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.
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.
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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.
Made simultaneous spectrum and audio recordings. Blog post comparing the two coming shortly. cc @SWLingDotCom @lambdaprog https://t.co/PX7h892OLx pic.twitter.com/Ehw0Kr5JW6
— London Shortwave (@LondonShortwave) November 6, 2020
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.
.@radiorebelde_en coming in nicely. 🇨🇺 pic.twitter.com/7yw4FU0fYG
— London Shortwave (@LondonShortwave) November 12, 2020
Radio New Zealand International on 12/11/20 at 08:00
Very clear reception, with SDR#'s I/Q noise reduction providing a marked improvement over Belka's own audio demodulation.
Lovely @RNZPacific signal this morning. ☀️ pic.twitter.com/Jx8h2EqsEZ
— London Shortwave (@LondonShortwave) November 12, 2020
CQ contest on 40m on 21/11/20 at 15:33
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.
Mystery 21 Radio just now. #YouLoop on the balcony. pic.twitter.com/0rqZstxXic
— London Shortwave (@LondonShortwave) November 30, 2020
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:
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Antarctic night sky. Source: Chris Wilson, Australian Antarctic Division |
Every year, the BBC World Service makes this special programme for just 40 listeners: the team of scientists and support staff isolated at British research stations in the Antarctic midwinter. The Antarctic Midwinter Broadcast is unlike anything else on the BBC World Service. Presented by Cerys Matthews, it features messages from family and friends at home as well as music requests from Antarctica. For decades it has been part of the traditional midwinter celebrations.
To listen to the 21:30 BST broadcast on 21st June on shortwave, please tune to:
5790 kHz from Woofferton UK
7360 kHz from Woofferton UK
9580 kHz from Ascension Islands
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Satellite view of Voice of the Islamic Republic of Iran transmitter site in Sirjan |
Might be old news but compared to my recordings from last year, Iran have really fixed their transmitter and the audio is no longer severely under-modulated. Recorded yesterday with #AirSpy HF+ discovery and #YouLoop on the balcony, all times BST. pic.twitter.com/P9QanKEeRt— London Shortwave (@LondonShortwave) June 20, 2020
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Marina Bay Sands, Singapore. © 2019 London Shortwave |
East Coast Park, 29/08/2019
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Spectrum capture QTH on 29/08/2019 |
My recording set-up consisted of the GPDWin 5" mini-computer running Windows 10 and SDR# 1631, AirSpy HF+ Discovery and a long wire antenna:
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Myanmar Radio QSL card. Image from Pavel Zhuravlev |
Radio New Zealand International (RNZ Pacific)
KCBS Pyongyang
The Korean Central Broadcasting Station (KCBS) (Korean: 조선중앙방송, Chinese: 朝鲜中央放送, Japanese: 朝鮮中央放送) is the main domestic radio network in the DPRK. It sits under the Central Broadcasting Committee of the DPRK (called the Radio and Television Committee of the DPRK until 2009).
KCBS broadcasts from 5am to 3am local time via a network of medium wave and shortwave transmitters that cover the nation. The powerful transmissions can easily be heard in neighbouring countries, including South Korea where some of its frequencies are jammed.
A central program is broadcast from Pyongyang on most transmitters through the entire broadcast day, but some are reported to carry regional programming between 2pm and 3pm.
Echo of Hope
South Korea's clandestine counter-broadcast on shortwave, beamed into North Korea from Hwaseong but picked up very clearly in Singapore. There isn't much information available on this broadcaster online, although apparently a few listeners managed to obtain the station's QSL cards via South Korea's international broadcaster, KBS World Radio. Below is a one hour recording of their signal.
VMW Marine Weather Station, Wiluna, Australia
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Australia Marine Radio Broadcast Areas. Source: The Australian Bureau of Meteorology |
Radio Nikkei 1
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Radio Tampa QSL card from the late 70s. Source: kusanagi1965 |
The station features the following four genres as the core of its programming: finance, JRA horse racing (weekends), health-medical, and culture.
Voice of Vietnam National Channel 4
BBC World Service transmitting from Kranji, Singapore
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Kranji transmitting station. Source: Google StreetView |
Pasir Ris Park, 27/08/2019
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Spectrum capture QTH on 27/08/2019 |
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View from the recording location towards Serangoon Island. © 2019 London Shortwave |
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View towards Changi Airport approach. © 2019 London Shortwave |
Voice of Vietnam's English language service to South East Asia and the Pacific
NHK World Radio Japan
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Members of A.B.C-Z |
Republic of Yemen Radio (clandestine / Saudi Arabia)
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Distance calculation by Google |
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