This blog is dedicated to shortwave radio listening in the 21st century: the art of tuning into the signals of radio stations that are transmitting from thousands of kilometres away without the use of the Internet. It can be viewed as a fun hobby but also as a way to maintain an alternative, independent means of obtaining information in our digital age. Posts cover topics including shortwave radio equipment and accessories, station profiles, program recordings and shortwave radio history.
Lately, I have been able to make more frequent outdoor trips for recording parts of the shortwave radio spectrum using my portable set-up. While reviewing one such recording from August 31st, 2021, I noticed something highly unusual: a continuous music mix on one of the amateur bands, modulated as a lower single sideband audio signal. For readers who are unfamiliar with radio communication regulations, broadcasting music is strictly prohibited on all amateur bands in most jurisdictions. However, it turns out that the frequency in question – 7055 kHz – has now been used for some years by a number of hams for antagonistic on-air exchanges. It is likely that, in an act of desperation, someone had decided to put a stop to that (at least temporarily) by relentlessly broadcasting music using their single sideband transceiver.
The music itself is a mixture of trance, ambient house and drum & bass, but what makes this recording truly special are the various amateur radio artefacts that get superimposed onto it, such as morse code and other non-voice communications. To my ears, this gives the transmission the atmospheric feel that is so emblematic of shortwave radio in general, although perhaps in a somewhat exaggerated form. Below is the full recording for your listening pleasure:
Without any further introduction, below are three shortwave pirate radio transmissions, extracted from an outdoor spectrum capture I made yesterday with a GPD Win handheld laptop, AirSpy HF+ Discovery and a 2x6m dipole antenna. The music is mostly rock and oldies, which are the staple genres of European shortwave pirates. I hope you enjoy these recordings!
This post comes on the heels of the takeover of Kabul by the Taliban. When it became clear on Sunday that the U.S.-backed Afghan government would be unable to sustain itself against the Taliban's rapid advance into the capital city, I grabbed my portable SDR-based spectrum capture combo and headed to a nearby park. The set-up comprised of my newly purchased GPD MicroPC, AirSpy Mini, SpyVerter 2 and the 2x6m dipole antenna, which I managed to spread out across some tree branches. Using this set-up I was able to make a 3-hour long, 6 MHz wide recording between 1600 and 1900 UTC. This included the 39, 31 and 25 metre bands in their entirety. Below is a preview of what the tail end of that recording looked like when played back in SDR#:
When I returned home, I quickly scanned the spectrum capture to identify the most relevant individual shortwave transmissions. These turned out to be the BBC World Service in English and Pashto, out of Singapore, the Voice of America Deewa Radio, also in Pashto and out of Udon Thani, Thailand, and a new and seemingly unidentified transmission in Dari on 7600 kHz, continuously mentioning the Taliban. I chose 1800 UTC as the starting time for extracting individual station recordings, as by then the presidential palace had already been captured.
The BBC World Service in English has an eerie ending, as the Voice of America in Korean goes live on the same frequency before the BBC's broadcast is finished. Almost two days later, the mystery transmission on 7600 kHz was identified by Alokesh Gupta as the audio feed of Afghanistan International Television, run out of the UK by Volant Media:
The next day, I returned to the same spot – this time with a GPD Win handheld laptop, AirSpy HF+ Discovery and the same 2x6m dipole antenna as I used on the previous day. I recorded the 39 metre band between 1700 and 1900 UTC, for which HF+ Discovery offered much greater sensitivity. When I returned home, I extracted the same stations as the day before, starting at the same time:
Unfortuately I do not understand Pashto or Dari, so cannot fully appreciate most of the broadcasts that I have recorded. However, I hope they turn out to be of value and historical significance to those who speak these languages.
A coronavirus outbreak that sent New Zealand’s biggest city into a snap lockdown over the weekend involved the more transmissable UK variant, health officials confirmed on Monday, the first time the strain has been detected locally.
Auckland’s nearly 2 million residents were plunged into a new three-day lockdown on Sunday after three new COVID-19 cases were detected in the city.
Genome sequencing of two the cases - all three are immediate family - revealed they were the B1.1.7 variant. The source of the cases remains unknown, authorities said, adding they were scanning international genome databases for a match.
I used my Belka-DX to grab RNZ Pacific's 10pm broadcast, which covered this story in detail, including a lengthy listener-led Q&A session with a local epidemiologist. I got my Zoom H1 recorder to capture Belka's I/Q output, which I then demodulated in SDR#.
