Shortwave playlist part 1

Thursday, April 30, 2015
Over the past two years, shortwave radio listening has exposed me to lots of new music from around the world. Starting from this entry, I shall occasionally post short playlists of some of the more interesting records I have heard.

1. Ibrahim Maalouf - Sensuality
Medi 1, July 2013

2. Morenito - Los Almonteños
Radio Exterior de España, June 2014

3. Harold Lopez Nussa Trio - Bailando Suiza
Radio Habana Cuba, December 2013

4. Alexis Boulgourtzis - Choris Prova
Voice of Greece, November 2013

5. Lin Hai - Happy Together
China Radio International, August 2013


Recording the spectrum with portable SDR

Friday, April 17, 2015
Update (15/11/16): this article describes an older version of my portable SDR configuration. Jump to this post to see my current set-up.

As my friend Thomas Witherspoon frequently points out in his excellent blog, one of the great things about using a software defined radio package like SDR# is that one can record entire regions of the frequency space instead of a single station. Although I've always wanted to try this out, my home is plagued by tremendous electromagnetic interference and the challenge has always been finding the optimal equipment settings for a single station. Under such circumstances, capturing parts of the spectrum didn't really make sense. Now that I finally have a convenient portable SDR solution, I decided to give spectrum recording a go.

On the evening of 15/04/2015 I went out to a nearby park and set up my equipment as follows:

I used a thin SMA to BNC wire to reduce the strain on FunCube's RF front end connector.
Hiding the gadgets from prying eyes inside the carrier bag (all listening done via a pair Bluetooth headphones)
The feed line cable has a velcro strap which is great for attaching the former to a tree branch.
12m of wire were wrapped around the tree branches (two 6m wires connected to the balun in a dipole fashion)

I fired up SDR#, set the centre frequency to 12095 kHz and started recording the spectrum to disk. This is what it looked like:

FunCube Dongle Pro+ spectrum circa 1600 UTC on 15/4/2015 (click above to enlarge)
The frequency window of the captured spectrum was 192 kHz, which is the maximum that the FunCube Dongle Pro+ can provide. While this is only a small fraction of the entire shortwave spectrum, it it is still possible to simultaneously capture a fairly large number of radio signals within it. When I got home I replayed the spectrum data through SDR# several times to extract the following station recordings:

Voice of America (Somali service), 12055 kHz, 1600 UTC. The strongest signal in the above screenshot (unsurprising, as it happens to be transmitted from the closest geographical location). The SDR# / FunCube Dongle Pro+ combo did well not to produce audio artefacts given that the carrier peak occasionally inched close to 0db.

Radio Australia, 12065 kHz, 1559 UTC. SDR#'s passband tuning and synchronous detection were of invaluable help here because of VOA's blowtorch beam was destroying the lower sideband of Radio Australia's signal. A cheap portable radio almost certainly wouldn't cope in these circumstances!

NHK Radio, 12045 kHz, 1559 UTC. SDR# did a brilliant job of pulling this exceptionally weak station out from the static. However, once the nearby VOA powerhouse got going on 12055 kHz at 1600 UTC, it buried this signal almost completely, which you can hear towards the end of this short recording.

Voice of Korea, 12015 kHz, 1602 UTC. North Korea's international radio service in German. SDR# allows the user to select arbitrary audio filter widths, which was useful for this signal as its bandwidth was roughly 20kHz, making the sound come out in somewhat higher fidelity.

Radio Free Asia, 12075 kHz, 1600 UTC. Broadcasting from Tinian Island in the Pacific Ocean, the station comes through remarkably well. That is, until the Chinese start jamming it, which can be heard in the later part of the recording.

BBC World Service, 12095 kHz, 1559 UTC. BBC's signal is surprisingly crisp considering it is coming all the way from Madagascar.

Radio Farda, 12005 kHz, 1559 UTC broadcasting from Udon Thani in Thailand.

Radio Dialog, 12115 kHz, 1602 UTC broadcasting from Talata-Volondry in Madagascar (presumably airing the recording of their earlier Sunday morning program).

IBRA Radio, 12125 kHz, 1600 UTC broadcasting from Yerevan in Armenia.

Trans World Radio, 12160 kHz, 1602 UTC broadcasting from Tashkent in Uzbekistan.

All in all, I am really pleased with what I could pick up. If you have SDR# installed you can be the judge by downloading the spectrum recording itself. Unzip the file, select it after choosing "IQ file" as the input source in the application, and press play (make sure you tick "Swap IQ" and "Correct IQ" in radio options).


Portable SDR update

Friday, April 03, 2015
Update (15/11/16): this article describes my old portable SDR configuration. Jump to this post to see my current set-up.

This is a quick entry describing an update to my portable SDR setup. Readers may remember that my previous configuration suffered from the tablet's radio interference leaking into the FunCube Dongle Pro+ SDR. I solved the problem by using a galvanic USB isolator and a separate portable USB power supply for the dongle. When I posted this configuration on in August, Alexander DL4NO advised me that it's possible to get rid of the USB isolator. Because my balun has two terminals, he said, I can use it to make a dipole antenna (an antenna with two wires) that balances the radio current before it gets passed down into the SDR dongle, which ought to prevent tablet interference from getting into the antenna system.

At the time I wasn't sure this would work. His other suggestion — using a ferrite ring choke on the antenna feedline cable — didn't do much to suppress the tablet noise, which made me assume that it was FunCube Dongle's design that was at fault, and that the noise was getting in from the USB end and not via the antenna.

Wellbrook UMB130 balun
However, when I finally tried out Alexander's suggestion, I could not believe what a drastic effect the addition of the second wire has: as soon as I connect it to the balun, the noise disappears, even with the USB isolator "out of the loop". This simplifies my portable SDR configuration substantially. Below is a demo video:

There is no sound here because I was listening to Radio Australia's 12065 kHz signal using a pair of Bluetooth headphones. Note the low noise floor and the absence of any interference on the spectrum. This has a substantial impact on the overall cost:

1) On The Go USB host cable for Toshiba's micro USB connector: $7
2) FunCube Dongle Pro+: $186
3) Wellbrook HF Balun: $60
4) Feedline cables $7
5) 12 metres of thick copper antenna wire: $16

The total without the tablet comes to $276, and if you buy an HP Stream 7, you only need to add $90 more. A complete on-the-go SDR solution for $366 doesn't sound too bad, does it? Many thanks to DL4NO for making my set-up that much more portable!