial:


This article is a follow up to the submission I made to the SWLing Post a little while ago. In short, the idea was to combine the FunCube Dongle Pro+ USB-based software defined radio (SDR) with an 8″ Windows tablet running SDR# to have a portable, on-the-go SDR solution.

The original inspiration

The original inspiration

Tablet radio interference

At the outset, I thought that all that was necessary was a tablet (I chose Toshiba Encore 8″), the FunCube dongle itself and just some antenna wire. This turned out to be a naive assumption because the tablet’s USB interface injected enormous amounts of radio frequency interference (RFI) into the SDR, making listening on some shortwave frequencies essentially impossible. Just to be sure that I wasn’t being plagued by a defect of my chosen tablet model, I tried out the same set-up on a Dell Venue 8, with identical results.

To deal with the issue of tablet-generated RFI, I bought a galvanic USB isolator, which, in essence, is a box that breaks the electrical connection between the USB dongle and the tablet’s USB interface while allowing USB data to pass through in both directions.

Heros Technology galvanic USB isolator

Heros Technology galvanic USB isolator

Additional power for the SDR


The isolator resolved the RFI issue completely, but created another problem altogether: the device specifications state that the isolator’s power output is restricted to 100mA at 5V. This is sufficient for USB devices that are self-powered but not for the FunCube dongle that draws all of its power from the USB port to which it is connected.

USB Y cable

USB Y cable

One way to supply extra power to a USB device is to use a “Y-cable”. Such cables have one extra USB plug that can be attached to a source of additional power (for example, a USB power bank). This solution is commonly used to connect power-hungry items, such as large hard disks, to low-power, portable computing devices (laptops and tablets). Having bought this cable, my next step was to find/improvise a battery that meets the USB power specifications (5V, 500mA).

Yet more interference

My first thought was to use the mobile USB power bank that I use to charge my iPhone while on the go. After all, it already has a USB port and supplies power with the right voltage. Once again, my expectations were confounded and RFI reared its ugly head! The power bank radiates significant interference into the circuit because it uses a switching regulator to maintain steady voltage. Luckily, I came across Gomadic’s portable AA battery pack with regulated 5V output that emits way less interference than any of the other USB batteries I tried (my intermediate solution used 4 rechargeable AA batteries and a makeshift USB connector, and although this resulted in zero additional interference I decided that it’s not safe to supply the SDR with unregulated voltage that doesn’t match the rest of the circuit). I used the handy passthrough USB voltmeter I bought in Maplin to check that Gomadic’s nice-looking gadget does indeed give out 5V as advertised.

So, what can one do with the remaining RFI from the additional power supply? It turns out that it can be mitigated quite effectively by inserting a balun (item 10 on Figure 2) between the SDR and the antenna wire (item 12). The balun is connected to the SDR with a coaxial cable (the “feed line”, item 11). Additionally, ferrite choke rings (item 9) attached to the feed line help reduce this RFI further: winding the feed line through the choke rings several times is sufficient. However, neither the balun nor the chokes are effective enough to replace the USB isolator! It appears they only help with the noise generated by the power supply, which is relatively minor anyway.

 Cost vs Portability

When SWLing Post published the details of my intermediate solution, Dennis Walter – one of the engineers behind Bonito RadioJet – popped up in the comments section and suggested that my setup is too tedious, as it involves lots of cables, and that his SDR is superior in terms of portability and the supplied software. While I haven’t had the chance to evaluate RadioJet, I pointed out that the cost of his radio is significantly higher than that of all of my components put together. I also mentioned that the free SDR# software I use is superb: it sounds excellent and offers a number of features that many software packages and conventional radios don’t have. So, having finalised my design, I thought that it might be time to tally up the cost and listen to the results.