This is a quick "how-to" post on making spectrum recordings with the latest
model of the ultra-portable Belka shortwave receiver, the Belka-DX.
A number of positive reviews of the previous model of this receiver have
already been posted online. The new version boasts greater sensitivity,
extended shortwave coverage and the ability to monitor I/Q – or radio
spectrum – data in real time.
A separate 3.5mm stereo port is used for outputting I/Q data in analogue
format. This seems an unusual design choice: nowadays, most SDRs send I/Q data
digitally over USB (e.g. see FunCube Dongle Pro+).To get SDR applications to
work with this data, Belka's I/Q output needs to be connected to the line input
of a regular PC sound card. The digital —> analogue —> digital
conversion chain will inevitably result in the addition of small amounts of
noise to the final spectrum output. However, one advantage of this design
choice is that it is possible to capture this data using a portable audio
recorder.
Belka DX I/Q output port
While Belka's I/Q sample rate is reportedly 192 kHz, few recorders are capable
of capturing audio at this rate (and none of them are cheap or particularly
compact), and the 96 kHz option is far more widely available. In practice,
recording at this rate means that roughly 48 khz on each side of the centre
frequency become truncated, but on shortwave, 96 khz can still pack several
broadcast stations (or, alternatively, a few dozen ham radio transmissions).
Additionally, DSP tools in SDR applications such as SDR# can be used to clean
up I/Q recordings in ways that are far superior to what's possible to achieve
with regular post-processing of audio recordings.
I made several field spectrum recordings with my Zoom H1, connecting Belka's
I/Q output to the recorder's line input and using the "WAV @ 96 kHz / 16 bit"
setting. I found that keeping the input level between -24dB and -12dB results
in sufficient gain for later analysis without overloading the recorder.
It's worth noting that the gain and the slight offset from the tuned centre
frequency seem to change depending on both the frequency and the chosen
demodulation mode.
Results
First up is the Voice of America recording I made on 06/11/20 in a London park.
To assess the quality of my I/Q capture method I recorded the audio output in
parallel using my Sony ICD-PX333. I set Belka's demodulation mode to "AM2", which
is its pseduo-synchronous AM detection setting. Below are the two
recordings, with the I/Q data demodulated in SDR#:
Belka's own demodulation is a little on the distorted side compared with SDR#'s I/Q demodulation. This is probably due to the specifics of its "AM2" setting.
Note that I'm using SDR#'s handy "invert spectrum" and "correct IQ" options,
and that I've modified the spectrum recording file names so that the centre
frequency is displayed correctly.
Below are two more examples of this I/Q capture method and their audio recording counterparts. For the latter, I set Belka's mode to LSB with 50 Hz lower and 4 kHz upper frequency cutoffs. I also used Youssef's excellent noise reduction plugin when demodulating I/Q.
Radio Rebelde on 12/11/20 at 07:01 UTC
Radio Rebelde was barely registering on Belka's SNR meter but the audio is perfectly intelligible, while SDR#'s noise reduction takes this intelligebility to an entirely new level.
Finally, here is a full I/Q capture of a CQ constest on 40m on 21/11/20, recorded in the same park location (click here to download the original WAV file). An
Over The Horizon Radar signal makes an unfortunate appearance during the first
20 minutes of the recording, causing severe interference. You will also notice a few hams ignoring the contest altogether and happily rag chewing!
Overall, this is by far my most portable shortwave spectrum capture combo: it
is handheld and absolutely no antenna set-up is required – just plug in the
supplied telescopic whip and you are good to go. The reduced bandwidth
compared to my AirSpy SDRs is a significant limitation, but it was only a few
years ago that I was making recordings with a FunCube Dongle Pro+ that only
provided double the above sample rate. It would be amazing if Belka's next
model included a microSD card slot and the ability to record the I/Q data
directly to it, but for now I am very happy with this way of making spectrum
recordings on the move.
This morning, while casually exploring the shortwave bands from home using Twente WebSDR, I stumbled across an AM transmission on 4860 kHz. The station was playing some great Euro Pop so I immediately hit "record" and switched over to my local shortwave monitoring set-up (AirSpy HF+ Discovery / YouLoop antenna mounted on the balcony). It turned out that I could pick up their signal quite nicely over here too, albeit with somewhat greater noise levels compared to the WebSDR copy, owing to local QRM:
The station ID was "Mystery 21" and their Facebook page suggests that they are located in Germany. Below is the full WebSDR recording for your listening pleasure:
This blog was started on a hot and sunny afternoon in July 2013, while enjoying listening to some distant signals with a Roberts R9962 shortwave radio.
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