Below is the full component list:

1) Toshiba Encore 8″ tablet $194

2) On The Go USB host cable for Toshiba’s micro USB connector: $7

3) Heros Technology USB Isolator: $125

4) USB Y cable with two males + 1 female plugs: $8

5) Gomadic Portable AA Battery Pack with regulated 5V output: $20

6) Gomadic female USB connector tip: $6

7) FunCube Dongle Pro+: $208

8) USB volt-meter (optional): $33

9) 2 ferrite choke rings: $10

10) Wellbrook HF Balun: $50

11) Feedline cables $7

12) 6 metres of thick copper antenna wire: $8

Adding up the prices of items 2 – 12 (and excluding the optional voltmeter) brings the total cost to  $449 vs. Bonito RadioJet’s $689. For the price difference you can throw in the Toshiba tablet at $194 and still have some change, enough to buy a carrier bag and perhaps even a nice pair of headphones!

Figure 1. Radio components

Figure 1. Radio components

Figure 2. Antenna components

Figure 2. Antenna components

In terms of portability, the entire setup fits nicely into an 11″ laptop carrier bag.

Figure 3. Packing the components into an 11" carrier bag

Figure 3. Packing the components into an 11″ carrier bag

Figure 4. Ready to go

Figure 4. Ready to go

Setting things up in the field is not particularly cumbersome, either:

Figure 5. Portable SDR setup in action in a local park

Figure 5. Portable SDR setup in action in a local park

As for the results, listen to the below snippets and be the judge. The only thing I will say is that none of my other portable radios have ever given me this kind of performance, not even with the long wire antenna attached:

And while we’re at it, here’s a demo video:

Portable SDR on Toshiba Encore 8″ Tablet from London Shortwave on Vimeo.

At one point I wanted to build an enclosure to house the FunCube dongle, the power supply and the USB isolator in a single tidy unit, but I no longer see the need. It’s easy to pack all of those items into the carrier bag and also they are all useful individually: the USB isolator can be paired with other SDRs, and I recently discovered a neat additional use for the Gomadic battery pack.

Well, that brings me to the end of this post. I hope my design will inspire you to come up with your own portable SDR system, and that you will share your results with me in the comments section. Happy listening!


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Field Recording with the Tecsun PL-380 and Transcend MP330

PL-380SWLing Post reader, London Shortwave, shared photos of his portable recording kit on Twitter yesterday. It consists of a Tecsun PL-380, Transcend MP330, in ear headphones, and a simple clip-on antenna (supplied with the PL-380). He recorded Radio New Zealand International with this gear.


I love the compact form factor of the Transcend MP330–ideal for field recording. I’m curious if there are other high-capacity USB memory/recording sticks on the market.


The PL-380 is a superb ultralight radio; my favorite small travel radio, in fact. The PL-380 can be found for about $42 US shipped via Amazon; an impressive value.

Many thanks to London Shortwave for sharing images of his ultralight DXing & recording kit!

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Designing a truly portable SDR

SWLing Post reader, London Shortwave, is working on a portable SDR (software defined radio) system based on his Toshiba Encore 8″ Windows tablet, FunCube Dongle Pro+, and supported by the excellent SDR# application. Today, he shared this photo of his entire kit, including his comments. If you’re interested in a similar portable SDR, take note of the USB isolator and extra (AA battery) power supply.

LondonShortwave-PortableLondon Shortwave plans to make an enclosure for the SDR, AA power supply, and USB isolator.

And although it may be easier said than done, it would be super if this enclosure has the same footprint as the Toshiba tablet, and the whip antenna can be mounted on the enclosure…He would then essentially have a case that he could attach to the tablet for instant portable shortwave radio fun.  (Oops–did I just raise the bar for you? Ha!)

Thanks for sharing, London Shortwave!

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The World Cup on shortwave, continents apart

WorldCupBall-001Yesterday, I was primed to follow the FIFA World Cup semi-final match featuring the Netherlands vs. Argentina. Moreover, we have good friends from Germany visiting; of course, they wanted to see who their winning team will be playing in the final match come Sunday.

But as we live in a fairly rural area, and don’t place much of a priority on television (radio, anyone?), we have no cable, no satellite, and with no more than a rabbit-ear indoor antenna on our only telly, no local over-the-air broadcasters available. But we found we were able to watch the match stream live on ESPN via an Apple TV box attached to our only television.

Of course, I also tuned in the match on shortwave radio–via the BBC World Service on 11,810 kHz out of Ascension Island–starting a little after 20:00 UTC. And guess which stream was more “live” (i.e., immediate), ESPN or shortwave?  Here’s the recording:

Answer:  You guessed it–the shortwave coverage was one full minute in advance of the ESPN “live” stream. My friends watching television in another room marveled at my clairvoyance…

When the match went into extra time, as Argentina and the Netherlands were tied 0-0, the BBC World Service dropped the frequency to KBS (you’ll hear a few minutes of KBS in the recording).  At this point I was resigned to watching the match on ESPN, as I didn’t want to miss any of the action while trying to find another broadcaster covering the match.

Then, radio to the rescue:  I received the following tweet from SWLing Post reader/contributor @LondonShortwave:

So I quickly tuned to Radio Nacional Amazonia on 6,180, where I discovered a booming signal and full match coverage. Even though the commentary was in Portuguese, a language I can’t speak, I could still follow the match knowing player and team names. When Argentina won the penalty kicks after extra time, commentators exploded with excitement. Listen for yourself:

What made the match all the better, besides watching it with my good friends here at home, was following it with my shortwave friends across the globe. As we exchanged tweets (while following coverage) it was as if we were all in the same room. Indeed, here’s what @LondonShortwave said:

So true–!  While using the Internet to communicate, we were listening to the same and far-more-efficient shortwave station for coverage.

Now on to Sunday, and hoping I can catch the final match on the BBC World Service…with the rest of the world. If you can, join us. Game on!

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SDR# now has AM synchronous detection


SWLing Post reader, London Shortwave writes with a remarkable story about the free SDR application, SDR#(or, “SDR sharp”). He writes:

“Two days ago, I emailed Youssef (SDR# developer lead) to ask if he would consider adding synchronous AM detection to his software at some point.

To my great surprise he e-mailed me back the same day and told me that it wouldn’t take him long to write the necessary code. A few hours later he sent me a preview copy of the software with the feature included (all I had to do was to swap one .dll file in the version I had installed at the time). The following day, he integrated it into the latest release!

With the new sync detector the software is rapidly becoming my favourite SDR application.

Here’s a demo video I made for Youssef (and everyone else!) to show how I’ve been getting on with it:

This is amazing–what’s especially impressive is that a first iteration of AM sync should be so well implemented.  I love the way you can use the IF shift to block out interference within a sideband, much like USB/LSB selectable sideband. There are paid and OEM SDR applications that can’t do this.

London Shortwave: you’ve convinced me to see if SDR# will drive any of my receivers. Many thanks!

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Testing SDR#’s noise reduction in a London park


Yesterday, SWLing Post reader London Shortwave took his laptop, FunCube Dongle Pro+, and 6 meter long wire antenna to a local park where he tested SDR#‘s new IF noise reduction.

He made the following screencast/video where he toggles the IF noise reduction feature while receiving the BBC World Service’s Pashto language service on shortwave:

Most impressive! Indeed, I believe SDR#’s noise reduction might rival that of OEM applications. While I’m not the biggest fan of noise reduction for everyday use (due to inherent digital artifacts) it is a valuable tool when noise levels are high.

 Click here to follow @LondonShortwave on Twitter.

If you would like to experiment with SDR#, click here to download your free copy. SDR# has a number of additional plugins and dedicated users/developers who communicate via this this Yahoo! Group.

Many thanks to @LondonShortwave.

Any other readers using SDR#? Please comment.

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Another solution for whole-house shortwave

London Shortwave posts the following on Twitter:

Inspired by @SWLingDotCom‘s RaspberryPi post I put this together to listen to the radio in my shack around the house http://youtu.be/vOX41wIS1Qk 

On YouTube, London Shortwave explains that much of his modern system was inspired by a drawing from a 1930s shortwave listening magazine.

Below is a scan of the original illustration that inspired him:


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